Sip Passthrough; Table 29 Sip Call Progression; Appendix H Sip Passthrough - ZyXEL Communications ZyWall 35 User Manual

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Table of Contents

The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol that

handles the setting up, altering and tearing down of voice and multimedia sessions over the

Internet. SIP is used in VoIP (Voice over IP), the sending of voice signals over the Internet

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 circuit-switched telephone networks.

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 e-mail address identifies an e-mail account. The

format of a SIP identity is SIP-Number@SIP-Service-Domain.

The SIP number is the part of the SIP URI that comes before the "@" symbol. A SIP number

can use letters like in an e-mail address (johndoe@your-ITSP.com for example) or numbers

like a telephone number (1122334455@VoIP-provider.com for example).

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 1122334455@VoIP-provider.com, then "VoIP-provider.com" is

the SIP service domain.

SIP Call Progression

The following figure displays the basic steps in the setup and tear down of a SIP call. A calls

P P E N D I X

SIP Passthrough

ZyWALL 35 User's Guide