draft-ietf-tsvwg-admitted-realtime-dscp-07.txt   rfc5865.txt 
Transport Working Group F. Baker Internet Engineering Task Force (IETF) F. Baker
Internet-Draft J. Polk Request for Comments: 5865 J. Polk
Updates: 4542,4594 Cisco Systems Updates: 4542, 4594 Cisco Systems
(if approved) M. Dolly Category: Standards Track M. Dolly
Intended status: Standards Track AT&T Labs ISSN: 2070-1721 AT&T Labs
Expires: Sept 8, 2010 March 8, 2010 May 2010
DSCP for Capacity-Admitted Traffic A Differentiated Services Code Point (DSCP)
draft-ietf-tsvwg-admitted-realtime-dscp-07 for Capacity-Admitted Traffic
Abstract Abstract
This document requests one Differentiated Services Code Point (DSCP) This document requests one Differentiated Services Code Point (DSCP)
from the Internet Assigned Numbers Authority (IANA) for a class of from the Internet Assigned Numbers Authority (IANA) for a class of
real-time traffic. This class conforms to the Expedited Forwarding real-time traffic. This traffic class conforms to the Expedited
Per Hop Behavior. It is also admitted using a CAC procedure Forwarding Per-Hop Behavior. This traffic is also admitted by the
involving authentication, authorization, and capacity admission. network using a Call Admission Control (CAC) procedure involving
This differs from a real-time traffic class conforming to the authentication, authorization, and capacity admission. This differs
Expedited Forwarding Per Hop Behavior but not subject to capacity from a real-time traffic class that conforms to the Expedited
admission or subject to very coarse capacity admission. Forwarding Per-Hop Behavior but is not subject to capacity admission
or subject to very coarse capacity admission.
Legal
This documents and the information contained therein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE
ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six Status of This Memo
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at This is an Internet Standards Track document.
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at This document is a product of the Internet Engineering Task Force
http://www.ietf.org/shadow.html. (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on September 8, 2010. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5865.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with carefully, as they describe your rights and restrictions with respect
respect to this document. Code Components extracted from this to this document. Code Components extracted from this document must
document must include Simplified BSD License text as described in include Simplified BSD License text as described in Section 4.e of
Section 4.e of the Trust Legal Provisions and are provided without the Trust Legal Provisions and are provided without warranty as
warranty as described in the BSD License. described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this 10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Problem . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2. Problem . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Candidate Implementations of the Admitted Telephony 2. Candidate Implementations of the Admitted Telephony
Service Class . . . . . . . . . . . . . . . . . . . . . . . 7 Service Class . . . . . . . . . . . . . . . . . . . . . . . 7
2.1. Potential implementations of EF in this model . . . . . . 7 2.1. Potential implementations of EF in this model . . . . . . 7
2.2. Capacity admission control . . . . . . . . . . . . . . . 8 2.2. Capacity admission control . . . . . . . . . . . . . . . 9
2.3. Recommendations on implementation of an Admitted 2.3. Recommendations on implementation of an Admitted
Telephony Service Class . . . . . . . . . . . . . . . . . 10 Telephony Service Class . . . . . . . . . . . . . . . . . 10
3. Summary: changes from RFC 4594 . . . . . . . . . . . . . . . 10 3. Summary: changes from RFC 4594 . . . . . . . . . . . . . . . 11
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . 12 7.1. Normative References . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . 12 7.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
This document requests one Differentiated Services Code Point (DSCP) This document requests one Differentiated Services Code Point (DSCP)
from the Internet Assigned Numbers Authority (IANA) for a class of from the Internet Assigned Numbers Authority (IANA) for a class of
real-time traffic. This class conforms to the Expedited Forwarding real-time traffic. This class conforms to the Expedited Forwarding
[RFC3246] [RFC3247] Per Hop Behavior. It is also admitted using a (EF) [RFC3246] [RFC3247] Per-Hop Behavior. It is also admitted using
CAC procedure involving authentication, authorization, and capacity a CAC procedure involving authentication, authorization, and capacity
admission. This differs from a real-time traffic class conforming admission. This differs from a real-time traffic class that conforms
to the Expedited Forwarding Per Hop Behavior but not subject to to the Expedited Forwarding Per-Hop Behavior but is not subject to
capacity admission or subject to very coarse capacity admission. capacity admission or subject to very coarse capacity admission.
It also recommends that certain classes of video described in In addition, this document recommends that certain classes of video
[RFC4594] be treated as requiring capacity admission as well. described in [RFC4594] be treated as requiring capacity admission.
Real-time traffic flows have one or more potential congestion points Real-time traffic flows have one or more potential congestion points
between the endpoints. Reserving capacity for these flows is between the endpoints. Reserving capacity for these flows is
important to application performance. All of these applications important to application performance. All of these applications have
have low tolerance to jitter (aka delay variation) and loss, as low tolerance to jitter (aka delay variation) and loss, as summarized
summarized in Section 2, and most (except for multimedia in Section 2, and most (except for multimedia conferencing) have
conferencing) have inelastic flow behavior from Figure 1 of inelastic flow behavior from Figure 1 of [RFC4594]. Inelastic flow
[RFC4594]. Inelastic flow behavior and low jitter/loss tolerance behavior and low jitter/loss tolerance are the service
are the service characteristics that define the need for admission characteristics that define the need for admission control behavior.
control behavior.
