Assured services session initiation protocol

Written by stephen byron cooper Google
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Assured services session initiation protocol
Assured Services SIP is a protocol for carrying telephone calls over the Internet. (businesswoman image by Paul Moore from

The Session Initiation Protocol (SIP) is used in Voice over Internet Protocol (VoIP) to handle the call-signalling functions of a VoIP call. Assured Services Session Initiation Protocol (AS-SIP) is a variation on SIP defined by the Defense Information Systems Agency (DISA) for mission-critical communication.


AS-SIP includes all the standard functions of SIP. These are the functions of a regular telephone--ringing, pick up, busy, call reject and call termination. The added functionality of AS-SIP is that its data packets are prioritised over other traffic on a network and the AS-SIP packets are encrypted.


The terminology of SIP is incorporated in AS-SIP. The calling device is called the User Agent Client (UAC) and the called device is called the User Agent Server (UAS). Each User Agent (UA) channels its calls to a proxy that handles calls for all UAs in a particular domain (for example, a company). This is called "Service Provider Architecture" with the proxy acting as service provider and adding the AS-SIP features of security. Prioritisation is handled by a second device called an "Access Router."


Although AS-SIP was developed by a US defence organisation, it is an open standard. The protocol is published and distributed by the Internet Engineering Task Force (IETF).

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