The Session Description Protocol (SDP) 'trafficclass' Attribute
draft-ietf-mmusic-traffic-class-for-sdp-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Expired".
|
|
|---|---|---|---|
| Authors | James Polk , Subha Dhesikan , Paul Jones | ||
| Last updated | 2011-10-24 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-mmusic-traffic-class-for-sdp-00
Network WG James Polk
Internet-Draft Subha Dhesikan
Expires: April 24, 2012 Paul Jones
Intended Status: Standards Track (PS) Cisco Systems
October 24, 2011
The Session Description Protocol (SDP) 'trafficclass' Attribute
draft-ietf-mmusic-traffic-class-for-sdp-00
Abstract
This document proposes a new Session Description Protocol (SDP)
attribute to identify the traffic class a session is requesting
in its offer/answer exchange.
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
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
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 24, 2012.
Polk, et al. Expires April 24, 2012 [Page 1]
Internet-Draft SDP trafficclass Attribute Oct 2011
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Traffic Class Framework and String Definitions . . . . . . . 5
3. Traffic Class Attribute Definition . . . . . . . . . . . . . 11
4. Offer/Answer Behavior . . . . . . . . . . . . . . . . . . . . 14
4.1 Offer Behavior . . . . . . . . . . . . . . . . . . . . . 14
4.2 Answer Behavior . . . . . . . . . . . . . . . . . . . . . 14
5. Security considerations . . . . . . . . . . . . . . . . . . . 16
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 20
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].
1. Introduction
The Session Description Protocol (SDP) [RFC4566] provides a means
for an offerer to describe the specifics of a session to an
answerer, and for the answerer to respond back with its session
specifics to the offerer. These session specifics include offering
the codec or codecs to choose from, the specific IP address and port
number the offerer wants to receive the RTP stream(s) on/at, the
particulars about the codecs the offerer wants considered or
mandated, and so on.
Polk, et al. Expires April 24, 2012 [Page 2]
Internet-Draft SDP trafficclass Attribute Oct 2011
There are many facets within SDP to determine the Real-time
Transport Protocol (RTP) [RFC3550] details for the session
establishment between one or more endpoints, but identifying how the
underlying network should process each stream still remains
under-specified.
The ability to identify a traffic flow by port number gives an
indication to underlying network elements to treat traffic with
dissimilar ports in a different way, the same or in groups the same
- but different from other ports or groups of ports.
Within the context of realtime communications, the labeling of an
RTP session based on media descriptor lines as just a voice and/or
video session is insufficient, and provides no guidelines to the
underlying network on how to treat the traffic. A more granular
labeling helps on several fronts to
- inform application layer elements in the signaling path the
intent of this session.
- inform the network on how to treat the traffic if the network is
configured to differentiate session treatments based on the type
of session the RTP is, including the ability to provide call
admission control based on the type of traffic in the network.
- allow network monitoring/management of traffic types realtime and
after-the-fact analysis.
Some network operators want the ability to guarantee certain traffic
gets a minimum amount of network bandwidth per link or through a
series of links that perhaps makes up a network such as a campus or
WAN, or a backbone. For example, a call center voice application
gets at least 20% of a link as a minimum bandwidth.
Some network operators want the ability to allow certain users or
devices access to greater bandwidth during non-busy hours, than
during busy hours of the day. For example, all desktop video to
operate at 1080p during non-peak times, but curtail a similar
session between the same users or devices to 720p or 360p during
peak hours. This case is not as clear as accepting or denying
similar sessions during different times of the day, but tuning the
access to the bandwidth based on the type of session. In other
words, tune down the bandwidth for desktop video during peak hours
to allow a 3-screen telepresense session that would otherwise look
like the same type of traffic (RTP, and more granular, video).