One of the reasons behind this is the need for classes of traffic One of the reasons behind the requirement for capacity admission is
that are handled under special policies. Service providers need to the need for classes of traffic that are handled under special
distinguish between special-policy traffic and other classes, policies. Service providers need to distinguish between special-
particularly the existing VoIP services that perform no capacity policy traffic and other classes, particularly the existing Voice
admission or only very coarse capacity admission and can exceed over IP (VoIP) services that perform no capacity admission or only
their allocated resources. very coarse capacity admission and can exceed their allocated
resources.
The requested DSCP applies to the Telephony Service Class described The requested DSCP applies to the Telephony Service Class described
in [RFC4594]. in [RFC4594].
Since video classes have not had the history of mixing admitted and Since video classes have not had the history of mixing admitted and
non-admitted traffic in the same Per-Hop Behavior (PHB) as has non-admitted traffic in the same Per-Hop Behavior (PHB) as has
occurred for EF, an additional DSCP code point is not recommended occurred for EF, an additional DSCP code point is not recommended
within this document for video. Instead, the recommended "best within this document for video. Instead, the recommended "best
practice" is to perform admission control for all traffic in three practice" is to perform admission control for all traffic in three of
of [RFC4594]'s video classes: the the video classes from [RFC4594]:
o Interactive Real-Time Traffic (CS4, used for Video conferencing o The Interactive Real-Time Traffic (CS4, used for Video
and Interactive gaming), conferencing and Interactive gaming),
o Broadcast TV (CS3) for use in a video on demand context, and o The Broadcast TV (CS3) for use in a video on demand context, and
o AF4 Multimedia Conferencing (video conferencing).
Other video classes are believed to not have the current problem of o The AF4 Multimedia Conferencing (video conferencing).
Other video classes are believed not to have the current problem of
confusion with unadmitted traffic and therefore would not benefit confusion with unadmitted traffic and therefore would not benefit
from the notion of a separate DSCP for admitted traffic. Within an from the notion of a separate DSCP for admitted traffic. Within an
ISP and on inter-ISP links (i.e. within networks whose internal ISP and on inter-ISP links (i.e., within networks whose internal
paths are uniform at hundreds of megabits per second or faster), one paths are uniform at hundreds of megabits per second or faster), one
would expect all of this traffic to be carried in the Real-Time would expect all of this traffic to be carried in the Real-Time
Traffic (RTP) Class described in [RFC5127]. Traffic (RTP) class described in [RFC5127].
1.1. Definitions 1.1. Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
The following terms and acronyms are used in this document. The following terms and acronyms are used in this document.
PHB: A Per-Hop-Behavior (PHB) is the externally observable PHB: A Per-Hop Behavior (PHB) is the externally observable
forwarding behavior applied at a Differentiated Services forwarding behavior applied at a Differentiated Services
compliant node to a DS behavior aggregate [RFC2475]. It may be compliant node to a DS behavior aggregate [RFC2475]. It may
thought of as a program configured on the interface of an be thought of as a program configured on the interface of an
Internet host or router, specified in terms of drop Internet host or router, specified in terms of drop
probabilities, queuing priorities or rates, and other handling probabilities, queuing priorities or rates, and other handling
characteristics for the traffic class. characteristics for the traffic class.
DSCP: The Differentiated Services Code Point (DSCP), as defined in DSCP: The Differentiated Services Code Point (DSCP), as defined in
[RFC2474], is a value which is encoded in the DS field, and which [RFC2474], is a value that is encoded in the DS field, and
each DS Node MUST use to select the PHB which is to be that each DS Node MUST use to select the PHB that is to be
experienced by each packet it forwards [RFC3260]. It is a 6-bit experienced by each packet it forwards [RFC3260]. It is a
number embedded into the 8-bit TOS field of an IPv4 datagram or 6-bit number embedded into the 8-bit TOS (type of service)
the Traffic Class field of an IPv6 datagram. field of an IPv4 datagram or the Traffic Class field of an
IPv6 datagram.
CAC: Call Admission Control includes concepts of authorization and CAC: Call Admission Control includes concepts of authorization and
capacity admission. "Authorization" refers to any procedure that capacity admission. "Authorization" refers to any procedure
identifies a user, verifies the authenticity of the that identifies a user, verifies the authenticity of the
identification, and determines whether the user is authorized to identification, and determines whether the user is authorized
use the service under the relevant policy. "Capacity Admission" to use the service under the relevant policy. "Capacity
refers to any procedure that determines whether capacity exists Admission" refers to any procedure that determines whether
supporting a session's requirements under some policy. capacity exists supporting a session's requirements under some
policy.
