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

26 HP-UX C SIP Stack Programmer’s Guide

Transport Support

 INFO method (RFC 2976)—for mid-call information exchange

without changing the call state.

 MESSAGE method (draft-ietf-sip-message-0x)—for instant

messaging.

 UPDATE method (RFC 3311)—to allow a client to update

parameters of a session (such as the set of media streams and

their codecs) without changing the dialog state. Sample code for

sending/receiving this method is included.

TRANSPORT

UPPORT

The SIP Stack supports SIP over UDP, TCP, and TLS, and provides full UDP

reliability as defined in the SIP specification. You can configure the SIP Stack to

listen to several UDP, TCP and TLS local addresses.

TLS TLS is a security protocol which is typically layered on top of connection-

oriented transports such as TCP. TLS allows client/server applications to

communicate over TCP in a way that is designed to prevent eavesdropping,

tampering, or message forgery. TLS 1.0 is defined in RFC 2246.

TLS is now an integral part of baseline SIP (RFC 3261) as a recommended

feature of User Agents and a mandatory feature for SIP servers. TLS provides a

solution to many of the security issues SIP applications face and it ties in well

with the existing SSL/TLS infrastructure that serves HTTP applications.

PERSISTENT

CONNECTION

In many cases, a single TCP/TLS connection can be reused for different

messages, transactions or dialogs. The frequent opening and closing of TCP

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

handshake (and even more so in TLS connections). For this reason, SIP permits

connection persistency, which is the reuse of an open connection. The SIP Stack

enables connection reuse by identifying that a message can be sent on an

existing open connection. The following levels of persistency are available:

 Transaction user

 Transaction persistency

 No persistency

IPV6 The SIP Stack supports IP version 6 (IPv6). You can configure the SIP Stack to

listen to IPv6 and IPv4 addresses simultaneously, and to receive and send SIP

messages using IPv6 packets.

ENHANCED

FEATURES

The enhanced features of the SIP Stack are described in the sections below.