TSVWG
Network Working Group J. Babiarz
Internet-Draft
Request for Comments: 4594 K. Chan
Expires: August 20, 2006
Category: Informational Nortel Networks
F. Baker
Cisco Systems
February 16,
August 2006
Configuration Guidelines for DiffServ Service Classes
draft-ietf-tsvwg-diffserv-service-classes-02
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Abstract
This document describes service classes configured with Diffserv, Diffserv and
recommends how they can be used and how to construct them using
Differentiated Service Services Code Points (DSCP), (DSCPs), traffic conditioners, Per-
Hop
Per-Hop Behaviors (PHB), (PHBs), and Active Queue Management (AQM)
mechanisms. There is no intrinsic requirement that particular DSCPs,
traffic conditioners, PHBs, and AQM be used for a certain service
class, but as a policy and for interoperability it is useful to apply
them consistently.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 ....................................................3
1.1. Requirements Notation . . . . . . . . . . . . . . . . . . 5 ......................................4
1.2. Expected use Use in the Network . . . . . . . . . . . . . . . 5 ................................4
1.3. Service Class Definition . . . . . . . . . . . . . . . . . 5 ...................................5
1.4. Key Differentiated Services Concepts . . . . . . . . . . . 6 .......................5
1.4.1. Queuing . . . . . . . . . . . . . . . . . . . . . . . 6 .............................................6
1.4.1.1. Priority Queuing . . . . . . . . . . . . . . . . . 7 ...........................6
1.4.1.2. Rate Queuing . . . . . . . . . . . . . . . . . . . 7 ...............................6
1.4.2. Active Queue Management . . . . . . . . . . . . . . . 7 .............................7
1.4.3. Traffic Conditioning . . . . . . . . . . . . . . . . . 8 ................................7
1.4.4. Differentiated Services Code Point (DSCP) . . . . . . 9 ...........8
1.4.5. Per-Hop Behavior (PHB) . . . . . . . . . . . . . . . . 9 ..............................8
1.5. Key Service Concepts . . . . . . . . . . . . . . . . . . . 9 .......................................8
1.5.1. Default Forwarding (DF) . . . . . . . . . . . . . . . 9 .............................9
1.5.2. Assured Forwarding (AF) . . . . . . . . . . . . . . . 10 .............................9
1.5.3. Expedited Forwarding (EF) . . . . . . . . . . . . . . 10 ..........................10
1.5.4. Class Selector (CS) . . . . . . . . . . . . . . . . . 11 ................................10
1.5.5. Admission Control . . . . . . . . . . . . . . . . . . 11 ..................................11
2. Service Differentiation . . . . . . . . . . . . . . . . . . . 12 ........................................11
2.1. Service Classes . . . . . . . . . . . . . . . . . . . . . 12 ...........................................12
2.2. Categorization of User Service Classes . . . . . . . . . . 13 ....................13
2.3. Service Class Characteristics . . . . . . . . . . . . . . 17 .............................16
2.4. Deployment Scenarios . . . . . . . . . . . . . . . . . . . 22 ......................................21
2.4.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . 22 ..........................................21
2.4.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . 23 ..........................................23
2.4.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . 26 ..........................................25
3. Network Control Traffic . . . . . . . . . . . . . . . . . . . 27 ........................................27
3.1. Current Practice in The the Internet . . . . . . . . . . . . . 28 ..........................27
3.2. Network Control Service Class . . . . . . . . . . . . . . 28 .............................27
3.3. OAM Service Class . . . . . . . . . . . . . . . . . . . . 30 .........................................29
4. User Traffic . . . . . . . . . . . . . . . . . . . . . . . . . 31 ...................................................30
4.1. Telephony Service Class . . . . . . . . . . . . . . . . . 32 ...................................31
4.2. Signaling Service Class . . . . . . . . . . . . . . . . . 33 ...................................33
4.3. Multimedia Conferencing Service Class . . . . . . . . . . 35 .....................35
4.4. Real-time Real-Time Interactive Service Class . . . . . . . . . . . 38 .......................37
4.5. Multimedia Streaming Service Class . . . . . . . . . . . . 39 ........................39
4.6. Broadcast Video Service Class . . . . . . . . . . . . . . 41 .............................41
4.7. Low Latency Low-Latency Data Service Class . . . . . . . . . . . . . . 43 ............................43
4.8. High Throughput High-Throughput Data Service Class . . . . . . . . . . . . 45 ........................45
4.9. Standard Service Class . . . . . . . . . . . . . . . . . . 47 ....................................47
4.10. Low Priority Low-Priority Data . . . . . . . . . . . . . . . . . . . . 48 ........................................48
5. Additional Information on Service Class Usage . . . . . . . . 49 ..................49
5.1. Mapping for Signaling . . . . . . . . . . . . . . . . . . 49 .....................................49
5.2. Mapping for NTP . . . . . . . . . . . . . . . . . . . . . 49 ...........................................50
5.3. VPN Service Mapping . . . . . . . . . . . . . . . . . . . 50 .......................................50
6. Security Considerations . . . . . . . . . . . . . . . . . . . 50 ........................................51
7. Summary of Changes from Previous Version . . . . . . . . . . . 51
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 54
9. ...............................................52
8. Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 54
9.1. .....................................................53
8.1. Explanation of Ring Clipping . . . . . . . . . . . . . . . 54
10. ..............................53
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 55
10.1. .....................................................54
9.1. Normative References . . . . . . . . . . . . . . . . . . . 55
10.2. ......................................54
9.2. Informative References . . . . . . . . . . . . . . . . . . 56
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 58
Intellectual Property and Copyright Statements . . . . . . . . . . 59 ....................................55
1. Introduction
For
To aid in understanding the role of this document document, we use an useful analogy,
starting from the fact that analogy:
the Differentiated Services specifications are fundamentally a toolkit - the
toolkit. The specifications provide the equivalent of band saws,
planers, drill presses, etc. and other tools. In the hands of an expert, there's
there is no limit to what can be built, but such a toolkit can be
intimidating to the point of being inaccessible to a non-expert who
just wants to build a bookcase. This document should be viewed as a
set of "project plans" for building all the (diffserv) furniture that
one might want. The user may choose what to build (e.g., perhaps our
non-expert doesn't need a china cabinet right now), and how to go
about building it (e.g., plans for a non-expert probably won't employ
mortise/tenon construction, but that absence does not imply that
mortise/tenon construction is forbidden or unsound). The authors
hope that these diffserv "project plans" will provide a useful guide
to Network Administrators in the use of diffserv techniques to
implement quality of service quality-of-service measures appropriate for their network's
traffic.
This document describes service classes configured with Diffserv, Diffserv and
recommends how they can be used and how to construct them using
Differentiated Service Services Code Points (DSCP), (DSCPs), traffic conditioners, Per-
Hop
Per-Hop Behaviors (PHB), (PHBs), and Active Queue Management (AQM)
mechanisms. There is no intrinsic requirement that particular DSCPs,
traffic conditioners, PHBs, and AQM be used for a certain service
class, but as a policy and for interoperability it is useful to apply
them consistently.
Service classes class definitions are defined based on the different traffic
characteristics and required performance of the applications/
services.
applications/services. This approach allows us to map current and
future applications/services of similar traffic characteristics and
performance requirements into the same service class. Since the
applications'/services' characteristics and required performance are
end to end, the service class notion needs to be preserved end to
end. With this approach, a limited set of service classes is
required. For completeness, we have defined twelve different service
classes, two for network operation/administration and ten for user/
subscriber
user/subscriber applications/services. However, we expect that
network administrators will implement a subset of these classes
relevant to their customers and their service offerings. Network
Administrators may also find it of value to add locally defined
service classes, although these will not necessarily enjoy end to end end-to-end
properties of the same type.
Section 1, 1 provides an introduction and overview of technologies that
are used for service differentiation in IP networks. Section 2, 2 is an
overview of how service classes are constructed to provide service
differentiation
differentiation, with examples of deployment scenarios. Section 3, 3
provides configuration guidelines of service classes that are used
for stable operation and administration of the network. Section 4, 4
provides configuration guidelines of service classes that are used
for differentiation of user/subscriber traffic. Section 5, 5 provides
additional guidance on mapping different applications/protocol applications/protocols to
service classes. Section 6, address 6 addresses security considerations.
1.1. Requirements Notation
The key words "SHOULD", "SHOULD NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119].
1.2. Expected use Use in the Network
In the Internet today, corporate LANs and ISP WANs are generally not
heavily utilized - they utilized. They are commonly 10% utilized at most. For this
reason, congestion, loss, and variation in delay within corporate
LANs and ISP backbones is virtually unknown. This clashes with user
perceptions, for three very good reasons.
o The industry moves through cycles of bandwidth boom and bandwidth
bust, depending on prevailing market conditions and the periodic
deployment of new bandwidth-hungry applications.
o In access networks, the state is often different. This may be
because throughput rates are artificially limited, limited or are over over-
subscribed, or because of access network design trade-offs.
o Other characteristics, such as database design on web servers
(that may create contention points, e.g. e.g., in filestore), filestore) and
configuration of firewalls and routers, often look externally like
a bandwidth limitation.
The intent of this document is to provide a consistent marking,
conditioning, and packet treatment strategy so that it can be
configured and put into service on any link which itself that is itself congested.
1.3. Service Class Definition
A "service class" represents a set of traffic that requires specific
delay, loss, and jitter characteristics from the network.
Conceptually, a service class pertains to applications with similar
characteristics and performance requirements, such as a "High "High-
Throughput Data" service class for applications like the web and
electronic mail, or a "Telephony" service class for real-time traffic
such as voice and other telephony services. Such a service class may
be defined locally in a Differentiated Services (DS) domain, or
across multiple DS domains, including possibly extending end to end.
A service class as defined here is essentially a statement of the
required characteristics of a traffic aggregate. The required
characteristics of these traffic aggregates can be realized by the
use of defined per-hop behavior (PHB) [RFC2474]. The actual
specification of the expected treatment of a traffic aggregate within
a domain may also be defined as a per domain per-domain behavior (PDB)
[RFC3086].
Each domain may choose to implement different service classes, classes or to
use different behaviors to implement the service classes, classes or to
aggregate different kinds of traffic into the aggregates and still
achieve their required characteristics. For example, low delay,
loss, and jitter may be realized using the EF PHB, or with an over over-
provisioned AF PHB. This must be done with care as it may disrupt
the end to end end-to-end performance required by the applications/services.
This document provides recommendations on usage of PHBs for specific
service classes for their consistent implementation, these implementation. These
recommendations are not to be construed as prohibiting use of other
PHBs that realize behaviors sufficient for the relevant class of
traffic.
The Default Forwarding "Standard" service class is REQUIRED, REQUIRED; all
other service classes are OPTIONAL. It is expected that network
administrators will choose base their choice of the level of service
differentiation that they will support based on their need, starting off
with three or four service classes for user traffic and add adding others
as the need arises.
1.4. Key Differentiated Services Concepts
The reader SHOULD be familiar with the principles of the
Differentiated Services Architecture [RFC2474]. We recapitulate key
concepts here only to provide convenience for the reader, with the
referenced RFCs providing the authoritative definitions.
1.4.1. Queuing
A queue is a data structure that holds packets that are awaiting
transmission. The packets may be delayed while in the queue,
possibly due to lack of bandwidth, or because it is low in priority.
There are a number of ways to implement a queue, a queue. A simple model of a
queuing system, however, is a set of data structures for packet data,
which we will call queues queues, and a mechanism for selecting the next
packet from among them, which we call a scheduler.
1.4.1.1. Priority Queuing
A priority queuing system is a combination of a set of queues and a
scheduler that empties them in priority sequence. When asked for a
packet, the scheduler inspects the highest priority queue, and queue and, if
there is data present present, returns a packet from that queue. Failing
that, it inspects the next highest priority queue, and so on. A
freeway onramp with a stoplight for one lane, but which lane that allows vehicles in
the high occupancy vehicle high-occupancy-vehicle lane to pass, pass is an example of a priority
queuing system; the high occupancy vehicle high-occupancy-vehicle lane represents the
"queue" having priority.
In a priority queuing system, a packet in the highest priority queue
will experience a readily calculated delay - it delay. This is proportional to
the amount of data remaining to be serialized when the packet arrived
plus the volume of the data already queued ahead of it in the same
queue. The technical reason for using a priority queue relates
exactly to this fact: it limits delay and variations in delay, delay and
should be used for traffic which that has that requirement.
A priority queue or queuing system needs to avoid starvation of lower
priority
lower-priority queues. This may be achieved through a variety of means
means, such as admission control, rate control, or network
engineering.
1.4.1.2. Rate Queuing
Similarly, a rate-based queuing system is a combination of a set of
queues and a scheduler that empties each at a specified rate. An
example of a rate based rate-based queuing system is a road intersection with a
stoplight - the
stoplight. The stoplight acts as a scheduler, giving each lane a
certain opportunity to pass traffic through the intersection.
In a rate-based queuing system, such as WFQ Weighted Fair Queuing (WFQ)
or WRR, Weighted Round Robin (WRR), the delay that a packet in any given
queue will experience is dependant depends on the parameters and occupancy of its
queue and the parameters and occupancy of the queues it is competing
with. A queue whose traffic arrival rate is much less than the rate
at which it lets traffic depart will tend to be empty empty, and packets in
it will experience nominal delays. A queue whose traffic arrival
rate approximates or exceeds its departure rate will tend not to be not
empty, and packets in it will experience greater delay. Such a
scheduler can impose a minimum rate, a maximum rate, or both, on any
queue it touches.
1.4.2. Active Queue Management
"Active queue management"
Active Queue Management, or AQM AQM, is a generic name for any of a
variety of procedures that use packet dropping or marking to manage
the depth of a queue. The canonical example of such a procedure is
Random Early Detection, Detection (RED), in that a queue is assigned a minimum
and maximum threshold, and the queuing algorithm maintains a moving
average of the queue depth. While the mean queue depth exceeds the
maximum threshold, all arriving traffic is dropped. While the mean
queue depth exceeds the minimum threshold but not the maximum
threshold, a randomly selected subset of arriving traffic is marked
or dropped. This marking or dropping of traffic is intended to
communicate with the sending system, causing its congestion avoidance
algorithms to kick in. As a result of this behavior, it is
reasonable to expect that TCP's cyclic behavior is desynchronized, desynchronized and
that the mean queue depth (and therefore delay) should normally
approximate the minimum threshold.
A variation of the algorithm is applied in Assured Forwarding PHB
[RFC2597], in that the behavior aggregate consists of traffic with
multiple DSCP marks, which are intermingled in a common queue.
