16-05-2012, 04:45 PM
SESSION INITIATION PROTOCOL
RADVISIONSIPProtocolOverview.pdf (Size: 112.03 KB / Downloads: 48)
INTRODUCTION
The Session Initiation Protocol (SIP) is a signaling protocol for initiating,
managing and terminating voice and video sessions across packet networks. SIP
sessions involve one or more participants and can use unicast or multicast
communication. Borrowing from ubiquitous Internet protocols, such as HTTP
and SMTP, SIP is text-encoded and highly extensible. SIP may be extended to
accommodate features and services such as call control services, mobility,
interoperability with existing telephony systems, and more.
SIP is being developed by the SIP Working Group, within the Internet
Engineering Task Force (IETF). The protocol is published as IETF RFC 2543
and currently has the status of a proposed standard.
This section describes the key constituents of SIP.
SIP ENTITIES A SIP network is composed of four types of logical SIP entities. Each entity has
specific functions and participates in SIP communication as a client (initiates
requests), as a server (responds to requests), or as both. One “physical device”
can have the functionality of more than one logical SIP entity. For example, a
network server working as a Proxy server can also function as a Registrar at the
same time.
Following are the four types of logical SIP entities:
USER AGENT
In SIP, a User Agent (UA) is the endpoint entity. User Agents initiate and
terminate sessions by exchanging requests and responses. RFC 2543 defines the
User Agent as an application, which contains both a User Agent client and User
Agent server, as follows:
6 RADVISION SIP Overview
User Agent Client (UAC)—a client application that initiates
SIP requests.
User Agent Server (UAS)—a server application that contacts
the user when a SIP request is received and that returns a
response on behalf of the user.
Some of the devices that can have a UA function in a SIP network are:
workstations, IP-phones, telephony gateways, call agents, automated answering
services.
PROXY SERVER
A Proxy Server is an intermediary entity that acts as both a server and a client
for the purpose of making requests on behalf of other clients. Requests are
serviced either internally or by passing them on, possibly after translation, to
other servers. A Proxy interprets, and, if necessary, rewrites a request message
before forwarding it.
REDIRECT SERVER
A Redirect Server is a server that accepts a SIP request, maps the SIP address
of the called party into zero (if there is no known address) or more new
addresses and returns them to the client. Unlike Proxy servers, Redirect Servers
do not pass the request on to other servers.
RADVISIONSIPProtocolOverview.pdf (Size: 112.03 KB / Downloads: 48)
INTRODUCTION
The Session Initiation Protocol (SIP) is a signaling protocol for initiating,
managing and terminating voice and video sessions across packet networks. SIP
sessions involve one or more participants and can use unicast or multicast
communication. Borrowing from ubiquitous Internet protocols, such as HTTP
and SMTP, SIP is text-encoded and highly extensible. SIP may be extended to
accommodate features and services such as call control services, mobility,
interoperability with existing telephony systems, and more.
SIP is being developed by the SIP Working Group, within the Internet
Engineering Task Force (IETF). The protocol is published as IETF RFC 2543
and currently has the status of a proposed standard.
This section describes the key constituents of SIP.
SIP ENTITIES A SIP network is composed of four types of logical SIP entities. Each entity has
specific functions and participates in SIP communication as a client (initiates
requests), as a server (responds to requests), or as both. One “physical device”
can have the functionality of more than one logical SIP entity. For example, a
network server working as a Proxy server can also function as a Registrar at the
same time.
Following are the four types of logical SIP entities:
USER AGENT
In SIP, a User Agent (UA) is the endpoint entity. User Agents initiate and
terminate sessions by exchanging requests and responses. RFC 2543 defines the
User Agent as an application, which contains both a User Agent client and User
Agent server, as follows:
6 RADVISION SIP Overview
User Agent Client (UAC)—a client application that initiates
SIP requests.
User Agent Server (UAS)—a server application that contacts
the user when a SIP request is received and that returns a
response on behalf of the user.
Some of the devices that can have a UA function in a SIP network are:
workstations, IP-phones, telephony gateways, call agents, automated answering
services.
PROXY SERVER
A Proxy Server is an intermediary entity that acts as both a server and a client
for the purpose of making requests on behalf of other clients. Requests are
serviced either internally or by passing them on, possibly after translation, to
other servers. A Proxy interprets, and, if necessary, rewrites a request message
before forwarding it.
REDIRECT SERVER
A Redirect Server is a server that accepts a SIP request, maps the SIP address
of the called party into zero (if there is no known address) or more new
addresses and returns them to the client. Unlike Proxy servers, Redirect Servers
do not pass the request on to other servers.