Network Working Group Jerry Ash Internet Draft Bur Goode Jim Hand Expiration Date: August 2003 AT&T Raymond Zhang Infonet Services Corporation February, 2003 Requirements for End-to-End VoIP Header Compression 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. ABSTRACT: VoIP typically uses the encapsulation voice/RTP/UDP/IP/. When MPLS labels are added, this becomes voice/RTP/UDP/IP/MPLS. For an MPLS VPN, the packet header is at least 48 bytes, while the voice payload is typically no more than 30 bytes. VoIP header compression can significantly reduce the VoIP overhead through various compression mechanisms. This is important on access links where bandwidth is scarce, and can be important on backbone facilities, especially where costs are high (e.g., some global cross-sections). This draft gives a problem statement and requirements for end-to-end VoIP header compression, possibly over MPLS. Table of Contents 1. Introduction 2. Problem Statement 3. Requirements 4. Security Considerations 5. References 6. Authors' Addresses 7. Full Copyright Statement 1. Introduction Voice over IP (VoIP) typically uses the encapsulation voice/RTP/UDP/IP/. When MPLS labels are added, this becomes voice/RTP/UDP/IP/MPLS. For an MPLS VPN, the packet header is at least 48 bytes, while the voice payload is typically no more than 30 bytes. The interest in VoIP header compression is the possibility of significantly reducing the VoIP overhead through various compression mechanisms. This draft gives a problem statement and requirements for end-to-end VoIP header compression, possibly over MPLS. 2. Problem Statement Voice over IP (VoIP) typically uses the encapsulation voice/RTP/UDP/IP/. When MPLS labels are added, this becomes voice/RTP/UDP/IP/MPLS. Typically, VoIP will use voice compression mechanisms (e.g., G.729) in order to conserve bandwidth. For an MPLS VPN, the packet header is at least 48 bytes, while the compressed voice payload is typically no more than 30 bytes. With VoIP header compression, significantly more bandwidth could be saved. Therefore, end-to-end VoIP header compression, possibly over MPLS, is required in order to significantly reduce the VoIP overhead through compression mechanisms. The need may be important on access links where bandwidth is more scarce, but it could be important on backbone facilities, especially where costs are high (e.g., some global cross-sections). For example, carrying VoIP headers for the entire voice load of a large domestic network with 300 million or more calls per day could consume on the order of about 20-40 gigabits-per-second on the backbone network for headers alone. This overhead could translate into considerable bandwidth capacity. 3. Requirements End-to-end VoIP header compression, possibly over MPLS, MUST: a. avoid link-by-link compression/decompression cycles. Compression should be performed end-to-end through the MPLS network, e.g., from CE1 --> PE1 --> P --> PE2 --> CE2, where CE1 is the compressor and CE2 is the decompressor ([E2E-VoMPLS], [E2E-cRTP]). b. provide for efficient voice transport. c. support various voice encoding (G.729, G.723.1, etc.). d. use standard compress/decompress algorithms (e.g., [cRTP], [SIMPLE]). e. operate in RFC2547 VPN context [MPLS-VPN]. f. operate in MPLS [MPLS-ARCH] networks using either [LDP] or [RSVP] signaling. g. be scalable to a very large number of CE --> CE flows. - use standard protocols to aggregate RSVP-TE signaling (e.g., [RSVP-AGG]). - minimize setups of tunnels & call sessions h. use standard protocols to signal context identification and control information (e.g., [RSVP], [RSVP-TE]). i. use standard protocols to prioritize packets (e.g., [DIFFSERV, DIFF-MPLS]). j. use standard protocols to allocate LSP bandwidth (e.g., [DS-TE]). k. use standard protocols to make [cRTP] more tolerant of packet loss (e.g., [cRTP-ENHANCE]). l. add minimal delay to the VoIP media flows. 4. Security Considerations No new requirements. 5. References [cRTP] Casner, S., Jacobsen, V., "Compressing IP/UDP/RTP Headers for Low-Speed Serial Links", RFC 2508, February 1999. [cRTP-ENHANCE] Koren, T., et. al., "Compressing IP/UDP/RTP Headers on Links with High Delay, Packet Loss, and Reordering," work in progress. [DIFF-MPLS] Le Faucheur, F., et. al., "MPLS Support of Diff-Serv", RFC 3270, May 2002. [DIFFSERV] Blake, S., et. al., "An Architecture for Differentiated Services", RFC 2475, December 1998. [E2E-VoMPLS] Ash, G., Goode, B., Hand, J., "End-to-End VoIP over MPLS Header Compression", work in progress. [E2E-cRTP] Ash, G., Goode, B., Hand, J., "End-to-End VoIP Header Compression Using cRTP", work in progress. [KEY] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [LDP] Andersson, L., et. al., "LDP Specification", RFC 3036, January 2001. [LDP-PWE3] Rosen, E., "LDP-based Signaling for L2VPNs", work in progress. [MPLS-ARCH] Rosen, E., et. al., "Multiprotocol Label Switching Architecture," RFC 3031, January 2001. [DS-TE] Le Faucheur, F., et. al., "Requirements for support of Diff-Serv-aware MPLS Traffic Engineering," work in progress. [MPLS-VPN] Rosen, E., Rekhter, Y., "BGP/MPLS VPNs", RFC 2547, March 1999. [MPLSF-HC] MPLS Forum Technical Committee, "Voice over MPLS - BearerTransport Implementation Agreement," March 2001. [RSVP] Braden, R. et al., "Resource ReSerVation Protocol (RSVP) -- Version 1, Functional Specification", RFC 2205, September 1997. [RSVP-AGG] Baker, F., et. al., "Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175, September 2001. [RSVP-TE] Awduche, D., et. al., "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, December 2001. [SIMPLE] Swallow, G., Berger, L., "Simple Header Compression", work in progress. 6. Authors' Addresses Jerry Ash AT&T Room MT D5-2A01 200 Laurel Avenue Middletown, NJ 07748, USA Phone: +1 732-420-4578 Email: gash@att.com Bur Goode AT&T Phone: + 1 203-341-8705 E-mail: bgoode@att.com Jim Hand AT&T Room MT A2-4F36 200 Laurel Avenue Middletown, NJ 07748, USA Phone: +1 732-420-6179 E-mail: jameshand@att.com Raymond Zhang Infonet Services Corporation 2160 E. Grand Ave. El Segundo, CA 90025 USA Email: raymond_zhang@infonet.com 7. Full Copyright Statement Copyright (C) The Internet Society (2003). 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. 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