SIP (Session Initiation Protocol) SIP sessions include voice communications, instant messaging, and multimedia applications & in most cases a much lower cost and provides excellent QOS Quality of Service, making the call experience the most clear and noise free available. SIP is most widely used to initiate and terminate Voice Over Internet Protocol (VOIP) calls.

The goal of SIP was to provide users with many of the functions and features they typically expect with making phone calls, such as familiar rings, hearing the ring back tone when a call is placed, and the process of dialing a number. SIP goes beyond this however, also implementing a number of advanced features. Despite its? convenient interface that mirrors that of a typical telephone call, SIP is based on an internet protocol rather than that of the telephone industry. Because of this, SIP is able to work seamlessly alongside other internet based protocols. Sip also allows for coordination amongst the various participants in deciding upon what call features will be supported, as well as providing the protocol for call management which allows for adding, dropping, or transferring call participants. It also allows for coordination amongst the various participants in deciding upon what call features will be supported, as well as providing the protocol for call management which allows for adding, dropping, or transferring call participants.

One of the most exceptional benefits of Session Initiation Protocol (SIP) is its application with Private Branch Exchange (PBX). A private branch exchange is a private telephone network used within an enterprise in which users share a certain number of outside lines for external telephone calls. This provides a significant cost savings to the company because it allows companies to quickly and easily make calls within their institution, as well as save by limiting the number of external phone lines that must be maintained. SIP can extend these cost savings dramatically by offering users free long distance calls worldwide. Once again, because SIP is internet based rather than running over traditional telephone lines, the cost of call transmission are as cheap as say sending an e-mail, that is to say, Free! While PBX is already an efficient use of office resources incorporating SIP into a PBX means taking such savings and capabilities to a new level. Incorporating SIP gives users? access to free interoffice communications, long distance calls, as well as huge savings in setup and transaction costs. These transaction cost savings are due to the fact that SIP is based on internet protocol allowing for the ability to physically move phones without any need for rewiring or new setup costs. Because that the system is peer-to-peer rather than cog and wheel like hardwired telephony means that there is no complicated setup necessary, but rather users can simply plug the phone into any available broadband connection and without the need for any complicated hardware or software, calls are ready to be made and received.

Session Initiation Protocol (SIP) offers customers of traditional telephony fantastic cost savings, the flexibility to make free calls from anywhere in the world at any time, and the ability to expand a PBX system with no setup costs. Because there is no complicated hardware or software necessary to setup SIP in a PBX, implementing the technology is as simple as having access via broadband to the internet. Due to these benefits as well as innumerable others, expanded use of SIP in PBX and in a variety of other settings is simply a matter of expanded customer exposure to the possibilities of SIP.

Through the widespread use of instant messaging, SIP endpoints have become commonplace in the office setting. Instant messaging applications including Microsoft MSN Messenger and Apple iChat are SIP clients that can be used to transport voice and video free of charge. The popularity of instant messaging has lead to the creation of specific instant messaging protocols based on the SIP standard. Extensible Messaging and Presence Protocol (XMPP) and Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions (SIMPLE) are two SIP based protocols that allow presence information to be exchanged between SIP endpoints. Presence information is an indicator of a participant's willingness to communicate with another participant. For example, in an instant messaging client, the icon that tells others that you are online is a presence indicator.