VoIP Service

Introduction

IceWarp Server VoIP service implements SIP. The SIP (Session Initiation Protocol) is designed to allow devices, both software and hardware, to establish a communication session.

The VoIP service in IceWarp Server is actually a SIP domain which is to be defined within IceWarp Server as a domain or domain alias. This domain must have a valid DNS "A" record.

The four basic components of a SIP session are:

SIP User Agents

These are the end-user devices.

These can be software devices, running on PCs, PDAs, cell phones, etc. or they can be SIP-enabled network devices such as SIP-phones, or even, via SIP gateways, ordinary telephony devices.

A SIP call is initiated by a user agent client and responded to by user agent server.

SIP Registrar Servers

These are databases containing the location of all user agents within a domain. There servers retrieve and send IP addresses and other information at the request of a SIP proxy server.

SIP Proxy Server

A SIP proxy server accepts session requests from a user agent and queries a SIP registrar for the recipient's address. Then it forwards the session invitation directly to the user agent if it is in the same domain or to another proxy server in the case the user agent is in another domain.

SIP Redirect Servers

These allow proxy servers to locate other, external proxy servers (rather like a DNS for SIP).