LAN AND I/O CONVERGENCE - A SURVEY OF THE ISSUES

Although they are both interconnects that move information from one place to another, local area network and computer I/O architectures have traditionally been regarded as fundamentally different technologies. LANs connected independent and widely separated computers, whereas I/O channels connected a host to peripheral devices such as disks and tape drives. However, modern system requirements, together with recent technology developments, are now causing a convergence of the two architectures in certain environments. Discussion focuses on the changes in requirements for interconnect distances, information models, and computation models on which LANs and channels have been based. Both LANs and channels have benefited from fiber-optic technology advances that extend the combination of bandwidth and interconnect distance. At the same time, the information model-driven by multimedia applications using voice and video-is evolving to include information with very different characteristics. In the evolving I/O computation model, data are increasingly off-loaded from the host to intelligent file servers that form the basis of client/server architectures. The result is that a traditional LAN peer-to-peer interconnect quite naturally supports the current I/O computation model. There are few differences between LAN and I/O architectures developed to serve the demands of multimedia and client/server applications, and even these differences may disappear in the next decade. An overview of major LANs and channels is presented, noting the similarities and differences of architectures-such as ATM, FDDI, ESCON channel, Fibre Channel, and HiPPI-in the context of nine key architectural aspects.