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

Working with Transmitters 211

WORKING WITH TRANSMITTERS

INTRODUCTION The SIP Stack uses transmitter objects (transmitters) for message sending. Each

transaction holds a single transmitter and uses it to send SIP messages and

message retransmissions. The transaction creates its transmitter upon

initialization and terminates it only upon destruction. The transmitter is

responsible for all message sending activities, including address resolution, Via

header handling, and the actual message sending.

The application can also directly use transmitters. The application can create

transmitters and use them to send SIP messages that are not related to

transactions. Each transmitter can send a single SIP message (Request or

Response). Applications will need to use transmitters in several situations. For

example, a proxy application should use transmitters to proxy responses that

were not mapped to any transaction or the ACK on the 2xx response to

INVITE. A transmitter can also be used to send non-SIP messages. The

application can use the transmitter to send any buffer it wishes to its chosen

destination.

This chapter focuses on how the application uses transmitters to send SIP

messages. The section, Sending Buffers with Transmitter Objects, explains how

to use the transmitter to send a non-SIP message.

TRANSMITTER ENTITIES The Transmitter API relates to the following two entities:

 Transmitter (transmitter)

 Transmitter Manager (TransmitterMgr)