AVTEXT Working Group K. Carlberg Internet-Draft G11 Intended Status: Standards Track Oct 14, 2013 Expires: April 14, 2014 A Real-time Transport Protocol (RTP) Classifier Header Extension draft-carlberg-avtext-classifier-00 Abstract This document defines a new RTP header extension. The purpose of the extension is to provide additional information that further distinguishes the RTP datagram (and its payload) from other datagrams containing the same type of payload. The information may be used by application layer gateways to drop packets, or place them in a lower priority outbound queue. Or, through deep packet inspection, information stored in the classifier header extension may be used to (re)set diff-serv code points set in the IP header that may be have reset at ingress/egress boundaries of a diff-serv domain. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on April 14, 2014. Copyright Notice Copyright (c) 2013 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 Carlberg Expires April 14, 2014 [Page 1] Internet Drafts Classifier Extension Header for RTP Oct 14, 2013 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 Simplified BSD License. 1. Introduction This document defines a new RTP Header extension. The purpose of the extension it to provide additional information that distinguishes the RTP datagram (and its payload) from other datagrams containing the same type of payload. This distinction can be viewed as a generalized abbreviation of the significance of the payload. It is important to note that this document uses the term classification, NOT priority, in distinguishing payloads. This is because the word priority tends to convey a definitive importance of the packet, as well as an expected Quality of Service (QoS). In addition, the concept of priority may be different on aper application or per user community basis. Hence, local policy is required to determine the relationship of various classifications. This policy may be associated with the administrative policy defined for a domain. The form, support of, and dissemination of local policy is outside the scope of this document. Another advantage in appending a classifier extension to the RTP header is that it provides a means by which a forwarding node aquires information from the source without the need to breach confidentiality (through the use of Secure RTP) or support of the codec used to produce the RTP payload. 1.2 Terminology and Abbreviations 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 RFC2119 [RFC2119]. 2. Related Work There have been several efforts that have added classification, in the more narrow scope of priority to other applications. These efforts include: (1) a Resource Priority Header in the Session Initiation Protocol (SIP) [rfc4412] and (2) a priority extension for the Simple Mail Transfer Protocol (SMTP) [rfc6710]. In each of these examples, the priority classification was accomplished by dividing the solution space into two parts. The first identified a namespace associated with the set of priorities. The second part identified the specific priority. Initial example values would be defined in the respective RFC, while future values would be placed in a registry maintained by IANA. The advantage in using this two-part Carlberg Expires April 14, 2014 [Page 2] Internet Drafts Classifier Extension Header for RTP Oct 14, 2013 solution was that various "communities of interest" had the freedom to define the form of the classification (in their case, priority) and the number of classifications. In addition, the registry provided a common place where various vendors and user groups could access and agree on a single set of values that assisted in interopability. 3. Classifier Header Extension The classifier header extension for RTP is divided into two parts: a Namespace entry and a Value entry. This information is carried in an RTP header extension element as by "A General Mechanism for RTP Header Extensions" [rfc5285]. The payload of the classifier header extension element can be encoded using either the one-byte or two-byte header defined in [RFC5285]. Figures 1 and 2 show sample audio level encodings with each of these header formats. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID | len=1 | Namespace | Value | 0 (pad) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Classifier Using the One-Byte Header 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID | Len=2 | Namespace | Value | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Classifier Using the Two-Byte Header 3.1 Example A Authors note: There have been recent discussions in the Transport Services working group (TSVWG) on the relative importance of different types of payloads. There has also been recent work concerning the mapping of diff-serv code points related to RTP payloads. In both of these cases, the focus has been with the characteristics of specific types of applications. On the other hand, and as discussed above in section 2, previous related work has gravitated to supporting classifications (specifically, priorities) based on a user community. One can easily observe that these are two different and possibly divergent motivations in adding classification information to an RTP payload. A question to the Carlberg Expires April 14, 2014 [Page 3] Internet Drafts Classifier Extension Header for RTP Oct 14, 2013 community is should both interests be supported by a new RTP classifier header? Examples exist in the case of Namespaces correlating to a user community. This section shoulw, at a minimum, present an example Namespace that correpates to eitehr a specific application or a set of applications. A question to the community is whether the latter can be achieved since it would reduce the number of Namespaces that would need to be supported by implementors. 4. IANA Considerations At present, this section is listed as To Be Done. Eventually, a description and statement requirement of a registry will need to be described. 5. Security Considerations To Be Done 6. Acknowledgements An earlier work-in-progress related effort concerning the specification of a classifier extension header for RTP was presented to the IETF community in 2002. The author thanks James Polk and Dave Oran for earlier discussions on this topic. The author also thanks Toerless Eckert and Cheng-Jai Lai for recent discussion on the topic. 7. References 7.1 Normative [rfc2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [rfc5285] Singer, D., et. al., "A General Mechanism for RTP Header Extensions", RFC 5285, IETF, July 2008 7.2 Informative [rfc4412] Schulzrinne, H., J. Polk, "Communications Resource Priority for the Session Inititiation Protocol (SIP)" RFC 4412, IETF, Feb 2006 [rfc6710] Melnikov, A., K. Carlberg, "Simple Mail Transfer Protocol Extension for Message Transfer Priorities", Carlberg Expires April 14, 2014 [Page 4] Internet Drafts Classifier Extension Header for RTP Oct 14, 2013 RFC 6710, IETF, Aug 2012 Author's Addresses Ken Carlberg G11 1600 Clarendon Blvd Arlington VA USA Email: carlberg@g11.org.uk Carlberg Expires April 14, 2014 [Page 5]