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Fundamentals of Fibre Channel

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Fibre Channel is a high-speed network technology used to connect server to data storage area network. It handles high performance of disk storage for applications on many corporate networks. It supports data backup and replication.
Fibre Channel is needed, as it is very flexible and enables the transfer of data at a faster speed.

The topologies, that bring about the flexibility in the fibre channel are –

  1. Point to point topology.
  2. Fibre channel arbitrated loop.
  3. Switched fabric topology.

Topology refers to the physical/logical arrangement of nodes or other devices in a network.

Basic port details, to know to understand the mentioned topologies –

Port Type Associated Topology
N_port Node Point to point or Fabric.
NL_port Node Node connected to an arbitrated loop.
F_port Fabric Fabric port.
FL_port Fabric Fabric connected to an arbitrated loop.
L_port Loop Hub port on an arbitrated loop.
L_C_F Loop Link Control Facility [L_C_F] is a hardware facility that binds to each end of the link and governs transmission and reception of information.
E_port Node This inter-switch expansion port is used to connect to an E_port of another switch to build a larger fabric.
FC_switch Switch A network switch that interconnects servers and storage ports.

Point to point topology :

  • A single link connects two ports in this topology.
  • This topology is inexpensive but it doesn’t require a hub.
  • To create point to point configuration, you can provide multiple ‘N’ ports on each node.
  • Each point to point connection provides the full bandwidth supported by ‘N’ ports. Depending on the type of the link (multi-mode or single-mode fiber), the two nodes can be separated by up to 500m ( multi-mode fiber ) or 10km (single-mode fiber).

Fibre channel arbitrated loop topology [FC-AL] :

  • It is a high-speed fibre channel [FC] topology in which fibre channel ports/hubs use arbitration to establish a point-to-point circuit and prevent multiple ports/hubs from sending frames at the same time.
  • Here devices are connected in a one-way ring. So, when ports/hubs in a loop topology have information to transmit, they must send out an arbitration signal to decide, which port/hub can use the channel. The port in control of the channel then sends an ‘open’ arbitrated signal to the destination port and transmits its information. Since all the ports in the loop are connected, every port will see and pass along the data, but ignore the data unless it is addressed to that particular port.
  • FC-AL can join up to 126 ports on one controller.
  • It is still used internally in many fibre channel switches but rarely to connect hosts to storage these days.
  • FC- hubs provide bypass circuits that prevent the loop from breaking if one device fails or is removed.

A bypass circuit bypasses high-frequency components of power supply.

Switched Fabric Topology :

  • This is the topology, that is very much in use nowadays.
  • The network of switches in a fibre channel habitat is referred to as a fabric.
  • Ports on one node can communicate with ports on other nodes attached to the same fabric. With the fabric topology, many connections can be alert at a time.
  • The any-to-any connection service and peer-peer communication service provided by a fabric is fundamental to fibre channel architecture. Fibre channel can hold-up both channel and network protocol simultaneously.
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Last Updated : 07 Sep, 2020
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