In the Internet, these are separate functions, while in the PSTN In the Internet, these are separate functions; while in the
they and call routing are carried out together. Public Switched Telephone Network (PSTN), they and call
routing are carried out together.
UNI: A User/Network Interface (UNI) is the interface (often a UNI: A User/Network Interface (UNI) is the interface (often a
physical link or its virtual equivalent) that connects two physical link or its virtual equivalent) that connects two
entities that do not trust each other, and in which one (the entities that do not trust each other, and in which one (the
user) purchases connectivity services from the other (the user) purchases connectivity services from the other (the
network). network).
Figure 1 shows two user networks connected by what appears to Figure 1 shows two user networks connected by what appears to
each of them to be a single network ("The Internet", access to each of them to be a single network ("The Internet", access to
which is provided by their service provider) that provides which is provided by their service provider) that provides
connectivity services to other users. connectivity services to other users.
UNIs tend to be the bottlenecks in the Internet, where users UNIs tend to be the bottlenecks in the Internet, where users
purchase relatively low amounts of bandwidth for cost or service purchase relatively low amounts of bandwidth for cost or
reasons, and as a result are most subject to congestion issues service reasons, and as a result are most subject to
and therefore issues requiring traffic conditioning and service congestion issues and therefore issues requiring traffic
prioritization. conditioning and service prioritization.
NNI: A Network/Network Interface (NNI) is the interface (often a NNI: A Network/Network Interface (NNI) is the interface (often a
physical link or its virtual equivalent) that connects two physical link or its virtual equivalent) that connects two
entities that trust each other within limits, and in which the entities that trust each other within limits, and in which the
two are seen as trading services for value. Figure 1 shows three two are seen as trading services for value. Figure 1 shows
service networks that together provide the connectivity services three service networks that together provide the connectivity
that we call "the Internet". They are different administrations services that we call "the Internet". They are different
and are very probably in competition, but exchange contracts for administrations and are very probably in competition, but
connectivity and capacity that enable them to offer specific exchange contracts for connectivity and capacity that enable
services to their customers. them to offer specific services to their customers.
NNIs may not be bottlenecks in the Internet if service providers NNIs may not be bottlenecks in the Internet if service
contractually agree to provision excess capacity at them, as they providers contractually agree to provision excess capacity at
commonly do. However, NNI performance may differ by ISP, and the them, as they commonly do. However, NNI performance may
performance guarantee interval may range from a month to a much differ by ISP, and the performance guarantee interval may
shorter period. Furthermore, a peering point NNI may not have range from a month to a much shorter period. Furthermore, a
contractual performance guarantees or may become overloaded under peering point NNI may not have contractual performance
certain conditions. They are also policy-controlled interfaces, guarantees or may become overloaded under certain conditions.
especially in BGP. As a result, they may require traffic They are also policy-controlled interfaces, especially in BGP.
prioritization policy. As a result, they may require a traffic prioritization policy.
Queue: There are multiple ways to build a multi-queue scheduler. Queue: There are multiple ways to build a multi-queue scheduler.
Weighted Round Robin (WRR) literally builds multiple lists and Weighted Round Robin (WRR) literally builds multiple lists and
visits them in a specified order, while a calendar queue (often visits them in a specified order, while a calendar queue
used to implement Weighted Fair Queuing, or WFQ) builds a list (often used to implement Weighted Fair Queuing, or WFQ) builds
for each time interval and queues at most a stated amount of data a list for each time interval and queues at most a stated
in each such list for transmission during that time interval. amount of data in each such list for transmission during that
While these differ dramatically in implementation, the external time interval. While these differ dramatically in
difference in behavior is generally negligible when they are implementation, the external difference in behavior is
properly configured. Consistent with the definitions used in the generally negligible when they are properly configured.
Differentiated Services Architecture [RFC2475], these are treated Consistent with the definitions used in the Differentiated
as equivalent in this document, and the lists of WRR and the Services Architecture [RFC2475], these are treated as
classes of a calendar queue will be referred to uniformly as equivalent in this document, and the lists of WRR and the
"queues". classes of a calendar queue will be referred to uniformly as
"queues".
_.--------. _.--------.
,-'' `--. ,-'' `--.
,-' `-. ,-' `-.
,-------. ,',-------. `. ,-------. ,',-------. `.
,' `. ,',' `. `. ,' `. ,',' `. `.
/ User \ UNI / / Service \ \ / User \ UNI / / Service \ \
( Network +-----+ Network ) `. ( Network +-----+ Network ) `.
