TOPS: an architecture for telephony over packet networks

摘要

Packet telephony is of increasing interest in both thentelecommunications and Internet communities. The emergence of packetntelephony will create new services, and presents an opportunity tonrethink how conventional telephony services are implemented. In thisnpaper, we present an architecture for telephony over packet networksn(TOPS). TOPS allows users to move between terminals or to use mobilenterminals while being reachable by the same name. TOPS users can havenmultiple terminals and control how calls are routed to them. TOPS allowsnfor terminals with a range of capabilities such as support for video,nwhiteboard, and other media with a variety of coding formats. TOPSnretains the necessary information on terminal capabilities to determinenthe appropriate type of communication to be established with the remotenterminal. The architecture assumes that the underlying network supportsnthe establishment of end-to-end connectivity between terminals, with annappropriate quality of service. The components of TOPS are a directorynservice, an application layer signaling protocol, and a logical channelnabstraction for communication between end-systems. The directory servicenmaps a user's name to a set of terminals where the user may be reached.nA user can control the translation operation by specifying profiles thatncustomize how his name is mapped to a set of terminals where he can benreached. Terminal capabilities are also stored in the directory service.nThe application layer signaling protocol establishes and maintains callnstate between communicating terminals. The logical channel abstractionnprovides a shared end-to-end context for a call's constituent media andncontrol streams, while isolating the applications from the details ofnthe network transport mechanisms. In addition to supporting simplenpoint-to-point calls, the architecture supports both centralized andndecentralized conferencing. We also introduce a simple encapsulationnformat for voice