HP-UX C SIP Stack Programmer's Guide (Novembery 2007)

Working with Transactions 91

WORKING WITH TRANSACTIONS

INTRODUCTION A SIP transaction comprises all messages, from the first request sent by the

client to the server to a final (non-1xx) response to the request sent by the server

to the client.

The Transaction API of the SIP Stack contains a set of functions and function

callbacks that can be used for two purposes. The first is for handling

transactions that are related to the User Agent (UA) and not related to a call-leg.

An example of such a transaction is OPTIONS.

Using the Transaction API, you can create and initialize a transaction and

control a transaction according to the transaction state. You can create a

transaction with any method (except CANCEL and ACK that have a dedicated

API).

Note In order to send a transaction that is related to a call-leg, you should use

the Call-leg API. For more information, see the Working with Call-legs (Dialogs)

chapter.

The second purpose of the Transaction API is for writing a SIP server. Using the

Transaction API, you can implement a Proxy server, Redirect server and

Registrar. You can receive incoming requests and decide whether to redirect or

proxy the request according to the request method and the transaction state. The

Transaction API contains a set of functions and states dedicated specifically for

the purpose of writing a Proxy server. Using these functions, you can fully

implement both stateless and stateful proxies.