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Fibre Channel

As the speed and memory capacity of personal computers, workstations, and servers have grown, and as applications have become ever more complex, with greater reliance on graphics and video, the requirement for greater speed in delivering data to the processor has grown. This requirement affects two methods of data communications with the processor: I/O channel and network communications.

An I/O channel is a direct point-to-point or multipoint communications link, predominantly hardware based and designed for high speed over very short distances. The I/O channel transfers data between a buffer at the source device and a buffer at the destination device, moving only the user contents from one device to another, without regard to the format or meaning of the data. The logic associated with the channel typically provides the minimum control necessary to manage the transfer plus hardware error detection. I/O channels typically manage transfers between processors and peripheral devices, such as disks, graphics equipment, CD-ROMs, and video I/O devices.

A network is a collection of interconnected access points with a software protocol structure that enables communication. The network typically allows many different types of data transfer, using software to implement the networking protocols and to provide flow control, error detection, and error recovery.

Fibre Channel is designed to combine the best features of both technologies—the simplicity and speed of channel communications with the flexibility and interconnectivity that characterize protocol-based network communications. This fusion of approaches allows system designers to combine traditional peripheral connection, host-to-host internetworking, loosely coupled processor clustering, and multimedia applications in a single multiprotocol interface. The types of channel-oriented facilities incorporated into the Fibre Channel protocol architecture include the following:

  • Data-type qualifiers for routing frame payload into particular interface buffers

  • Link-level constructs associated with individual I/O operations

  • Protocol interface specifications to allow support of existing I/O channel architectures, such as the Small Computer System Interface (SCSI)

The types of network-oriented facilities incorporated into the Fibre Channel protocol architecture include the following:

  • Full multiplexing of traffic between multiple destinations

  • Peer-to-peer connectivity between any pair of ports on a Fibre Channel network

  • Capabilities for internetworking to other connection technologies

Depending on the needs of the application, either channel or networking approaches can be used for any data transfer. Fibre Channel specifications have been developed by the Fibre Channel Association, an industry consortium, and provide for data rates of from 100 Mbps to 800 Mbps on a single line (full duplex, 200 Mbps to 1600 Mbps per link).

The key elements of a Fibre Channel network are the end systems, called nodes, and the network itself, which consists of one or more switching elements. The collection of switching elements is referred to as a fabric. These elements are interconnected by point-to-point links between ports on the individual nodes and switches. Communication consists of the transmission of frames across the point-to-point links.

Each node includes one or more ports, called N_ports, for interconnection. Similarly, each fabric-switching element includes multiple ports, called F_ports. Interconnection is by means of bi-directional links between ports. Any node can communicate with any other node connected to the same fabric, using the services of the fabric. All routing of frames between N_ports is done by the fabric. Frames may be buffered within the fabric, making it possible for different nodes to connect to the fabric at different data rates.

A fabric can be implemented as a single fabric element with attached nodes (a simple star arrangement) or as a more general network of fabric elements, as shown in Figure 2. In either case, the fabric is responsible for buffering and for routing frames between source and destination nodes.

Figure 2

Fibre Channel network.

The Fibre Channel network is quite different from the IEEE 802 LANs. Fibre Channel is more like a traditional circuit-switching or packet-switching network, in contrast to the typical shared-medium LAN. Thus, Fibre Channel need not be concerned with medium access-control issues. Because it's based on a switching network, the Fibre Channel scales easily in terms of N_ports, data rate, and distance covered. This approach provides great flexibility. Fibre Channel can readily accommodate new transmission media and data rates by adding new switches and F_ports to an existing fabric. Thus, an existing investment is not lost with an upgrade to new technologies and equipment. Further, the layered protocol architecture accommodates existing I/O interface and networking protocols, preserving the preexisting investment.

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