Abstract: A Look at the IP Multimedia Subsystem (IMS)

Dave Meyer, Cisco

The IP Multimedia Subsystem, or IMS, as defined by 3GPP, is an IETF SIP-based control plane designed with the promise of enabling media rich applications for the mobile (cellular) world. Such applications include Push to talk Over Cellular (PoC), and other video-based applications. IMS has also been proposed as the basis of various other standards organizations' Next Generation Network (NGN) control planes (e.g., ITU-T, ATIS, and ETSI). Most recently, IMS is being proposed as the standard wireline control services control plane, thereby enabling, in theory, fixed-mobile service convergence.

Recently, however, questions have arisen regarding the complexity of IMS, the viability of such "Systems Standards" (compare to the "Component" standards produced by the IETF), as well as the business model implemented by IMS. In particular, the IMS architecture's complexity derives from the following aspects of the IMS architecture:

  1. Subscriber binding to a "home" service provider, with provider-mediated roaming to the networks of other providers,
  2. Per-session QoS, with policy mediated by each service provider on the signaling path, and data constrained to follow the signaling path, and
  3. Direct coupling of higher-layer billable service to the packet transport, including the QoS policies associated with (2) above.
Further, IMS implements a so-called "walled garden" business model which at a high level is roughly analogous to the model currently implmented by most cellular carriers. In particular, in IMS all SIP messages are intercepted and routed to a Call Session Control Function, or CSCF (think of these as SIP proxies of various types) where policy is applied. This results in an environment which puts the intelligence in the network (as opposed to on the edges), and as a result in some cases violates the end-to-end principle.

The purpose of this panel is to introduce the IMS architecture to the Internet operator community, and examine the impacts that it may have on Internet operations.

About the Presenter
David Meyer is currently Director of Business Development at Cisco Systems. Prior to that he served as Senior Scientist and Director of IP Technology Development at Sprint. He is also Director of the Advanced Network Technology Center at the University of Oregon. Prior to working at Sprint, he worked at Cisco, where he was involved in software development, working both on multicast and BGP. He is active in the IETF, where he chairs the MBONED, GROW, DNSOP and MSDP working groups, as well as being a member of several IETF directorates and Internet Research Task Force research groups. He is also active in the operator community and in standards organizations such as ANSI T1X1.

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