Reinventing SIP

Work on the Session Initiation Protocol (News - Alert) (SIP) began in 1996 and the first standards track specification (RFC 2543) was out in 1999. The expectation was that SIP, as a peer-to-peer protocol, would redefine the very nature of telecommunications. No longer would telephony depend upon a central agency — the “phone company.” Instead individuals would directly connect with other individuals. But a decade later SIP’s peer-to-peer story has been lost. VoIP is deployed but SIP’s impact has been limited.

Indeed, the biggest telecom story of the past 12 years has been the global adoption of mobile phones — over 3 billion of them in just 12 years — all using traditional circuit-switched telephony. And arguably, the most interesting telephony service enhancement, after mobility, has come from Skype (News - Alert) with its seamless integration of presence, instant messaging, wideband audio and video. But Skype is based on proprietary protocols, not SIP. And VoIP has helped drive down the cost of international calling, but this is the result of VoIP based on MGCP, H.248 or H.323 more than SIP, at least so far.

SIP has been adopted by PBX (News - Alert) manufacturers in recent years, but this hasn’t revolutionized business practices. The IT department still buys the PBX and the telephone sets from a single vendor and then contracts with a service provider to handle calls outside the enterprise.

Finally, SIP itself has evolved from its focus on peer-to-peer communications to become the centerpiece of a complex family of protocols called IP Multimedia Subsystem (News - Alert) (IMS) conceived by telecom traditionalists and defined by the 3rd Generation Partnership Project (3GPP). With IMS, everything is mediated by a service provider. Some might say SIP has been co-opted.

What went wrong? SIP by itself didn’t work in the presence of firewalls and network address translation (NAT); i.e., with the real Internet. The Internet community responded with workaround protocols like STUN, TURN and ICE, but these require servers in the network; i.e., a central agency.

Peer-to-Peer, Take Two

Just when the original vision seemed entirely lost, a new IETF group has arisen under the name Peer-to-Peer SIP (p2psip) chartered to “develop protocols and mechanisms for the use of the Session Initiation Protocol (SIP) in settings where the service of establishing and managing sessions is handled by a collection of intelligent endpoints, rather than centralized servers.” More significantly, this effort is proceeding on the assumption that NATs and firewalls exist and that the P2P SIP networks must support the servers needed to handle NAT and firewalls.

One gets a sense of Skype jealousy, but that’s good. Open standards that facilitate end-to-end solutions for the real Internet are just what we need to reclaim the vision and bring about a real revolution in telecommunications. IT

Brough Turner (News - Alert) is Senior VP of Technology, CTO and Co-Founder of NMS Communications (www.nmscommunications.com).

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