host adaptor

Fibre Channel

Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards (INCITS), an American National Standards Institute (ANSI)–accredited standards committee. It started use primarily in the supercomputer field, but has become the standard connection type for storage area networks (SAN) in enterprise storage. Despite common connotations of its name, Fibre Channel signaling can run on both twisted pair copper wire and fiber-optic cables.

Fibre Channel Protocol (FCP) is a transport protocol (similar to TCP used in IP networks) which predominantly transports SCSI commands over Fibre Channel networks.


Fibre Channel started in 1985, with ANSI standard approval in 1994, as a way to simplify the HIPPI system then in use for similar roles. HIPPI used a massive 50-pair cable with bulky connectors, and had limited cable lengths. Fibre Channel was primarily concerned with simplifying the connections and increasing distances, as opposed to increasing speeds. Later, designers added the goals of connecting SCSI disk storage, providing higher speeds and far greater numbers of connected devices.

It also added support for any number of "upper layer" protocols, including SCSI, ATM, and IP, with SCSI being the predominant usage.

Fibre Channel Variants
NAME Line-Rate (Gbps) '''Throughput (MBps)
1GFC 1.0625 100
2GFC 2.125 200
4GFC 4.25 400
8GFC 8.5 800
10GFC Serial 10.51875 1000
20GFC 10.52 2000
10GFC Parallel 12.75

Fibre Channel topologies

There are three major Fibre Channel topologies, describing how a number of ports are connected together. A port in Fibre Channel terminology is any entity that actively communicates over the network, not necessarily a hardware port. This port is usually implemented in a device such as disk storage, an HBA on a server or a Fibre Channel switch.

  • Point-to-Point (FC-P2P). Two devices are connected back to back. This is the simplest topology, with limited connectivity.
  • Arbitrated loop (FC-AL). In this design, all devices are in a loop or ring, similar to token ring networking. Adding or removing a device from the loop causes all activity on the loop to be interrupted. The failure of one device causes a break in the ring. Fibre Channel hubs exist to connect multiple devices together and may bypass failed ports. A loop may also be made by cabling each port to the next in a ring.
    • A minimal loop containing only two ports, while appearing to be similar to FC-P2P, differs considerably in terms of the protocol.
  • Switched fabric (FC-SW). All devices or loops of devices are connected to Fibre Channel switches, similar conceptually to modern Ethernet implementations. Advantages of this topology over FC-P2P or FC-AL include:
    • The switches manage the state of the fabric, providing optimized interconnections.
    • Multiple pairs of ports may communicate simultaneously.
    • Failure of a port is isolated and should not affect operation of other ports.

Attribute Point-to-Point Arbitrated loop Switched fabric
Max ports 2 127 ~16777216 (224)
Address size N/A 8-bit ALPA 24-bit port ID
Side effect of port failure N/A Loop fails (until port bypassed) N/A
Mixing different link rates N/A No Yes
Frame delivery In order In order Not guaranteed
Access to medium Dedicated Arbitrated Dedicated

Fibre Channel layers

Fibre Channel is a layered protocol. It consists of 5 layers, namely:

  • FC0 The physical layer, which includes cables, fiber optics, connectors, pinouts etc.
  • FC1 The data link layer, which implements the 8b/10b encoding and decoding of signals.
  • FC2 The network layer, defined by the FC-PI-2 standard, consists of the core of Fibre Channel, and defines the main protocols.
  • FC3 The common services layer, a thin layer that could eventually implement functions like encryption or RAID.
  • FC4 The Protocol Mapping layer. Layer in which other protocols, such as SCSI, are encapsulated into an information unit for delivery to FC2.

FC0, FC1, and FC2 are also known as FC-PH, the physical layers of fibre channel.

Fibre Channel routers operate up to FC4 level (i.e. they may operate as SCSI routers), switches up to FC2, and hubs on FC0 only.

