Chapter 23 - SIP Networks

Abstract

The functions of a session initiation protocol (SIP) network can be broken down into various main areas, which include mobility and routing, authentication, authorization, accounting, assertion of identities, security, interworking and border functions, and provision of network-based services. Mobility and routing refers to the capability to route terminating calls to users who might be changing their location, that is, their IP address, which is achieved through the introduction of three entities, the SIP registrar, the location service, and the SIP (inbound) proxy. Authorization is a network function that can be implemented in proxies and it allows the service provider to control the media requested by the users and to assure that network resources are used for what they are authorized. Accounting is an important network function, especially in scenarios where the service providers want to charge for offering their service. Privacy is an interesting security service that may be provided by the network, both at the control plane and at the media plane. While interconnecting two different service providers' IP communication infrastructures, additional functions that are implemented in the network and that involve the control plane and the media plane are required. There can be various approaches for delivering value-added services (VAS) in SIP. One approach is the end-to-end approach, where services sit in the endpoints, and in another approach the applications sit in the network.