Fibre Channel Interfaces

The committee charged with developing Fibre Channel technology was established within the American National Standards Institute in 1989. Two years later IBM, Hewlett-Packard Co. and Sun Microsystems Inc. joined forces to create the Fibre Channel Systems Initiative (FCSI), with the objective of ensuring the interoperability between products and to kick-starting the Fibre Channel the market. In 1994 Fibre Channel was accepted as an ANSI standard and a year later the duties of the FCSI were handed over to the larger Fibre Channel Association.

Fibre Channel has revolutionised the way network storage is organised. When first introduced, it operated at speeds no faster than SCSI-3, which meant that its real value in Storage Area Networks (SAN) was the distance benefit, not the speed. Indeed, Fibre Channel’s 10,000 metre limit can be extended to 100km using special optic transceivers, giving it a far greater range than SCSI. However, times have changed, and when the 2Gbit/sec version of Fibre Channel was released in 2000, it meant that the technology now outstriped SCSI both in terms of range and performance.

Fibre Channel is structured as a set of hierarchical functions, similar to the ISO OSI Reference Model. There are five layers, each being responsible for a certain set of functions or capabilities:

Name Layer Function
FC-4 Protocol Mapping Layer Specifies the mapping rules for several legacy upper-layer protocols, allowing Fibre Channel to carry data from other networking protocols (such as SCSI) and to concurrently transport both network and channel information over the same physical interface.
FC-3 Common Services Layer Defines special service features such as multi-casting and striping.
FC-2 Framing and Signaling Layer Defines the sequencing and flow control rules used to segment/reassemble data packets sent/received by the device.
FC-1 Transmission Protocol Layer Defines the transmission protocol including serial encoding and decoding rules, special characters, timing recovery and error control.
FC-0 Physical Layer Defines the basic physical link, including the cabling, connectors, and optical/electrical parameters for a variety of data rates.

Fibre Channel can be implemented in the form of a continuous arbitrated loop (FCAL) that can have hundreds of separate storage devices and host systems attached, with connection via a high-speed switching fabric (much like a network switch) another option. All this makes it a very flexible and fault-tolerant technology and, by attaching disk arrays and backup devices directly to the loop rather than onto any one server, the technology can be used to construct an independent SAN. That, in turn, allows data to be carried to and from servers and backed up with little or no impact on ordinary network traffic – of real advantage when it comes to data warehousing and other data-intensive client/server applications.

The benefits of SANs are directly related to the increased accessibility and manageability of data offered by the Fibre Channel architecture. Data becomes more accessible when the Fibre Channel fabric scales to encompass hundreds of storage devices and servers. The data is also more available when multiple concurrent transactions can be sent across Fibre Channel’s switched architecture. Fibre channel also overcomes distance limitations when Fibre Channel links span hundreds of kilometres or are sent over a WAN.

Fibre Channel hardware interconnects storage devices with servers to form the Fibre Channel fabric. The fabric consists of the physical layer, interconnect devices and translation devices. The physical layer consists of copper and fibre-optic cables that carry Fibre Channel signals between transceiver pairs. Interconnect devices, such as hubs and switches route Fibre Channel frames at gigabit rates. Translation devices – such as host bus adapters, routers, adapters, gateways and bridges – are the intermediaries between Fibre Channel protocols and upper layer protocols such as SCSI, Ethernet and ATM.

With work on a 10 Gbit/sec specification underway, Fibre Channel is expected to continue to expand into the storage markets, which will make use of its benefits over traditional channel technologies such as SCSI. Its combination of performance and range is important to a number of applications, such as multimedia, medical imaging and scientific visualisation. Because of the distances it can cover and the fact that storage devices can be placed remotely, Fibre Channel has significant advantages in disaster recovery situations.