492 IBM Flex System V7000 Storage Node Introduction and Implementation Guide
Whatever the topology, information is sent between two nodes, which are the source
(transmitter or initiator) and destination (receiver or target). A node is a device, such as a
server (compute node), or peripheral device, such as IBM Flex System V7000 Storage Node
or tape drive. Frames of information are passed between nodes, and the structure of the
frame is defined by a protocol. Logically, a source and target node must use the same
protocol, but each node can support several different protocols or data types. In the IBM Flex
System Enterprise Chassis the compute nodes are the initiators with IBM Flex System V7000
Storage Node being the target.
Fibre Channel architecture is extremely flexible in its potential application. Fibre Channel
transport layers are protocol independent, enabling the transmission of multiple protocols.
Using a credit based flow control methodology, Fibre Channel is able to deliver data as fast as
the destination device buffer is able to receive it. And low transmission overheads enable high
sustained utilization rates without loss of data. Therefore, Fibre Channel combines the best
characteristics of traditional I/O channels with those of computer networks such as within the
IBM Flex System Enterprise Chassis.
11.5.1 The concept of layers
This section describes the various layers in the model.
Fibre Channel layers
Fibre Channel (FC) is broken up into a series of five layers. The concept of layers, starting
with the ISO/OSI seven-layer model, allows the development of one layer to remain
independent of the adjacent layers. Although FC contains five layers, those layers follow the
general principles stated in the ISO/OSI model.
The five layers can be categorized into two:
Physical and signaling layer
Upper layer
Fibre Channel is a layered protocol. as shown here in Figure 11-37, which can be compared
to Figure 11-8 on page 469, where the FC layer can be seen to be encapsulated within the
FCoE stack.
Figure 11-37 Upper and physical FC Layers
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