Different minima and maxima are configured for the several DSCPs
separately, such that traffic that exceeds a stated rate at ingress
is more likely to be dropped or marked than traffic that is within
its contracted rate.
1.4.3. Traffic Conditioning
Additionally,
In addition, at the first router in a network that a packet crosses,
arriving traffic may be measured, measured and dropped or marked according to a
policy, or perhaps shaped on network ingress ingress, as in A "A Rate Adaptive
Shaper for Differentiated Services Services" [RFC2963]. This may be used to
bias feedback loops, such as is done in Assured "Assured Forwarding PHB PHB"
[RFC2597], or to limit the amount of traffic in a system, as is done
in Expedited "Expedited Forwarding PHB PHB" [RFC3246]. Such measurement procedures
are collectively referred to as "traffic conditioners". Traffic
conditioners are normally built using token bucket meters, for
example with a committed rate and a burst size, as in Section 1.5.3 of
the DiffServ Model [RFC3290]. With The Assured Forwarding PHB [RFC2597]
uses a variation on a meter with multiple rate and burst size
measurements added to the basic single rate single burst size token
bucket meter to achieve test and identify multiple levels of conformance used by
Assured Forwarding PHB [RFC2597]. conformance.
Multiple rates and burst sizes can be realized using multiple levels
of token buckets or more complex token buckets, buckets; these are
implementation details. Some The following are some traffic conditioners
that may be used in deployment of differentiated
services are: services:
o For Class Selector (CS) PHBs, a single token bucket meter to
provide a rate plus burst size control control.
o For Expedited Forwarding (EF) PHB, a single token bucket meter to
provide a rate plus burst size control control.
o For Assured Forwarding (AF) PHBs, usually two token bucket meters
configured to provide behavior as outlined in Two "Two Rate Three
Color Marker (trTCM) (trTCM)" [RFC2698] or the Single "Single Rate Three Color Marker
(srTCM)
(srTCM)" [RFC2697]. The two rate three color two-rate, three-color marker is used to
enforce two rates whereas, rates, whereas the single rate three color single-rate, three-color marker is
used to enforce a committed rate with two burst lengths.
1.4.4. Differentiated Services Code Point (DSCP)
The DSCP is a number in the range 0..63, 0..63 that is placed into an IP
packet to mark it according to the class of traffic it belongs in.
Half of these values are earmarked for standardized services, and the
other half of them are available for local definition.
1.4.5. Per-Hop Behavior (PHB)
In the end, the mechanisms described above are combined to form a
specified set of characteristics for handling different kinds of
traffic, depending on the needs of the application. This document
seeks to identify useful traffic aggregates and to specify what PHB
should be applied to them.
1.5. Key Service Concepts
While Differentiated Services is a general architecture that may be
used to implement a variety of services, three fundamental forwarding
behaviors have been defined and characterized for general use. These
are basic Default Forwarding (DF) behavior for elastic traffic, the
Assured Forwarding (AF) behavior, and the Expedited Forwarding (EF)
behavior for real-time (inelastic) traffic. The facts that four code
points are recommended for AF, AF and that one code point is recommended
for EF, EF are arbitrary choices, and the architecture allows any
reasonable number of AF and EF classes simultaneously. The choice of
four AF classes and one EF class in the current document is also
arbitrary, and operators MAY choose to operate more or fewer of
either.
The terms "elastic" and "real-time" are defined in [RFC1633] [RFC1633], Section
3.1, as a way of understanding broad brush broad-brush application requirements.
This document should be reviewed to obtain a broad understanding of
the issues in quality of service, just as [RFC2475] should be
reviewed to understand the data plane architecture used in today's
Internet.
1.5.1. Default Forwarding (DF)
The basic forwarding behavior behaviors applied to any class of traffic are
those described in [RFC2474] and [RFC2309]. Best Effort Best-effort service may
be summarized as "I will accept your packets", packets" and is typically
configured with some bandwidth guarantee. Packets in transit may be
lost, reordered, duplicated, or delayed at random. Generally,
networks are engineered to limit this behavior, but changing traffic
loads can push any network into such a state.
Application traffic in the internet which that uses default forwarding is
expected to be "elastic" in nature. By this, we mean that the sender
of traffic will adjust its transmission rate in response to changes
in available rate, loss, or delay.
For the basic best effort best-effort service, a single DSCP value is provided to
identify the traffic, a queue to store it, and active queue
management to protect the network from it and to limit delays.
1.5.2. Assured Forwarding (AF)
The Assured Forwarding PHB [RFC2597] behavior is explicitly modeled
on Frame Relay's DE Discard Eligible (DE) flag or ATM's CLP capability, and Cell Loss
Priority (CLP) capability. It is intended for networks that offer
average-rate SLAs Service Level Agreements (SLAs) (as FR and ATM networks
do). This is an enhanced best effort best-effort service; traffic is expected to
be "elastic" in nature. The receiver will detect loss or variation
in delay in the network and provide feedback such that the sender
adjusts its transmission rate to approximate available capacity.
For such behaviors, multiple DSCP values are provided (two or three,
perhaps more using local values) to identify the traffic, a common
queue to store the aggregate aggregate, and active queue management to protect
the network from it and to limit delays. Traffic is metered as it
enters the network, and traffic is variously marked depending on the
arrival rate of the aggregate. The premise is that it is normal for
users to occasionally to use more capacity than their contract
stipulates, perhaps up to some bound. However, if traffic should be
marked or lost to manage the queue, this excess traffic will be
marked or lost first.
1.5.3. Expedited Forwarding (EF)
The intent of Expedited Forwarding PHB [RFC3246] is to provide a
building block for low loss, low delay, low-loss, low-delay, and low jitter low-jitter services. It
can be used to build an enhanced best effort best-effort service: traffic remains
subject to loss due to line errors and reordering during routing
changes. However, using queuing techniques, the probability of delay
or variation in delay is minimized. For this reason, it is generally
used to carry voice and for transport of data information that
requires "wire like" behavior through the IP network. Voice is an
inelastic "real-time" application that sends packets at the rate the
codec produces them, regardless of availability of capacity. As
such, this service has the potential to disrupt or congest a network
if not controlled. It also has the potential for abuse.
To protect the network, at minimum one SHOULD police traffic at
various points to ensure that the design of a queue is not over-run, overrun,
and then the traffic SHOULD be given a low delay low-delay queue (often using
priority, although it is asserted that a rate-based queue can do
this) to ensure that variation in delay is not an issue, to meet
application needs.
1.5.4. Class Selector (CS)
Class Selector provides support for historical codepoint definitions
and PHB requirement. The Class Selector DS field provides a limited
backward compatibility with legacy (pre DiffServ) practice, as
described in [RFC2474] [RFC2474], Section 4. Backward compatibility is
addressed in two ways. First, there are per-hop behaviors that are
already in widespread use (e.g. (e.g., those satisfying the IPv4 Precedence
queuing requirements specified in [RFC1812], [RFC1812]), and we wish to permit
their continued use in DS-compliant networks. In addition, there are
some codepoints that correspond to historical use of the IP
Precedence field field, and we reserve these codepoints to map to PHBs that
meet the general requirements specified in [RFC2474] [RFC2474], Section
4.2.2.2.
No attempt is made to maintain backward compatibility with the "DTR"
or TOS Type of Service (TOS) bits of the IPv4 TOS octet, as defined in [RFC0791]and
[RFC0791] and [RFC1349].
A DS-compliant network can be deployed with a set of one or more
Class Selector compliant Selector-compliant PHB groups. As well, Also, a network administrator
may configure the network nodes to map codepoints to PHBs PHBs,
irrespective of bits 3-5 of the DSCP field field, to yield a network that
is compatible with historical IP Precedence use. Thus, for example,
codepoint '011000' would map to the same PHB as codepoint '011010'.
1.5.5. Admission Control
Admission control including (including refusal when policy thresholds are
crossed,
crossed) can assure high quality ensure high-quality communication by ensuring the
availability of bandwidth to carry a load. Inelastic real-time flows
like VoIP
such as Voice over Internet Protocol (VoIP) (telephony) or video
conferencing services can benefit from use of an admission control
mechanism, as generally the telephony service is configured with over subscription,
over-subscription, meaning that some
user(s) users may not be able to make a
call during peak periods.
For VoIP (telephony) service, a common approach is to use signaling
protocols such as SIP, H.323, H.248, MEGACO, RSVP, etc. and Resource Reservation
Protocol (RSVP) to negotiate admittance and use of network transport
capabilities. When a user has been authorized to send voice traffic,
this admission procedure has verified that data rates will be within
the capacity of the network that it will use. Since Many RTP voice does not
payloads are inelastic and cannot react to loss or delay in any
substantive way, way. For these voice payloads, the network SHOULD police
at ingress to ensure that the voice traffic stays within its
negotiated bounds. Having thus assured a predictable input rate, the
network may use a priority queue to ensure nominal delay and
variation in delay.
Another approach that may be used in small and bandwidth constrained bandwidth-constrained
networks for limited number of flows is RSVP [RFC2205] [RFC2996].
However, there is concern with the scalability of this solution in
large networks where aggregation of reservations[RFC3175] reservations [RFC3175] is
considered to be required.
2. Service Differentiation
There are practical limits on the level of service differentiation
that should be offered in the IP networks. We believe we have
defined a practical approach in delivering service differentiation by
defining different service classes that networks may choose to
support in order to provide the appropriate level of behaviors and
performance needed by current and future applications and services.
The defined structure for providing services allows several
applications having similar traffic characteristics and performance
requirements to be grouped into the same service class. This
approach provides a lot of flexibility in providing the appropriate
level of service differentiation for current and new new, yet unknown
applications without introducing significant changes to routers or
network configurations when a new traffic type is added to the
network.
2.1. Service Classes
Traffic flowing in a network can be classified in many different
ways. We have chosen to divide it into two groupings, network
control and user/subscriber traffic. To provide service
differentiation, different service classes are defined in each
grouping. The network control traffic group can further be divided
into two service classes (see Section 3 for detailed definition of
each service class):
o "Network Control" for routing and network control function.
o "OAM" (Operations, Administration Administration, and Management) for network
configuration and management functions.
The user/subscriber traffic group is broken down into ten service
classes to provide service differentiation for all the different
types of applications/services, applications/services (see Section 4 for detailed definition
of each service class) in summary: class):
o Telephony service class is best suited for applications that
require very low delay variation and are of constant rate, such as
IP telephony (VoIP) and circuit emulation over IP applications.
o Signaling service class is best suited for peer-to-peer and
client-server signaling and control functions using protocols such
as SIP, SIP-T, H.323, H.248, MGCP, etc. and Media Gateway Control Protocol
(MGCP).
o Multimedia Conferencing service class is best suited for
applications that require very low delay, delay and have the ability to
change encoding rate (rate adaptive), such as H.323/V2 and later
video conferencing service.
o Real-time Real-Time Interactive service class is intended for interactive
variable rate inelastic applications that require low jitter, jitter and
loss and very low delay, such as interactive gaming applications
that use RTP/UDP streams for game control commands, and video
conferencing applications that do not have the ability to change
encoding rates or to mark packets with different importance indications, etc.
indications.
o Multimedia Streaming service class is best suited for variable
rate elastic streaming media applications where a human is waiting
for output and where the application has the capability to react
to packet loss by reducing its transmission rate, such as
streaming video and audio, web cast, etc. audio and webcast.
o Broadcast Video service class is best suited for inelastic
streaming media applications that may be of constant or variable
rate, requiring low jitter and very low packet loss, such as
broadcast TV and live events, video surveillance surveillance, and security.
o Low Latency Low-Latency Data service class is best suited for data processing
applications where a human is waiting for output, such as web-
based ordering, ordering or an Enterprise Resource Planning (ERP) application,
etc.
application.
o High Throughput High-Throughput Data service class is best suited for store and
forward applications such as FTP, FTP and billing record transfer, etc. transfer.
o Standard service class is for traffic that has not been identified
as requiring differentiated treatment and is normally referred to
as best effort.
o Low Priority Low-Priority Data service class is intended for packet flows where
bandwidth assurance is not required.
2.2. Categorization of User Service Classes
The ten defined user/subscriber service classes listed above can be
grouped into a small number of application categories. For some
application categories, it was felt that more than one service class
was needed to provide service differentiation within that category
due to the different traffic characteristic of the applications,
control function function, and the required flow behavior. Figure 1 provides
a summary of service class grouping into four application categories.
Application Control category: Category
o The Signaling service class is intended to be used to control
applications or user endpoints. Examples of protocols that would
use this service class are, are SIP or H.248 for IP telephone service
and SIP or IGMP Internet Group Management Protocol (IGMP) for control
of broadcast TV service to subscribers. Although user signaling
flows have similar performance requirements as Low Latency Data Low-Latency Data,
they need to be distinguished and marked with a different DSCP.
The essential distinction is something like "administrative
control and management" of the traffic affected as the protocols
in this class tend to be tied to the media stream/session they
signal and control.
Media-Oriented category: Category
Due to the vest vast number of new (in process of being deployed) and already in use
already-in-use media-oriented services in IP networks, five service
classes have been defined.
o Telephony service class is intended for IP telephony (VoIP)
service as well it
service. It may also be used for other applications that meet the
defined traffic characteristics and performance requirements.
o Real-time Real-Time Interactive service class is intended for inelastic
video flows from applications such application like SIP based as SIP-based desktop video
conferencing applications and for interactive gaming.
o Multimedia Conferencing service class is for video conferencing
solutions that have the ability to reduce their transmission rate
on detection of congestion, therefore these congestion. These flows can therefore be
classified as rate adaptive. As currently there are both two types of video
conferencing equipment are used in IP networks, ones networks (ones that generate
inelastic traffic and ones that generate rate adaptive traffic,
therefore rate-adaptive traffic),
two service class are needed. Real-time The Real-Time Interactive service
class should be used for equipment that generate generates inelastic video
flows and the Multimedia Conferencing service class for equipment
that generate rate adaptive generates rate-adaptive video flows.
o Broadcast Video service class is to be used for inelastic traffic
flows
flows, which is are intended for broadcast TV service and for
transport of live video and audio events.
o Multimedia Streaming service class is to be used for elastic
multimedia traffic flows. This multimedia content is typically
stored before being transmitted, as well it transmitted. It is also buffered at the
receiving end before being played out. The buffering is
sufficiently large to accommodate any variation in transmission
rate that is encountered in the network. Multimedia entertainment
over IP delivery services that are being developed can generate
both elastic and/or and inelastic traffic flows, therefore flows; therefore, two service
classes are defined to address this space. space, respectively:
Multimedia Streaming and Broadcast Video.
