Network WG James Polk Internet-Draft Subha Dhesikan Expires: September 14, 2011 Cisco Systems Intended Status: Standards Track (PS) March 14, 2011 The Session Description Protocol (SDP) 'trafficclass' Attribute draft-polk-mmusic-traffic-class-for-sdp-01 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 September 14, 2011. Polk & Dhesikan Expires September 14, 2011 [Page 1] Internet-Draft SDP trafficclass Attribute Mar 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. SDP Attribute Definition . . . . . . . . . . . . . . . . . . 5 3. Offer/Answer Behavior . . . . . . . . . . . . . . . . . . . . 7 3.1 Offer Behavior . . . . . . . . . . . . . . . . . . . . . 8 3.2 Answer Behavior . . . . . . . . . . . . . . . . . . . . . 8 4. Security considerations . . . . . . . . . . . . . . . . . . . 8 5. IANA considerations . . . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 12 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 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. There are many facets within SDP to determine the Real-time Polk & Dhesikan Expires September 14, 2011 [Page 2] Internet-Draft SDP trafficclass Attribute Mar 2011 Transport Protocol (RTP) [RFC3550] details established 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 indicate to underlying network elements treat traffic with different ports differently, 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. Video was broken down into 4 categories in that RFC, and voice into Polk & Dhesikan Expires September 14, 2011 [Page 3] Internet-Draft SDP trafficclass Attribute Mar 2011 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 a 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. The idea of traffic - or service - identification is not new; it has been described in [RFC5897]. If that RFC is used as a guideline, Polk & Dhesikan Expires September 14, 2011 [Page 4] Internet-Draft SDP trafficclass Attribute Mar 2011 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. 2. 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] app-type *( add-param ) app-type = "Broadcast-video" / "Realtime-Interactive" / "Multimedia-Conferencing" / "Multimedia-Streaming" / "Telephony" / "Voice-Admit" / "unknown" / extension-mech extension-mech = token add-param = "." sub-app-type / "." cac-class sub-app-type = "telepresence" / "immersive" / "desktop" / "personal" /"webex" / "call center" / "trading floor" / Polk & Dhesikan Expires September 14, 2011 [Page 5] Internet-Draft SDP trafficclass Attribute Mar 2011 "handheld" / generic-param ; from RFC3261 cac-class = "admitted" / "non-admitted" The attribute is named "trafficclass", for traffic classification, identifying which one of the six 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 application type traffic classes defined in this document for SDP are an augmented version of the application labels introduced by table 3 of RFC 4594. RFC 5685 updated the guidelines set forth in RFC 4594 by creating a new voice classification where call admission control (CAC) has been applied. There are four video classifications and two voice classifications - Broadcast-video - Realtime-Interactive - Multimedia-Conferencing - Multimedia-Streaming - Telephony - Voice-Admit - unknown The "unknown" application type is for the scenario in which the application type is not known, but the sub-application type is. The application types (app-type) can be further subdivided into sub-application types with the sub-app-type identifiers for more granular application distinction of the traffic. Sub-application types are separated from traffic class by a "." if any are present in an instance of this attribute. One or more sub-app-types MAY be present in the trafficclass attribute. There MUST NOT be more than one application type in a single instance of the trafficclass attribute. If there is a sub-application type, there MUST be an application type, where the "unknown" is permissible. This document creates the following sub-application types - telepresence - immersive - desktop - personal - webex - call center - trading floor - handheld In addition to, of as an alternative to one or more sub-application types, a cac-class value MAY be present indicating whether or not a Polk & Dhesikan Expires September 14, 2011 [Page 6] Internet-Draft SDP trafficclass Attribute Mar 2011 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. Any application, sub-application or cac-class not understood MUST be ignored, leaving all that is understood to be processed. The following is an example of media level description with a 'trafficclass' attribute: m=audio 50000 RTP/AVP 112 a=trafficclass multimedia-conferencing.telepresence.immersive. admitted The above indicates a multiscreen telepresence session that has had call admission control applied to the traffic. An sub-application type does not have to be defined within this document or an update/extension to this document to be used. The 'trafficclass' attribute is allowed to have one or more vendor specific (i.e., proprietary) sub-application types. These vendor specific sub-application types MUST have an underscore "_" character immediately after one of the "." characters in the 'trafficclass' attribute. The following is an example of media level description with a 'trafficclass' attribute that has proprietary sub-application identifiers: m=audio 50000 RTP/AVP 0 a=trafficclass multimedia-conferencing.telepresence._foo._bar 3.0 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 Broadcast Video instead of Real-time Interactive video), decided on a per domain basis - instead of exclusively by the offering domain. Polk & Dhesikan Expires September 14, 2011 [Page 7] Internet-Draft SDP trafficclass Attribute Mar 2011 3.1 Offer Behavior Offerers include the 'trafficclass' attribute with a single well known token (from list in Section 2) to obtain configurable and predictable treatment between the answerer and the offerer. It can also instead include a private token within a single domain (e.g., enterprise networks). Offerers of this 'trafficclass' attribute MUST NOT change the token in transit (e.g., wrt to B2BUAs). SBCs at domain boundaries can change this attribute through local policy. Offers containing a 'trafficclass' token not understood are ignored by default (i.e., as if there was no 'trafficclass' attribute in the Offer). 3.2 Answer Behavior Upon receiving an offer containing a 'trafficclass' attribute, if the offer is accepted, the answerer will use this attribute to set the session or media (level) traffic accordingly towards the offerer. 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 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. 4. 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 Polk & Dhesikan Expires September 14, 2011 [Page 8] Internet-Draft SDP trafficclass Attribute Mar 2011 of the signaling between endpoints, which is recommended by RFC 5897. 5. IANA considerations 5.1 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] 5.2 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 the Session Description Protocol (SDP) Parameters registry: Registry Name: "trafficclass" SDP Application Type Attribute Values Reference: [this document] Registration Procedures: Specification Required Attribute Values Reference ---------------- --------- Broadcast video [this document] Real-time Interactive [this document] Multimedia Conferencing [this document] Multimedia Streaming [this document] Telephony [this document] Voice-Admit [this document] Polk & Dhesikan Expires September 14, 2011 [Page 9] Internet-Draft SDP trafficclass Attribute Mar 2011 5.3 The Traffic Classification Sub-Application Type Registration This document requests IANA to create a new registry for the traffic sub-application classes similar to the following table within the Session Description Protocol (SDP) Parameters registry: Registry Name: "trafficclass" Attribute Sub-Application Type Values Reference: [this document] Registration Procedures: Specification Required Attribute Values Reference ---------------- --------- Telepresence [this document] immersive [this document] desktop [this document] personal [this document] webex [this document] call center [this document] trading floor [this document] handheld [this document] 5.4 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] 6. Acknowledgments To Dave Oran, Toerless Eckert, Henry Chen, David Benham and Paul Jones for their comments and suggestions. 7. References 7.1. Normative References Polk & Dhesikan Expires September 14, 2011 [Page 10] Internet-Draft SDP trafficclass Attribute Mar 2011 [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 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. 7.2. 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 & Dhesikan Expires September 14, 2011 [Page 11] Internet-Draft SDP trafficclass Attribute Mar 2011 Author's Addresses James Polk 3913 Treemont Circle Colleyville, Texas, USA +1.817.271.3552 mailto: jmpolk@cisco.com Subha Dhesikan 170 W Tasman St San Jose, CA, USA +1.408-902-3351 mailto: sdhesika@cisco.com Polk & Dhesikan Expires September 14, 2011 [Page 12]