A role for ATM in telephony and IP networks

Abstract

Public telecommunication network operators are now concentrating their attention on the Internet, not only for realising datacommunication services but also for a network infrastructure for providing telephony services. This has resulted in a reluctance to invest in existing circuit-switched technology and in the implementation of a number of Internet protocol (IP) telephony services. This paper concentrates on two topics – firstly, quality of service (QoS) in IP and asynchronous transfer mode (ATM) networks and secondly, the use of ATM networks for providing large-scale telephony, or more generally “narrowband”, services that are usually supported by public circuit-switched networks. The methods of providing a range of qualities of service in IP routers and ATM switches are reviewed and the applicability of these mechanisms to the support of telephony is considered. Although public telephony services over the Internet are offered today with reasonable quality (some network operators claim that voice quality in general is better than for a call involving a mobile phone) the volume of traffic is generally low and Internet service providers overprovision their networks to improve service quality. A number of scenarios in which ATM can be used as an infrastructure for narrowband services are presented. If bandwidth is neither abundant nor inexpensive, ATM can provide a cost-effective means of supporting both existing narrowband circuit-switched services and datacommunications. A possible migration path is outlined from the current circuit-switched networks through use of an ATM network infrastructure to a potential integrated IP network. This paper is tutorial in nature and represents the personal opinions of the author (rather than a corporate position).