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Proxy Server
A proxy server is an intermediate entity that receives SIP requests and forwards them
on behalf of the requestor. Proxy servers route requests to the users current location,
authenticate and authorize users for services, and implement provider call-routing
policies. It also enforces polices for a user and provides name mapping.
For each new request, a proxy can function either in stateful or stateless mode. When
it functions as a stateless proxy server, it acts as a simple forwarding element. A stateless
proxy server discards information about a message after the message is forwarded. A
stateful proxy server remembers information (specifically, transaction state) about each
incoming request and also about requests it sends as a result of processing the incoming
request. It uses this information to influence the processing of future messages associated
with that request.
SIP proxy servers use presence services to track users and to check the willingness and
ability of users to communicate with other users on the network. A presence service is
an application of the SIP-specific event notification mechanism (RFC 3265 (Session
Initiation Protocol (SIP) - Specific Event Notification)). It enables a user to be located
regardless of the physical location. It also accepts presence information from users,
stores, and distributes the presence information to other interested users.
Posted by sagitraz
Identify User location: Locates the User Agent Client. If the Proxy cannot locate or connect to the user, it manages the operations necessary to complete those requirements
Determine and Negotiate User Capabilities. Must identify the common capabilities and parameters that will allow to User devices to communicate. Determine priorities for common capabilities. List languages spoken
Determine User availability. Determines the willingness of the called party to engage in communications
Call Setup. Includes "ringing", establishment of call parameters at both called and calling party
Call handling. Includes transfer and termination of calls. Call redirection is described in ITU recommendation H.450.3
Posted by srini_murali
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