\ / ; \ / : \ / ; \ / :
`. ,' ; `. .+ : `. ,' ; `. .+ :
skipping to change at page 6, line 35 skipping to change at page 6, line 38
,' `. : ,' `+ ; ,' `. : ,' `+ ;
/ User \ UNI / Service \ ; / User \ UNI / Service \ ;
( Network +-----+ Network ) ,' ( Network +-----+ Network ) ,'
\ / \ \ / / \ / \ \ / /
`. ,' `.`. ,' ,' `. ,' `.`. ,' ,'
'-------' `.'-------' ,' '-------' `.'-------' ,'
`-. ,-' `-. ,-'
`--. _.-' `--. _.-'
`--------'' `--------''
Figure 1: UNI and NNI interfaces Figure 1: UNI and NNI Interfaces
1.2. Problem 1.2. Problem
In short, the Telephony Service Class described in [RFC4594] permits In short, the Telephony Service Class, described in [RFC4594],
the use of capacity admission in implementing the service, but permits the use of capacity admission in implementing the service,
present implementations either provide no capacity admission but present implementations either provide no capacity admission
services or do so in a manner that depends on specific traffic services or do so in a manner that depends on specific traffic
engineering. In the context of the Internet backbone, the two are engineering. In the context of the Internet backbone, the two are
essentially equivalent; the edge network depends on specific essentially equivalent; the edge network depends on specific
engineering by the service provider that might not be present, engineering by the service provider that might not be present,
especially in a mobile environment. especially in a mobile environment.
However, services are being requested of the network that would However, services are being requested of the network that would
specifically make use of capacity admission, and would distinguish specifically make use of capacity admission, and would distinguish
among users or the uses of available Voice-over-IP or Video-over-IP among users or the uses of available Voice-over-IP or Video-over-IP
capacity in various ways. Various agencies would like to provide capacity in various ways. Various agencies would like to provide
services as described in section 2.6 of [RFC4504] or in [RFC4190]. services as described in RFC [RFC4190] or in Section 2.6 of
[RFC4504].
This requires the use of capacity admission to differentiate among This requires the use of capacity admission to differentiate among
users to provide services to them that are not afforded to users to provide services to them that are not afforded to non-
non-capacity admitted customer-to-customer IP telephony sessions. capacity admitted customer-to-customer IP telephony sessions.
2. Candidate Implementations of the Admitted Telephony Service Class 2. Candidate Implementations of the Admitted Telephony Service Class
2.1. Potential implementations of EF in this model 2.1. Potential Implementations of EF in This Model
There are at least two possible ways to implement isolation between There are at least two possible ways to implement isolation between
the Capacity Admitted PHB and the Expedited Forwarding PHB in this the Capacity Admitted PHB and the Expedited Forwarding PHB in this
model. They are to implement separate classes as a set of model. They are to implement separate classes as a set of
o Multiple data plane traffic classes, each consisting of a policer o Multiple data plane traffic classes, each consisting of a policer
and a queue, and the queues enjoying different priorities, or and a queue, with the queues enjoying different priorities, or
o Multiple data plane traffic classes, each consisting of a policer o Multiple data plane traffic classes, each consisting of a policer
but feeding into a common queue or multiple queues at the same but feeding into a common queue or multiple queues at the same
priority. priority.
We will explain the difference, and describe in what way they differ We will explain the difference and describe in what way they differ
in operation. The reason this is necessary is that there is current in operation. The reason this is necessary is that there is current
confusion in the industry. confusion in the industry.
The multi-priority model is shown in Figure 2. In this model, The multi-priority model is shown in Figure 2. In this model,
traffic from each service class is placed into a separate priority traffic from each service class is placed into a separate priority
queue. If data is present in more than one queue, traffic from one queue. If data is present in more than one queue, traffic from one
of them will always be selected for transmission. This has the of them will always be selected for transmission. This has the
effect of transferring jitter from the higher priority queue to the effect of transferring jitter from the higher-priority queue to the
lower priority queues, and reordering traffic in a way that gives lower-priority queues, and reordering traffic in a way that gives the
the higher priority traffic a smaller average queuing delay. Each higher-priority traffic a smaller average queuing delay. Each queue
queue must have its own policer, however, to protect the network must have its own policer, however, to protect the network from
from errors and attacks; if a traffic class thinks it is carrying a errors and attacks; if a traffic class thinks it is carrying a
certain data rate but an abuse sends significantly more, the effect certain data rate but an abuse sends significantly more, the effect
of simple prioritization would not preserve the lower priorities of of simple prioritization would not preserve the lower priorities of
traffic, which could cause routing to fail or otherwise impact an traffic, which could cause routing to fail or otherwise impact a
SLA. service level agreement (SLA).
. .
policers priorities |`. policers priorities |`.
Admitted EF <=> ----------||----+ `. Admitted EF <=> ----------||----+ `.
high| `. high| `.
Unadmitted EF <=> ----------||----+ .'----------- Unadmitted EF <=> ----------||----+ .'-----------
. medium .' . medium .'
rate queues |`. +-----+ .' Priority rate queues |`. +-----+ .' Priority
AF1------>||----+ `. / low |' Scheduler AF1------>||----+ `. / low |' Scheduler
| `. / | `. /
AF2------>||----+ .'-+ AF2------>||----+ .'-+
| .' | .'
CS0------>||----+ .' Rate Scheduler CS0------>||----+ .' Rate Scheduler
|' (WFQ, WRR, etc) |' (WFQ, WRR, etc.)