RFC 4594 established a guideline for classifying the various flows
in the network and the Differentiated Services Codepoints (DSCP)
that apply to many traffic types (table 3 of [RFC4594]), including
RTP based voice and video traffic sessions. The RFC also defines the
per hop network behavior that is strongly encouraged for each of
these application traffic types based on the traffic characteristics
Polk, et al. Expires April 24, 2012 [Page 3]
Internet-Draft SDP trafficclass Attribute Oct 2011
and tolerances to delay, loss and jitter within each traffic class.
Video was broken down into 4 categories in that RFC, and voice into
another single category. We do not believe this satisfies the
technical and business requirements to accomplish sufficiently
unique labeling of RTP traffic.
A question arises about once we properly label the traffic, what
does that get us? This is a fair question, but out of scope for
this document because that answer lies within other RFCs and IDs in
other WGs and/or Areas (specifically the Transport Area). That
said, we can discuss some of the ideas here for completeness.
If the application becomes aware of traffic labeling,
- this can be coded into layer 3 mechanisms.
- this can be coded into layer 4 protocols and/or mechanisms.
- this can be coded into a combination of mechanisms and protocols.
The layer 3 mechanism for differentiating traffic is either the port
number or the Differentiated Services Codepoint (DSCP) value
[RFC2474]. Within the public Internet, if the application is not
part of a managed service, the DSCP likely will be best effort (BE).
Within the corporate LAN, this is usually completely configurable
and a local IT department can take full advantage of this labeling
to shape and manage their network as they see fit. Communications
between enterprise networks will likely have to take advantage of
MPLS.
Within a network core, where only MPLS is used, Diffserv typically
does not apply. That said, Diffserv can be used to identify which
traffic goes into which MPLS tunnels [RFC4124].
Labeling realtime traffic types using a layer 4 protocol would
likely mean RSVP [RFC2205] or NSIS [RFC4080]. RSVP has an
Application Identifier (app-ID) defined in [RFC2872] that provides a
means for carrying a traffic class label along the data path. An
advantage with this mechanism is for the label to inform each domain
along the media path what type of traffic this traffic flow is, and
allow each domain to adjust the appropriate DSCP (set by each domain
for use within that domain). Meaning, if a DSCP is set by an
endpoint or a router in the first domain and gets reset by a SP, the
far end domain will be able to reset the DSCP to the intended
traffic class. There is a proposed extension to RSVP which creates
individual profiles for what goes into each app-ID field to describe
these traffic classes [ID-RSVP-PROF], which will take advantage of
what is described in this document.
There are several proprietary mechanisms to take advantage of this
labeling, but none of those will be discussed here.
Polk, et al. Expires April 24, 2012 [Page 4]
Internet-Draft SDP trafficclass Attribute Oct 2011
The idea of traffic - or service - identification is not new; it has
been described in [RFC5897]. If that RFC is used as a guideline,
identification that leads to stream differentiation can be quite
useful. One of the points within RFC 5897 is that users cannot be
allowed to assign any identification (fraud is but one reason
given). In addition, RFC 5897 recommends that service identification
should be done in signaling, rather than guessing or deep packet
inspection. The network will have to currently guess or perform deep
packet inspection to classify and offer the service as per RFC 4594
since such service identification information is currently not
available in SDP and therefore to the network elements. Since SDP
understands how each stream is created (i.e., the particulars of the
RTP stream), this is the right place to have this service
differentiated. Such service differentiation can then be
communicated to and leveraged by the network.
[Editor's Note: the words "traffic" and "service" are similar enough
that the above paragraph talks about RFC 5897's
"service identification", but this document is only
wanting to discuss and propose traffic indications
in SDP.]
This document proposes a simple attribute line to identify the
application a session is requesting in its offer/answer exchange.
This document uses previously defined service class strings for
consistency between IETF documents.
This document modifies the traffic classes originally created in RFC
4594 in Section 2, incrementing each class with application
identifiers and optional adjective strings. Section 3 defines the
new SDP attribute "trafficclass". Section 4 discusses the offerer
and answerer behavior when generating or receiving this attribute.
