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Fibre Channel - technical definition

An American National Standards Institute (ANSI) specification (X.3230, 1994) for a high-speed link between computers and peripherals, primarily high speed external storage devices. Developed to replace High Performance Parallel Interface (HIPPI) and as a high-speed alternative to the distance-limited Small Computer System Interface (SCSI), Fibre Channel is intended to support applications such as data backup and mirroring, and is the predominant data link technology employed in storage area networks (SANs). Fibre Channel is connected at Layer 1, the Physical Layer, by fibre, a term the Fibre Channel industry coined to refer to a network comprising a close-knit fabric of access including both optical fiber and copper twisted pair for large data transfers with low overhead, low-latency switching, and minimal interruptions to the flow of data. The preferred physical medium is optical fiber, which can be multimode fiber (MMF) of either 62.5

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A high-speed transport technology used to build storage area networks (SANs). Although Fibre Channel can be used as a general-purpose network carrying ATM, IP and other protocols, it has been primarily used for transporting SCSI traffic from servers to disk arrays. The Fibre Channel Protocol (FCP) serializes SCSI commands into Fibre Channel frames and uses IP for in-band SNMP network management (see SNMP). For more about storage networks, see SAN.

Specifications
Using singlemode or multimode fibers, Fibre Channel can be configured point-to-point (FC-P2P), as a switched topology (FC-SW) or in an arbitrated loop (FC-AL) with or without a hub, which can connect up to 127 nodes (see below). Transmission rates up to 12.75 Gbps in each direction are supported.

Fibre Channel uses the Gigabit Ethernet physical layer and IBM's 8B/10B encoding method, where each byte is transmitted as 10 bits. Fibre Channel provides both connection-oriented and connectionless services. Following are the class and functional levels. See FCIP, FCoE, IP storage and Director-class switch.

 Connection-oriented services
 Class 1    With acknowledgment, full bandwidth
 Class 4    Virtual connections, QoS,
             fractional bandwidth
 Class 6    Uni-directional

 Connectionless services
 Class 2    With acknowledgment
 Class 3    Without acknowledgment


 Node levels
 FC-4  Translation between Fibre Channel and
        command sets that use it: HiPPI, SCSI, IPI,
        SBCCS, IP, IEEE 802.2, audio, video
 FC-3  Common services across multiple ports

 Port levels (FC-PH standard)
 FC-2  Framing and flow control
 FC-1  8B/10B encoding, error detection
 FC-0  Electrical and optical characteristics

Arbitrated Loop

The arbitrated loop is widely used and can connect up to 127 nodes without using a switch. All devices share the bandwidth, and only two can communicate with each other at the same time, with each node repeating the data to its adjacent node. TX means transmit, and RX means receive.

Switch Fabric

A switch fabric is the most flexible topology, enabling all servers and storage devices to communicate with each other. It also provides for a failover architecture in the event a server or disk array ceases to operate.