Optimising bandwidth reservation in IP/ATM internetworks using the guaranteed delay service C. A. MaJcher Bastos Dept de Enl de Telecomunicar;oes, Universidade Federal Fluminense Rua Passo da Patria 156, 24210-240 Niter6i RJ, Brazil telefax: +55 21 620 3935; e-mail: cmbastos@telecom.uff.br M. A. Stanton Dept de Informatica, Catholic University of Rio de Janeiro Rua M. de S. Vicente 225, 22453-900 Rio de Janeiro RJ, Brazil fax: +55 21 511 5645; e-mail: michael@inf.puc-rio.br http://www.inf.puc-rio.br/-michael Abs1ract The service model proposed by the IETF for integrated services in IP internets, including the Internet, specifies, amongst others, a guaranteed delay service, which offers a deterministic delay for packet delivery. An analysis is presented of implementation aspects of this service, when ATM subnets are used. An evaluation is made of the reserved bandwidth necessary to guarantee a given maximum delay for a given application, taking into consideration alternative strategies for implementing IP over ATM, and factors such as traffic profile, end- to-end hop count, packet transmission with or without fragmentation, and bandwidth reservation for individual flows or groups of flows. It is shown that the reserved bandwidth necessary to guarantee a given delay is reduced by interleaving cells from different packets, by making flow group reservations, and by reducing the number of intermediate nodes. In large-scale internetworks implemented over (similarly large-scale) ATM subnets, switched virtual channels (VCs) have to be used. In such a situation, in order to perform flow group The original version of this chapter was revised: The copyright line was incorrect. This has been corrected. The Erratum to this chapter is available at DOI: © IFIP International Federation for Information Processing 1998 H. R. van As (ed.), High Performance Networking 10.1007/978-0-387-35388-3_42