Transaction Management Layer

SIP is based on a request/response transaction model that is similar to the model that is used by HTTP. A transaction comprises a request that is sent by a client to a server and all of the responses to that request that are sent back from the server. The transaction management layer handles application-level retransmissions, matching responses to requests, and application-level timeouts. A User Agent Client (UAC) performs tasks by using a series of transactions.