This article has double significance. It aids
in understanding how to build call control applications using Parlay. It also
gives insights into how to build gateways that support mapping onto SIP. The
authors give an overview of the Parlay call control APIs. The mapping issues
are then dealt with. The article next describes the implementation of the
gateway. After that the authors discuss related work and lessons learned. The
conclusion provides a summary and identifies areas for further work. Two main
sets of standards have emerged for Internet telephony: H.323 from the
International Telecommunication Union--Telecommunication Standardization Sector
and session initiation protocol (SIP) from the Internet Engineering Task Force.
Parlay, a set of standard object-oriented and signaling protocol-neutral
application programming interfaces (APIs), is an alternative. Call control
makes it possible to establish, modify, and tear down calls. It is the main
functionality offered by Internet telephony networks. The authors have built a
call control application in a SIP environment, using the call control APIs
offered by Parlay. This article describes the case study. The mapping of the
APIs onto SIP is presented, and its implementation is described. Related work
is reviewed, and the lessons learned are discussed. Parlay call control APIs
are suitable for application development in Internet telephony. However, well
isolated extensions are needed to realize their full potential