Operation Manual

Chapter 4
SIP
Introduction
This chapter describes the main features of the SIP standard, the protocols
supported, the implementation of the call processes in the AT-RG213 and
how to configure and operate the AT-RG213 to provide, or connect to, a
VoIP Network.
SIP Protocol
SIP (Session Initiation Protocol) is a protocol developed to assist in
providing advanced telephony services across the Internet. Internet
telephony is evolving from its use as a ʺcheapʺ (but low quality) way to
make international phone calls to a serious business telephony capability.
SIP is one of a group of protocols required to ensure that this evolution can
occur.
SIP is part of the IETF standards process and is modeled upon other Internet
protocols such as SMTP (Simple Mail Transfer Protocol) and HTTP
(Hypertext Transfer Protocol.) It is used to establish, change and tear down
(end) calls between one or more users in an IP-based network. In order to
provide telephony services there is a need for a number of different
standards and protocols to come together - specifically to ensure transport
(RTP), signalling inter-working with today’s telephony network, to be able
to guarantee voice quality (RSVP, YESSIR), to be able to provide directories