Data category: Category
The data category is divided into three service classes.
o Low Latency Low-Latency Data for applications/services that require low delay
or latency for bursty but short lived short-lived flows.
o High Throughput High-Throughput Data for applications/services that require good
throughput for long lived long-lived bursty flows. High Throughput and
Multimedia Steaming are close in their traffic flow
characteristics with High Throughput being a bit more bursty and
not as long lived long-lived as Multimedia Streaming.
o Low Priority Low-Priority Data for applications or services that can tolerate
short or long interruptions of packet flows. Low Priority The Low-Priority
Data service class can be viewed as don't care "don't care" to some degree.
Best Effort category:
Best-Effort Category
o All traffic that is not differentiated in the network falls into
this category and is mapped into the Standard service class. If a
packet is marked with a DSCP value that is not supported in the
network, it SHOULD be forwarded using the Standard service class.
Figure 1 below 1, below, provides a grouping of the defined user/subscriber
service classes into four categories categories, with indications of which ones
use an independent flow for signaling or control, control; type of flow
behavior elastic, (elastic, rate adaptive adaptive, or inelastic inelastic); and finally the last column
provides end user QoS Quality of Service (QoS) rating as defined in ITU-T
Recommendation G.1010.
-----------------------------------------------------------------
| Application | Service | Signaled | Flow | G.1010 |
| Categories | Class | | Behavior | Rating |
|-------------+---------------+----------+-----------+------------|
| Application | Signaling | N.A. Not | Inelastic | Responsive |
| Control | | | |applicable| | |
|-------------+---------------+----------+-----------+------------|
| | Telephony | Yes | Inelastic | Interactive|
| |---------------+----------+-----------+------------|
| | Real-time Real-Time | Yes | Inelastic | Interactive|
| | Interactive | | | |
| |---------------+----------+-----------+------------|
| Media- | Multimedia | Yes | Rate | Interactive|
| Oriented | Conferencing | | Adaptive | |
| |---------------+----------+-----------+------------|
| |Broadcast Video| Yes | Inelastic | Responsive |
| |---------------+----------+-----------+------------|
| | Multimedia | Yes | Elastic | Timely |
| | Streaming | | | |
|-------------+---------------+----------+-----------+------------|
| | Low Latency Low-Latency | No | Elastic | Responsive |
| | Data | | | |
| |---------------+----------+-----------+------------|
| Data |High Throughput| |High-Throughput| No | Elastic | Timely |
| | Data | | | |
| |---------------+----------+-----------+------------|
| | Low Priority Low-Priority | No | Elastic |Non-critical|
| | Data | | | |
|-------------+---------------+----------+-----------+------------|
| Best Effort | Standard | Not Specified |Non-critical|
-----------------------------------------------------------------
Note: N.A. = Not Applicable.
Figure 1: 1. User/Subscriber Service Classes Grouping
Here is a short explanation of the end user QoS category as defined
in ITU-T Recommendation G.1010. User traffic is divided into four
different categories, namely, interactive, responsive, timely, and
non-critical. An example of interactive traffic is between two
humans and is most sensitive to delay, loss, and jitter. Another
example of interactive traffic is between two servers where very low
delay and loss is are needed. Responsive traffic is typically between a
human and a server but also can also be between two servers. Responsive
traffic is less affected by jitter and can tolerate longer delays
than interactive traffic. Timely traffic is either between servers
or servers and humans and the delay tolerance is significantly longer
than responsive traffic. Non-critical traffic is normally between
servers/machines where delivery may be delay for period of time.
2.3. Service Class Characteristics
This document provides guidelines for network administrator administrators in
configuring their network for the level of service differentiation
that is appropriate in their network to meet their QoS needs. It is
expected that network operators will configure and provide in their
networks a subset of the defined service classes. Our intent is to
provide guidelines for configuration of Differentiated Services for a
wide variety of applications, services services, and network configurations.
Additionally,
In addition, network administrators may choose to define and deploy
in their network
other service classes. classes in their network.
Figure 2 provides a behavior view for traffic serviced by each
service class. The traffic characteristics column defines the
characteristics and profile of flows serviced serviced, and the tolerance to
loss, delay delay, and jitter columns define the treatment the flows will
receive. End-to-end quantitative performance requirements may be
obtained from ITU-T Recommendation Recommendations Y.1541 and Y.1540.
-------------------------------------------------------------------
|Service Class | | Tolerance to |
| Name | Traffic Characteristics | Loss |Delay |Jitter|
|===============+==============================+======+======+======|
| Network |Variable size packets, mostly | | | |
| Control |inelastic short messages, but | Low | Low | Yes |
| | traffic can also burst (BGP) | | | |
|---------------+------------------------------+------+------+------|
| | Fixed size Fixed-size small packets, | Very | Very | Very |
| Telephony | constant emission rate, | Low | Low | Low |
| | inelastic and low rate low-rate flows | | | |
|---------------+------------------------------+------+------+------|
| Signaling | Variable size packets, some | Low | Low | Yes |
| | what bursty short lived short-lived flows| | | |
|---------------+------------------------------+------+------+------|
| Multimedia | Variable size packets, | Low | Very | |
| Conferencing | constant transmit interval, | - | Low | Low |
| |rate adaptive, reacts to loss |Medium| | |
|---------------+------------------------------+------+------+------|
| Real-time Real-Time | RTP/UDP streams, inelastic, | Low | Very | Low |
| Interactive | mostly variable rate | | Low | |
|---------------+------------------------------+------+------+------|
| Multimedia | Variable size packets, |Low - |Medium| Yes |
| Streaming | elastic with variable rate |Medium| | |
|---------------+------------------------------+------+------+------|
| Broadcast | Constant and variable rate, | Very |Medium| Low |
| Video | inelastic, non bursty non-bursty flows | Low | | |
|---------------+------------------------------+------+------+------|
| Low Latency Low-Latency | Variable rate, bursty short short- | Low |Low - | Yes |
| Data | lived elastic flows | |Medium| |
|---------------+------------------------------+------+------+------|
| OAM | Variable size packets, | Low |Medium| Yes |
| | elastic & inelastic flows | | | |
|---------------+------------------------------+------+------+------|
|High Throughput|
|High-Throughput| Variable rate, bursty long long- | Low |Medium| Yes |
| Data | lived elastic flows | |- High| |
|---------------+------------------------------+------+------+------|
| Standard | A bit of everything | Not Specified |
|---------------+------------------------------+------+------+------|
| Low Priority Low-Priority | Non real-time Non-real-time and elastic | High | High | Yes |
| Data | | | | |
-------------------------------------------------------------------
Figure 2: 2. Service Class Characteristics
Note:
Notes for Figure 2: A "Yes" in the jitter-tolerant column implies
that data is buffered in the endpoint, endpoint and that a moderate level of
network-induced variation in delay will not affect the application.
Applications that use TCP as a transport are generally good examples.
Routing protocols and peer-to-peer signaling also fall in this class; while
although loss can create problems in setting up calls, a moderate
level of jitter merely makes call placement a little less predictable
in duration.
Service classes indicate the required traffic forwarding treatment in
order to meet user, application application, or network expectations. Section 3
in this document
defines the service classes that MAY be used for forwarding network
control traffic traffic, and Section 4 defines the service classes that MAY
be used for forwarding user traffic with examples of intended
application types mapped into each service class. Note that the
application types are only examples and are not meant to be all-
inclusive or prescriptive. Also it should be noted Also, note that the service class naming
or ordering does not imply any priority ordering. They are simply
reference names that are used in this document with associated QoS
behaviors that are optimized for the particular application types
they support. Network administrators MAY choose to assign different
service class names, names to the service classes that they will support.
Figure 3 defines the RECOMMENDED relationship between service classes
and DS codepoint(s) codepoint assignment with application examples. It is
RECOMMENDED that this relationship be preserved end to end.
------------------------------------------------------------------
| Service | DSCP | DSCP | Application |
| Class name Name | name Name | value Value | Examples |
|===============+=========+=============+==========================|
|Network Control| CS6 | 110000 | Network routing |
|---------------+---------+-------------+--------------------------|
| Telephony | EF | 101110 | IP Telephony bearer |
|---------------+---------+-------------+--------------------------|
| Signaling | CS5 | 101000 | IP Telephony signaling |
|---------------+---------+-------------+--------------------------|
| Multimedia |AF41,AF42|100010,100100| H.323/V2 video |
| Conferencing | AF43 | 100110 | conferencing (adaptive) |
|---------------+---------+-------------+--------------------------|
| Real-time Real-Time | CS4 | 100000 | Video conferencing and |
| Interactive | | | Interactive gaming |
|---------------+---------+-------------+--------------------------|
| Multimedia |AF31,AF32|011010,011100| Streaming video and |
| Streaming | AF33 | 011110 | audio on demand |
|---------------+---------+-------------+--------------------------|
|Broadcast Video| CS3 | 011000 |Broadcast TV & live events|
|---------------+---------+-------------+--------------------------|
| Low Latency Low-Latency |AF21,AF22|010010,010100|Client/server transactions|
| Data | AF23 | 010110 | Web-based ordering |
|---------------+---------+-------------+--------------------------|
| OAM | CS2 | 010000 | OAM&P |
|---------------+---------+-------------+--------------------------|
|High Throughput|AF11,AF12|001010,001100|
|High-Throughput|AF11,AF12|001010,001100| Store and forward |
| Data | AF13 | 001110 | applications |
|---------------+---------+-------------+--------------------------|
| Standard | DF (CS0)| 000000 | Undifferentiated |
| | | | applications |
|---------------+---------+-------------+--------------------------|
| Low Priority Low-Priority | CS1 | 001000 | Any flow that has no BW |
| Data | | | assurance |
------------------------------------------------------------------
Figure 3: 3. DSCP to Service Class Mapping
Note
Notes for Figure 3:
o Default Forwarding (DF) and Class Selector 0
(CS0) provide equivalent behavior and use the same DS codepoint codepoint,
'000000'.
It is expected that network administrators will choose base their choice of
the service classes that they will support based on their need, starting
off with three or four service classes for user traffic and add adding
others as the need arises.
Figure 4 provides a summary of DiffServ QoS mechanisms that SHOULD be
used for the defined service classes that are further detailed in
Section
Sections 3 and Section 4 of this document. Based on According to what
applications/services that need to be differentiated, network
administrators can choose the service class(es) that need to be
supported in their network.
------------------------------------------------------------------
| Service | DSCP | Conditioning at | PHB | Queuing| AQM|
| Class | | DS Edge | Used | | |
|===============+======+===================+=========+========+====|
|Network Control| CS6 | See Section 3.1 | RFC2474 | Rate |Yes | Yes|
|---------------+------+-------------------+---------+--------+----|
| Telephony | EF |Police using sr+bs | RFC3246 |Priority| No |
|---------------+------+-------------------+---------+--------+----|
| Signaling | CS5 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+------+-------------------+---------+--------+----|
| Multimedia | AF41 | Using two rate two-rate, | | | Yes|
| Conferencing | AF42 |three color |three-color marker | RFC2597 | Rate | per|
| | AF43 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+------+-------------------+---------+--------+----|
| Real-time Real-Time | CS4 |Police using sr+bs | RFC2474 | Rate | No |
| Interactive | | | | | |
|---------------+------+-------------------+---------|--------+----|
| Multimedia | AF31 | Using two rate two-rate, | | | Yes|
| Streaming | AF32 |three color |three-color marker | RFC2597 | Rate | per|
| | AF33 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+------+-------------------+---------+--------+----|
|Broadcast Video| CS3 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+------+-------------------+---------+--------+----|
| Low Low- | AF21 | Using single rate | single-rate,| | | Yes|
| Latency | AF22 |three color |three-color marker | RFC2597 | Rate | per|
| Data | AF23 | (such as RFC2697) | RFC 2697)| | |DSCP|
|---------------+------+-------------------+---------+--------+----|
| OAM | CS2 |Police using sr+bs | RFC2474 | Rate | Yes|
|---------------+------+-------------------+---------+--------+----|
| High High- | AF11 | Using two rate two-rate, | | | Yes|
| Throughput | AF12 |three color |three-color marker | RFC2597 | Rate | per|
| Data | AF13 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+------+-------------------+---------+--------+----|
| Standard | DF | Not applicable | RFC2474 | Rate | Yes|
|---------------+------+-------------------+---------+--------+----|
| Low Priority Low-Priority | CS1 | Not applicable | RFC3662 | Rate | Yes|
| Data | | | | | |
------------------------------------------------------------------
Figure 4: 4. Summary of QoS Mechanisms used Used for each Each Service Class
Notes for Figure 4:
o Conditioning at DS edge, edge means that traffic conditioning is
performed at the edge of the DiffServ network where untrusted user
devices are connected or between two DiffServ networks.
o "sr+bs" represents a policing mechanism that provides single rate
with burst size control.
o The single rate three color single-rate, three-color marker (srTCM) behavior SHOULD be
equivalent to RFC 2697 2697, and the two rate three color two-rate, three-color marker
(trTCM) behavior SHOULD be equivalent to RFC 2698.
o The PHB for Real-time Real-Time Interactive service class SHOULD be
configured to provide high bandwidth assurance. It MAY be
configured as a second EF PHB that uses relaxed performance
parameters and a rate scheduler.
o The PHB for Broadcast Video service class SHOULD be configured to
provide high bandwidth assurance. It MAY be configured as a third
EF PHB that uses relaxed performance parameters and a rate
scheduler.
o In network segments that use IP precedence marking, only one of
the two service classes can be supported, High Throughput High-Throughput Data or
Low Priority
Low-Priority Data. We RECOMMEND that the DSCP value(s) of the
unsupported service class to be changed to 000xx1 on ingress and
changed back to original value(s) on egress of the network segment
that uses precedence marking. For example, if Low Priority Low-Priority Data
is mapped to Standard service class, then 000001 DSCP marking MAY
be used to distinguish it from Standard marked packets on egress.
2.4. Deployment Scenarios
It is expected that network administrators will choose base their choice of
the service classes that they will support based on their need, starting
off with three or four service classes for user traffic and add adding
more service classes as the need arises. In this section section, we provide
three examples of possible deployment scenarios.
2.4.1. Example 1
A network administrator determined determines that they need he needs to provide different
performance levels (quality of service) in their his network for the
services that they he will be offering to their his customers. They
need He needs to
enable their his network to provide:
o Reliable VoIP (telephony) service, equivalent to PSTN Public Switched
Telephone Network (PSTN).
o A low delay low-delay assured bandwidth data service service.
o As well, support Support for current Internet services services.
