HOW DOES FIBRE CHANNEL WORK?

In the past days, I have talked many about the Ethernet. Actually, there are many other networking protocols used in data transports. Fibre Channel (FC), my topic today, is one of them. Fibre Channel is a set of standard that define a high performance data transport connection technology. It is developed to satisfy the increasing demands for high-speed, high-volume data transfers in storage and network services. So, how does Fibre Channel work to achieve these applications?

Physical Components

Fibre Channel carries data over many types of electrical and optical cable. To choose the type of overall network interconnection is crucial. The decision usually depends on the distances between the Fibre Channel devices being connected. Generally, copper cabling is cheaper and performs as well as fiber optic cabling when the distance between devices is less than 2.9 meters. But to get higher speed and for longer distance, fiber optic cabling with single-mode or multimode option is the ideal choice. In addition, fiber optic cabling is more flexible for extensions in the future.

Cable is one of the physical component of FC. It connect to ports on the devices to form a link. There are different types of FC ports. The following table summarizes sevent FC port types:

Short Name Descriptive Name Device Type Port Function
N-port Network Port Nodes Node port used to connect a node to a Fibre Channel switch
F-port Fabric Port Switches Switch port used to connect the Fibre Channel fabric to a node
L-port Loop Port Nodes Node port used to connect a node to a Fibre Channel loop
NL-port Network + Loop Port Nodes Node port that connects to both loops and switches
FL-port Fabric + Loop Port Switches Switch port that connects to both loops and switches
E-port Extender Port Switches Used to cascade Fibre Channel switches together
G-port General Port Switches General purpose port that can be configured to emulate other port types

A transceiver or transmitter/receiver is the fiber optic port of a device where the fiber optic cables connect. For Fibre Channel network, the Fibre Channel transceiver modules are used. In today’s market, the Fibre Channel modules in data rate of 2, 4, 8 Gbps or above, e.g. 16 Gbps are commonly used, and generally packaged in the form factor of SFP (2/4Gbps Fibre Channel SFP) and SFP+ (8Gbps Fibre Channel SFP+). Other form factor, such GBIC or XFP is also available according to the port applications.

Topologies

Three distinct topologies are defined for Fibre Channel to meet various of application and installation requirements. These topologies exhibit different performance characteristics, and are subject to different scalability limits.

Point-to-point

Point-to-Point topology is the most basic and simple Fibre Channel topology. As its name suggests, two devices are directly connected by a Fibre Channel cable when using this topology. Addressing is simple and device availability is complete. However, it is not a common topology today. In general, it has been used to connect RAID (Redundant Array of Independent Disks) and other storage subsystems to servers in server-centric computing environments.

point-to-point

Arbitrated Loop

Arbitrated loop topology provides economical interconnection to applications. It is possible for individual transmission paths, or loops, to be time-shared by up to 126 devices. Each time a loop is available for use, the devices arbitrate to determine which device gets to send data or commands next. This topology is usually used to connect disk drives to RAID controllers or host bus adapters (HBA).

loop

Switched fabric

Switched fabric is a powerful FC topology used in modern Storage Area Network (SAN). It essentially consists of one or more switches, controlling a large amount of port-to-port transfers of data and commands (also know as frames) between nodes. Within a fabric, multiple interconnections happen concurrently—and all frames are routed to their proper destinations. System wide bandwidth can be as much as an order of magnitude greater than the speed of any single Fibre Channel link. With such high transfer rates, many users in a workflow can work with the same data at the same time, facilitating collaboration and increasing productivity.

Fabric

Upper-Level Protocol Mapping

There are five protocol layers of Fibre Channel—FC-0, FC-1, FC-2, FC-3, and FC-4. An upper-level protocol mapping to FC-FS (Fibre Channel Framing and Signaling) constitutes an FC-4 that is the highest level in FC structure. To insure device interoperability, standards have been developed to map some of these higher-level protocols to a format that Fibre Channel can transmit. For example, one protocol defines how to translate SCSI (Small Computer System Interface) command descriptors, which would normally be sent in parallel, into serial Fibre Channel format, and back to parallel SCSI when they are received by the target device. The following network and channel protocol mappings have been specified or proposed:

  • Small Computer System Interface (SCSI)
  • Internet Protocol (IP)
  • High Performance Parallel Interface (HIPPI) Framing Protocol
  • Link Encapsulation (FC-LE)
  • Single Byte Command Code Sets (SBCCS)
  • Audio Video Fast File Transfer
  • Audio Video Real Time Stream Transfer
  • More…

Reference:

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Source: http://www.fiber-optic-transceiver-module.com/how-does-fibre-channel-work.html

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