Figure 2: Implementation as a data plane priority Figure 2: Implementation as a Data Plane Priority
The multi-policer model is shown in Figure 3. In this model, The multi-policer model is shown in Figure 3. In this model, traffic
traffic from each service class is policed according to its SLA from each service class is policed according to its SLA requirements,
requirements, and then placed into a common priority queue. Unlike and then placed into a common priority queue. Unlike the multi-
the multi-priority model, the jitter experienced by the traffic priority model, the jitter experienced by the traffic classes in this
classes in this case is the same, as there is only one queue, but case is the same, as there is only one queue, but the sum of the
the sum of the traffic in this higher priority queue experiences traffic in this higher-priority queue experiences less average jitter
less average jitter than the elastic traffic in the lower priority. than the elastic traffic in the lower-priority.
policers priorities . policers priorities .
Admitted EF <=> -------\ |`. Admitted EF <=> -------\ |`.
--||----+ `. --||----+ `.
Unadmitted EF <=> -------/ high| `. Unadmitted EF <=> -------/ high| `.
. | .'-------- . | .'--------
rate queues |`. +-----+ .' rate queues |`. +-----+ .'
AF1------>||----+ `. / low | .' Priority AF1------>||----+ `. / low | .' Priority
| `. / |' Scheduler | `. / |' Scheduler
AF2------>||----+ .'-+ AF2------>||----+ .'-+
| .' | .'
CS0------>||----+ .' Rate Scheduler CS0------>||----+ .' Rate Scheduler
|' (WFQ, WRR, etc) |' (WFQ, WRR, etc.)
Figure 3: Implementation as a data plane policer Figure 3: Implementation as a Data Plane Policer
The difference between the two operationally is, as stated, the The difference between the two operationally is, as stated, the
issues of loss due to policing and distribution of jitter. issues of loss due to policing and distribution of jitter.
If the two traffic classes are, for example, voice and video, If the two traffic classes are, for example, voice and video,
datagrams containing video data can be relatively large (often of datagrams containing video data can be relatively large (often of
variable sizes up to the path MTU) while datagrams containing voice variable sizes up to the path MTU), while datagrams containing voice
are relatively small, on the order of only 40 to 200 bytes, are relatively small, on the order of only 40 to 200 bytes, depending
depending on the codec. On lower speed links (less than 10 MBPS), on the codec. On lower-speed links (less than 10 MBPS), the jitter
the jitter introduced by video to voice can be disruptive, while at introduced by video to voice can be disruptive, while at higher
higher speeds the jitter is nominal compared to the jitter speeds, the jitter is nominal compared to the jitter requirements of
requirements of voice. At access network speeds, therefore, voice. Therefore, at access network speeds, [RFC4594] recommends the
[RFC4594] recommends separation of video and voice into separate separation of video and voice into separate queues, while at optical
queues, while at optical speeds [RFC5127] recommends that they use a speeds, [RFC5127] recommends that they use a common queue.
common queue.
If, on the other hand, the two traffic classes are carrying the same If, on the other hand, the two traffic classes are carrying the same
type of application with the same jitter requirements, then giving type of application with the same jitter requirements, then giving
one preference in this sense does not benefit the higher priority one preference in this sense does not benefit the higher-priority
traffic and may harm the lower priority traffic. In such a case, traffic and may harm the lower-priority traffic. In such a case,
using separate policers and a common queue is a superior approach. using separate policers and a common queue is a superior approach.
2.2. Capacity admission control 2.2. Capacity Admission Control
There are at least six major ways that capacity admission is done or There are at least six major ways that capacity admission is done or
has been proposed to be done for real-time applications. Each will has been proposed to be done for real-time applications. Each will
be described below, then Section 3 will judge which ones are likely be described below, and Section 3 will judge which ones are likely to
to meet the requirements of the Admitted Telephony service class. meet the requirements of the Admitted Telephony service class. These
These include: include:
o Drop Precedence used to force sessions to voluntarily exit, o Drop Precedence used to force sessions to voluntarily exit,
o Capacity admission control by assumption or engineering, o Capacity admission control by assumption or engineering,
o Capacity admission control by call counting, o Capacity admission control by call counting,
o End-point capacity admission performed by probing the network, o Endpoint capacity admission performed by probing the network,
o Centralized capacity admission control via bandwidth broker, and o Centralized capacity admission control via bandwidth broker, and
o Distributed capacity admission control using protocols such as o Distributed capacity admission control using protocols such as
RSVP or NSIS. Resource Reservation Protocol (RSVP) or Next Steps in Signaling
(NSIS).
The problem with dropping traffic to force users to hang up is that The problem with dropping traffic to force users to hang up is that
it affects a broad class of users - if there is capacity for N calls it affects a broad class of users -- if there is capacity for N calls
and the N+1 calls are active, data is dropped randomly from all and the N+1 calls are active, data is dropped randomly from all
sessions to ensure that offered load doesn't exceed capacity. On sessions to ensure that offered load doesn't exceed capacity. On
very fast links, that is acceptable, but on lower speed links it can very fast links, that is acceptable, but on lower speed links it can
seriously affect call quality. There is also a behavioral issue seriously affect call quality. There is also a behavioral issue
involved here, in which users who experience poor quality calls tend involved here, in which users who experience poor quality calls tend
to hang up and call again, making the problem better - then worse. to hang up and call again, making the problem better -- then worse.
