Internet Engineering Task Force Internet Draft James M. Polk Expiration: May 15th, 2002 Cisco Systems File: draft-polk-avt-rtpext-res-pri-00.txt RTP Header Extension for Communications Resource Priority November 14th, 2001 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. Conventions used in this document 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]. Abstract This document defines an extension to the Real-Time Protocol RTP [1] for Communication Resource Priority (CRP). The intent of this extension is to give a relative preferential order to RTP packets moving through an infrastructure within a Domain whose infrastructure recognizes this extension. Polk draft-polk-avt-rtpext-res-pri-00.txt Page 1 Internet Draft RTP Ext for Comm Resource Priority Nov 14th, 2001 Table of Contents Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.0 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.0 Communications Resource Priority RTP Extension. . . . . . . . . 2 3.0 Communications Resource Priority in RTCP . . . . . . . . . . . 4 4.0 Security Considerations . . . . . . . . . . . . . . . . . . . . 4 5.0 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 6.0 References . . . . . . . . . . . . . . . . . . . . . . . . . . 4 7.0 Author Information . . . . . . . . . . . . . . . . . . . . . . 5 1.0 Introduction This document defines an extension to the Real-Time Protocol RTP [1] for Communication Resource Priority (CRP). The intent of this extension is to give a relative preferential order to RTP packets moving through an infrastructure within a Domain whose infrastructure recognizes this extension. With this CRP extension, some packets therefore will receive preferential treatment by the underlying and supporting infrastructure relative to other CRP-enabled RTP packets. Some CRP-enabled packets will be of equal value and receive no distinguishable or preferential treatment relative to others at the same level. The packet treatment mechanism within this extension is independent of L3 mechanisms such as Diffserv [2] and RSVP [3], and might be used in conjunction with either, both, or others, including L2 mechanisms. The usage of this interaction is outside the scope of this document. The CRP marking of RTP packets isn't to give absolute levels of behavior or treatment, merely relative behavior or treatment transiting a single infrastructure node at a time. No symmetrical session awareness will be defined here within the Domain. 2.0 Communications Resource Priority RTP Extension Below is the Extension to all CRP-enabled RTP Headers (inserted immediately after the CSRC if utilized within a packet, otherwise immediately after the SSRC): 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | defined by profile | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | CRP | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. Extension layout Extension Type: 16 bits -- [1] states only one extension can exist in any packet. Polk draft-polk-avt-rtpext-res-pri-00.txt Page 2 Internet Draft RTP Ext for Comm Resource Priority Nov 14th, 2001 Length: 16 bits -- [1] allows this value to be zero if no further bits are required to satisfy this extension, and none do. Reserved: 16 bits -- [1] states this field shall not be utilized CRP: 16 bits -- See Table 1 above for this value Per [1 in section 5.3.1], "This mechanism is designed so that the header extension may be ignored by other interoperating implementations that have not been extended", ensuring backwards compatibility with this new extension. The following is the relative priority of the new values of this CRP extension for RTP packets: Hex Dec Name --- --- ---- 001 - 1 - CRITIC/ECP 010 - 2 - Flash Override 011 - 3 - Flash 100 - 4 - Immediate 101 - 5 - Priority 110 - 6 - Routine Table 1. CRP levels This is a reduced list taken from [4], but inverted in value/numeric/bit /name order here. These Priority Levels coincide with the new draft [5] into the SIP WG for their signaling of RTP sessions between UA's, with one caveat. The specific use of the "CRITIC/ECP" ("Critical and Emergency Call Priority") value is outside the scope this document, but it is RECOMMENDED that this value or level not be used between endpoints other than that of a regional/national emergency *and* by Government (authorized) individuals only. Related work is occurring to define this value's scope within the International Emergency Preparedness Scheme (IEPS) folks [6] that are trying to get a WG formed within the IETF. The CRITIC/ECP level here should map directly to the IAM SS7 code point for "authorized emergency" service. The order of relative Priority of the list in Table 1 has "001 û 1 û CRITC/ECP" as the Highest Priority, descending in linear order of Pri- ority to "110 û 6 û Routine". Routine is RECOMMENED as the default for what's usually considered normal, everyday communications. The method for elevation of any sessions higher in Priority from Routine is outside the scope of this document. Initial extension inclusion may be generated at endpoints (ex through SIP UA's or Gateway signaling to endpoints or terminations) or IP entry points (Edge Routers) into the CRP-enabled Domain. Polk draft-polk-avt-rtpext-res-pri-00.txt Page 3 Internet Draft RTP Ext for Comm Resource Priority Nov 14th, 2001 This extension may be inserted by GSTN Gateways entering an IP-Domain to achieve a desired treatment within that infrastructure. Certain IP- domains likely will mandate this extension within their domain. 3.0 Communications Resource Priority in RTCP *** note û this section needs recommendations for format and normative language Same levels as in Table 1 above 4.0 Security Considerations If all devices utilizing RTP within an IP-Managed Domain use authenti- cated access to the infrastructure, there should not be any security considerations. Misuse of this extension in domains that have preferential treatment of packets can cause troubles and unfairness within that domain if authentication and authorization is not closely administered. Admission controls and effective policing strategies are necessary to prevent this starving of resources that can be overtaken with Prioritized traffic. Exact methods are outside the scope of this document. 5.0 IANA Considerations Include this CRP Extension as the first for RTP, with a value of 1 6.0 References [1] RFC 1889 "RTP: A Transport Protocol for Real-Time Applications", H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, Jan 1996 [2] RFC 2475 "An Architecture for Differentiated Service", S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W Weiss, Dec. 1998. [3] RFC 2205, "Resource ReSerVation Protocol (RSVP) -- Version 1, Functional Specification", R. Braden Ed., L. Zhang, S. Berson, S. Herzog, S. Jamin, September 1997. [4] RFC 791 "Internet Protocol", J. Postel, September 1981 [5] "draft-polk-sip-res-pri-header-00.txt" work in progress, J. Polk, H. Schulzrinne, November 2001 [6] "draft-carlberg-ieps-framework-02.txt" work in progress, K. Carlberg, I. Brown, October 2001 Polk draft-polk-avt-rtpext-res-pri-00.txt Page 4 Internet Draft RTP Ext for Comm Resource Priority Nov 14th, 2001 7.0 Author Information James M. Polk Cisco Systems 2200 East President George Bush Turnpike Richardson, Texas 75082 USA jmpolk@cisco.com "Copyright (C) The Internet Society (February 23rd, 2001). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTA- BILITY OR FITNESS FOR A PARTICULAR PURPOSE." The Expiration date for this Internet Draft is: May 15th, 2002 Polk draft-polk-avt-rtpext-res-pri-00.txt Page 5