Network WG James Polk Internet-Draft Subha Dhesikan Expires: January 5, 2011 Cisco Systems Intended Status: Standards Track (PS) July 5, 2010 The Session Description Protocol (SDP) 'servclass' Attribute draft-polk-mmusic-service-class-for-sdp-00 Abstract This document proposes a simple Session Description Protocol (SDP) 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. 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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 . . . . . . . . . . . . . . . . . . 4 2.1 Are Tags Required? . . . . . . . . . . . . . . . . . . . 5 3. Offer/Answer Behavior . . . . . . . . . . . . . . . . . . . . 6 3.1 Offer Behavior . . . . . . . . . . . . . . . . . . . . . 6 3.2 Answer Behavior . . . . . . . . . . . . . . . . . . . . . 6 4. Security considerations . . . . . . . . . . . . . . . . . . . 6 5. IANA considerations . . . . . . . . . . . . . . . . . . . . . 7 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Normative References . . . . . . . . . . . . . . . . . 8 7.2. Informative References . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 8 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. These 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 Transport Protocol (RTP) [RFC3550] specifics established between one or more endpoints, but identifying how the underlying network should Polk Expires January 5, 2011 [Page 2] Internet-Draft SDP servclass Attribute July 2010 process each stream still remains under-defined. RFC 4594 [RFC4594] established a guideline for classifying the various flows in the network and the Differentiated Services Codepoints (DSCP) that apply to these traffic types. It also defines the per hop network behavior that is required for each of these application traffic types. When looking at RTP from a voice and video standpoint, merely separating RTP into either voice or video is not as granular as is needed, as demonstrated by Differentiated Services Codepoint guidelines in RFC 4594 [RFC4594]. Within that document, there are 4 distinct video classifications of RTP: - The Broadcast video (CS5) - The Real-time Interactive (CS4) - The Multimedia Conferencing (AF4x) - The Multimedia Streaming (AF3x) In addition, there are 2 voice classes: - The VOIP class (EF). - the Voice-Admit (Voice-Admit) from RFC 5865 [RFC5865] Each of the media type classifications may require different quality of service handling in the network. However, the network does not currently have sufficient information to perform the above classification since such information is not available in the SDP signaling. The idea of service identification is not new; it has been defined 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. This document proposes how SDP [RFC4566] uniquely identifies which Application class a stream is for network handling and policy purposes. This can also be leveraged for call signaling policies such as acceptance or rejection, authorization of a certain type of application by call controlling entities, and synchronization with lower layers for network handling. Polk Expires January 5, 2011 [Page 3] Internet-Draft SDP servclass Attribute July 2010 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 'servclass' session and media-level SDP [RFC4566] attribute. The following is their Augmented Backus-Naur Form (ABNF) [RFC5234] syntax, which is based on the SDP [RFC4566] grammar: attribute =/ service-classification service-classification = "servclass" ":" [SP] app-type app-type = "Broadcast video" / "Real-time Interactive" / "Multimedia Conferencing" / "Multimedia Streaming" / "VoIP" / "Voice-Admit" / extension-mech extension-mech = token The attribute is named "servclass", for service classification, identifying, which one of the six service classes listed above applies to the media stream. The service classes defined in this document for SDP align with the application labels introduced by table 3 of RFC 4594. RFC 5685 updates the guidelines set forth in RFC 4594 by creating a new voice classification where call admission control (CAC) has been applied. So, there are four video classifications and two voice classifications - Broadcast video - Real-time Interactive - Multimedia Conferencing - Multimedia Streaming - VoIP - Voice-Admit [Editor's Note: should Voice-admit (i.e., what is defined in RSVP 5865) be included in this list?] The attribute is named "servclass", for service classification. The following is an example of an 'm' line with a 'servclass' Polk Expires January 5, 2011 [Page 4] Internet-Draft SDP servclass Attribute July 2010 attribute: m=audio 50000 RTP/AVP 0 a=servclass real-time interactive The above signals a telepresence type of session. 2.1 Are Tags Required? The authors are considering two tags to this "a=servclass" line, - whether this "a=" line is optional or mandatory in the answer and - whether there should be a direction tag If the WG believes either is necessary, this proposal will define a default value for either (or both). 2.1.1 Is the "servclass" 'Optional' or 'Mandatory'? There can be an optional or mandatory tag within the "a=servclass" line for whether the offerer wants the answerer to include this "a=servclass" in the answer. a=servclass (optional/mandatory) real-time interactive [Editor's Note: The authors are currently leaning away from including this parameter. We would like feedback on scenarios in which this should be included.] 2.1.2 Is a "servclass" Direction Tag Necessary? Additionally, there can be a direction tag included in this "a=servclass" proposal. a=servclass Voice-Admit (sendonly/recvonly/sendrecv) [Editor's Note: The authors believe that the direction of the service class will be picked up by the direction of the flow that the m-line(s) indicate. Since this is an attribute of the flow, the flow's direction determines the direction of the attribute. Therefore, we are currently leaning away from including this parameter. We would like feedback on scenarios in which this should be included.] Polk Expires January 5, 2011 [Page 5] Internet-Draft SDP servclass Attribute July 2010 3.0 Offer/Answer Behavior Through the inclusion of the 'servclass' 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. 3.1 Offer Behavior Offerers include the 'servclass' attribute with a single well known token (from list in Section 2) to obtain predictable treatment. It can also instead include a private token within a single domain (e.g., enterprise networks). Offerers of this 'servclass' attribute MUST NOT change the token in transit (e.g., wrt to SBCs). Offers containing a 'servclass' token not understood are ignored (i.e., as if there was no 'servclass' attribute in the Offer). 3.2 Answer Behavior Upon receiving an offer containing a 'servclass' attribute, the answerer binds this session or media (level) attribute with the RTP traffic received at the session or media level. Offer 'servclass' attribute tokens SHOULD match what is in the Answer, if the offer is accepted. An Answer MAY have a 'servclass' attribute where 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 'servclass' 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. That document highly recommends the user not being able to set any classification. Barring a hack within an endpoint (i.e., to intentionally miss-classifying (i.e., lying) about which classification an RTP stream is), this document's solution makes the Polk Expires January 5, 2011 [Page 6] Internet-Draft SDP servclass Attribute July 2010 classification part of the signaling between endpoints, which is recommended by RFC 5897. 5. IANA considerations 5.1 Registration of the SDP 'servclass' 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: servclass Long-form attribute name: Service Classification Type of attribute: Session and Media levels Subject to charset: No Purpose of attribute: To indicate the Service 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) servclass [this document] 7.2 The Service Classification Application Registration This document requests IANA to create a new registry for the application service classes similar to the following table within the Session Description Protocol (SDP) Parameters registry: Registry Name: "servclass" SDP 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] VoIP [this document] Voice-Admit [this document] Polk Expires January 5, 2011 [Page 7] Internet-Draft SDP servclass Attribute July 2010 6. Acknowledgments Your name here... 7. References 7.1. 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 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 [RFC5897] J. Rosenberg, "Identification of Communications Services in the Session Initiation Protocol (SIP)", RFC 5897, June 2010 7.2. Informative References [RFC4594] J. Babiarz, K. Chan, F Baker, "Configuration Guidelines for Diffserv Service Classes", RFC 4594, August 2006 Authors' 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 Expires January 5, 2011 [Page 8]