Internet Engineering Task Force A. Johnston Internet Draft D. Rawlins Document: draft-johnston-sip-osp-token-01.txt H. Sinnreich November 2000 WorldCom Expires: June 2001 Stephen Thomas TransNexus OSP Authorization Token Header for SIP Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026[1]. 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 This draft proposes a new SIP (Session Initiation Protocol) header OSP-Authorization-Token for carrying an OSP (Open Settlements Protocol) authorization token between domains. 1 Introduction The problem of interdomain IP telephony calls with QoS is an important problem being addressed using AAA protocols. The new SIP [1] header proposed here is part of an approach to solving this problem, which is detailed in another draft [2]. 2 Design Alternatives The OSP Token is an opaque string to SIP which must be carried in the INVITE passed between domains. As such, the Token could be carried as a MIME attachment. However, there are three issues with this: - Since the Token must be carried with the SDP, the INVITE would need to have a multipart MIME message body. If either User Agents do not support multipart MIME, the call will fail. Johnston, et al. [Page 1] Internet Draft OSP Authorization Token Header for SIP November 2000 - The Token is used by both proxies and User Agents. As such, the proxy would have to decode the multipart MIME message body to extract the token. The general design of SIP is for message bodies to contain information of interest to end-points only, with information needed by proxies contained in headers. - Multipart MIME encoding/decoding adds more delay to an already lengthy call setup procedure, as compared to header processing. For these reasons, a new SIP header is proposed instead of a new MIME type for OSP authorization tokens. Note that since OSP tokens are commonly constructed according to Cryptographic Message Syntax [3], their size may depend on the size of X.509 certificates embedded in the CMS format. In some cases the addition of a token may increase the size of a SIP INVITE datagram beyond the 576-byte or 1500-byte fragmentation limits. When such behavior is not desirable, it is recommended that systems use the abbreviated token format described in Annex D of [4]. 3 Terminology In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in RFC 2119 [5] and indicate requirement levels for compliant SIP caller preferences implementations. 4 Header Field Definition Table 1 specifies an extension of Table 5 in RFC 2543 [1] for the new header defined here. where enc e-e ACK BYE CAN INV OPT REG OSP-Authorization-Token R n h - - - o - - Table 1: Summary of header field. The "where" column describes the request and response types with which the header filed can be used. The "enc" column describes whether this message header field MAY be encrypted end to end. "o": optional "-": not applicable, "R': request header, "r": response header, "g": general header, "*": needed if message body is not empty. A numeric value in the "type" column indicates the status code the header field is used with. OSP-Authorization-Token = "OSP-Authorization-Token"":" Token Token = quoted-string 6 Protocol Semantics Johnston, et al. [Page 2] Internet Draft OSP Authorization Token Header for SIP November 2000 The OSP Token is always encoded per base64 and only allowed in INVITE requests and 200 OK responses to INVITEs. 6.1 User Agents The UAC include the header an INVITE requesting QoS using AAA. If it is absent in the INVITE, an AAA/QoS UAS determines the token and adds the header, otherwise it validates it. 6.2 Proxies A proxy participating in the AAA exchange will examine and validate the token. Otherwise, the header is ignored. 7 Example Message INVITE sip:+1-972-555-5555@sip.domain2.com;user=phone SIP/2.0 Via: SIP/2.0/UDP sip.domain1.com:5060;branch=3a56d3.1 Via: SIP/2.0/UDP phone1.domain1.com:5060 From: Henry Sinnreich To: Call-ID: 123456@domain1.com CSeq: 1 INVITE Contact: sip:henry.sinnreich@phone1.domain1.com Record-Route: OSP-Authorization-Token: _YT64VqpfyF467GhIGfHfYT6jH77n8HHGghyHhHUujhJh756t HGTrfvbnjn8HHGTrfvhJhjH776tbB9HG4VQbnj7567GhIGfH 6ghyHhHUujpfyF47GhIGfHfYT64VQbnj_ Content-Type: application/sdp Content-Length: 184 v=0 o=hsinnreich 9735285123 9721273312 IN IP4 122.32.11.6 s=Discussion of SIP QoS OSP for AAAArch c=IN IP4 122.32.11.6 t=0 0 m=audio 9876 RTP/AVP 0 a=qos:mandatory recv confirm 8 Security Considerations Johnston, et al. [Page 3] Internet Draft OSP Authorization Token Header for SIP November 2000 Since the AAA scheme [2] assumes authentication between client and server as well as IPSec AH between the server and the OSP server, the message and its contents (and therefore the token) can be trusted. The token can also be encrypted. No other security issues are introduced by this new header. 9 References [1] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: session initiation protocol," Request for Comments (Proposed Standard) 2543, Internet Engineering Task Force, March 1999. [2] H. Sinnreich, D. Rawlins, A. Johnston, S. Donovan, and S. Thomas, _AAA Usage for IP Telephony with QoS_ Internet Draft, July 2000. [3] R. Housley, "Cryptographic Message Syntax", RFC 2630, June 1999. [4] European Telecommunications Standards Institute. "Telecommunications and Internet Protocol Harmonization Over Networks (TIPHON); Open Settlement Protocol (OSP) for Inter-domain pricing, authorization, and usage exchange". Technical Specification 101 321. Version 2.1.0. [5] S. Bradner, "Key words for use in RFCs to indicate requirement levels," Request for Comments (Best Current Practice) 2119, Internet Engineering Task Force, March 1997. Authors' Addresses Alan Johnston WorldCom 100 S. 4th Street St. Louis, Missouri 63104 alan.johnston@wcom.com Henry Sinnreich WorldCom 400 International Parkway Richardson, Texas 75081 USA henry.sinnreich@wcom.com Diana Rawlins WorldCom 901 International Parkway Richardson, Texas 75081 Johnston, et al. [Page 4] Internet Draft OSP Authorization Token Header for SIP November 2000 USA diana.rawlins@wcom.com Stephen Thomas TransNexus 430 Tenth Street NW, Suite N204 Atlanta, GA 30318 USA stephen.thomas@transnexus.com Copyright Notice "Copyright (C) The Internet Society 2000. All Rights Reserved. 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