A COMPARATIVE STUDY OF THE SWITCHING PERFORMANCE OF CONNECTION-MODE NETWORK LAYER RELAYS Authors: Mário Bernardes, Edmundo Monteiro, André Rodrigues, and Fernando Boavida Affiliation and Address: Laboratório de Informática e Sistemas Universidade de Coimbra Urb. Quinta da Boavista, Lote 1, 1º P-3000 COIMBRA PORTUGAL Tel.: +351 39 701775 Fax: +351 39 701266 e-mail: boavida@mercurio.uc.pt Abstract This paper presents a simulation-based comparative study of two different approaches for connection-mode network layer relays - the service relay approach and the protocol relay approach - for LAN/WAN interconnection, that are currently the subject of standardization activities. In order to evaluate the relative performance characteristics of the two different relay types, a number of simulation studies were carried out, using several traffic conditions and relay models. In spite of the architectural overhead associated with service relays, the obtained results show that this type of relays behaves well even under considerable load, and so more attention should be given to the service relay approach by standards developers and relay implementors. KEY WORDS: Internetworking, service relay, protocol relay, network layer relays 1. Introduction To prevent incompatibilities between different LAN/WAN interconnection solutions, there is an ongoing functional standardization activity in ISO aiming at the development of International Standardized Profiles (ISP), that benefits from the harmonized input of regional workshops (EWOS 1 , 1 European Workshop for Open Systems NIST OIW 2 , and AOW 3 ). This will, hopefully, lead to standardized and compatible implementations of relays for the interconnection of those types of networks. This paper presents a simulation-based study of the switching performance of connection-mode relay systems for LAN/WAN interworking. The study is focused on CSMA/CD LANs and X.25 PSDNs but its results can be easily extended to other subnetwork types. For this particular interworking scenario, two different relay approaches are possible: the service relay and the protocol relay, classified, according to the ISO taxonomy [1], as RB51.1xxx and RC51.1xxx, respectively (the xxx stands for the identifier of the X.25 PSDN access method). One of the objectives of the work described in this paper is to evaluate the impact of each of the above mentioned solutions in terms of the switching performance of the relay system. In this paper, section 2 introduces some basic concepts regarding network layer relays. Section 3 presents a description of the relay models, traffic conditions and simulation strategies used in the presented work. The study results are presented and analyzed in section 4. Section 5 presents the study conclusions and future work directions. 2 National Institute for Standards and Technology - OSI Implementors Workshop 3 Asian and Oceanic Workshop