William Todd Marshall

TOPS: an architecture for telephony over packet networks

Packet telephony is of increasing interest in both the telecommunications and Internet communities. The emergence of packet telephony will create new services, and presents an opportunity to rethink how conventional telephony services are implemented. In this paper, we present an architecture for telephony over packet networks (TOPS). TOPS allows users to move between terminals or to use mobile terminals while being reachable by the same name. TOPS users can have multiple terminals and control how calls are routed to them. TOPS allows for terminals with a range of capabilities such as support for video, whiteboard, and other media with a variety of coding formats. TOPS retains the necessary information on terminal capabilities to determine the appropriate type of communication to be established with the remote terminal. The architecture assumes that the underlying network supports the establishment of end-to-end connectivity between terminals, with an appropriate quality of service. The components of TOPS are a directory service, an application layer signaling protocol, and a logical channel abstraction for communication between end-systems. The directory service maps a users name to a set of terminals where the user may be reached. A user can control the translation operation by specifying profiles that customize how his name is mapped to a set of terminals where he can be reached. Terminal capabilities are also stored in the directory service. The application layer signaling protocol establishes and maintains call state between communicating terminals. The logical channel abstraction provides a shared end-to-end context for a calls constituent media and control streams, while isolating the applications from the details of the network transport mechanisms. In addition to supporting simple point-to-point calls, the architecture supports both centralized and decentralized conferencing. We also introduce a simple encapsulation format for voice.

DOSA: an architecture for providing a robust IP telephony service

An increasing number of communication services are moving to an IP-based infrastructure. Packet telephony is probably the first important real-time service that must be supported well over an IP network. The use of IP presents a tremendous opportunity for service providers to exploit endpoint intelligence to offer creative new services going far beyond the current telephony service model. However, to support telephony, signaling protocols are needed that allow the service provider to offer network-layer service differentiation and, at the same time, to control access to both the enhanced network-layer quality of service as well as other services. This paper describes the distributed open signaling architecture (DOSA), which incorporates protocols that meet these needs. A key contribution of our work is a recognition of the need for coordination between call signaling, which controls access to telephony-specific services, and resource management, which controls access to network-layer resources.

Integration of call signaling and resource management for IP telephony

One challenge to realizing a robust Internet Telephony service is the need to integrate resource management with a call signaling architecture. Also important in deploying the service is the need to preserve user privacy and security. The Distributed Open Signaling Architecture meets these requirements. DOSA establishes a framework for coordination between call signaling, which controls access to telephony-specific services, and resource management, which controls access to network-layer resources. The authors describe the architecture and an implementation approach that has proved viable in detailed simulations from real usage data.

Xunet 2: lessons from an early wide-area ATM testbed

This paper is a retrospective on the design of Xunet 2, one of the earliest functional wide-area asynchronous transfer mode (ATM) networks. Work on Xunet 2 began in 1989 and the network, consisting of experimental ATM switches, IP routers, and 45 Mb/s transmission lines, has been operational since October 1991. The network serves as a laboratory without walls for eight research groups across the United States. While Xunet 2 has only a small number of nodes, it was designed as a prototype of a nationwide ATM network. This paper reviews some of the design decisions and lessons learned in the project and points out the research directions motivated by this work, focusing on the areas of traffic management, ATM switch design, network control, and the implementation of an IP router.