What is a Fiber Channel?

Fiber channel (FC) is a high-speed network technology. Using an FC network interface, data can be sent with lasers over a fiber-optic cable that is many miles or kilometers in length. The FC protocols and topologies can also be used on shorter-distance Ethernet networks over copper cables. FC is often used in storage networking to interconnect the storage devices and the servers which distribute their data. It is also commonly used in the infrastructure of the Internet and enterprise intranets.

Development began on fiber channel technology in 1988 and it became a standard in 1994. The designers originally focused on long-distance communication using a simple connection. The alternative was the High Performance Parallel Interface (HIPPI), a supercomputer-based standard with relatively short and bulky connections. Over time, FC transmission speed increased and it became a common interface for storage area network (SAN) devices. Serial Storage Architecture was a competitor in the early 1990s, but FC soon achieved much higher bandwidths.

Unlike the Open Systems Interconnection (OSI) model, the fiber channel network model has only five layers. The highest layer is where other protocols are prepared for transmission through the network layer. FC supports many high-level protocols including Internet Protocol (IP), Small Computer System Interface (SCSI) and video protocols. The network, data link and physical layers—the lower three model layers—are where the FC-specific protocols actually send the data. Some of the higher-speed FC standards are not backward-compatible with slower speeds due to data link layer encoding differences.

When a group of devices are connected using FC, the interconnections are referred to as the fiber channel fabric. Three different topologies can be used to create a fiber channel fabric. Switched Fabric is similar to Ethernet, with individual devices plugged into a central network switch. This is the most efficient arrangement when multiple devices are transferring data at once. It also prevents a failed device or switch port from shutting down the rest of the fabric.

A second topology, similar in some ways to Token Ring, is known as Arbitrated Loop. It connects all the devices in a loop, and only two can talk to each other at the same time. Any device failure disrupts the ring, as does removing or adding a functioning device. The third topology consists simply of two devices connected directly together. The advantage of these two topologies over Switched Fabric is that each fiber channel frame is guaranteed to be delivered.

Large SANs need very fast and reliable connections between the networked storage devices and the servers which distribute their data. As it is usually highly efficient for transferring large blocks of data, fiber channel technology is often used in SANs. The distribution servers generally use slower, less reliable and less expensive connections to reach other servers and end users. Even without a SAN, fiber channel frequently connects high-end storage devices to individual servers. FC can also be used to connect a remote storage backup system to an individual computer many miles away.