2. Traffic Class Framework and String Definitions
The framework of the traffic class attribute will have at least two
parts, allowing for several more to be included. The intention is to
have a parent class (e.g., Conversational) that merely serves as the
anchor point for an application component that when paired together,
form the highest level traffic class. An adjective component
provides further granularity for the application.
The traffic class label will have the following structure,
parent.application(.adjective)(.adjective)(.admitted/non-admitted)
[Editor's Note: the above is not exactly the ABNF to be used.
The order is right. The parent and application
MUST appear (each only once) and zero or more
adjectives can appear.]
Polk, et al. Expires April 24, 2012 [Page 5]
Internet-Draft SDP trafficclass Attribute Oct 2011
Where
1) the 1st component is the human understandable category;
2) the 2nd component is the application;
3) an optional 3rd component or series of components are
adjective(s) used to further refine the application component;
and
4) an optional 4th component is to classify this flow as a CAC
admitted or non-admitted traffic flow. The default is
non-admitted, whether present or not.
The construction of the traffic class label for Telepresence video
would follow the form like this:
Conversational.video.immersive
There is no traffic class or DSCP value associated with just
"Conversational". There is a traffic class associated with
"Conversational.video", creating a differentiation between it and a
"Conversational.video.immersive" traffic class, which would have
DSCP associated with the latter traffic class, depending on local
policy. Each parent component is defined below, as are several of
application and adjective strings.
[Editor's Note: We're not yet sure how much of what's below will be
proposed for IANA registration, but the 5 parent
components will be, as well as at least some
application components per parent component. Some
adjective components will also likely be proposed
for IANA registration.
The 5 parent components of the traffic class attribute are as
follows:
o Conversational
o Multimedia Conferencing
o Real-Time Interactive
o Multimedia Streaming
o Broadcast
The following application components of the traffic class attribute
are as follows:
o Audio
o Video
o Text
o application-sharing
o Presentation-data
o Whiteboarding
o Web (conference) chat/instant messaging
o Gaming
Polk, et al. Expires April 24, 2012 [Page 6]
Internet-Draft SDP trafficclass Attribute Oct 2011
o Virtual-desktop (interactive)
o Remote-desktop
o Telemetry (e.g., NORAD missile control)
o Multiplex (i.e., combined streams)
o (something to cover theater quality Netflix movies)
o (something to cover YouTube)
o Webcast
o IPTV
o Live-events (though not the buffered ones)
o surveillance
The following adjective components of the traffic class attribute
are as follows:
o Immersive
o Desktop-video
o Realtime-Text
o web
Each of the above 3 lists will be defined in the following
subsections.
2.1 Conversational Parent Traffic Class
The Conversational traffic class is best suited for applications
that require very low delay variation and generally intended to
enable real-time, bi-directional person-to-person or
multi-directional via an MTP communication, such as the following
application components:
o Audio (voice)
o Video
o Text (i.e., real-time text required by deaf users)
With adjective substrings to the above (which may or may not get
IANA registered)
Immersive (TP) - An interactive audio-visual communications
experience between remote locations, where the users enjoy a
strong sense of realism and presence between all participants
by optimizing a variety of attributes such as audio and video
quality, eye contact, body language, spatial audio,
coordinated environments and natural image size.
Desktop-video - An interactive audio-visual communication
experience that is not immersive in nature, though can have a
high resolution video component.
Polk, et al. Expires April 24, 2012 [Page 7]
Internet-Draft SDP trafficclass Attribute Oct 2011
Realtime-Text (RTT) - a term for real-time transmission of text in
a character-by-character fashion for use in conversational
services, often as a text equivalent to voice-based
conversational services. Conversational text is defined in the
ITU-T Framework for multimedia services, Recommendation F.700
[RFC5194].
