Figure 1–2: Fabric Topology
N_Port
Node 1
Node 2
Transmit
Receive
Transmit
Receive
Transmit
Receive
Transmit
Receive
Transmit
Receive
Transmit
Receive
Transmit
Receive
Transmit
Receive
F_Port
Fabric
Node 3
Node 4
F_Port
F_Port
F_Port
N_Port
N_Port
N_Port
ZK-1536U-AI
1.2.3 Arbitrated Loop Topology
In an arbitrated loop topology, frames are routed around a loop that is set
up by the links between the nodes. The hub maintains loop continuity by
bypassing a node when the node or its cabling fails, when the node is powered
down, or when the node is removed for maintenance. The hub is transparent
to the protocol. It does not consume any Fibre Channel arbitrated loop
addresses so it is not addressable by a Fibre Channel arbitrated loop port.
The nodes arbitrate to gain control (become master) of the loop. After a
node becomes master, the nodes select (by way of setting bits in a bitmask)
their own Arbitrated Loop Physical Address (AL_PA). The AL_PA is used
to address nodes on the loop. The AL_PA is dynamic and can change each
time the loop is initialized, a node is added or removed, or at any other time
that an event causes the membership of the loop to change. When a node is
ready to transmit data, it transmits Fibre Channel primitive signals that
include its own identifying AL_PA.
In the arbitrated loop topology, a node port is called an NL_Port (node loop
port), and a fabric port is called an FL_Port (fabric loop port).
Figure 1–3 shows an example of an arbitrated loop topology.
Fibre Channel Overview 1–5
