Asynchronous Transfer Mode (ATM)

In this chapter we look at the basics of ATM and how it works. In effect there are two distinct aspects. On the one hand ATM provides a universal switching fabric supporting the ATM bearer service. On the other hand the services to be carried have to be adapted so that they fit on to this ATM bearer service. The bearer service can be tailored to meet the requirements of the service being carried, and we have looked at how the network polices each connection to make sure that the appropriate quality of service is maintained. We have also looked at how services are adapted to map on to the bearer service. There is often confusion about how Frame Relay, SMDS and ATM relate to each other. The truth is that Frame Relay and SMDS are services whilst ATM is a network infrastructure that can carry them. So the introduction of ATM networking will not make Frame Relay or SMDS obsolete any more than it will make any other service, such as telephony, obsolete. We have looked at how frame relay and SMDS are carried over an ATM network. In particular we have seen how connectionless services such as SMDS need connectionless switches overlaid on the connection-orientated ATM network.