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

Working with the Transport Layer 285

WORKING WITH THE TRANSPORT

LAYER

INTRODUCTION The Transport layer is responsible for the actual transmission of requests and

responses over network transports. SIP permits the usage of unreliable

transports, such as UDP, and reliable transports, such as TCP and TLS (over

TCP), using both IPv4 and IPv6 addresses. TCP, TLS and UDP differ in many

ways. The most fundamental difference is that UDP is connection-less, while

TCP and TLS are connection-oriented and therefore create a reliable data

transfer service.

This chapter focuses on the connection-oriented reliable transport types. The

SIP Stack supports TCP and TLS connection-oriented transports. This chapter

explains how to maintain a persistent connection and how to use the TCP and

TLS transports with the SIP Stack API. In addition, this chapter describes the

abilities that the SIP Stack provides for monitoring row buffers that are sent or

received from the sockets, and the usage of IPv6 addresses.

PERSISTENT

ONNECTION

ANDLING

In many cases, a single connection (TCP or TLS) may be reused for different

messages, transactions or dialogs. Opening and closing TCP connections often

is not desirable because of the extra messaging overhead of the TCP handshake

and even more so in TLS connections. Therefore, RFC 3261 permits connection

persistency, which is the reuse of an open client connection. The Persistent

Connection feature of the SIP Stack adds the capability of identifying that a

message can be sent on an existing open connection. The message is then sent

using this connection.