For this example, the network administrator's needs are addressed
with the deployment of the following six service classes:
o Network Control service class for routing and control traffic that
is needed for reliable operation of the provider's network network.
o Standard service class for all traffic that will receive normal
(undifferentiated) forwarding treatment through their the network for
support of current Internet service service.
o Telephony service class for VoIP (telephony) bearer traffic traffic.
o Signaling service class for Telephony signaling to control the
VoIP service service.
o Low Latency Low-Latency Data service class for the low delay low-delay assured bandwidth
differentiated data service service.
o OAM service class for operation and management of the network network.
Figure 5, 5 provides a summary of the mechanisms needed for delivery of
service differentiation for Example 1.
-------------------------------------------------------------------
| Service | DSCP | Conditioning at | PHB | | |
| Class | | DS Edge | Used | Queuing| AQM|
|===============+=======+===================+=========+========+====|
|Network Control| CS6 | See Section 3.1 | RFC2474 | Rate | Yes|
|---------------+-------+-------------------+---------+--------+----|
| Telephony | EF |Police using sr+bs | RFC3246 |Priority| No |
|---------------+-------+-------------------+---------+--------+----|
| Signaling | CS5 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+-------+-------------------+---------+--------+----|
| Low Low- | AF21 | Using single rate | single-rate,| | |Yes | Yes|
| Latency | AF22 |three color |three-color marker | RFC2597 | Rate |Per | per|
| Data | AF23 | (such as RFC2697) | RFC 2697)| | |DSCP|
|---------------+-------+-------------------+---------+--------+----|
| OAM | CS2 |Police using sr+bs | RFC2474 | Rate | Yes|
|---------------+-------+-------------------+---------+--------+----|
| Standard |DF(CS0)| Not applicable | RFC2474 | Rate | Yes|
| | +other| | | | |
-------------------------------------------------------------------
Figure 5: 5. Service Provider Network Configuration Example 1
Notes for Figure 5:
o "sr+bs" represents a policing mechanism that provides single rate
with burst size control.
o The single rate three color single-rate, three-color marker (srTCM) behavior SHOULD be
equivalent to RFC 2697.
o Any packet that is marked with DSCP value that is not represented
by the supported service classes, classes SHOULD be forwarded using the
Standard service class.
2.4.2. Example 2
With this example example, we show how network operators with Example 1
capabilities can evolve their service offering to provide three new
additional services to their customers. The new additional service
capabilities that are to be added are:
o SIP based SIP-based desktop video conference capability to complement VoIP
(telephony) service service.
o Provide TV and on demand on-demand movie viewing service to residential
subscribers subscribers.
o Provide network based Network-based data storage and file backup service to business customers
customers.
The new additional services that the network administrator would like
to offer are addressed with the deployment of the following four
additional service classes. (These classes (these are additions to the six service
classes already defined in Example 1):
o Real-time Real-Time Interactive service class for transport of MPEG-4 real-
time video flows to support desktop video conferencing. The
control/signaling for video conferencing is done using the
Signaling service class.
o Broadcast Video service class for transport of IPTV broadcast
information. The channel selection and control is via IGMP
(Internet Group Management Protocol) mapped
into the Signaling service class.
o Multimedia Streaming service class for transport of stored MPEG-2
or MPEG-4 content. The selection and control of streaming
information is done using the Signaling service class. The
selection of Multimedia Streaming service class for on demand on-demand
movie service was chosen as the set-top box used for this service
has local buffering capability to compensate for the bandwidth
variability of the elastic streaming information. Note, Note that if
transport of on demand on-demand movie service is inelastic, then the
Broadcast Video service class SHOULD be used.
o High Throughput High-Throughput Data service class is for transport of bulk data
for network based network-based storage and file backup service to business
customers.
Figure 6, 6 provides a summary of the mechanisms needed for delivery of
service differentiation for all the service classes used in Example
2.
-------------------------------------------------------------------
| Service | DSCP | Conditioning at | PHB | | |
| Class | | DS Edge | Used | Queuing| AQM|
|===============+=======+===================+=========+========+====|
|Network Control| CS6 | See Section 3.1 | RFC2474 | Rate |Yes | Yes|
|---------------+-------+-------------------+---------+--------+----|
| Telephony | EF |Police using sr+bs | RFC3246 |Priority| No |
|---------------+-------+-------------------+---------+--------+----|
| Signaling | CS5 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+-------+-------------------+---------+--------+----|
| Real-time | CS4 |Police using sr+bs | RFC2474 | Rate | No |
| Interactive | | | | | |
|---------------+-------+-------------------+---------+--------+----|
|Broadcast Video| CS3 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+-------+-------------------+---------+--------+----|
| Multimedia | AF31 | Using two rate two-rate, | | |Yes |
| Streaming | AF32 |three color |three-color marker | RFC2597 | Rate |Per |per |
| | AF33 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+-------+-------------------+---------+--------+----|
| Low Low- | AF21 | Using single rate | single-rate,| | |Yes |
| Latency | AF22 |three color |three-color marker | RFC2597 | Rate |Per |per |
| Data | AF23 | (such as RFC2697) | RFC 2697)| | |DSCP|
|---------------+-------+-------------------+---------+--------+----|
| OAM | CS2 |Police using sr+bs | RFC2474 | Rate |Yes | Yes|
|---------------+-------+-------------------+---------+--------+----|
| High High- | AF11 | Using two rate two-rate, | | |Yes |
| Throughput | AF12 |three color |three-color marker | RFC2597 | Rate |Per |per |
| Data | AF13 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+-------+-------------------+---------+--------+----|
| Standard |DF(CS0)| Not applicable | RFC2474 | Rate |Yes | Yes|
| | +other| | | | |
-------------------------------------------------------------------
Figure 6: 6. Service Provider Network Configuration Example 2
Notes for Figure 6:
o "sr+bs" represents a policing mechanism that provides single rate
with burst size control.
o The single rate three color single-rate, three-color marker (srTCM) behavior SHOULD be
equivalent to RFC 2697 2697, and the two rate three color two-rate, three-color marker
(trTCM) behavior SHOULD be equivalent to RFC 2698.
o Any packet that is marked with DSCP value that is not represented
by the supported service classes, classes SHOULD be forwarded using the
Standard service class.
2.4.3. Example 3
An enterprise network administrator determined determines that they need to
provide different performance levels (quality of service) in their
network for the new services that are being offered to corporate
users. The enterprise network needs to:
o Provide reliable corporate VoIP service service.
o Provide video conferencing service to selected Conference Rooms Rooms.
o Support on demand on-demand distribution of prerecorded audio and video
information to large number of users users.
o Provide a priority data transfer capability for engineering teams
to share design information information.
o Reduce or deny bandwidth during peak traffic periods for selected
applications
applications.
o Continue to provide normal IP service to all remaining
applications and services services.
For this example, the enterprise's network needs are addressed with
the deployment of the following nine service classes:
o Network Control service class for routing and control traffic that
is needed for reliable operation of the enterprise network network.
o OAM service class for operation and management of the network network.
o Standard service class for all traffic that will receive normal
(undifferentiated) forwarding treatment treatment.
o Telephony service class for VoIP (telephony) bearer traffic traffic.
o Signaling service class for Telephony signaling to control the
VoIP service service.
o Multimedia Conferencing service class for support of inter inter-
Conference Room video conferencing service using H.323/V2 or
similar equipment.
o Multimedia Streaming service class for transfer of prerecorded
audio and video information information.
o High Throughput High-Throughput Data service class to provide bandwidth assurance
for timely transfer of large engineering files files.
o Low Priority Low-Priority Data service class for selected background
applications where data transfer can be delayed or suspended for a
period of time during peak network load conditions conditions.
Figure 7, 7 provides a summary of the mechanisms need needed for delivery of
service differentiation for Example 3.
-------------------------------------------------------------------
| Service | DSCP | Conditioning at | PHB | | |
| Class | | DS Edge | Used | Queuing| AQM|
|===============+=======+===================+=========+========+====|
|Network Control| CS6 | See Section 3.2 | RFC2474 | Rate | Yes|
|---------------+-------+-------------------+---------+--------+----|
| Telephony | EF |Police using sr+bs | RFC3246 |Priority| No |
|---------------+-------+-------------------+---------+--------+----|
| Signaling | CS5 |Police using sr+bs | RFC2474 | Rate | No |
|---------------+-------+-------------------+---------+--------+----|
| Multimedia | AF41 | Using two rate two-rate, | | | Yes|
| Conferencing | AF42 | three color three-color marker| RFC2597 | Rate | Per| per|
| | AF43 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+-------+-------------------+---------+--------+----|
| Multimedia | AF31 | Using two rate two-rate, | | | Yes|
| Streaming | AF32 | three color three-color marker| RFC2597 | Rate | Per| per|
| | AF33 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+-------+-------------------+---------+--------+----|
| OAM | CS2 |Police using sr+bs | RFC2474 | Rate | Yes|
|---------------+-------+-------------------+---------+--------+----|
| High High- | AF11 | Using two rate two-rate, | | |Yes |
| Throughput | AF12 |three color |three-color marker | RFC2597 | Rate |Per |per |
| Data | AF13 | (such as RFC2698) | RFC 2698)| | |DSCP|
|---------------+-------+-------------------+---------+--------+----|
| Low Priority Low-Priority | CS1 | Not applicable | RFC3662 | Rate | Yes|
| Data | | | | | |
|---------------+-------+-------------------+---------+--------+----|
| Standard |DF(CS0)| Not applicable | RFC2474 | Rate | Yes|
| | +other| | | | |
-------------------------------------------------------------------
Figure 7: 7. Enterprise Network Configuration Example
Notes for Figure 7:
o "sr+bs" represents a policing mechanism that provides single rate
with burst size control.
o The single rate three color single-rate, three-color marker (srTCM) behavior SHOULD be
equivalent to RFC 2697 2697, and the two rate three color two-rate, three-color marker
(trTCM) behavior SHOULD be equivalent to RFC 2698.
o Any packet that is marked with DSCP value that is not represented
by the supported service classes, classes SHOULD be forwarded using the
Standard service class.
3. Network Control Traffic
Network control traffic is defined as packet flows that are essential
for stable operation of the administered network as well as for
information that may be exchanged between neighboring networks across
a peering point where SLAs are in place. Network control traffic is
different from user application control (signaling) that may be
generated by some applications or services. Network control traffic
is mostly between routers and network nodes that are used for
operating, administering, controlling controlling, or managing the network
segments. Network Control Traffic may be split into two service
classes, i.e. i.e., Network Control and OAM.
3.1. Current Practice in The the Internet
Based on today's routing protocols and network control procedures
that are used in The the Internet, we have determined that CS6 DSCP value
SHOULD be used for routing and control and that CS7 DSCP value SHOULD
be reserved for future use, potentially for future routing and/or or control
protocols. Network administrator administrators MAY use a Local/
Experimental DSCP therefore Local/Experimental DSCP;
therefore, they may use a locally defined service class within their
network to further differentiate their routing and control traffic.
RECOMMENDED Network Edge Conditioning for CS7 DSCP marked packets:
o Drop or remark CS7 marked packets at ingress to DiffServ network domain.
o CS7 marked packets SHOULD NOT be sent across peering points.
Exchange of control information across peering points SHOULD be
done using CS6 DSCP, using DSCP and the Network Control service class.
3.2. Network Control Service Class
The Network Control service class is used for transmitting packets
between network devices (routers) that require control (routing)
information to be exchanged between nodes within the administrative
domain as well as across a peering point between different
administrative domains. Traffic transmitted in this service class is
very important as it keeps the network operational operational, and it needs to
be forwarded in a timely manner.
The Network Control service class SHOULD be configured using the
DiffServ Class Selector (CS) PHB PHB, defined in [RFC2474]. This service
class SHOULD be configured so that the traffic receives a minimum
bandwidth guarantee, to ensure that the packets always receive timely
service. The configured forwarding resources for Network Control
service class SHOULD be such that the probability of packet drop
under peak load is very low in this service class. The Network
Control service class SHOULD be configured to use a Rate Queuing
system such as defined in Section 1.4.1.2 of this document.
Examples
The following are examples of protocols and application applications that SHOULD
use the Network Control service class:
o Routing packet flows: OSPF, BGP, ISIS, RIP RIP.
o Control information exchange within and between different
administrative domains across a peering point where SLAs are in
place
place.
o LSP setup using CR-LDP and RSVP-TE RSVP-TE.
The following protocols and applications SHOULD NOT use the Network
Control service class:
o User traffic.
The following are traffic
Traffic characteristics of packet flows in the
Network Control service class:
o Mostly messages sent between routers and network servers servers.
o Ranging from 50 to 1,500 byte packet sizes, Variable size packets, normally one packet at a time time, but traffic
can also burst (BGP) (BGP).
o User traffic is not allowed to use this service class. By user
traffic
traffic, we mean packet flows that originate from user controlled user-controlled
end points that are connected to the network.
The RECOMMENDED DSCP marking is CS6 (Class Selector 6) 6).
RECOMMENDED Network Edge Conditioning:
o At peering points (between two DiffServ networks) where SLAs are
in place, CS6 marked packets SHOULD be policed, e.g. e.g., using a
single rate with burst size (sr+bs) token bucket policer to keep
the CS6 marked packet flows to within the traffic rate specified
in the SLA.
o CS6 marked packet flows from untrusted sources (for example, end
user devices) SHOULD be dropped or remarked at ingress to the
DiffServ network.
o Packets from users/subscribers are not permitted access to the
Network Control service classes.
The fundamental service offered to the Network Control service class
is enhanced best effort best-effort service with high bandwidth assurance. Since
this service class is used to forward both elastic and inelastic
flows, the service SHOULD be engineered so that the Active Queue
Management (AQM) [RFC2309] is applied to CS6 marked packets.
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth, and the max-threshold specifies the
queue depth above which all traffic is dropped or ECN marked. Thus,
in this service class, the following inequality should hold in queue
configurations:
o min-threshold CS6 < max-threshold CS6
o max-threshold CS6 <= memory assigned to the queue
Note: Many other AQM algorithms exist and are used; they should be
configured to achieve a similar result.
3.3. OAM Service Class
The OAM (Operations, Administration Administration, and Management) service class is
RECOMMENDED for OAM&P (Operations, Administration Administration, and Management and
Provisioning) using protocols such as SNMP, TFTP, Simple Network Management
Protocol (SNMP), Trivial File Transfer Protocol (TFTP), FTP, Telnet, COPS,
etc.
and Common Open Policy Service (COPS). Applications using this
service class require a low packet loss but are relatively not
sensitive to delay. This service class is configured to provide good
packet delivery for intermittent flows.
