P/N 480-0049-00-13
1-15
Chapter 1: Overview
SIP User Agent
SIP (Session Initiation Protocol) is a signaling protocol used to establish a session on an IP network
for voice control and management; it is a request-response protocol that closely resembles Hypertext
Transfer Protocol (HTTP), which forms the basis of the World Wide Web. SIP re-uses many of the
constructs and concepts of Internet protocols such as HTTP and Simple Mail Transfer Protocol
(SMTP). The purpose of SIP is only to establish/change/terminate sessions. SIP is not concerned
with the content or details of the session.
SIP is Transport layer-independent, which means it can be used with any transport protocol: UDP,
TCP, ATM, etc. It is text-based, so it requires no encoding/decoding like H.323. And SIP supports
user mobility, using proxies and redirecting requests to your current location.
When configured for SIP the Tenor will act as a SIP User Agent (Endpoint) as defined in IETF
RFC3261. Multiple user agents allow for separate agents to be allocated to each SIP call. It will be
able to gateway calls to and from the IP network, and Customer Premise Equipment (CPE) such as
phones, PBX's, and FAX machines, or the Public Switched Telephone Network (PSTN). The Tenor
SIP User Agent will work in conjunction with an external SIP proxy or redirect server to route and
connect calls over SIP based networks.
There are three basic components of SIP:
1. User Agent (Endpoint)
•
client element, initiates calls
•
server element, answers calls
2. Network Server (Proxy Server or Redirect Server)
•
name resolution
•
user location
•
redirect and forking
3. Registrar
•
Stores registration information in a location service using a non-SIP protocol.
