IBM System Storage DS3500 Introduction And Implementation Manual page 27

Draft Document for Review March 28, 2011 12:24 pm
All devices or loops of devices are connected to Fibre Channel switches, similar
conceptually to modern Ethernet implementations. Advantages of this topology over
FC-P2P or FC-AL include:
– The switches manage the state of the fabric, providing optimized interconnections.
– The traffic between two ports flows through the switches only, it is not transmitted to
any other port.
– Failure of a port is isolated and should not affect operation of other ports.
– Multiple pairs of ports may communicate simultaneously in a fabric.
FC protocol layers
Fibre Channel does not follow the OSI model layering, but is split similarly into 5 layers as
shown in Figure 1-1. These layers include:
FC0 is the physical layer, which describes cabling, connectors, signalling, and so on. This
layer defines the physical media implementation.
Data link layer, which implements line coding of signals. This layer contains the 8b/10b
encoding and decoding of signals for transmission across the physical media.
FC2 is the network layer and defines the main FC protocols. This layer defines how the
frames are transferred.
FC3 is the common services layer. This layer provides services such as multi-casting and
striping.
FC4 is the application protocol mapping layer. In storage connectivity applications, FCP
protocol is used to encapsulate SCSI data into FC frames.
Layers FC0 through FC2 are also known as FC-PH, the physical layers of Fibre Channel.
Fibre Channel routers operate up to FC4 level (i.e. they may operate as SCSI routers),
switches up to FC2, and hubs on FC0 only.
Fibre Channel products are available at 1, 2, 4, 8, 10 and 20 Gbit/s. Products based on the 2,
4 and 8 Gbit/s standards should be interoperable and backward compatible. The 10 Gbit/s
standard and its 20 Gbit/s derivative, however, are not backward compatible with any of the
slower speed devices, as they differ considerably on FC1 level in using 64b/66b encoding
instead of 8b/10b encoding, and are primarily used as inter-switch links.
Figure 1-1 Fibre Channel Layers
FC cable types
FC implementations can utilize either single-mode or multi-mode FC cables.
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Chapter 1. Disk attachment technology
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