The OAM service class SHOULD use the Class Selector (CS) PHB defined
in [RFC2474]. This service class SHOULD be configured to provide a
minimum bandwidth assurance for CS2 marked packets to ensure that
they get forwarded. The OAM service class SHOULD be configured to
use a Rate Queuing system such as defined in Section 1.4.1.2 of this
document.
The following applications SHOULD use the OAM service class:
o For provisioning Provisioning and configuration of network elements elements.
o For performance Performance monitoring of network elements elements.
o For any Any network operational alarms
Traffic alarms.
The following are traffic characteristics:
o Variable size packets (50 to 1500 bytes in size) packets.
o Intermittent traffic flows flows.
o Traffic may burst at times times.
o Both elastic and inelastic flows flows.
o Traffic not sensitive to delays delays.
RECOMMENDED DSCP marking:
o All flows in this service class are marked with CS2 (Class
Selector 2) 2).
Applications or IP end points SHOULD pre-mark their packets with CS2
DSCP value. If the end point is not capable of setting the DSCP
value, then the router topologically closest to the end point SHOULD
perform Multifield (MF) Classification Classification, as defined in [RFC2475].
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o Packet flow marking (DSCP setting) from untrusted sources (end
user devices) SHOULD be verified at ingress to DiffServ network
using Multifield (MF) Classification methods methods, defined in
[RFC2475].
o Packet flows from untrusted sources (end user devices) SHOULD be
policed at ingress to DiffServ network, e.g. e.g., using single rate
with burst size token bucket policer to ensure that the traffic
stays within its negotiated or engineered bounds.
o Packet flows from trusted sources (routers inside administered
network) MAY not require policing.
o Normally OAM&P CS2 marked packet flows are not allowed to flow
across peering points, if points. If that is the case, then CS2 marked
packets SHOULD be policed (dropped) at both egress and ingress
peering interfaces.
The fundamental service offered to "OAM" traffic is enhanced best best-
effort service with controlled rate. The service SHOULD be
engineered so that CS2 marked packet flows have sufficient bandwidth
in the network to provide high assurance of delivery. Since this
service class is used to forward both elastic and inelastic flows,
the service SHOULD be engineered so that Active Queue Management
[RFC2309] is applied to CS2 marked packets.
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth for each DSCP, and the max-threshold
specifies the queue depth above which all traffic with such a DSCP is
dropped or ECN marked. Thus, in this service class, the following
inequality should hold in queue configurations:
o min-threshold CS2 < max-threshold CS2
o max-threshold CS2 <= memory assigned to the queue
Note: Many other AQM algorithms exist and are used; they should be
configured to achieve a similar result.
4. User Traffic
User traffic is defined as packet flows between different users or
subscribers. It is the traffic that is sent to or from end-terminals
and that support supports a very wide variety of applications and services.
User traffic can be differentiated in many different ways, therefore ways; therefore,
we investigated several different approaches to classify classifying user
traffic. We looked at differentiating user traffic as real-time
versus non real-time, non-real-time, elastic or rate adaptive rate-adaptive versus inelastic,
sensitive versus insensitive to loss as well as traffic
categorization as interactive, responsive, timely timely, and non-critical non-critical,
as defined in ITU-T Recommendation G.1010. At In the end, final analysis, we added up using
used all of the above for service differentiation, mapping of applications
application types that seemed to have the matching traffic characteristics that fit the traffic
profile and different sets of performance
sensitivities, and requirements of the defined to different service classes.
Network administrators can categorize their applications based on according to
the type of behavior that they require and MAY choose to support all
or a subset of the defined service classes. Figure 3 provides some
common applications and the forwarding service class classes that best supports them
support them, based on their performance requirements.
4.1. Telephony Service Class
The Telephony service class is RECOMMENDED for applications that
require real-time, very low delay, very low jitter, and very low
packet loss for relatively constant-rate traffic sources (inelastic
traffic sources). This service class SHOULD be used for IP telephony
service.
The fundamental service offered to traffic in the Telephony service
class is minimum jitter, delay, and packet loss service up to a
specified upper bound. Operation is in some respect similar to an
ATM CBR service, which has guaranteed bandwidth and which, if it
stays within the negotiated rate, experiences nominal delay and no
loss. The EF PHB has a similar guarantee.
Typical configurations negotiate the setup of telephone calls over IP
IP, using protocols such as H.248, MEGACO, H.323, or SIP. When a
user has been authorized to send telephony traffic, the call
admission procedure should have verified that the newly admitted flow
will be within the capacity of the Telephony service class forwarding
capability in the network. For VoIP (telephony) service, call
admission control is usually performed by a telephony call server/
gatekeeper using signaling (SIP, H.323, H.248, MEGACO, etc.) on
access points to the network. The bandwidth in the core network and
the number of simultaneous VoIP sessions that can be supported needs
to be engineered and controlled so that there is no congestion for
this service. Since the inelastic types of RTP telephony flows payloads in this
class do not react to loss or
substantial significant delay in any substantive
way, the Telephony service class SHOULD forward packet packets as soon as
possible. Some RTP payloads that may be used in telephony
applications are adaptive and will not be in this class.
The Telephony service class SHOULD use Expedited Forwarding (EF) PHB PHB,
as defined in [RFC3246] [RFC3246], and SHOULD be configured to receive
guaranteed forwarding resources so that all packets are forwarded
quickly. The Telephony service class SHOULD be configured to use a
Priority Queuing system such as that defined in Section 1.4.1.1 of
this document.
The following application applications SHOULD use the Telephony service class:
o VoIP (G.711, G.729 and other codecs) codecs).
o Voice-band data over IP (modem, fax) fax).
o T.38 fax over IP IP.
o Circuit emulation over IP, virtual wire, etc.
o IP VPN Virtual Private Network (VPN) service that specifies single single-
rate, mean network delay that is slightly longer then network
propagation delay, very low jitter jitter, and a very low packet loss
Traffic loss.
The following are traffic characteristics:
o Mostly fixed size fixed-size packets for VoIP (60, 70, 120 or 200 bytes in
size)
size).
o Packets emitted at constant time intervals intervals.
o Admission control of new flows is provided by telephony call
server, media gateway, gatekeeper, edge router, end terminal terminal, or
access node that provides flow admission control function.
Applications or IP end points SHOULD pre-mark their packets with EF
DSCP value. If the end point is not capable of setting the DSCP
value, then the router topologically closest to the end point SHOULD
perform Multifield (MF) Classification Classification, as defined in [RFC2475].
The RECOMMENDED DSCP marking is EF for the following applications:
o VoIP (G.711, G.729 and other codecs) codecs).
o Voice-band data over IP (modem and fax) fax).
o T.38 fax over IP IP.
o Circuit emulation over IP, virtual wire, etc.
RECOMMENDED Network Edge Conditioning:
o Packet flow marking (DSCP setting) from untrusted sources (end
user devices) SHOULD be verified at ingress to DiffServ network
using Multifield (MF) Classification methods methods, defined in
[RFC2475].
o Packet flows from untrusted sources (end user devices) SHOULD be
policed at ingress to DiffServ network, e.g. e.g., using single rate
with burst size token bucket policer to ensure that the telephony
traffic stays within its negotiated bounds.
o Policing is OPTIONAL for packet flows from trusted sources whose
behavior is assured ensured via other means (e.g., administrative controls
on those systems).
o Policing of Telephony packet flows across peering points where SLA
is in place is OPTIONAL as telephony traffic will be controlled by
admission control mechanism between peering points.
The fundamental service offered to "Telephony" traffic is enhanced
best effort
best-effort service with controlled rate, very low delay delay, and very
low loss. The service MUST be engineered so that EF marked packet
flows have sufficient bandwidth in the network to provide guaranteed
delivery. Normally traffic in this service class does not respond
dynamically to packet loss. As such, Active Queue Management
[RFC2309] SHOULD NOT be applied to EF marked packet flows.
4.2. Signaling Service Class
The Signaling service class is RECOMMENDED for delay sensitive delay-sensitive
client-server (traditional telephony) and peer-to-peer application
signaling. Telephony signaling includes signaling between IP phone
and soft-switch, soft-client and soft-switch, and media gateway and soft-
switch
soft-switch as well as peer-to-peer using various protocols. This
service class is intended to be used for control of sessions and
applications. Applications using this service class requiring require a
relatively fast response response, as there are typically several message messages of
different size sizes sent for control of the session. This service class
is configured to provide good response for short lived, short-lived, intermittent
flows that require real-time packet forwarding. To minimize the
possibility of ring clipping at start of call for VoIP service that
interfaces to a circuit switch Exchange in the Public Switch Switched
Telephone Network (PSTN), the Signaling service class SHOULD be
configured so that the probability of packet drop or significant
queuing delay under peak load is very low in IP network segments that
provide this interface. The term "ring clipping" refers to those
instances where the front end of a ringing signal is altered because
the bearer path is not made available in time to carry all of the
audible ringing signal. This condition may occur due to a race
condition between when the tone generator in the circuit switch
Exchange is turn turned on and when the bearer path through the IP network
is enabled. See Section 9.1 8.1 for additional explanation of "ring
clipping" and Section 5.1 for explanation of mapping different
signaling methods to service classes.
The Signaling service class SHOULD use the Class Selector (CS) PHB PHB,
defined in [RFC2474]. This service class SHOULD be configured to
provide a minimum bandwidth assurance for CS5 marked packets to
ensure that they get forwarded. The Signaling service class SHOULD
be configured to use a Rate Queuing system such as that defined in
Section 1.4.1.2 of this document.
The following applications SHOULD use the Signaling service class:
o Peer-to-peer IP telephony signaling (e.g., using SIP, H.323) H.323).
o Peer-to-peer signaling for multimedia applications (e.g., using
SIP, H.323) H.323).
o Peer-to-peer real-time control function function.
o Client-server IP telephony signaling using H.248, MEGACO, MGCP, IP
encapsulated ISDN ISDN, or other proprietary protocols protocols.
o Signaling to control IPTV applications using protocols such as
IGMP (Internet Group Management Protocol)
IGMP.
o Signaling flows between high capacity high-capacity telephony call servers or
soft switches using protocol such as SIP-T. Such high capacity high-capacity
devices may control thousands of telephony (VoIP) calls.
Traffic
The following are traffic characteristics:
o Variable size packets (50 to 1500 bytes in size) packets, normally one packet at a time.
o Intermittent traffic flows flows.
o Traffic may burst at times times.
o Delay sensitive Delay-sensitive control messages sent between two end-points end points.
RECOMMENDED DSCP marking:
o All flows in this service class are marked with CS5 (Class
Selector 5) 5).
Applications or IP end points SHOULD pre-mark their packets with CS5
DSCP value. If the end point is not capable of setting the DSCP
value, then the router topologically closest to the end point SHOULD
perform Multifield (MF) Classification Classification, as defined in [RFC2475].
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o Packet flow marking (DSCP setting) from untrusted sources (end
user devices) SHOULD be verified at ingress to DiffServ network
using Multifield (MF) Classification methods defined in [RFC2475].
o Packet flows from untrusted sources (end user devices) SHOULD be
policed at ingress to DiffServ network, e.g. e.g., using single rate
with burst size token bucket policer to ensure that the traffic
stays within its negotiated or engineered bounds.
o Packet flows from trusted sources (application servers inside
administered network) MAY not require policing.
o Policing of packet flows across peering points SHOULD be performed
to the Service Level Agreement (SLA).
The fundamental service offered to "Signaling" traffic is enhanced
best effort
best-effort service with controlled rate and delay. The service
SHOULD be engineered so that CS5 marked packet flows have sufficient
bandwidth in the network to provide high assurance of delivery and
low delay. Normally Normally, traffic in this service class does not respond
dynamically to packet loss. As such, Active Queue Management
[RFC2309] SHOULD NOT be applied to CS5 marked packet flows.
4.3. Multimedia Conferencing Service Class
The Multimedia Conferencing service class is RECOMMENDED for
applications that require real-time service for rate adaptive rate-adaptive
traffic. H.323/V2 and later versions of video conferencing equipment
with dynamic bandwidth adjustment is are such an application. applications. The traffic
sources (applications) in this service class have the
capability ability to dynamically change
their transmission rate based on feedback received from the receiving end, within bounds of packet
loss by receiver. One
approach used in H.323/V2 equipment is, when the receiver is sent using the applications control stream detects a
pre-configured level of packet loss, it signals to the transmitter as an
the indication of possible congestion; on-path congestion. When available, the
transmitter then selects a lower transmission rate based on pre-
configured encoding rates (or transmission rates). Note, today codec. Note that
today, many H.323/V2 video conferencing solutions implement fixed fixed-
step bandwidth change (usually reducing the rate), traffic resembling
step-wise CBR.
Typical video conferencing configurations negotiate the setup of
multimedia session using protocols such as H.323. When a user/
end-point user/end-
point has been authorized to start a multimedia session session, the
admission procedure should have verified that the newly admitted data
rate will be within the engineered capacity of the Multimedia
Conferencing service class. The bandwidth in the core network and
the number of simultaneous video conferencing sessions that can be
supported SHOULD be engineered to control traffic load for this
service.
The Multimedia Conferencing service class SHOULD use the Assured
Forwarding (AF) PHB PHB, defined in [RFC2597]. This service class SHOULD
be configured to provide a bandwidth assurance for AF41, AF42, and
AF43 marked packets to ensure that they get forwarded. The
Multimedia Conferencing service class SHOULD be configured to use a
Rate Queuing system such as that defined in Section 1.4.1.2 of this
document.
The following application applications SHOULD use the Multimedia Conferencing
service class:
o H.323/V2 and later versions of video conferencing applications
(interactive video) video).
o Video conferencing applications with rate control or traffic
content importance marking marking.
o Application server-to-application server to application server non bursty non-bursty data transfer
requiring very low delay delay.
o IP VPN service that specifies two rates and mean network delay
that is slightly longer then network propagation delay.
o Interactive, time critical time-critical, and mission critical mission-critical applications.
Traffic
The following are traffic characteristics:
o Variable size packets (50 to 1500 bytes in size) packets.
o Higher The higher the rate, the higher is the density of large packets packets.
o Constant packet emission time interval interval.
o Variable rate rate.
o Source is capable of reducing its transmission rate based on
detection of packet loss at the receiver receiver.