Web - for realtime aspects of web conferencing; mutually exclusive
of both Immersive and Desktop video experiences
**The above substrings might also be used within Multimedia
Conferencing**
+--------------------------------------------------------------------+
|Traffic Class | | Tolerance to |
| Name | Traffic Characteristics | Loss |Delay |Jitter|
|===============+===============================+======+======+======|
| | High priority, typically | Very | Very | Very |
|Conversational | small packets (large video | Low | Low | Low |
| | frames produce large packets),| | | |
| | generally sustained high | | | |
| | packet rate, low inter-packet | | | |
| | transmission interval, | | | |
| | usually UDP framed in (S)RTP | | | |
+---------------+-------------------------------+------+------+------+
2.2 Multimedia-Conferencing Parent Traffic Class
Multimedia-Conferencing traffic class is best suited for
applications that are generally intended for communication between
human users, but are less demanding in terms of delay, packet loss,
and jitter than what Conversational applications require. These
applications require low to medium delay and may have the ability to
change encoding rate (rate adaptive) or transmit data at varying
rates, such as the following application components:
o application-sharing (that webex does or protocols like T.128) -
An application that shares the output of one or more running
applications or the desktop on a host. This can utilize
vector graphics, raster graphics or video.
o Presentation-data - can be a series of still images or motion
video.
o Whiteboarding - an application enabling the exchange of graphical
information including images, pointers and filled and
unfilled parametric drawing elements (points, lines,
polygons and ellipses).
o (RTP-based) file transfer
Polk, et al. Expires April 24, 2012 [Page 8]
Internet-Draft SDP trafficclass Attribute Oct 2011
o Web (conference) chat/instant messaging
+--------------------------------------------------------------------+
|Traffic Class | | Tolerance to |
| Name | Traffic Characteristics | Loss |Delay |Jitter|
|===============+===============================+======+======+======|
| Multimedia | Variable size packets, | Low | Low | Low |
| Conferencing | Variable transmit interval, | - | - | - |
| | rate adaptive, reacts to |Medium|Medium|Medium|
| | loss, usually TCP-based | | | |
+---------------+-------------------------------+------+------+------+
2.3 Realtime-Interactive Parent Traffic Class
Realtime-Interactive traffic class is intended for interactive
variable rate inelastic applications that require low jitter and
loss and very low delay, such as the following application
components:
o Gaming - interactive player video games with other users on other
hosts (e.g., Doom)
o Virtual desktop (interactive) - similar to an X-windows station,
has no local hard drive, or is operating an application with no
local storage
o Remote Desktop - controlling a remote node with local peripherals
(i.e., monitor, keyboard and mouse)
o Telemetry - a communication that allows remote measurement and
reporting of information (e.g., post launch missile status or
energy monitoring)
+--------------------------------------------------------------------+
|Traffic Class | | Tolerance to |
| Name | Traffic Characteristics | Loss |Delay |Jitter|
|===============+===============================+======+======+======|
| Realtime | Inelastic, mostly variable | Low | Very | Low |
| Interactive | rate, rate increases with | | Low | |
| | user activity | | | |
+---------------+-------------------------------+------+------+------+
2.4 Multimedia-Streaming Parent Traffic Class
Multimedia-Streaming traffic 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 the following
application components:
Polk, et al. Expires April 24, 2012 [Page 9]
Internet-Draft SDP trafficclass Attribute Oct 2011
o Audio
o Video
o Multiplex (i.e., combined streams)
With adjective substrings to the above (which may or may not get
IANA registered)
(something to cover theater quality Netflix movies)
(something to cover YouTube)
Webcast
The primary difference from the Multimedia-streaming parent class
and the Broadcast parent class is about the length of time for
buffering. Buffered streaming audio and/or video (e.g., Netflix or
previously-recorded videos on web sites like CNN, ESPN or from an
internal corporate server). Buffering here can be from seconds to
hours (as opposed to Broadcast buffering which is minimal). The
buffering aspect is what differentiates this parent class from the
Broadcast class (which has minimal or no buffering).