The problem with capacity admission by assumption, which is widely The problem with capacity admission by assumption, which is widely
deployed in today's VoIP environment, is that it depends on the deployed in today's VoIP environment, is that it depends on the
assumptions made. One can do careful traffic engineering to ensure assumptions made. One can do careful traffic engineering to ensure
needed bandwidth, but this can also be painful, and has to be needed bandwidth, but this can also be painful, and has to be
revisited when the network is changed or network usage changes. revisited when the network is changed or network usage changes.
The problem with call counting based admission control is it gets The problem with call-counting-based admission control is that it
exponentially worse the farther you get from the control point gets exponentially worse the farther you get from the control point
(e.g., it lacks sufficient scalability out into the network). (e.g., it lacks sufficient scalability on the outskirts of the
network).
There are two fundamental problems with depending on the endpoint to There are two fundamental problems with depending on the endpoint to
perform capacity admission; it may not be able to accurately measure perform capacity admission: it may not be able to accurately measure
the impact of the traffic it generates on the network, and it tends the impact of the traffic it generates on the network, and it tends
to be greedy (e.g., it doesn't care). If the network operator is to be greedy (e.g., it doesn't care). If the network operator is
providing a service, he must be able to guarantee the service, which providing a service, he must be able to guarantee the service, which
means that he cannot trust systems that are not controlled by his means that he cannot trust systems that are not controlled by his
network. network.
The problem with capacity controls via a bandwidth broker is The problem with capacity controls via a bandwidth broker is that
centralized servers lack far away awareness, and also lack effective centralized servers lack far away awareness, and also lack effective
real-time reaction to dynamic changes in all part of the network real-time reaction to dynamic changes in all parts of the network at
at all instances of time. all instances of time.
The problem with mechanisms that do not enable the association of a The problem with mechanisms that do not enable the association of a
policy with the request is that they do not allow for multi-policy policy with the request is that they do not allow for multi-policy
services, which are becoming important. services, which are becoming important.
The operator's choice of admission procedure MUST, for this DSCP, The operator's choice of admission procedure MUST, for this DSCP,
ensure the following: ensure the following:
o The actual links that a session uses have enough bandwidth to o The actual links that a session uses have enough bandwidth to
support it. support it.
o New sessions are refused admission if there is inadequate o New sessions are refused admission if there is inadequate
bandwidth under the relevant policy. bandwidth under the relevant policy.
o If multiple policies are in use in a network, that the user is o A user is identified and the correct policy is applied if multiple
identified and the correct policy applied. policies are in use in a network.
o Under periods of network stress, the process of admission of new o Under periods of network stress, the process of admission of new
sessions does not disrupt existing sessions, unless the service sessions does not disrupt existing sessions, unless the service
explicitly allows for disruption of calls. explicitly allows for disruption of calls.
2.3. Recommendations on implementation of an Admitted Telephony 2.3. Recommendations on Implementation of an Admitted Telephony
Service Class Service Class
When coupled with adequate AAA and capacity admission procedures as When coupled with adequate Authentication, Authorization, and
described in Section 2.2, either of the two PHB implementations Accounting (AAA) and capacity admission procedures as described in
described in Section 2.1 is sufficient to provide the services Section 2.2, either of the two PHB implementations described in
required for an Admitted Telephony service class. If preemption is Section 2.1 is sufficient to provide the services required for an
required, as described in section 2.3.5.2 of [RFC4542], this Admitted Telephony service class. If preemption is required, Section
provides the tools for carrying out the preemption. If preemption is 2.3.5.2 of [RFC4542] provides the tools for carrying out the
not in view, or if used in addition to preemptive services, the preemption. If preemption is not in view, or if used in addition to
application of different thresholds depending on call precedence has preemptive services, the application of different thresholds
the effect of improving the probability of call completion by depending on call precedence has the effect of improving the
admitting preferred calls at a time that other calls are being probability of call completion by admitting preferred calls at a time
refused. Routine and priority traffic can be admitted using the when other calls are being refused. Routine and priority traffic can
same DSCP value, as the choice of which calls are admitted is be admitted using the same DSCP value, as the choice of which calls
handled in the admission procedure executed in the control plane, are admitted is handled in the admission procedure executed in the
not the policing of the data plane. control plane, not the policing of the data plane.