Applications or IP end points SHOULD pre-mark their packets with DSCP
values as shown below. If the end point is not capable of setting
the DSCP value, then the router topologically closest to the end
point SHOULD perform Multifield (MF) Classification Classification, as defined in
[RFC2475] and mark all packets as AF4x. Note: In this case, the two
rate three color
two-rate, three-color marker will be configured to operate in Color-Blind Color-
Blind mode.
RECOMMENDED DSCP marking when performed by router closest to source:
o AF41 = up to specified rate "A" "A".
o AF42 = in excess of specified rate "A" but below specified rate
"B"
"B".
o AF43 = in excess of specified rate "B" "B".
o Where "A" < "B" "B".
Note: One might expect "A" to approximate the sum of the mean rates
and "B" to approximate the sum of the peak rates.
RECOMMENDED DSCP marking when performed by H.323/V2 video
conferencing equipment:
o AF41 = H.323 video conferencing audio stream RTP/UDP RTP/UDP.
o AF41 = H.323 video conferencing video control RTCP/TCP RTCP/TCP.
o AF41 = H.323 video conferencing video stream up to specified rate
"A"
"A".
o AF42 = H.323 video conferencing video stream in excess of
specified rate "A" but below specified rate "B" "B".
o AF43 = H.323 video conferencing video stream in excess of
specified rate "B" "B".
o Where "A" < "B" "B".
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o The two rate three color two-rate, three-color marker SHOULD be configured to provide
the behavior as defined in trTCM [RFC2698].
o If packets are marked by a trusted sources or previous a previously trusted
DiffServ domain, domain and the color marking is to be preserved, then the two rate three color
two-rate, three-color marker SHOULD be configured to operate in
Color-Aware mode.
o If the packet marking is not trusted or the color marking is not
to be preserved, then the two rate three color two-rate, three-color marker SHOULD be
configured to operate in Color-Blind mode.
The fundamental service offered to "Multimedia Conferencing" traffic
is enhanced best effort best-effort service with controlled rate and delay. For
video conferencing service, typically a 1% packet loss detected at
the receiver triggers an encoding rate change, dropping to the next
lower provisioned video encoding rate. As such, Active Queue
Management [RFC2309] SHOULD be used primarily to switch the video
encoding rate under congestion, changing from high rate to lower rate i.e.
rate, i.e., 1472 kbps to 768 kbps. The probability of loss of AF41
traffic MUST NOT exceed the probability of loss of AF42 traffic,
which in turn MUST NOT exceed the probability of loss of AF43
traffic.
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth for each DSCP, and the max-threshold
specifies the queue depth above which all traffic with such a DSCP is
dropped or ECN marked. Thus, in this service class, the following
inequality should hold in queue configurations:
o min-threshold AF43 < max-threshold AF43
o max-threshold AF43 <= min-threshold AF42
o min-threshold AF42 < max-threshold AF42
o max-threshold AF42 <= min-threshold AF41
o min-threshold AF41 < max-threshold AF41
o max-threshold AF41 <= memory assigned to the queue
Note: This configuration tends to drop AF43 traffic before AF42 and
AF42 before AF41. Many other AQM algorithms exist and are used; they
should be configured to achieve a similar result.
4.4. Real-time Real-Time Interactive Service Class
The Real-time Real-Time Interactive service class is RECOMMENDED for
applications that require low loss, loss and jitter and very low delay for
variable rate inelastic traffic sources. Interactive gaming and
video conferencing applications that do not have the ability to
change encoding rates or to mark packets with different importance
indications are such applications. The traffic sources in this
traffic class does do not have the ability to reduce their transmission
rate based on according to feedback received from the receiving end.
Typically, applications in this service class are configured to
negotiate the setup of RTP/UDP control session. When a user/
end-point user/end-
point has been authorized to start a new session session, the admission
procedure should have verified that the newly admitted data rates
will be within the engineered capacity of the Real-time Real-Time Interactive
service class. The bandwidth in the core network and the number of
simultaneous Real-time Interactive sessions that can be supported
SHOULD be engineered to control traffic load for this service.
The Real-time Real-Time Interactive service class SHOULD use the Class Selector
(CS) PHB PHB, defined in [RFC2474]. This service class SHOULD be
configured to provide a high assurance for bandwidth for CS4 marked
packets to ensure that they get forwarded. The Real-time Real-Time Interactive
service class SHOULD be configured to use a Rate Queuing system such
as that defined in Section 1.4.1.2 of this document. Note, Note that this
service class MAY be configured as a second EF PHB that uses relaxed
performance parameter, a rate scheduler scheduler, and CS4 DSCP value.
The following application applications SHOULD use the Real-time Real-Time Interactive
service class:
o Interactive gaming and control control.
o Video conferencing applications without rate control or traffic
content importance marking marking.
o IP VPN service that specifies single rate and mean network delay
that is slightly longer then network propagation delay delay.
o Inelastic, interactive, time critical time-critical, and mission critical mission-critical
applications requiring very low delay
Traffic delay.
The following are traffic characteristics:
o Variable size packets (50 to 1500 bytes in size) packets.
o Variable rate non bursty rate, non-bursty.
o Application is sensitive to delay variation between flows and
sessions
sessions.
o Packets lost Lost packets, if any any, are usually ignored by application application.
RECOMMENDED DSCP marking:
o All flows in this service class are marked with CS4 (Class
Selector 4) 4).
Applications or IP end points SHOULD pre-mark their packets with CS4
DSCP value. If the end point is not capable of setting the DSCP
value, then the router topologically closest to the end point SHOULD
perform Multifield (MF) Classification Classification, as defined in [RFC2475].
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o Packet flow marking (DSCP setting) from untrusted sources (end
user devices) SHOULD be verified at ingress to DiffServ network
using Multifield (MF) Classification methods defined in [RFC2475].
o Packet flows from untrusted sources (end user devices) SHOULD be
policed at ingress to DiffServ network, e.g. e.g., using single rate
with burst size token bucket policer to ensure that the traffic
stays within its negotiated or engineered bounds.
o Packet flows from trusted sources (application servers inside
administered network) MAY not require policing.
o Policing of packet flows across peering points SHOULD be performed
to the Service Level Agreement (SLA).
The fundamental service offered to "Real-time "Real-Time Interactive" traffic is
enhanced best effort best-effort service with controlled rate and delay. The
service SHOULD be engineered so that CS4 marked packet flows have
sufficient bandwidth in the network to provide high assurance of
delivery. Normally Normally, traffic in this service class does not respond
dynamically to packet loss. As such, Active Queue Management
[RFC2309] SHOULD NOT be applied to CS4 marked packet flows.
4.5. Multimedia Streaming Service Class
The Multimedia Streaming service class is RECOMMENDED for
applications that require near-real-time packet forwarding of
variable rate elastic traffic sources that are not as delay sensitive
as applications using the Multimedia Conferencing service class.
Such applications include streaming audio and video, some video
(movies) on demand applications on-demand applications, and Web casts. webcasts. In general, the
Multimedia Streaming service class assumes that the traffic is
buffered at the source/destination and source/destination; therefore, it is less sensitive
to delay and jitter.
The Multimedia Streaming service class SHOULD use the Assured
Forwarding (AF) PHB PHB, defined in [RFC2597]. This service class SHOULD
be configured to provide a minimum bandwidth assurance for AF31, AF32
AF32, and AF33 marked packets to ensure that they get forwarded. The
Multimedia Streaming service class SHOULD be configured to use Rate
Queuing system such as that defined in Section 1.4.1.2 of this
document.
The following applications SHOULD use the Multimedia Streaming
service class:
o Buffered streaming audio (unicast) (unicast).
o Buffered streaming video (unicast) (unicast).
o Web casts Webcasts.
o IP VPN service that specifies two rates and is less sensitive to
delay and jitter
Traffic jitter.
The following are traffic characteristics:
o Variable size packets (50 to 4196 bytes in size) packets.
o Higher The higher the rate, the higher the density of large packets packets.
o Variable rate rate.
o Elastic flows flows.
o Some bursting at start of flow from some applications applications.
Applications or IP end points SHOULD pre-mark their packets with DSCP
values as shown below. If the end point is not capable of setting
the DSCP value, then the router topologically closest to the end
point SHOULD perform Multifield (MF) Classification Classification, as defined in
[RFC2475]
[RFC2475], and mark all packets as AF3x. Note: In this case, the two
rate three color
two-rate, three-color marker will be configured to operate in Color-Blind Color-
Blind mode.
RECOMMENDED DSCP marking:
o AF31 = up to specified rate "A" "A".
o AF32 = in excess of specified rate "A" but below specified rate
"B"
"B".
o AF33 = in excess of specified rate "B" "B".
o Where "A" < "B" "B".
Note: One might expect "A" to approximate the sum of the mean rates
and "B" to approximate the sum of the peak rates.
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o The two rate three color two-rate, three-color marker SHOULD be configured to provide
the behavior as defined in trTCM [RFC2698].
o If packets are marked by a trusted sources or previous a previously trusted
DiffServ domain, domain and the color marking is to be preserved, then the two rate three color
two-rate, three-color marker SHOULD be configured to operate in
Color-Aware mode.
o If the packet marking is not trusted or the color marking is not
to be preserved, then the two rate three color two-rate, three-color marker SHOULD be
configured to operate in Color-Blind mode.
The fundamental service offered to "Multimedia Streaming" traffic is
enhanced best effort best-effort service with controlled rate and delay. The
service SHOULD be engineered so that AF31 marked packet flows have
sufficient bandwidth in the network to provide high assurance of
delivery. Since the AF3x traffic is elastic and responds dynamically
to packet loss, Active Queue Management [RFC2309] SHOULD be used
primarily to reduce forwarding rate to the minimum assured rate at
congestion points. The probability of loss of AF31 traffic MUST NOT
exceed the probability of loss of AF32 traffic, which in turn MUST
NOT exceed the probability of loss of AF33.
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth for each DSCP, and the max-threshold
specifies the queue depth above which all traffic with such a DSCP is
dropped or ECN marked. Thus, in this service class, the following
inequality should hold in queue configurations:
o min-threshold AF33 < max-threshold AF33
o max-threshold AF33 <= min-threshold AF32
o min-threshold AF32 < max-threshold AF32
o max-threshold AF32 <= min-threshold AF31
o min-threshold AF31 < max-threshold AF31
o max-threshold AF31 <= memory assigned to the queue
Note: This configuration tends to drop AF33 traffic before AF32 and
AF32 before AF31. Note: Many other AQM algorithms exist and are
used; they should be configured to achieve a similar result.
4.6. Broadcast Video Service Class
The Broadcast Video service class is RECOMMENDED for applications
that require near-real-time packet forwarding with very low packet
loss of constant rate and variable rate inelastic traffic sources
that are not as delay sensitive as applications using the Real-time Real-Time
Interactive service class. Such applications include broadcast TV,
streaming of live audio and video events, some video on demand
applications video-on-demand
applications, and video surveillance. In general, the Broadcast
Video service class assumes that the destination end point has a
dejitter buffer, for video application usually a 2 - 8 video frames video-frame
buffer (66 to several hundred of milliseconds) therefore, milliseconds), and therefore that it
is less sensitive to delay and jitter.
The Broadcast Video service class SHOULD use the Class Selector (CS)
PHB
PHB, defined in [RFC2474]. This service class SHOULD be configured
to provide high assurance for bandwidth for CS3 marked packets to
ensure that they get forwarded. The Broadcast Video service class
SHOULD be configured to use Rate Queuing system such as that defined
in Section 1.4.1.2 of this document. Note, Note that this service class
MAY be configured as a third EF PHB that uses relaxed performance
parameter, a rate scheduler scheduler, and CS3 DSCP value.
The following applications SHOULD use the Broadcast Video service
class:
o Video surveillance and security (unicast) (unicast).
o TV broadcast including HDTV (multicast) (multicast).
o Video on demand (unicast) with control (virtual DVD) DVD).
o Streaming of live audio events (both unicast and multicast) multicast).
o Streaming of live video events (both unicast and multicast)
Traffic multicast).
The following are traffic characteristics:
o Variable size packets (50 to 4196 bytes in size) packets.
o Higher The higher the rate, the higher the density of large packets packets.
o Mixture of variable rate and constant rate flows flows.
o Fixed packet emission time intervals intervals.
o Inelastic flows flows.
RECOMMENDED DSCP marking:
o All flows in this service class are marked with CS3 (Class
Selector 3) 3).
o In some cases, like such as those for security and video surveillance
applications, it may be desirable to use a different DSCP marking.
If so, then locally user definable (EXP/LU) codepoint(s) codepoints in the
range '011xx1' MAY be used to provide unique traffic
identification. The locally user definable (EXP/LU) codepoint(s)
MAY be associated with the PHB that is used for CS3 traffic.
Further,
Furthermore, depending on the network scenario, additional network
edge conditioning policy MAY be need needed for the EXP/LU codepoint(s)
used.
Applications or IP end points SHOULD pre-mark their packets with CS3
DSCP value. If the end point is not capable of setting the DSCP
value, then the router topologically closest to the end point SHOULD
perform Multifield (MF) Classification Classification, as defined in [RFC2475].
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o Packet flow marking (DSCP setting) from untrusted sources (end
user devices) SHOULD be verified at ingress to DiffServ network
using Multifield (MF) Classification methods defined in [RFC2475].
o Packet flows from untrusted sources (end user devices) SHOULD be
policed at ingress to DiffServ network, e.g. e.g., using single rate
with burst size token bucket policer to ensure that the traffic
stays within its negotiated or engineered bounds.
o Packet flows from trusted sources (application servers inside
administered network) MAY not require policing.
o Policing of packet flows across peering points SHOULD be performed
to the Service Level Agreement (SLA).
The fundamental service offered to "Broadcast Video" traffic is
enhanced best effort best-effort service with controlled rate and delay. The
service SHOULD be engineered so that CS3 marked packet flows have
sufficient bandwidth in the network to provide high assurance of
delivery. Normally Normally, traffic in this service class does not respond
dynamically to packet loss. As such, Active Queue Management
[RFC2309] SHOULD NOT be applied to CS3 marked packet flows.
4.7. Low Latency Low-Latency Data Service Class
The Low Latency Low-Latency Data service class is RECOMMENDED for elastic and
responsive typically client/server based client-/server-based applications. Applications
forwarded by this service class are those requiring that require a relatively
fast response and typically have asymmetrical bandwidth need, i.e. i.e.,
the client typically sends a short message to the server and the
server responds with a much larger data flow back to the client. The
most common example of this is when a user clicks a hyperlink (~few (~ few
dozen bytes) on a web page page, resulting in a new web page to be loaded
(Kbytes of data). This service class is configured to provide good
response for TCP [RFC1633] short lived short-lived flows that require real-time
packet forwarding of variable rate traffic sources.