+--------------------------------------------------------------------+
|Traffic Class | | Tolerance to |
| Name | Traffic Characteristics | Loss |Delay |Jitter|
|===============+===============================+======+======+======|
| Multimedia | Variable size packets, |Low - |Medium| High |
| Streaming | elastic with variable rate |Medium|- High| |
| | | | | |
+---------------+-------------------------------+------+------+------+
2.5 Broadcast Parent Traffic Class
Broadcast traffic 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 the following application
components:
o IPTV
o Live events (though not the buffered ones)
o Video surveillance
Polk, et al. Expires April 24, 2012 [Page 10]
Internet-Draft SDP trafficclass Attribute Oct 2011
+--------------------------------------------------------------------+
|Traffic Class | | Tolerance to |
| Name | Traffic Characteristics | Loss |Delay |Jitter|
|===============+===============================+======+======+======|
| Broadcast | Constant and variable rate, | Very |Low - |Low - |
| | inelastic, generally | Low |Medium|Medium|
| | non-bursty flows, generally | | | |
| | sustained high packet rate, | | | |
| | low inter-packet transmission | | | |
| | interval, usually UDP framed | | | |
| | in (S)RTP | | | |
+---------------+-------------------------------+------+------+------+
3. SDP Attribute Definition
This document proposes the 'trafficclass' session and media-level
SDP [RFC4566] attribute. The following is the Augmented
Backus-Naur Form (ABNF) [RFC5234] syntax for this attribute, which
is based on the SDP [RFC4566] grammar:
attribute =/ traffic-classification
traffic-classification = "trafficclass" ":" [SP] parent-class
"." app-type *( app-param )
parent-class = "Broadcast" /
"Realtime-Interactive" /
"Multimedia-Conferencing" /
"Multimedia-Streaming" /
"Conversational" /
extension-mech
extension-mech = token
app-type = "audio" / "video" / "text" /
"application-sharing" /
"presentation-data" /
"whiteboarding" / "webchat/IM" /
"gaming" / "virtual-desktop" /
"remote-desktop" / "telemetry"/
"multiplex" / "Netflix" / "youtube" /
"webcast" / "IPTV" / "live-events" /
"surveillance"
app-param = "." adjective / "." cac-class
adjective = "immersive" / "desktop-video" /
"Realtime-Text" /"web" /
generic-param ; from RFC3261
cac-class = "admitted" / "non-admitted"
Polk, et al. Expires April 24, 2012 [Page 11]
Internet-Draft SDP trafficclass Attribute Oct 2011
The attribute is named "trafficclass", for traffic classification,
identifying which one of the five traffic classes applies to the
media stream. There MUST NOT be more than one trafficclass attribute
per media line. Confusion would result in where more than one exists
per m= line.
The parent classes in this document are an augmented version of the
application labels introduced by table 3 of RFC 4595 (which will be
rewritten based on the updated labels and treatments expected for
each traffic class defined in this document).
+-------------------------+------------------------------+
| Application Labels | Parent Classes Defined |
| Defined in RFC 4594 | in this document |
+=========================+==============================+
| Broadcast-video | Broadcast |
+-------------------------+------------------------------+
| Realtime-Interactive | Realtime-Interactive |
+-------------------------+------------------------------+
| Multimedia-Conferencing | Multimedia-Conferencing |
+-------------------------+------------------------------+
| Multimedia-Streaming | Multimedia-Streaming |
+-------------------------+------------------------------+
| Telephony | Conversational |
+-------------------------+------------------------------+
Table 6. Label Changes from RFC 4594
As is evident from the changes above, from left to right, two labels
are different and each of the meanings are different in this
document relative to how RFC 4594 defined them. These differences
are articulated in Section 2 of this document.
A parent class is a human understandable categorization, and MUST
NOT be the only part of the traffic class label present in the
attribute. The parent class string MUST always be paired with an
application type, with a "." as the string separator.
The application types (app-type) define the application of a
particular traffic flow. The application types are listed both in
the ABNF and defined in Section 2 of this document. Not every
combination parent class is paired with application types, at least
as defined in this document. Section 2.1 through 2.5 list many of
the expected combinations.
