Dialogic IP Phone 05-2239-009 User Manual

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Dialogic Corporation

When all channels between endpoint A and the gateway are closed, each must send a 
DisengageRequest (DRQ) message to the gatekeeper. This message lets the gatekeeper know that 
the bandwidth is being released. The gatekeeper sends a DisengageConfirm (DCF) message to both 
endpoint A and the gateway.

Session Initiation Protocol (SIP) is an ASCII-based, peer-to-peer protocol designed to provide 
telephony services over the Internet. The SIP standard was developed by the Internet Engineering 
Task Force (IETF) and is one of the most commonly used protocols for VoIP implementations. This 
section discusses the following topics about SIP:

 

Some of the advantages of using SIP include:

The SIP protocol stack is smaller and simpler than other commonly used VoIP protocols, such 
as H.323.

SIP-based systems are more easily scalable because of the peer-to-peer architecture used. The 
hardware and software requirements for adding new users to SIP-based systems are greatly 
reduced.

Functionality is distributed over different components. Control is decentralized. Changes made 
to a component have less of an impact on the rest of the system.

User agents (UAs) are appliances or applications, such as SIP phones, residential gateways and 
software that initiate and receive calls over a SIP network.

Servers are application programs that accept requests, service requests and return responses to 
those requests. Examples of the different types of servers are:

Location Server

Used by a SIP redirect or proxy server to obtain information about the location of the called 
party. 

Proxy Server

An intermediate program that operates as a server and a client and which makes requests on 
behalf of the client. A proxy server does not initiate new requests, it interprets and possibly 
modifies a request message before forwarding it to the destination.