Arbitrated loop

The arbitrated loop, also known as FC-AL, is a Fibre Channeltopology in which devices are connected in a one-way loop fashion in a ring topology.^[1] Historically it was a lower-cost alternative to a fabric topology. It allowed connection of many servers and computer storage devices without using then very costly Fibre Channel switches. The cost of the switches dropped considerably, so by 2007, FC-AL had become rare in server-to-storage communication. It is however still common within storage systems.

• It is a serial architecture that can be used as the transport layer in a SCSI network, with up to 127 devices. The loop may connect into a fibre channel fabric via one of its ports.
• The bandwidth on the loop is shared among all ports.
• Only two ports may communicate at a time on the loop. One port wins arbitration and may open one other port in either half or full duplex mode.
• A loop with two ports is valid and has the same physical topology as point-to-point, but still acts as a loop protocol-wise.
• Fibre Channel ports capable of arbitrated loop communication are NL_port (node loop port) and FL_port (fabric loop port), collectively referred to as the L_ports. The ports may attach to each other via a hub, with cables running from the hub to the ports. The physical connectors on the hub are not ports in terms of the protocol. A hub does not contain ports.
• An arbitrated loop with no fabric port (with only NL_ports) is a private loop.
• An arbitrated loop connected to a fabric (through an FL_port) is a public loop.
• Un NL_Port debe proporcionar facilidades de inicio de sesión de tejido (FLOGI) y registro de nombres para iniciar la comunicación con otro nodo a través del tejido (para ser un iniciador ).

El bucle arbitrado puede cablearse físicamente en forma de anillo o mediante un concentrador. El anillo físico deja de funcionar si falla alguno de los dispositivos de la cadena. El concentrador, por otro lado, si bien mantiene un anillo lógico, permite una topología en estrella a nivel de cable. Cada puerto de recepción del concentrador se conecta directamente al siguiente puerto de transmisión activo , sin pasar por los puertos inactivos o que hayan fallado.

Por lo tanto, los concentradores Fibre Channel tienen otra función: proporcionan circuitos de derivación que impiden que el bucle se interrumpa si un dispositivo falla o se retira. Si se retira un dispositivo de un bucle (por ejemplo, al desconectar su conector), el circuito de derivación del concentrador detecta la ausencia de señal e inmediatamente comienza a enrutar los datos entrantes directamente al siguiente puerto del bucle, omitiendo por completo el dispositivo que falta. Esto proporciona a los bucles cierto grado de resiliencia: el fallo de un dispositivo en un bucle no provoca que todo el bucle quede inoperable.

• red de área de almacenamiento
• Canal de fibra
• Tejido cambiado
• Lista de estándares Fibre Channel