For additional application type granularity, adjective strings can
be added (also listed in Section 2). One or more adjectives can be
within the same traffic class attribute. It is also permitted to
include one or more non-IANA registered adjective label, but these
MUST be prefaced by the additional delimiter "_", creating a
possibility such as
Polk, et al. Expires April 24, 2012 [Page 12]
Internet-Draft SDP trafficclass Attribute Oct 2011
parent-class.application-type.adjective._non-standard-adjective
^^^^
See the underscore
For example, this is valid:
m=audio 50000 RTP/AVP 112
a=trafficclass Conversational.video.immersive._foo._bar
where both "foo" and "bar" are not IANA registered adjectives, but
"immersive" is IANA registered. However, including non-registered
adjectives without the "_" delimiter are not valid, such as the
following:
m=audio 50000 RTP/AVP 112
a=trafficclass Conversational.video.immersive.foo.bar
There is no limit to the number of adjectives allowed, without
regard for whether they are registered or not. These non-registered
adjectives can be vendor generated, or merely considered to be
proprietary in nature.
It is important to note that the order of components matters, but
only for the components. In other words, the parent class component
MUST be before the application component, which MUST be before the
adjective component, which MUST be before the cac-class component.
If there are no adjective components, the cac-class component is
immediately after the application component.
If there is more than one adjective component describing a traffic
class, the order of the adjectives MUST NOT matter. Some algorithm
such as alphabetizing the list and matching the understood strings
SHOULD be used.
In addition to, or as an alternative to one or more adjectives, a
cac-class value MAY be present indicating whether or not a session
has had call admission control applied to it. The following two
values are created by this document for the cac-class value:
- admitted
- nonadmitted
The default cac-class value for any trafficclass attribute is
nonadmitted, even if not present. There MUST NOT be more than one
cac-class sub-string per m=line.
Any application, adjective or cac-class string component within this
attribute that is not understood MUST be ignored, leaving all that
is understood to be processed. Ignored string components SHOULD NOT
be deleted, as a downstream entity could understand the component(s)
and use it/them.
Polk, et al. Expires April 24, 2012 [Page 13]
Internet-Draft SDP trafficclass Attribute Oct 2011
Not understanding the parent class string SHOULD mean that this
attribute is ignored.
The following is an example of media level description with a
'trafficclass' attribute:
m=audio 50000 RTP/AVP 112
a=trafficclass conversational.video.immersive.admitted
The above indicates a multiscreen telepresence session that has had
call admission control applied to the media flow.
4. Offer/Answer Behavior
Through the inclusion of the 'trafficclass' attribute, an
offer/answer exchange identifies the application type for use by
endpoints within a session. Policy elements can use this attribute
to determine the acceptability and/or treatment of that session
through lower layers. One specific use-case is for setting of the
DSCP specific for that application type (say a Broadcast instead
of a conversational video), decided on a per domain basis -
instead of exclusively by the offering domain.
4.1 Offer Behavior
Offerers include the 'trafficclass' attribute with a single well
string comprised of two or more components (from the list in Section
2) to obtain configurable and predictable classification between the
answerer and the offerer. The offerer can also include a private set
of components, or a combination of IANA registered and private
components within a single domain (e.g., enterprise networks).
Offerers of this 'trafficclass' attribute MUST NOT change the label
in transit (e.g., wrt to B2BUAs). SBCs at domain boundaries can
change this attribute through local policy.
Offers containing a 'trafficclass' label not understood are ignored
by default (i.e., as if there was no 'trafficclass' attribute in the
offer).
4.2 Answer Behavior
Upon receiving an offer containing a 'trafficclass' attribute, if
the offer is accepted, the answerer will use this attribute to
classify the session or media (level) traffic accordingly towards
the offerer. This answer does not need to match the traffic class in
the offer, though this will likely be the case most of the time.
Polk, et al. Expires April 24, 2012 [Page 14]
Internet-Draft SDP trafficclass Attribute Oct 2011
In order to understand the traffic class attribute, the answerer
MUST check several components within the attribute, such as
1 - does the answerer understand the parent component?
