SIP - Chapter 1

1. SIP Request/Responses list:

SIP is a protocol which uses text format to send and receive request & response messages.

There are 6 basic request/Method types: (Note: Requests or Methods are same)

Request Types:

INVITE - This message is send by the UAC (User A) to UAS (Proxy)  or other UAC  (User B) to start a session with the User B

ACK - Message send by the UAC (User A) to UAC  (User B) for the 200 OK Response Message.

BYE - Ends a session send by any UAC (User A or User B)

CANCEL - Cancels establishing the session 

OPTIONS - Communicates information about the capabilities of the calling and receiving SIP phones

REGISTER - UAC registers his own ip address & URL with the registrar server.

Response Types:

SIP Requests are answered with SIP responses, of which there are 6 classes:

1xx = informational responses, such as 180, which means ringing
2xx = success responses
3xx = redirection responses
4xx = request failures
5xx = server errors
6xx = global failures

What is difference between dialog, Transaction & session in SIP? What are the parameters used to identify the dialog, transaction & Sessions?

Dialog - Dialog is identified by the CALL-ID, FROM and To Tag fields.

What are the minimum headers required for a SIP Request message?

Max-Forwards, To, From, Call-ID and CSeq headers are required.

What is Max-Forwards header field?

The

is initialized to some large integer and decremented by each SIP server, which

receives and forwards the request, providing simple loop detection.Max-Forwards header field, which
What is From and To Header?

To

originator and destination of the SIP request. When a name label is used, as in

this example, the SIP URI is enclosed in brackets and used for routing the

request. The name label could be displayed during alerting, for example, but is

not used by the protocol.and From header fields, which show the