Tuesday, 24 May 2016


In SIP Basics we discussed about components of SIP. It's time to understand a sample call flow. Before we start I would like to discuss few components of call flow:

Request: When a UAC (User Agent Client) wants to initiate a call it sends an Invite to the UAS (User Agent Server). In this case Invite is a request .

Response: A reply to UAC's request is called a response. In this case it would be 100 Trying, which we will discuss in a moment.

Tuesday, 17 May 2016




SIP Stands for Session Initiation Protocol. SIP is becoming a global standard for VoIP. SIP is a protocol which is used for signalling, controlling multimedia sessions such as voice and video between two endpoints or through a proxy server. SIP is also used for instant messaging, client presence, user mobility based on its current location.

SIP has been developed by IETF: Internet Engineering Task Force. This group is responsible for adding new features and modifying existing features in SIP. All concepts used in SIP are defined under RFC’s i.e. RFC 3261 which is one of the most important RFC for VoIP.