Tuesday, 12 July 2016

SIP Messages

When we talk about SIP call flow there are two important things that need to be understood SIP messages and response code. SIP messages and responses are used for setup , in session changes, info and for  tearing down a session. A response code is a response which is sent in response to a SIP message, and we can also get a SIP message in acknowledgement of response code.We will look into some quite frequent SIP messages in this post and response codes in the next post.

SIP Messages:

INVITE: Invite is very first message to set up a connection. It is also used to modify a session as re-invite (which we will discuss in later posts). User Agent sending an Invite is known as User Agent Client.

ACK: ACK is sent in response to a 200 OK message. ACK is used only with Invite or a Re-Invite message.