Keywords: SIP, IN, H.323, MGCP, inter-operation, VoIP
Received May 3, 2005; revised July 20, 2005; accepted August 4, 2005.
Communicated by Ten-Hwang Lai.
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Hung-Hsin Chang, Meng-Ta Hsu, Ming-Feng Chang and Chien-Chao Tseng
Department of Computer Science and Information Engineering
National Chiao Tung University
Hsinchu, 300 Taiwan
The traditional circuit-switched telecommunication network and the packet-switched
data network are converging to a single packet-switched network. One important application
of the converged network is telephony communications, also referred to as VoIP
(Voice over IP). Call signaling protocols, such as H.323, SIP and MGCP, have been developed
to support VoIP communications. To enable devices using different VoIP protocols
to communicate, gateways are needed to translate messages of one protocol to
messages of another. In this paper, we present a simple, flexible framework for this interworking
function. The framework is based on a half-call model where a call is controlled
by two half-call finite state machines (FSMs), one representing the state of the
caller and the other representing the state of the callee. The interworking function has
been implemented such that the caller FSM of one VoIP protocol can interact with the
callee FSM of any VoIP protocol. The development effort of the interworking function is
minimized since only two half-call FSMs for each VoIP protocol are needed and they
can be developed independently as long as the design conforms to the same interface
specification. We have developed an integrated call agent (ICA) that contains the halfcall
FSMs of H.323, SIP and MGCP. Calls between devices using these VoIP protocols
can be set up, maintained and terminated by the ICAs.
Received May 3, 2005; revised July 20, 2005; accepted August 4, 2005.
Communicated by Ten-Hwang Lai.