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Using CSTA for SIP phone user agents (uaCSTA)

1st edition, June 2004

The Session Initiation Protocol (SIP) is a control (signalling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences.

CSTA standardizes a very powerful and flexible set of application services to observe and control voice and non-voice media calls as well as control and observe non-call related features.

This Ecma Technical Report describes how CSTA can be used to provide a subset of CSTA call control functionality, called 1st party call control, for SIP user agents. The term uaCSTA (for user agent CSTA) refers to transporting ECMA-323 (CSTA XML) messages over a SIP session.

uaCSTA leverages SIP mechanisms to provide a highly featured, robust, and extensible set of features to support applications in the Enterprise environment.

uaCSTA can be implemented by several different types of SIP user agents:

  •  directly by a SIP user agent on a SIP phone;
  •  uaCSTA can also be implemented by a SIP B2BUA to augment 3PCC functionality;
  •  by a proxy server that is front-ending a PBX.


Download this standard


Technical CommitteeTC32

ISO/IEC numberTR 22767

ETSI numberTR 102 348