On the point of what protocols and procedures are required for On the point of what protocols and procedures are required for
authentication, authorization, and capacity admission, we note that authentication, authorization, and capacity admission, we note that
clear standards do not exist at this time for bandwidth brokers, clear standards do not exist at this time for bandwidth brokers, NSIS
NSIS has not been finalized at this time and in any event is limited has not been finalized at this time and in any event is limited to
to unicast sessions, and that RSVP has been standardized and has the unicast sessions, and that RSVP has been standardized and has the
relevant services. We therefore RECOMMEND the use of a protocol, relevant services. We therefore RECOMMEND the use of a protocol,
such as RSVP, at the UNI. Procedures at the NNI are business such as RSVP, at the UNI. Procedures at the NNI are business matters
matters to be discussed between the relevant networks, and are to be discussed between the relevant networks, and are RECOMMENDED
I RECOMMENDED but NOT REQUIRED. but NOT REQUIRED.
3. Summary: changes from RFC 4594 3. Summary: Changes from RFC 4594
To summarize, there are two changes to [RFC4594] discussed in this To summarize, there are two changes to [RFC4594] discussed in this
document: document:
Telephony class: The Telephony Service Class in RFC 4594 does not Telephony class: The Telephony Service Class in RFC 4594 does not
involve capacity admission, but depends on application layer involve capacity admission, but depends on
admission that only estimates capacity, and that through static application layer admission that only estimates
engineering. In addition to that class, a separate Admitted capacity, and does that through static engineering.
Telephony Class is added which performs capacity admission In addition to that class, a separate Admitted
dynamically. Telephony Class is added that performs capacity
admission dynamically.
Video classes: Capacity admission is added to three video classes. Video classes: Capacity admission is added to three video classes.
These are the Interactive Real-Time Traffic class, Broadcast TV These are the Interactive Real-Time Traffic class,
class when used for video on demand, and the Multimedia Broadcast TV class when used for video on demand,
Conferencing class. and the Multimedia Conferencing class.
4. IANA Considerations 4. IANA Considerations
This note requests that IANA assign a DSCP value to a second EF IANA assigned a DSCP value to a second EF traffic class consistent
traffic class consistent with [RFC3246] and [RFC3247] in the with [RFC3246] and [RFC3247] in the "Differentiated Services Field
"Differentiated Services Field Codepoints" registry. It implements Codepoints" registry. It implements the Telephony Service Class
the Telephony Service Class described in [RFC4594] at lower speeds described in [RFC4594] at lower speeds and is included in the Real-
and is included in the Real Time Treatment Aggregate [RFC5127] at Time Treatment Aggregate [RFC5127] at higher speeds. The code point
higher speeds. The recommended code point value should be from pool value should be from pool 1 within the dscp-registry. The value is
1 within the dscp-registry. This document RECOMMENDS retaining a parallel with the existing EF code point (101110), as IANA assigned
parallel with the existing EF code point (101110) by assigning a the code point 101100 -- keeping the (left-to-right) first 4 binary
value for the code point of 101100 -- keeping the (left to right) values the same in both. The code point described in this document
first 4 binary values the same in both. The code point described is referred to as VOICE-ADMIT and has been registered as follows:
within this document should be referred to as VOICE-ADMIT. Here is
the recommended addition to the Pool 1 Codepoint registry:
Sub-registry: Pool 1 Codepoints Sub-registry: Pool 1 Codepoints
Reference: [RFC2474] Reference: [RFC2474]
Registration Procedures: Standards Action Registration Procedures: Standards Action
Registry: Registry:
Name Space Reference Name Space Reference
--------- ------- --------- --------- ------- ---------
VOICE-ADMIT 101100 [this document] VOICE-ADMIT 101100 [RFC5865]
This traffic class REQUIRES the use of capacity admission, such as This traffic class REQUIRES the use of capacity admission, such as
RSVP services together with AAA services, at the User/Network RSVP services together with AAA services, at the User/Network
Interface (UNI); the use of such services at the NNI is at the Interface (UNI); the use of such services at the NNI is at the option
option of the interconnected networks. of the interconnected networks.
5. Security Considerations 5. Security Considerations
A major requirement of this service is effective use of a signaling A major requirement of this service is effective use of a signaling
Protocol, such as RSVP, with the capabilities to identify its user protocol, such as RSVP, with the capabilities to identify its user as
either as an individual or as a member of some corporate entity, and either an individual or a member of some corporate entity, and assert
assert a policy such as "normal", "routine" or some level of a policy such as "normal", "routine", or some level of "priority".
"priority".
This capability, one has to believe, will be abused by script This capability, one has to believe, will be abused by script kiddies
kiddies and others if the proof of identity is not adequately strong and others if the proof of identity is not adequately strong or if
or if policies are written or implemented improperly by the policies are written or implemented improperly by the carriers. This
carriers. This goes without saying, but this section is here for it goes without saying, but this section is here for it to be said.
to be said...