Fibre Channel products are available at 1 Gbit/s, 2 Gbit/s, 4 Gbit/s, 8 Gbit/s, 10 Gbit/s and 20 Gbit/s. Products based on the 1, 2, 4 and 8 Gbit/s standards should be interoperable, and backward compatible. The 10 Gbit/s standard (and 20 Gbit/s derivative), however, is not backward compatible with any of the slower speed devices, as it differs considerably on FC1 level (64b/66b encoding instead of 8b/10b encoding). 10Gb and 20Gb Fibre Channel is primarily deployed as a high-speed "stacking" interconnect to link multiple switches.


The following types of ports are defined by Fibre Channel:

  • node ports
    • N_port is a port on the node (e.g. host or storage device) used with both FC-P2P or FC-SW topologies. Also known as Node port.
    • NL_port is a port on the node used with an FC-AL topology. Also known as Node Loop port.
  • switch/router ports (used with FC-SW topology only)
    • F_port is a port on the switch that connects to a node point-to-point (i.e. connects to an N_port). Also known as Fabric port. An F_port is not loop capable.
    • FL_port is a port on the switch that connects to a FC-AL loop (i.e. to NL_ports). Also known as Fabric Loop port. Note that a switch port may automatically become either an F_port or an FL_port depending on what is connected.
    • E_port is the connection between two fibre channel switches. Also known as an Expansion port. When E_ports between two switches form a link, that link is referred to as an inter-switch link (ISL).
    • EX_port is the connection between a fibre channel router and a fibre channel switch. On the side of the switch it looks like a normal E_port, but on the side of the router it is a EX_port.
    • TE_port is a term used for multiple E_ports trunked together to create high bandwidth between switches. Also known as Trunking Expansion port.
  • general (catch-all) types
    • G_port or generic port on a switch can operate as an E_port or F_port.
    • L_port is the loose term used for any arbitrated loop port, NL_port or FL_port. Also known as Loop port.
    • U_port is the loose term used for any arbitrated port. Also known as Universal port.

Optical carrier medium variants

Media Type Speed (Mbyte/s) Transmitter Variant Distance
Single-Mode Fiber 400 1300 nm Longwave Laser 400-SM-LL-I 2 m - 2 km
200 1550 nm Longwave Laser 200-SM-LL-V 2 m - >50 km
1300 nm Longwave Laser 200-SM-LL-I 2 m - 2 km
100 1550 nm Longwave Laser 100-SM-LL-V 2 m - >50 km
1300 nm Longwave Laser 100-SM-LL-L 2 m - 10 km
1300 nm Longwave Laser 100-SM-LL-I 2 m - 2 km
Multimode Fiber (50µm) 400 850 nm Shortwave Laser

400-M5-SN-I 0.5 m - 150m
200 200-M5-SN-I 0.5 m - 300m

100-M6-SN-I 0.5 m - 300m
100-M6-SL-I 2 m - 175m

Fibre Channel Infrastructure

Fibre Channel switches are divided into two classes. These classes are not part of the standard, and the classification of every switch is a marketing decision of the manufacturer.

  • Directors offer a high port-count in a modular (slot-based) chassis with no single point of failure (high availability).
  • Switches are typically smaller, fixed-configuration (sometimes semi-modular), less redundant devices.

Brocade, Cisco and QLogic provide both directors and switches.

If multiple switch vendors are used in the same fabric (i.e. fabric is heterogeneous), the fabric will default to "interoperability mode", that is to a pure standardized Fibre Channel protocol. Some proprietary, advanced features may be disabled. ajai

Fibre Channel Host Bus Adapters

Fibre Channel HBAs are available for all major open systems, computer architectures, and buses, including PCI and SBus. Some are OS dependent. Each HBA has a unique World Wide Name (WWN), which is similar to an Ethernet MAC address in that it uses an Organizationally Unique Identifier (OUI) assigned by the IEEE. However, WWNs are longer (8 bytes). There are two types of WWNs on a HBA; a node WWN (WWNN), which is shared by all ports on a host bus adapter, and a port WWN (WWPN), which is unique to each port. Some Fibre Channel HBA manufacturers are Brocade, Emulex, LSI, QLogic and ATTO Technology.

See also


  • Clark, T. Designing Storage Area Networks, Addison-Wesley, 1999. ISBN 0-201-61584-3

External links

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