RFC 3327 (rfc3327) - Page 2 of 17
Session Initiation Protocol (SIP) Extension Header Field for Registering Non-Adjacent Contacts
Alternative Format: Original Text Document
RFC 3327 Path Extension Header Field for SIP December 2002 Table of Contents 1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Applicability Statement . . . . . . . . . . . . . . . . . . 3 4. Path Header Field Definition and Syntax . . . . . . . . . . 3 5. Usage of Path Header Field . . . . . . . . . . . . . . . . . 5 5.1 Procedures at the UA . . . . . . . . . . . . . . . . . . . . 5 5.2 Procedures at Intermediate Proxies . . . . . . . . . . . . . 5 5.3 Procedures at the Registrar . . . . . . . . . . . . . . . . 6 5.4 Procedures at the Home Proxy . . . . . . . . . . . . . . . . 6 5.5 Examples of Usage . . . . . . . . . . . . . . . . . . . . . 7 5.5.1 Example of Mechanism in REGISTER Transaction . . . . . . . . 7 5.5.2 Example of Mechanism in INVITE Transaction . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . 13 6.1 Considerations in REGISTER Request Processing . . . . . . . 13 6.2 Considerations in REGISTER Response Processing . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 15 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 Normative References . . . . . . . . . . . . . . . . . . . . 16 Non-Normative References . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 16 Full Copyright Statement . . . . . . . . . . . . . . . . . . 17 1. Background 3GPP established a requirement for discovering intermediate proxies during SIP registration and published this requirement in [5]. Scenario: UA1----P1-----P2-----P3------REGISTRAR UA1 wishes to register with REGISTRAR. However, due to network topology, UA1 must use P1 as an "outbound proxy", and all requests between UA1 and REGISTRAR must also traverse P1, P2, and P3 before reaching REGISTRAR. Likewise, all requests between REGISTRAR and UA1 must also traverse P3, P2, and P1 before reaching UA1. UA1 has a standing relationship with REGISTRAR. How UA1 establishes this relationship is outside the scope of this document. UA1 discovers P1 as a result of configuration, DHCP assignment or other similar operation, also outside the scope of this document. REGISTRAR has a similar "default outbound proxy" relationship with P3. Willis & Hoeneisen Standards Track
