AVTEXT Working Group Ken Carlberg INTERNET-DRAFT G11 Intended Status: Standards Track Toerless Eckert Expires: April 21, 2014 Cisco Oct 21, 2013 A Real-time Transport Protocol (RTP) Classifier Header Extension draft-carlberg-avtext-classifier-01 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 to assist functions performed by application layer gateways (such as Session Border Controller or MCUs) and/or by routers/switches through deep packet inspection. Examples of these functions include intelligent dropping of packets or (re)setting the IP header diff-serv code points 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 Carlberg Expires April 21, 2014 [Page 1] Internet Drafts Classifier Extension Header for RTP Oct 21, 2013 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 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 per-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 acquires 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], and (3) a priority policy element for the Resource Reservation Protocol (RSVP) [rfc6401]. 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 Carlberg Expires April 21, 2014 [Page 2] Internet Drafts Classifier Extension Header for RTP Oct 21, 2013 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 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 interoperability. 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] and shown below in Figure 1 and 2 below. 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 Author's notes: 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 Carlberg Expires April 21, 2014 [Page 3] Internet Drafts Classifier Extension Header for RTP Oct 21, 2013 classification information to an RTP payload. A question to the community is should both interests be supported by a new RTP classifier header? (the author's position is yes) Examples exist in the case of Namespaces correlating to a user community. This section should, at a minimum, present an example Namespace that correlates to either a specific application or a set of applications. Another 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. The author's position is that this could be achieved by having a Namespace and set of values that correspond to the existing set of defined differentiated services code points. As such, we recommend a Namespace assigned to a per-hop behaviour (e.g., the AFxx set of code points) Finally, we anticipate the possibility that two sets of users groups may choose to inject their own classifier information: one that corresponds to hop-by-hop forwarding, and the other at the destination end-point. However, we should encourage a minimalistic approach and discourage more than two (namespace, value) entries. 3.1 Example: AF Namespace TBD 4. SDP Signaling TBD 5. IANA Considerations At present, this section is listed as To Be Done. Eventually, a description and statement requirement of a registry will be needed. 6. Security Considerations To Be Done 7. 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 authors also thanks Cheng-Jai Lai for recent discussion on the topic. Carlberg Expires April 21, 2014 [Page 4] Internet Drafts Classifier Extension Header for RTP Oct 21, 2013 8. References 8.1 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 8.2 Informative [rfc4412] Schulzrinne, H., J. Polk, "Communications Resource Priority for the Session Inititiation Protocol (SIP)" RFC 4412, IETF, Feb 2006 [rfc6401] Le Faucher, F, et al, "RSVP Extensions for Admission Priority", RFC 6401, IETF, Oct 2011 [rfc6710] Melnikov, A., K. Carlberg, "Simple Mail Transfer Protocol Extension for Message Transfer Priorities", RFC 6710, IETF, Aug 2012 Author?s Addresses Ken Carlberg G11 Arlington VA USA Email: carlberg@g11.org.uk Toerless Eckert Cisco Systems, Inc. San Jose USA Email: eckert@cisco.com Carlberg Expires April 21, 2014 [Page 5]