The Low Latency Low-Latency Data service class SHOULD use the Assured Forwarding
(AF) PHB PHB, defined in [RFC2597]. This service class SHOULD be
configured to provide a minimum bandwidth assurance for AF21, AF22 AF22,
and AF23 marked packets to ensure that they get forwarded. The Low Low-
Latency Data service class SHOULD be configured to use a Rate Queuing
system such as that defined in Section 1.4.1.2 of this document.
The following applications SHOULD use the Low Latency Low-Latency Data service
class:
o Client/server applications applications.
o SNA Systems Network Architecture (SNA) terminal to host transactions
(SNA over IP using DLSw) Data Link Switching (DLSw)).
o Web based Web-based transactions (E-commerce) (E-commerce).
o Credit card transactions transactions.
o Financial wire transfers transfers.
o Enterprise Resource Planning (ERP) applications (e.g., SAP/BaaN) SAP/BaaN).
o VPN service that supports CIR (Committed Committed Information Rate) Rate (CIR) with up
to two burst sizes
Traffic sizes.
The following are traffic characteristics:
o Variable size packets (50 to 1500 bytes in size) packets.
o Variable packet emission rate rate.
o With packet bursts of TCP window size size.
o Short traffic bursts bursts.
o Source capable of reducing its transmission rate based on
detection of packet loss at the receiver or through explicit
congestion notification notification.
Applications or IP end points SHOULD pre-mark their packets with DSCP
values as shown below. If the end point is not capable of setting
the DSCP value, then the router topologically closest to the end
point SHOULD perform Multifield (MF) Classification Classification, as defined in
[RFC2475] and mark all packets as AF2x. Note: In this case, the
single rate three color
single-rate, three-color marker will be configured to operate in
Color-Blind mode.
RECOMMENDED DSCP marking:
o AF21 = flow stream with packet burst size up to "A" bytes bytes.
o AF22 = flow stream with packet burst size in excess of "A" but
below "B" bytes bytes.
o AF23 = flow stream with packet burst size in excess of "B" bytes bytes.
o Where "A" < "B" "B".
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o The single rate three color single-rate, three-color marker SHOULD be configured to
provide the behavior as defined in srTCM [RFC2697].
o If packets are marked by a trusted sources or previous a previously trusted
DiffServ domain, domain and the color marking is to be preserved, then the single rate three color
single-rate, three-color marker SHOULD be configured to operate in
Color-Aware mode.
o If the packet marking is not trusted or the color marking is not
to be preserved, then the single rate three color single-rate, three-color marker SHOULD
be configured to operate in Color-Blind mode.
The fundamental service offered to "Low Latency "Low-Latency Data" traffic is
enhanced best effort best-effort service with controlled rate and delay. The
service SHOULD be engineered so that AF21 marked packet flows have
sufficient bandwidth in the network to provide high assurance of
delivery. Since the AF2x traffic is elastic and responds dynamically
to packet loss, Active Queue Management [RFC2309] SHOULD be used
primarily to control TCP flow rates at congestion points by dropping
packet
packets from TCP flows that have large burst size. The probability
of loss of AF21 traffic MUST NOT exceed the probability of loss of
AF22 traffic, which in turn MUST NOT exceed the probability of loss
of AF23. Explicit Congestion Notification (ECN) [RFC3168] MAY also
be used with Active Queue Management.
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth for each DSCP, and the max-threshold
specifies the queue depth above which all traffic with such a DSCP is
dropped or ECN marked. Thus, in this service class, the following
inequality should hold in queue configurations:
o min-threshold AF23 < max-threshold AF23
o max-threshold AF23 <= min-threshold AF22
o min-threshold AF22 < max-threshold AF22
o max-threshold AF22 <= min-threshold AF21
o min-threshold AF21 < max-threshold AF21
o max-threshold AF21 <= memory assigned to the queue
Note: This configuration tends to drop AF23 traffic before AF22 and
AF22 before AF21. Many other AQM algorithms exist and are used; they
should be configured to achieve a similar result.
4.8. High Throughput High-Throughput Data Service Class
The High Throughput High-Throughput Data service class is RECOMMENDED for elastic
applications that require timely packet forwarding of variable rate
traffic sources and and, more specifically specifically, is configured to provide good
throughput for TCP longer lived longer-lived flows. TCP [RFC1633] or a transport
with a consistent Congestion Avoidance Procedure [RFC2581] [RFC2582] [RFC3782]
normally will drive as high a data rate as it can obtain over a long
period of time. The FTP protocol is a common example, although one
cannot definitively say that all FTP transfers are moving data in
bulk.
The High Throughput High-Throughput Data service class SHOULD use the Assured
Forwarding (AF) PHB PHB, defined in [RFC2597]. This service class SHOULD
be configured to provide a minimum bandwidth assurance for AF11, AF12
AF12, and AF13 marked packets to ensure that they are forwarded in a
timely manner. The High Throughput High-Throughput Data service class SHOULD be
configured to use a Rate Queuing system such as that defined in
Section 1.4.1.2 of this document.
The following applications SHOULD use the High Throughput High-Throughput Data
service class:
o Store and forward applications applications.
o File transfer applications applications.
o Email Email.
o VPN service that supports two rates (committed information rate
and excess or peak information rate)
Traffic rate).
The following are traffic characteristics:
o Variable size packets (50 to 1500 bytes in size) packets.
o Variable packet emission rate rate.
o Variable rate rate.
o With packet bursts of TCP window size size.
o Source capable of reducing its transmission rate based on
detection of packet loss at the receiver or through explicit
congestion notification notification.
Applications or IP end points SHOULD pre-mark their packets with DSCP
values as shown below. If the end point is not capable of setting
the DSCP value, then the router topologically closest to the end
point SHOULD perform Multifield (MF) Classification Classification, as defined in
[RFC2475]
[RFC2475], and mark all packets as AF1x. Note: In this case, the two
rate three color
two-rate, three-color marker will be configured to operate in Color-Blind Color-
Blind mode.
RECOMMENDED DSCP marking:
o AF11 = up to specified rate "A" "A".
o AF12 = in excess of specified rate "A" but below specified rate
"B"
"B".
o AF13 = in excess of specified rate "B" "B".
o Where "A" < "B" "B".
RECOMMENDED Conditioning Performed conditioning performed at DiffServ Network Edge: network edge:
o The two rate three color two-rate, three-color marker SHOULD be configured to provide
the behavior as defined in trTCM [RFC2698].
o If packets are marked by a trusted sources or previous a previously trusted
DiffServ domain, domain and the color marking is to be preserved, then the two rate three color
two-rate, three-color marker SHOULD be configured to operate in
Color-Aware mode.
o If the packet marking is not trusted or the color marking is not
to be preserved, then the two rate three color two-rate, three-color marker SHOULD be
configured to operate in Color-Blind mode.
The fundamental service offered to "High Throughput "High-Throughput Data" traffic is
enhanced best effort best-effort service with a specified minimum rate. The
service SHOULD be engineered so that AF11 marked packet flows have
sufficient bandwidth in the network to provide assured delivery. It
can be assumed that this class will consume any available bandwidth, bandwidth
and that packets traversing congested links may experience higher
queuing delays and/or or packet loss. Since the AF1x traffic is elastic and
responds dynamically to packet loss, Active Queue Management
[RFC2309] SHOULD be used primarily to control TCP flow rates at
congestion points by dropping packet packets from TCP flows that have higher
rates first. The probability of loss of AF11 traffic MUST NOT exceed
the probability of loss of AF12 traffic, which in turn MUST NOT
exceed the probability of loss of AF13. In such a case, if one
network customer is driving significant excess and another seeks to
use the link, any losses will be experienced by the high rate high-rate user,
causing him to reduce his rate. Explicit Congestion Notification
(ECN) [RFC3168] MAY also be used with Active Queue Management.
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth for each DSCP, and the max-threshold
specifies the queue depth above which all traffic with such a DSCP is
dropped or ECN marked. Thus, in this service class, the following
inequality should hold in queue configurations:
o min-threshold AF13 < max-threshold AF13
o max-threshold AF13 <= min-threshold AF12
o min-threshold AF12 < max-threshold AF12
o max-threshold AF12 <= min-threshold AF11
o min-threshold AF11 < max-threshold AF11
o max-threshold AF11 <= memory assigned to the queue
Note: This configuration tends to drop AF13 traffic before AF12 and
AF12 before AF11. Many other AQM algorithms exist and are used; they
should be configured to achieve a similar result.
4.9. Standard Service Class
The Standard service class is RECOMMENDED for traffic that has not
been classified into one of the other supported forwarding service
classes in the DiffServ network domain. This service class provides
the Internet's "best effort" "best-effort" forwarding behavior. This service class
typically has minimum bandwidth guarantee.
The Standard service class MUST use the Default Forwarding (DF) PHB PHB,
defined in [RFC2474] [RFC2474], and SHOULD be configured to receive at least a
small percentage of forwarding resources as a guaranteed minimum.
This service class SHOULD be configured to use a Rate Queuing system
such as that defined in Section 1.4.1.2 of this document.
The following application applications SHOULD use the Standard service class:
o Network services, DNS, DHCP, BootP BootP.
o Any undifferentiated application/packet flow transported through
the DiffServ enabled network
Traffic Characteristics: network.
The following is a traffic characteristic:
o Non deterministic, Non-deterministic, mixture of everything everything.
The RECOMMENDED DSCP marking is DF (Default Forwarding) '000000' '000000'.
Network Edge Conditioning:
There is no requirement that conditioning of packet flows be
performed for this service class.
The fundamental service offered to the Standard service class is best
effort
best-effort service with active queue management to limit over-all overall
delay. Typical configurations SHOULD use random packet dropping to
implement Active Queue Management [RFC2309] or Explicit Congestion
Notification [RFC3168], and MAY impose a minimum or maximum rate on
the queue.
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth, and the max-threshold specifies the
queue depth above which all traffic is dropped or ECN marked. Thus,
in this service class, the following inequality should hold in queue
configurations:
o min-threshold DF < max-threshold DF
o max-threshold DF <= memory assigned to the queue
Note: Many other AQM algorithms exist and are used; they should be
configured to achieve a similar result.
4.10. Low Priority Low-Priority Data
The Low Priority Low-Priority Data service class serves applications that run over
TCP [RFC0793] or a transport with consistent congestion avoidance
procedure
procedures [RFC2581] [RFC2582], [RFC3782] and which that the user is willing to accept
service without guarantees. This service class is specified in [QBSS]
[RFC3662] and [RFC3662]. [QBSS].
The following applications MAY use the Low Priority Low-Priority Data service
class:
o Any TCP based application/packet based-application/packet flow transported through the
DiffServ enabled network that does not require any bandwidth
assurances
Traffic Characteristics:
assurances.
The following is a traffic characteristic:
o Non real-time Non-real-time and elastic elastic.
Network Edge Conditioning:
There is no requirement that conditioning of packet flows be
performed for this service class class.
The RECOMMENDED DSCP marking is CS1 (Class Selector 1) 1).
The fundamental service offered to the Low Priority Low-Priority Data service
class is best effort best-effort service with zero bandwidth assurance. By
placing it into a separate queue or class, it may be treated in a
manner consistent with a specific service level agreement. Service Level Agreement.
Typical configurations SHOULD use Explicit Congestion Notification
[RFC3168] or random loss to implement Active Queue Management
[RFC2309].
If RED [RFC2309] is used as an AQM algorithm, the min-threshold
specifies a target queue depth, and the max-threshold specifies the
queue depth above which all traffic is dropped or ECN marked. Thus,
in this service class, the following inequality should hold in queue
configurations:
o min-threshold CS1 < max-threshold CS1
o max-threshold CS1 <= memory assigned to the queue
Note: Many other AQM algorithms exist and are used; they should be
configured to achieve a similar result.
5. Additional Information on Service Class Usage
In this section section, we provide additional information on how some
specific applications should be configured to use the defined service
classes.
5.1. Mapping for Signaling
There are many different signaling protocols, ways that signaling is
used and performance requirements from applications that are
controlled by these protocols. We believe that different signaling
protocols should use the service class that best meet meets the objectives
of application or service they control. The following mapping is
recommended:
o Peer-to-peer signaling using SIP/H.323 are is marked with CS5 DSCP
(use Signaling service class).
o Client-server signaling as used in many implementation for IP
telephony using H.248, MEGACO, MGCP, IP encapsulated ISDN ISDN, or
proprietary protocols are is marked with CS5 DSCP (use Signaling
service class).
o Signaling between call servers or soft-switches in carrier's
network using SIP, SIP-T, or IP encapsulated ISUP, are ISUP is marked with
CS5 DSCP (use Signaling service class).
o RSVP signaling, signaling depends on the application. If RSVP signaling is
"on-path" as used in IntServ, then it needs to be forwarded from
the same queue (service class) and marked with the same DSCP value
as application data that it is controlling. This may also apply
to the "on-path" NSIS signaling Next Steps in Signaling (NSIS) protocol.
o IGMP (Internet Group Management Protocol). If IGMP is used for multicast session control such as channel
changing in IPTV systems, then IGMP packets should be marked with
CS5 DSCP (use Signaling service class). When IGMP is used only
for the normal multicast routing purpose, it should be marked with
CS6 DSCP (use Network Control service class).
5.2. Mapping for NTP
From tests that were performed, indications are that precise time
distribution requires a very low packet delay variation (jitter)
transport. Therefore Therefore, we suggest that the following guidelines for NTP
(Network
Network Time Protocol) Protocol (NTP) be used:
o When NTP is used for providing high accuracy high-accuracy timing within an
administrator's (carrier's) network or to end users/clients, the
Telephony service class should be used used, and NTP packets should be
marked with EF DSCP value.
o For applications that require "wall clock" timing accuracy, the
Standard service class should be used used, and packets should be
marked with DF DSCP.
5.3. VPN Service Mapping
Differentiated
"Differentiated Services and Tunnels Tunnels" [RFC2983] considers the
interaction of DiffServ architecture with IP tunnels of various
forms. Further to guidelines provided in RFC 2983, below are
additional guidelines for mapping service classes that are supported
in one part of the network into a VPN connection. This discussion is
limit only
limited to VPNs that use DiffServ technology for traffic
differentiation.
o The DSCP value(s) that is/are used to represent a PHB or a PHB
group should be the same for the networks at both ends of the VPN
tunnel, unless remarking of DSCP is done as ingress/egress
processing function of the tunnel. DSCP marking needs to be
preserve end-to-end.
preserved end to end.
o The VPN may be configured to support one or more service
class(es). classes.
