TECH TALK: Next-Generation Networks: IMS
David Passmore, Research Director for the Burton Group, lays out the ITU vision of NGN:
The ITU NGN isnt just oriented towards voice, but is intended to support presence and instant messaging, push-to-talk, voice mail, video and other multimedia applications. This includes both real-time and streaming modesparticularly important for video.
Architecturally, the ITUs NGN relies heavily on the IP Multimedia Subsystem (IMS) framework, developed by the 3rd Generation Partnership Project (3GPP)/3GPP2 for 3G/UMTS and CDMA mobile networks. The IMS has been extended to cover wireline facilities, to create a converged, seamless mobile user experience. The ITU NGN also mandates IPv6, and uses traffic prioritization end-to-end to deliver service quality. It requires reservation and commitment of network resources before connections are established.
The IMS upon which NGN is based uses the Session Initiation Protocol (SIP) with extensions, and creates a telephony-oriented signalling network that sits on top of an underlying IP cloud; it replaces telco SS7 signalling and acts as a wireless/wireline control plane. An IMS network consists of many SIP proxy servers that mediate all customer/user connections and access to network resources. Just as with cellular networks, IMS assumes each user is associated with a home network, and supports the concept of roaming across other wired or wireless nets. IMS also includes a policy engine and authentication, authorization and accounting (AAA) server for operator control and security.
In this context, it is useful to understand IMS. Here is what Wikipedia has to say:
The IP Multimedia Subsystem (IMS) is an open, standardised, operator friendly, NGN multi-media architecture for mobile and fixed IP services. It’s a VoIP implementation based on a 3GPP variant of SIP, and runs over the standard Internet protocol (IP). It’s used by telecom operators in NGN networks (which combine voice and data in a single packet switched network), to offer network controlled multimedia services.
The aim of IMS is not only to provide new services but to provide all the services, current and future, that the Internet provides. In addition, users have to be able to execute all their services when roaming as well as from their home networks. To achieve these goals the IMS uses open standard IP protocols, defined by the IETF. So, a multi-media session between 2 IMS users, between an IMS user and a user on the Internet, and between 2 users on the Internet is established using exactly the same protocol. Moreover, the interfaces for service developers are also based in IP protocols. This is why the IMS truly merges the Internet with the cellular world; it uses cellular technologies to provide ubiquitous access and Internet technologies to provide appealing services.
Tomorrow: IMS (continued)