Implementation of WAN networks over ATM

The objective of this paper is to show the possible ways of implementing WAN networks over ATM networks. The first part is a presentation of the various standardised network data protocols for the transfer of data on public data networks and their relation to ATM. We quickly come to the realisation that the predominant protocol is currently the TCP/IP, which is also used on the known computer network, the Internet. This is followed by an analysis of overhead information, which is added by the ATM Adaptation Layer. Of special interest in data transfer are AAL 3/4 and AAL 5 protocols. ATM has at the moment defined adaptive classes of services: CBR, VBR, ABR and UBR. For data transfer, class ABR will be used mainly. As we have already mentioned, the TCP/IP is at present predominant. In the third chapter, we analyse the transfer of TCP/IP packets over a pilot ATM network. Particularly painful is the realisation that the loss of a single cell during transmission (usually due to a breach of the negotiated procedure) requires that we retransmit the whole packet. In spite of all its weaknesses, the TCP/IP will remain the most widespread protocol, though some correction will be necessary. Most of the findings also hold true for other protocols, like Frame Relay. The next chapter is on researching methods of allocating virtual paths in the ATM network. As long as ATM networks will be used merely for connecting LAN networks and as long as the ATM network is small in size, no problems are to be expected. The topic will gain in importance on the appearance of other larger commercial providers of ATM networks who will also provide other services, for example, speech transmission, video transmission, etc.. Our virtual path allocation proposal is a compromise between the use of virtual paths for determining the destination switch exchange and the utilisation of virtual paths for determining types of tributaries, which they contain. It enables simple supervision and management of ATM networks, and of course, on the other hand sets some limits, for instance, on the limited number of VBR type tributaries.