If not, the attribute SHOULD be ignored.
If yes, it checks the application component.
2 - does the answerer understand the application component?
If not, the answerer needs to check if it has a local policy to
proceed without an application component. The default for this
situation is as if the parent component was not understand,
i.e., the attribute SHOULD be ignored.
If yes, it checks there are any other component present in this
attribute to start its classification.
3 - does the answerer understand the adjective component or
components if any are present?
If not present, see if there is a cac-class component, and
before processing classification.
If yes, determine if there are more than one. Alphabetize all of
the adjective components and match the traffic classification.
4 - does the answerer understand the cac-class component if present?
If not, consider the media flow for this m= line to be
nonadmitted.
If yes, classify whether this component is CAC admitted or
nonadmitted.
The answerer will answer the offer with its own 'trafficclass'
attribute, which will likely be the same value, although this is not
mandatory (at this time).
The answerer should expect to receive RTP packets marked as
indicated by its 'trafficclass' attribute in the answer itself.
An Answer MAY have a 'trafficclass' attribute when one was not in
the offer. This will at least aid the local domain, and perhaps
each domain the session transits, to categorize the application type
of this RTP session.
Answerers that are middleboxes can use the 'trafficclass' attribute
to classify the RTP traffic within this session however local policy
Polk, et al. Expires April 24, 2012 [Page 15]
Internet-Draft SDP trafficclass Attribute Oct 2011
determines. In other words, this attribute can help in deciding
which DSCP an RTP stream is assigned within a domain, if the
answerer were an inbound SBC to a domain.
5. Security considerations
RFC 5897 [RFC5897] discusses many of the pitfalls of service
classification, which is similar enough to this idea of traffic
classification to apply here as well. That document highly
recommends the user not being able to set any classification.
Barring a hack within an endpoint (i.e., to intentionally
mis-classifying (i.e., lying) about which classification an RTP
stream is), this document's solution makes the classification part
of the signaling between endpoints, which is recommended by RFC
5897.
6. IANA considerations
6.1 Registration of the SDP 'trafficclass' Attribute
This document requests IANA to register the following SDP att-field
under the Session Description Protocol (SDP) Parameters registry:
Contact name: jmpolk@cisco.com
Attribute name: trafficclass
Long-form attribute name: Traffic Classification
Type of attribute: Session and Media levels
Subject to charset: No
Purpose of attribute: To indicate the Traffic Classification
application for this session
Allowed attribute values: IANA Registered Tokens
Registration Procedures: Specification Required
Type SDP Name Reference
---- ------------------ ---------
att-field (both session and media level)
trafficclass [this document]
6.2 The Traffic Classification Application Type Registration
This document requests IANA to create a new registry for the
traffic application classes similar to the following table within
Polk, et al. Expires April 24, 2012 [Page 16]
Internet-Draft SDP trafficclass Attribute Oct 2011
the Session Description Protocol (SDP) Parameters registry:
Registry Name: "trafficclass" SDP Application Type Attribute Values
Reference: [this document]
Registration Procedures: Specification Required
Parent Values Reference
---------------- ---------
Broadcast [this document]
Realtime-Interactive [this document]
Multimedia-Conferencing [this document]
Multimedia-Streaming [this document]
Conversational [this document]
6.3 The Traffic Classification Application Type Registration
This document requests IANA to create a new registry for the
traffic application classes similar to the following table
within the Session Description Protocol (SDP) Parameters registry:
Registry Name: "trafficclass" Attribute Application Type Values