Much of the security considerations from RFC 3246 [RFC3246] applies Many of the security considerations from RFC 3246 [RFC3246] apply to
to this document, as well as the security considerations in RFC this document, as well as the security considerations in RFC 2474 and
2474 and RFC 4542. RFC 4230 [RFC4230] analyzes RSVP, providing some RFC 4542. RFC 4230 [RFC4230] analyzes RSVP, providing some gap
gap analysis to the NSIS WG as they started their work. Keep in mind analysis to the NSIS WG as they started their work. Keep in mind
that this document is advocating RSVP at the UNI only, while RFC that this document is advocating RSVP at the UNI only, while RFC 4230
4230 discusses (mostly) RSVP from a more complete point of view discusses (mostly) RSVP from a more complete point of view (i.e., e2e
(i.e., e2e and edge2edge). When considering the RSVP aspect of this and edge2edge). When considering the RSVP aspect of this document,
document, understanding Section 6 of RFC 4230 is a good source of understanding Section 6 of RFC 4230 is a good source of information.
information.
6. Acknowledgements 6. Acknowledgements
Kwok Ho Chan, Georgios Karagiannis, Dan Voce, and Bob Briscoe Kwok Ho Chan, Georgios Karagiannis, Dan Voce, and Bob Briscoe
commented and offered text. The impetus for including Video in the commented and offered text. The impetus for including video in the
discussion, which initially only targeted voice, is from Dave discussion, which initially only targeted voice, is from Dave
McDysan. McDysan.
7. References 7. References
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474, December
December 1998. 1998.
[RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec, [RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
J., Courtney, W., Davari, S., Firoiu, V., and D. J., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, March 2002. Behavior)", RFC 3246, March 2002.
7.2. Informative References 7.2. Informative References
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., [RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998. Service", RFC 2475, December 1998.
[RFC3247] Charny, A., Bennet, J., Benson, K., Boudec, J., Chiu, A., [RFC3247] Charny, A., Bennet, J., Benson, K., Boudec, J., Chiu, A.,
Courtney, W., Davari, S., Firoiu, V., Kalmanek, C., and K. Courtney, W., Davari, S., Firoiu, V., Kalmanek, C., and K.
Ramakrishnan, "Supplemental Information for the New Ramakrishnan, "Supplemental Information for the New
Definition of the EF PHB (Expedited Forwarding Per-Hop Definition of the EF PHB (Expedited Forwarding Per-Hop
Behavior)", RFC 3247, March 2002. Behavior)", RFC 3247, March 2002.
[RFC3260] Grossman, D., "New Terminology and Clarifications for [RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, April 2002. Diffserv", RFC 3260, April 2002.
[RFC4190] Carlberg, K., Brown, I., and C. Beard, "Framework for [RFC4190] Carlberg, K., Brown, I., and C. Beard, "Framework for
Supporting Emergency Telecommunications Service (ETS) in Supporting Emergency Telecommunications Service (ETS) in
IP Telephony", RFC 4190, November 2005. IP Telephony", RFC 4190, November 2005.
[RFC4504] Sinnreich, H., Lass, S., and C. Stredicke, "SIP Telephony [RFC4504] Sinnreich, H., Ed., Lass, S., and C. Stredicke, "SIP
Device Requirements and Configuration", RFC 4504, Telephony Device Requirements and Configuration", RFC
May 2006. 4504, May 2006.
[RFC4542] Baker, F. and J. Polk, "Implementing an Emergency [RFC4542] Baker, F. and J. Polk, "Implementing an Emergency
Telecommunications Service (ETS) for Real-Time Services Telecommunications Service (ETS) for Real-Time Services in
in the Internet Protocol Suite", RFC 4542, May 2006. the Internet Protocol Suite", RFC 4542, May 2006.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594, Guidelines for DiffServ Service Classes", RFC 4594, August
August 2006. 2006.
[RFC5127] Chan, K., Babiarz, J., and F. Baker, "Aggregation of [RFC5127] Chan, K., Babiarz, J., and F. Baker, "Aggregation of
DiffServ Service Classes", RFC 5127, February 2008. DiffServ Service Classes", RFC 5127, February 2008.
[RFC4230] H. Tschofenig, R. Graveman, "RSVP Security Properties", [RFC4230] Tschofenig, H. and R. Graveman, "RSVP Security
RFC4230, December 2005 Properties", RFC 4230, December 2005.
Authors' Addresses Authors' Addresses
Fred Baker Fred Baker
Cisco Systems Cisco Systems
Santa Barbara, California 93117 Santa Barbara, California 93117
USA USA
Phone: +1-408-526-4257 Phone: +1-408-526-4257
Email: fred@cisco.com EMail: fred@cisco.com
James Polk James Polk
Cisco Systems Cisco Systems
Richardson, Texas 75082 Richardson, Texas 75082
USA USA
Phone: +1-817-271-3552 Phone: +1-817-271-3552
Email: jmpolk@cisco.com EMail: jmpolk@cisco.com
Martin Dolly Martin Dolly
AT&T Labs AT&T Labs
Middletown Township, New Jersey 07748 Middletown Township, New Jersey 07748
USA USA
Phone: +1-732-420-4574 Phone: +1-732-420-4574
Email: mdolly@att.com EMail: mdolly@att.com
 End of changes. 87 change blocks. 
307 lines changed or deleted 288 lines changed or added

This html diff was produced by rfcdiff 1.38. The latest version is available from http://tools.ietf.org/tools/rfcdiff/