VoIP Systems

SIP Guide

It’s pretty widely accepted now that telecom value is moving away from centralized network/service combinations (such as the traditional PSTN) towards distributed multimedia applications running over a common (converged) IP-based hardware/software infrastructure that includes both fixed and mobile elements and broadband transmission.

A key technology for this transformation is the IETF's Session Initiation Protocol (SIP). SIP is already making waves in the burgeoning VOIP world, where it is beginning to displace the earlier (and, in the views of many, overcomplex) ITU H.323 standard for call setup and control. But SIP goes much deeper than this, because it is the basis on which a lot of future sophisticated application and service software will rest. In particular, it will support the IP Multimedia Subsystem (IMS), the likely future platform for multimedia services in both fixed and mobile networks.

So SIP is beginning to loom large, and this tutorial aims to provide a timely, quick, and easy guide to some questions that are commonly asked about SIP. Answers to a number of basic questions are given. But readers may ask further questions on the message board attached to this article. If you want to send a private message, please email us at [email protected], and include "SIP Guide" in the subject field. Frequently posed questions will be answered in updates to this report.

For a basic understanding of SIP, here are the key starting points:

  • SIP will have a major impact on the telecom industry – including telcos, mobile operators, service providers, vendors, and others – because it allows users, devices, and software applications to set up and control end-to-end multimedia sessions independently of the media types involved or the underlying transport protocols.

  • The fundamental standard is well established, but there is a huge ongoing effort to build on and around it to address a large number of issues and requirements. SIP represents the biggest standards effort in the IETF’s history.

  • SIP implementations are increasing, and the industry is working hard to address interoperability, which remains a major issue. But there is still a lot of work to be done.
Here's a hyperlinked list of the questions we seek to answer in this report:

— Tim Hills is a freelance telecommunications writer and journalist. He's a regular author of Light Reading reports.

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