Reference: [this document]
Registration Procedures: Specification Required
Application Values Reference
------------------ ---------
Audio [this document]
Video [this document]
Text [this document]
application-sharing [this document]
Presentation-data [this document]
Whiteboarding [this document]
Webchat/instant messaging [this document]
Gaming [this document]
Virtual-desktop [this document]
Remote-desktop [this document]
Telemetry [this document]
Multiplex [this document]
Netflix* [this document]
YouTube* [this document]
Webcast [this document]
IPTV [this document]
Live-event [this document]
surveillance [this document]
[Editor's Note: these are placeholders until a more generic string
can be agreed to by the WG]
Polk, et al. Expires April 24, 2012 [Page 17]
Internet-Draft SDP trafficclass Attribute Oct 2011
6.4 The Traffic Classification Adjective Registration
This document requests IANA to create a new registry for the
traffic application classes similar to the following table
within the Session Description Protocol (SDP) Parameters registry:
Registry Name: "trafficclass" Attribute Adjective Values
Reference: [this document]
Registration Procedures: Specification Required
Application Values Reference
------------------ ---------
Immersive [this document]
Desktop-video [this document]
Realtime-Text [this document]
web [this document]
6.5 The Traffic Classification Attribute Call Admission Control Class
Registration
This document requests IANA to create a new registry for the
Call Admission Control Class similar to the following table within
the Session Description Protocol (SDP) Parameters registry:
Registry Name: "trafficclass" SDP Call Admission Control Class
(cac-class) Attribute Values
Reference: [this document]
Registration Procedures: Specification Required
Attribute Values Reference
---------------- ---------
Admitted [this document]
Non-admitted [this document]
7. Acknowledgments
To Dave Oran, Toerless Eckert, Henry Chen, David Benham, David
Benham, Mo Zanty, Michael Ramalho, Glen Lavers, Charles Ganzhorn,
and Greg Edwards for their comments and suggestions.
8. References
8.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
[RFC4566] M. Handley, V. Jacobson, C. Perkins, "SDP: Session
Polk, et al. Expires April 24, 2012 [Page 18]
Internet-Draft SDP trafficclass Attribute Oct 2011
Description Protocol", RFC 4566, July 2006
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC5865] F. Baker, J. Polk, M. Dolly, "A Differentiated Services Code
Point (DSCP) for Capacity-Admitted Traffic", RFC 5865,
May 2010
[RFC2474] K. Nichols, S. Blake, F. Baker, D. Black, "Definition of the
Differentiated Services Field (DS Field) in the IPv4 and
IPv6 Headers ", RFC 2474, December 1998
[RFC2205] R. Braden, Ed., L. Zhang, S. Berson, S. Herzog, S. Jamin,
"Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997
[RFC4080] R. Hancock, G. Karagiannis, J. Loughney, S. Van den Bosch,
"Next Steps in Signaling (NSIS): Framework", RFC 4080, June
2005
[RFC2872] Y. Bernet, R. Pabbati, "Application and Sub Application
Identity Policy Element for Use with RSVP", RFC 2872,
June 2000
[RFC5897] J. Rosenberg, "Identification of Communications Services in
the Session Initiation Protocol (SIP)", RFC 5897, June 2010
[RFC4124] F. Le Faucheur, Ed., " Protocol Extensions for Support of
Diffserv-aware MPLS Traffic Engineering ", RFC 4124,
June 2005
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
8.2. Informative References
[RFC4594] J. Babiarz, K. Chan, F Baker, "Configuration Guidelines for
Diffserv Service Classes", RFC 4594, August 2006
[ID-RSVP-PROF] J. Polk, S. Dhesikan, "Resource Reservation Protocol
(RSVP) Application-ID Profiles for Voice and Video Streams",
work in progress, Mar 2011
Polk, et al. Expires April 24, 2012 [Page 19]
Internet-Draft SDP trafficclass Attribute Oct 2011
Author's Addresses
James Polk
3913 Treemont Circle
Colleyville, Texas, USA
+1.818.271.3552
mailto: jmpolk@cisco.com
Subha Dhesikan
170 W Tasman St
San Jose, CA, USA
+1.408-902-3351
mailto: sdhesika@cisco.com
Paul E. Jones
mailto: paulej@packetizer.com
Polk, et al. Expires April 24, 2012 [Page 20]