Page 11 of 18 March 2001 Fibre Channel: Why another interface? Point-to-point topology is the simplest interconnect method. This topology is similar to a bus in that a dedicated cable connects two devices. The connection is not shared with any other devices. Simplicity and use of the full data transfer rate make this Fibre Channel topology an ideal extension to the standard SCSI bus interface. The arbitrated loop (FC_AL) topology provides a relatively simple method of connecting and sharing resources. FC_AL connects up to 126 devices or nodes in a single, continuous loop or ring. The loop is constructed by daisy-chaining the transmit and receive cables from one device to the next or by using a hub or switch to create a virtual loop. The loop can be self-contained or incorporated as an element in a larger network. All the devices in an FC_AL network share the available data transfer capacity of the Fibre Channel interface. When the loop is initialized, each device attached to the loop identifies itself. The devices use an arbitration protocol to determine which device controls the loop for data transfer. After a device gains control of the loop, it establishes a point-to-point connection with the recipient device and can then use the full data transfer capacity. Until the transmitting device releases the connection, no other devices can use the loop for data transfer. As a result, increasing the number of devices on the loop can reduce the overall performance of the loop because the amount of time each device can use the loop is reduced. x The point-to-point topology extends SCSI connectivity from a server to a peripheral device over longer distances x The arbitrated loop topology allows multiple servers and workstations to share resources Fibre Channel networks can use any combination of point-to-point, arbitrated loop (FC_AL), and switched fabric topologies to provide a variety of device sharing options. p1   p2   p3   p4   p5   p6   p7   p8   p9   p10   p11   p12   p13   p14   p15   p16   p17   p18