Design and applications of ATM LAN/WAN adapters

ATM networks are today operational, both as backbones for existing LAN technologies and as commercial wide-area multiservice networks. Still, in the early deployment of multi-site ATM networks, a number of difficulties have arisen out of the differences between the service definitions in local ATM networks and long distance carrier networks. In particular, the adaptation of LAN emulation protocols relying on switched, best-effort connections to the first generation of ATM WAN services turned out to require the introduction of specific functions. In this paper, we study and discuss the nature of these adaptation functions which include peak rate shaping in order to comply with the traffic contract at the public UNI, efficient buffering and selective cell discarding to optimize the performance of end-to-end data protocols and fairness mechanisms to improve resource sharing. We describe a flexible hardware platform which enabled a quick prototyping of these functions. It provides on-board support for efficient cell processing and for associated functions (rate control, buffering, etc.). The use of a cell processor enables a software-only implementation of the ATM cell handling, yielding short development times and easy debugging while being compatible with an operation at line speeds up to 155 Mbit/s. We finally give examples and measurements of the use of the adapters in LAN/WAN interworking situations.