Internet Draft
Internet Engineering Task Force A. Johnston
Internet Draft D. Rawlins
Document: draft-johnston-sip-osp-token-00.txt H. Sinnreich
July 2000 WorldCom
Expires: January 2001
AAAarch WG
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].
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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.
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Internet Draft OSP Authorization Token Header for SIP July 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.
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 [3] 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
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.
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Internet Draft OSP Authorization Token Header for SIP July 2000
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
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
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Internet Draft OSP Authorization Token Header for SIP July 2000
[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] 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
USA
diana.rawlins@wcom.com
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Internet Draft OSP Authorization Token Header for SIP July 2000
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