SIP’s Future: Complicated And Competitive
By John G. Waclawsky Ph.D.

Published February 2007; Posted August 2007

Abstract:

How important is it for applications and devices to share a common signaling protocol?

A decade of development effort has produced hundreds of engineering specifications but has failed to make the IETF’s Session Initiation Protocol (SIP) the signaling protocol of choice for popular voice and multimedia applications. Instead, most long distance voice sessions rely on old signaling standbys like SS7 or H.323, while the latest applications like instant messaging, peer-to-peer (P2P) file sharing and VOIP telephony are being built on newer signaling protocols, including IAX, Skype, XMPP and others.

SIP began auspiciously enough, by providing total endpoint control of the session initiation process, but the once-simple protocol has become complicated and overextended along the way. Since the 3GPP became interested in SIP, it has evolved towards providing more call control in the network core, via extensions to SIP and the use of techniques such as B2BUAs (back-to-back user agents) and private headers.

Now Internet advocates, who still want control at the edge, are frustrated by what they see as SIP becoming a tool for the core network to control user activities, and many of them have moved on to other protocols. Meanwhile, SIP’s more recent proponents, who in fact want extensive call control in the core, are frustrated as well, but by the controls and complexity that SIP still leaves in edge devices. No one seems to be happy.
 

About the author:

John G. Waclawsky is the chief software architect with Motorola. The views expressed are his own.

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