It is left up to the administrators of the two networks to agree
on the level of traffic differentiation that will be provide provided in
the network that supports VPN service. Service classes are then
mapped into the supported VPN traffic forwarding behaviors that
meet the traffic characteristics and performance requirements of
the encapsulated service classes.
o The traffic treatment in the network that is providing the VPN
service needs to be such that the encapsulated service class or
classes receive comparable behavior and performance in terms of
delay, jitter, and packet loss and that they are within the limits
of the service specified.
o The DSCP value in the external header of the packet forwarded
through the network providing the VPN service may be different
than
from the DSCP value that is used end-to-end end to end for service
differentiation in the end network.
o The guidelines for aggregation of two or more service classes into
a single traffic forwarding treatment in the network that is
providing the VPN service is for further study.
6. Security Considerations
This document discusses policy, policy and describes a common policy
configuration, for the use of a Differentiated Services Code Point by
transports and applications. If implemented as described, it should
require that the network to do nothing that the network has not already
allowed. If that is the case, no new security issues should arise
from the use of such a policy.
It is possible for the policy to be applied incorrectly, or for a
wrong policy to be applied in the network for the defined service
class. In that case, a policy issue exists that the network SHOULD
detect, assess, and deal with. This is a known security issue in any
network dependent on policy directed policy-directed behavior.
A well known well-known flaw appears when bandwidth is reserved or enabled for a
service (for example, voice transport) and another service or an
attacking traffic stream uses it. This possibility is inherent in
DiffServ technology, which depends on appropriate packet markings.
When bandwidth reservation or a priority queuing system is used in a
vulnerable network, the use of authentication and flow admission is
recommended. To the author's knowledge, there is no known technical
way to respond to an unauthenticated data stream using service that
it is not intended to use, and such is the nature of the Internet.
The use of a service class by a user is not an issue when the SLA
between the user and the network permits him to use it, or to use it
up to a stated rate. In such cases, simple policing is used in the
Differentiated Services Architecture. Some service classes, such as
Network Control, are not permitted to be used by users at all; such
traffic should be dropped or remarked by ingress filters. Where
service classes are available under the SLA only to an authenticated
user rather than to the entire population of users, authentication
and authorization services are required, such as those surveyed in
[I-D.iab-auth-mech].
7. Summary of Changes from Previous Version
NOTE TO RFC EDITOR: Please remove this section during the publication
process.
Changes made to draft-ietf-tsvwg-diffserv-service-classes-01 from
review by David Black, Kathie Nichols, and Charlie Liu:
1. In Abstract section on page 1, and Section 1 Introduction on
page 4 first paragraph.
Old Text: This paper summarizes the recommended correlation
between service classes and their usage, with references to
their corresponding recommended Differentiated Service Code
Points (DSCP), traffic conditioners, Per-Hop Behaviors (PHB)
and Active Queue Management (AQM) mechanism. There is no
intrinsic requirement that particular DSCPs, traffic
conditioner PHBs and AQM be used for a certain service class,
but as a policy it is useful that they be applied
consistently across the network.
New Text: This document describes service classes configured
with Diffserv, recommends how they can be used and how to
construct them using Differentiated Service Code Points
(DSCP), traffic conditioners, Per-Hop Behaviors (PHB), and
Active Queue Management (AQM) mechanisms. There is no
intrinsic requirement that particular DSCPs, traffic
conditioners, PHBs, and AQM be used for a certain service
class, but as a policy and for interoperability it is useful
to apply them consistently.
2. In Section 1 Introduction on page 4. Added new first paragraph:
For understanding the role of this document we use an useful
analogy, starting from the fact that the Differentiated
Services specifications are fundamentally a toolkit - the
specifications provide the equivalent of band saws, planers,
drill presses, etc. In the hands of an expert, there's no
limit to what can be built, but such a toolkit can be
intimidating to the point of inaccessible to a non-expert who
just wants to build a bookcase. This document should be
viewed as a set of "project plans" for building all the
(diffserv) furniture that one might want. The user may
choose what to build (e.g., perhaps our non-expert doesn't
need a china cabinet right now), and how to go about building
it (e.g., plans for a non-expert probably won't employ
mortise/tenon construction, but that absence does not imply
that mortise/tenon construction is forbidden or unsound).
The authors hope that these diffserv "project plans" will
provide a useful guide to Network Administrators in the use
of diffserv techniques to implement quality of service
measures appropriate for their network's traffic.
3. In Section 1.3 first paragraph on page 5.
Old Text: A "service class" represents a set of traffic that
requires specific delay, loss, and jitter characteristics
from the network for which a consistent and defined per-hop-
behavior (PHB) applies.
New Text: A "service class" represents a set of traffic that
requires specific delay, loss, and jitter characteristics
from the network.
4. In Section 1.3 second paragraph on page 5.
Old Text: A Service Class as defined here is essentially a
statement of the required characteristics of a traffic
aggregate; the actual specification of the expected treatment
of a traffic aggregate within a domain may also be defined as
a Per Domain Behavior [RFC3086].
New Text: A service class as defined here is essentially a
statement of the required characteristics of a traffic
aggregate. The required characteristics of these traffic
aggregates can be realized by the use of defined per-hop
behavior (PHB) [RFC2474]. The actual specification of the
expected treatment of a traffic aggregate within a domain may
also be defined as a per domain behavior (PDB) [RFC3086].
5. In Section 1.3 third paragraph on page 5.
Added New Paragraph: Each domain may choose to implement
different service classes, or use different behaviors to
implement the service classes, or aggregate different kinds
of traffic into the aggregates and still achieve their
required characteristics. For example, low delay, loss, and
jitter may be realized using the EF PHB, or with an over
provisioned AF PHB. This must be done with care as it may
disrupt the end to end performance required by the
applications/services. This document provides
recommendations on usage of PHBs for specific service classes
for their consistent implementation, these recommendations
are not to be construed as prohibiting use of other PHBs that
realize behaviors sufficient for the relevant class of
traffic.
6. In Section 1.4 first paragraph on page 5.
Old Text: The reader SHOULD be familiar with the principles of
the Differentiated Services Architecture [RFC2474]. However,
we recapitulate key concepts here to save searching.
New Text: The reader SHOULD be familiar with the principles of
the Differentiated Services Architecture [RFC2474]. We
recapitulate key concepts here only to provide convenience
for the reader, with the referenced RFCs providing the
authoritative definitions.
7. In Section 1.5.3 first paragraph first sentence on page 10.
Old Text: Expedited Forwarding PHB [RFC3246] behavior was
originally proposed as a way to implement a virtual wire, and
can be used in such a manner. It is an enhanced best effort
service:
New Text: The intent of Expedited Forwarding PHB [RFC3246] is to
provide a building block for low loss, low delay, and low
jitter services. It can be used to build an enhanced best
effort service:
8. In Section 2.3 second paragraph on page 16. Deleted the last
sentence:
There there is also new work currently underway in ITU-T that
applies no known technical
way to the respond to an unauthenticated data stream using service classes defined in this document.
9. In Section 2.4.3 Example 3, on page 25. Fixed typo: "Multimedia
Steaming", changed that
it is not intended to "Multimedia Streaming".
10. In Section 2.4.3 Example 3, on page 26. Deleted use, and such is the first note
under Notes for Figure 7: Deleted text "The Administrative nature of the Internet.
The use of a service class MAY be implemented using Rate queuing method as
long as sufficient amount of bandwidth by a user is guaranteed not an issue when the SLA
between the user and latency
of scheduler the network permits him to use it, or to use it
up to a stated rate. In such cases, simple policing is sufficiently low used in the
Differentiated Services Architecture. Some service classes, such as
Network Control, are not permitted to meet be used by users at all; such
traffic should be dropped or remarked by ingress filters. Where
service classes are available under the requirement. "
11. In Section 10 on page 53. Moving SLA only to an authenticated
user rather than to the first reference:
[I-D.iab-auth-mech] Rescorla, E., "A Survey entire population of Authentication
Mechanisms", draft-iab-auth-mech-04 (work users, authentication
and authorization services are required, such as those surveyed in progress),
September 2005.
From Normative References section to Informative References
section.
8.
[AUTHMECH].
7. Acknowledgements
The authors thank the TSVWG reviewers, David Black, Brian E Carpenter E.
Carpenter, and Alan O'Neill for their review and input to this draft.
document.
The authors acknowledge a great many inputs, most notably from Bruce
Davie, Dave Oran, Ralph Santitoro, Gary Kenward, Francois Audet,
Morgan Littlewood, Robert Milne, John Shuler, Nalin Mistry, Al
Morton, Mike Pierce, Ed Koehler Jr., Tim Rahrer, Fil Dickinson, Mike
Fidler
Fidler, and Shane Amante. Kimberly King, Joe Zebarth Zebarth, and Alistair
Munroe each did a thorough proof-reading, proofreading, and the document is better
for their contributions.
9.
8. Appendix A
9.1.
8.1. Explanation of Ring Clipping
The term "ring clipping" refers to those instances where the front
end of a ringing signal is altered because the bearer channel is not
made available in time to carry all of the audible ringing signal. This
condition may occur due to a race condition between when the tone
generator located in the circuit switch Exchange is turn turned on and
when the bearer path through the IP network is enabled. To reduce
ring clipping from occurring, delay of signaling path needs to be
minimized. Below is a more detailed explanation.
The bearer path setup delay target is defined as the ISUP Initial
Address Message (IAM) / Address Complete Message (ACM) round trip round-trip
delay. ISUP refers to ISDN User Part of Signaling System No. 7 (SS7)
(SS7), as defined by ITU-T. This consists of the amount of time it
takes for the ISUP Initial Address Message (IAM) to leave the Transit
Exchange, travel through the SS7 network (including any applicable
STPs (Signaling
STPs, or Signaling Transfer Points)), Points), and be processed by the End
Exchange thus generating the Address Complete Message (ACM) and for
the ACM to travel back through the SS7 network and return to the
Transit Exchange. If the bearer path has not been set up within the soft-
switch,
soft-switch media gateway and the IP network that is performing the
Transit Exchange function by the time the ACM is forwarded to the
originating End Exchange, the phenomenon known as ring clipping may
occur. If ACM processing within soft-switch, the soft-switch media gateway and
delay through the IP network is excessive, it will delay the setup of
the bearer path path, and therefore may cause clipping of the ring tone to
be heard.
A generic maximum
The intra-exchange ISUP IAM signaling delay value of 240ms for intra
Exchange, which should not exceed
240ms. This may consist of include soft-switch, media gateways, queuing
delay in routers and distance delays between media gateway gateway, router, and soft-
switch implementations is assumed.
propagation delay on the inter-exchange data path. This value
represents the threshold where ring clipping theoretically commences.
It is important to note that the 240ms delay objective as presented
is a maximum value. Service administrators are free to choose
specific IAM delay values based on according to their own preferences (i.e.,
they may wish to set a very low mean delay objective for strategic
reasons to differentiate themselves from other providers). In
summary, out of the 240ms 240-ms delay budget, 200ms is allocated as
cross-Exchange delay (soft-switch and media gateway) and 40ms for
network delay (queuing and distance).
10.
9. References
10.1.
9.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC1349] Almquist, P., "Type of Service in the Internet Protocol
Suite", RFC 1349, July 1992.
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC
1812, June 1995.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2309] Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering,
S., Estrin, D., Floyd, S., Jacobson, V., Minshall, G.,
Partridge, C., Peterson, L., Ramakrishnan, K., Shenker,
S., Wroclawski, J., and L. Zhang, "Recommendations on
Queue Management and Congestion Avoidance in the
Internet", RFC 2309, April 1998.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, December
1998.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services",
Service", RFC 2475, December 1998.
[RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597, June 1999.
[RFC3246] Davie, B., Charny, A., Bennet, J., J.C., Benson, K., Le
Boudec, J., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, March 2002.
[RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
Per-Domain Behavior (PDB) for Differentiated Services",
RFC 3662, December 2003.
10.2.
9.2. Informative References
[I-D.iab-auth-mech]
[AUTHMECH] Rescorla, E., "A Survey of Authentication Mechanisms",
draft-iab-auth-mech-04 (work
Work in progress), Progress, September 2005.
[QBSS] "QBone Scavenger Service (QBSS) Definition", Internet2
Technical Report Proposed Service Definition, March 2001.
[RFC1633] Braden, B., R., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview", RFC
1633, June 1994.
[RFC2205] Braden, B., R., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2581] Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
Control", RFC 2581, April 1999.
[RFC2582] Floyd, S. and T. Henderson, "The NewReno Modification to
TCP's Fast Recovery Algorithm", RFC 2582, April 1999.
[RFC2697] Heinanen, J. and R. Guerin, "A Single Rate Three Color
Marker", RFC 2697, September 1999.
[RFC2698] Heinanen, J. and R. Guerin, "A Two Rate Three Color
Marker", RFC 2698, September 1999.
[RFC2963] Bonaventure, O. and S. De Cnodder, "A Rate Adaptive Shaper
for Differentiated Services", RFC 2963, October 2000.
[RFC2983] Black, D., "Differentiated Services and Tunnels", RFC
2983, October 2000.
[RFC2996] Bernet, Y., "Format of the RSVP DCLASS Object", RFC 2996,
November 2000.
[RFC3086] Nichols, K. and B. Carpenter, "Definition of
Differentiated Services Per Domain Behaviors and Rules for
their Specification", RFC 3086, April 2001.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", RFC
3168, September 2001.
[RFC3175] Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
"Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC
3175, September 2001.
[RFC3290] Bernet, Y., Blake, S., Grossman, D., and A. Smith, "An
Informal Management Model for Diffserv Routers", RFC 3290,
May 2002.
[RFC3782] Floyd, S., Henderson, T., and A. Gurtov, "The NewReno
Modification to TCP's Fast Recovery Algorithm", RFC 3782,
April 2004.
Authors' Addresses
Jozef Babiarz
Nortel Networks
3500 Carling Avenue
Ottawa, Ont. K2H 8E9
Canada
Phone: +1-613-763-6098
Fax: +1-613-765-7462
Email:
EMail: babiarz@nortel.com
Kwok Ho Chan
Nortel Networks
600 Technology Park Drive
Billerica, MA 01821
US
Phone: +1-978-288-8175
Fax: +1-978-288-8700
Email:
EMail: khchan@nortel.com
Fred Baker
Cisco Systems
1121 Via Del Rey
Santa Barbara, CA 93117
US
Phone: +1-408-526-4257
Fax: +1-413-473-2403
Email:
EMail: fred@cisco.com
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