Fibre Channel Primer

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Chapter 6
CLASSES OF SERVICE
AND TOPOLOGIES
Fibre Channel provides five different Classes of Service:
l Class 1 – Acknowledged Connection Service
l Class 2 – Acknowledged Connectionless Service
l Class 3 – Unacknowledged Connectionless Service
l Class 4 – Fractional Bandwidth Connection-Oriented Service
l Class 6 – Uni-Directional Connection Service
Fibre Channel connects nodes using three physical topologies
that can have variants. Topologies include:
l Point-to-point
l Loop
l Switched
Loops connected to the enterprise through a switch are called public
loops. An isolated loop is called a private loop. Hubs are normally
used to connect nodes into a loop topology. The facility that connects
multiple N_Ports is called a “fabric.”
When Class of Service is combined with the various choices of
physical topologies, Fibre Channel offers an unprecedented capability
for delivering unmatched performance, and the ability to tune
configurations to optimally meet application needs.
Switch Topology. The primary function of a switch is to receive
frames from a source node and route them to the destination node.
Each node has a unique Fibre Channel address, used to make the
frame routing. The topology, routing path selection within a switch,
and the internal structure are transparent to the nodes.