Explanation
The FC architecture supports three basic interconnectivity options:
1) Point-To-point,
2) Arbitrated Loop (Fc-AL),
3) FC Switched Fabric
Point-to-Point
Point-to-point is the simplest FC configuration — two devices are connected directly to
each other, as shown in Fig.
➢ This configuration provides a dedicated connection for data transmission between nodes.
➢ The point-to-point configuration offers limited connectivity, as only two devices can
communicate with each other at a given time.
➢ It cannot be scaled to accommodate a large number of network devices. Standard DAS uses
point to- point connectivity.
Fibre Channel Arbitrated Loop
➢ In the FC-AL configuration, devices are attached to a shared loop, as shown in Fig 2.5.
➢ FC-AL has the characteristics of a token ring topology and a physical star topology.
➢ In FC-AL, each device contends with other devices to perform I/O operations. Devices on
the loop must “arbitrate” to gain control of the loop.
➢ At any given time, only one device can perform I/O operations on the loop.
➢ FC-AL implementations may also use hubs whereby the arbitrated loop is physically
connected in a star topology.
The FC-AL configuration has the following limitations in terms of scalability:
➢ FC-AL shares the bandwidth in the loop.
➢ Only one device can perform I/O operations at a time. Because each device in a loop
has to wait for its turn to process an I/O request, the speed of data transmission is
low in an FC-AL topology.
➢FC-AL uses 8-bit addressing. It can support up to 127 devices on a loop.
➢Adding or removing a device results in loop re-initialization, which can
cause a momentary pause in loop traffic.
Fibre Channel Switched Fabric(FC-SW)
➢ FC-SW provides dedicated data path and scalability.
➢ The addition and removal of a device does not affect the on-going traffic between other
devices.
➢ FC-SW is referred to as Fabric connect.
➢ A Fabric is a logical space in which all nodes communicate with one another in a network.
This virtual space can be created with a switch or a network of switches.
➢ Each switch in a fabric contains a a unique domain identifier, which is part of the fabric’s
addressing scheme.
➢ In a switched fabric, the link between any two switches is called an Interswitch link (ISL).
➢ ISLs enable switches to be connected together to form a single, larger fabric.
➢ ISLs are used to transfer host-to-storage data and fabric management traffic from one switch to
another.
➢ By using ISLs, a switched fabric can be expanded to connect a large number of nodes.
➢ A Fabric may contain tiers.
➢ The number of tiers in a fabric is based on the number of switches between two points that
are farthest from each other.
