Monday, April 7, 2008

SIP -- Main Purpose

The main purpose behind RFC 3261, Session Initiation Protocol (SIP), is to to set up, modify and tear down multi-media communications sessions on the internet.

An important feature of SIP is its addressing model:

To: E. Schroedinger <>
From: Werner Heisenberg <>

This addressing model is opaque for internet routing and direct access to user end-points. (If they were just e-mail addresses, we sould know how to address the SMTP servers.) Somehow SIP addresses need to be associated with actual end-point addresses on the network. IP addresses of users need to be obtained. That's where the rest of SIP comes in. Once you have these features, we can start talking about the use of SIP in VoIP, IP mobility, IMS and more.

[Names for addresses are inspired by examples in "SIP: Understanding the session initiation protocol" by Alan B. Johnson]

SSO, Single-Sign-On

Just finished reading an interesting article on Single Sign-On in GSM / UMTS environments . . . The article focuses on Single Sign-On protocols a la Liberty Alliance in GSM and UMTS environments. It provides the details of two protocols, one for GSM and one for UMTS. Both of these use a secret key, say Ki, stored in the SIM card and shared with the Public Land Mobile Network (PLMN) operator:

A. Pashalidis and C. J. Mitchell, "Using GSM/UMTS for single sign-on". in: Proceedings of SympoTIC '03, Joint IST Workshop on Mobile Future and Symposium on Trends in Communications, Bratislava, Slovakia, October 2003, IEEE Press, 2003, pp. 138-145.