The rise of SIP and IMS

Today we'll continue our retrospective on the past five years in the world of convergence, this time looking at what has evolved in the core network. When we started this newsletter five years ago, we defined one of the faces of convergence as "network convergence" - defining it as the integration of data and voice networks' transport and signaling infrastructures in a carrier's core network.

While it was pretty clear back then that the core was going be running on an optical infrastructure with an IP overlay, we weren't quite sure how the many demands of multimedia session control would be provided. Although Session Initiation Protocol (SIP) work had begun in the IETF in 1999, since then SIP has clearly emerged as the protocol of choice for VoIP.

What we didn't foresee was the introduction of IP Multimedia Subsystem (IMS) as an emerging architecture to provide further session control. IMS has its roots in the wireless world, and was created as a concept in 2000. IMS was designed to give 3G wireless providers a more effective way to offer applications and content services in multi-vendor, open-standards networks.

It hasn't taken long for both wireless and wireline service providers to embrace IMS. We expect that wireline operators will actually be among the heaviest users of IMS, because as they move forward to offer applications-level support (running on IP) they will have many millions of simultaneous IP sessions to control.

Another emerging trend is for fixed and mobile networks to converge. While mobile networks still carry more voice than data traffic, broadband access to mobile devices is evolving, and this evolution will encourage more data applications on mobile networks. In the next few years mobile networks will have to transition to an IP-centric core and will look more like today's fixed-line core networks.

The bottom line: core networks have undergone significant change in the last five years, enabling more efficient multimedia services support.

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