CHAPTER 5
Introduction to VoIP
This chapter provides background information on VoIP and SIP.
5.1 Introduction to VoIP
VoIP is the sending of voice signals over the Internet Protocol. This allows you to make phone calls and send faxes over the Internet at a fraction of the cost of using the traditional circuit- switched telephone network. You can also use servers to run telephone service applications like PBX services and voice mail. Internet Telephony Service Provider (ITSP) companies provide VoIP service. A company could alternatively set up an
5.2 Introduction to SIP
The Session Initiation Protocol (SIP) is an
SIP signaling is separate from the media for which it handles sessions. The media that is exchanged during the session can use a different path from that of the signaling. SIP handles telephone calls and can interface with traditional
5.2.1 SIP Identities
A SIP account uses an identity (sometimes referred to as a SIP address). A complete SIP identity is called a SIP URI (Uniform Resource Identifier). A SIP account's URI identifies the SIP account in a way similar to the way an
5.2.1.1 SIP Number
The SIP number is the part of the SIP URI that comes before the “@” symbol. A SIP number can use letters like in an
5.2.1.2 SIP Service Domain
The SIP service domain of the VoIP service provider is the domain name in a SIP URI. For example, if the SIP address is
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