Analysis of SIP and realization of advanced IP-PBX features

IP-PBX (Private Branch Exchange) is used widely in many fields, it provides robust, high performance and intelligent IP telephony functions it supports the industry standard protocol Session Initiation Protocol (SIP), and offers the sophisticated telephony functions that meet the full spectrum of business requirements. In this paper the characteristics of both IP-PBX function and other kind of SIP phone are analyzed in details, features such as call hold and its retrieve, call group, find me, music on hold, call transfer, call park and its retrieve etc. with kinds of SIP phone features are analyzed successfully. Most of the services shown in this document are implemented in the SIP user agents, these features are not intended to be an exhaustive set, but rather show implementations of common features likely to be implemented on SIP IP telephony in a business environment. This document provides examples of call flows detailing a SIP implementation of the following traditional telephony services and also presents a study over the standard VoIP protocol, Session Initiation Protocol (SIP), and how to capture the packets using the open source packet capture tool.