SIP services

SIP services are communication features that are intrinsic to SIP requests itself. These services include the following:

• Registration
• Audio/video call
• Instant message
• Presence

We will discuss all of them in detail, accompanied by a call-flow diagram.

Registering a SIP client

A SIP client, such as a SIP phone, SIP soft client, and SIP WebRTC web page, ought to register itself with the Registrar. The Registrar informs the VoIP systems about how you can be reached for an incoming event such as a call, instant message, and Presence update.

A Registrar notes down the physical address of each of the clients through the SIP REGISTER request and confirms their registration with a 200 OK response. The values obtained are copied to the HSS/Location Server as well.

The ideal scenario for the SIP Registration call flow without any authentication challenge is shown in the following diagram:

However, with the introduction of secure registration with authentication, the server throws an authentication...