How Fibre Channel Compares

Although IBM's Serial Storage Architecture (SSA) aims only at data storage, it compares with the Fibre Channel-Arbitrated Loop (FC-AL) in terms of topologies, the maximum number of participants, and cable lengths. SSA's transfer rates vary between 20 and 80 MBps. As an upper-level protocol (ULP), it uses almost exclusively the SCSI protocol.

Compared to the parallel SCSI bus, the Fibre Channel's advantages are higher transfer rates, higher cabling lengths, and lower costs. Parallel SCSI is currently limited to 40 MBps (16-bit Wide or Fast 20 SCSI). Although there are concepts to expand the SCSI bus to 32-bit (Wide 32) and to double the transfer speed to 40 MHz (Fast 40), resul ting in a total 160-MBps transfer rate, it is still not clear whether it is technically feasible. However, since parallel SCSI is extremely popular and widespread, it will continue to play an important role. The use of SCSI as a ULP in other technologies is an indicator of its continuing importance.

The local network technology FDDI was designed for multimedia data transmission via optical fiber similar to the FC-AL. Although its transfer rate of 12.5 MBps is lower than that of the FC-AL, it has proven to be sufficient for high-quality audio and video delivery on backbones. The big advantage of FDDI is its synchronous data transfer mode.The serial-bus standard IEEE- 1394-FireWire also has a maximum transfer rate of 12.5 MBps but allows isochronous multimedia transfer. It is restricted in cable lengths.

ATM's transfer rate is 19.4 MBps (155 Mbps). Because of the relatively small size of the data packets (53 bytes) and the high portion of the administration and control information of up to 10 percent in one cell, ATM is not appropriate for the connection of peripherals. Fibre Channel, however, with its payload of up to 2112 bytes per frame is optimized for PC applications with typical block sizes of 512 bytes.