Computer Networks and ISDN Systems

The IBM Zurich research laboratory's 1.13 Gb/s LAN/MAN prototype

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The paper describes the design concepts that were applied to the development of a Gb/s Local/Metropolitan Area Network (LAN/MAN). The prototype network is based on the folded bus topology, operates at a data rate of 1.13 Gb/s and can span distances in excess of 50 km. With optical fibers being used for data transmission, nodes may be spaced up to 35 km apart without the need for repeaters. Data transmission in the fiber is based on a new 8B/10B code that yields excellent transmission properties. The access protocol is based on a slotted media approach that permits concurrent access to the media by multiple, geographically separated nodes. The protocol is reservation-based and thus guarantees a high degree of fairness in serving the nodes. Data payloads are transmitted in consecutive slots and data contiguity is preserved. The network is controlled by a headend that issues cycles composed of a varying number of slots; the number is determined by previously collected node requests for data transmission. The hardware of a network node is partitioned into boards providing the Physical Layer functions (block coding, parallel-serial and electro-optical conversion, including all inverse operations), Media Access Control functions and Data Buffering/Device Attachment functions. For every function and for all board interconnections the most suitable leading-edge, commercial technology was chosen. Since essentially all the control functions must be performed in real time very limited use of microprocessors could be made. All the control functions in a node are implemented with high-speed programmable logic devices, microsequencers and an Arithmetic Logic Unit. Only in the headend, the node that performs bus scheduling, is a RISC-type microcontroller used. A four-node network, transporting FDDI-backbone and high-resolution image traffic over a distance of 10 km, was demonstrated in full operation at the TELECOM'91 exhibition in Geneva, Switzerland. © 1993.