HP StorageWorks XP Disk Array Mainframe Host Attachment and Operations Guide XP24000, XP20000 (A5951 - 96151, September 2007)

can be attached to the Fibre Channel switch in any combination, depending on configuration
requirements and available Fibre Channel switch resources.
Sharing a control unit through a Fibre Channel switch allows communication between a number of
channels and the control unit to occur either:
• Over one switch-to-CU link, such as when a control unit has only one link to the Fibre Channel
switch, or
• Over multiple-link interfaces, such as when a control unit has more than one link to the Fibre
Channel switch.
In a FICON switched point-to-point topology, one Fibre Channel link is attached to the FICON channel.
From the switch, the FICON channel communicates with a number of FICON CUs on different switch
ports. At the control unit, the control unit and device-addressing capability is the same as the
point-to-point topology. However, communication and addressing capabilities are increased for the
channel when it is connected to a Fibre Channel switch, and can use the domain and port address
portion of the 24-bit N_Port address to access multiple control units.
The communication path between a channel and a control unit consists of the physical channel path
and the logical path. In a FICON switched point-to-point topology with a single switch, the physical
paths are the Fibre Channel links (interconnection of two Fibre Channel links connected by a Fibre
Channel switch) that provide the physical transmission path between a channel and a control unit.
Figure 8 Example of a Switched Point-to-Point Topology
Cascaded FICON Topology
A FICON channel in FICON native (FC) mode connects one or more processor images to a Fibre
Channel link, which connects to a Fibre Channel switch, and then dynamically through one or more
FC switch ports (internally within the switch) to a second FC switch in a remote site via FC link(s).
From the second FC switch port, a number of Fibre Channel links connect to FICON CU ports, which
interconnect with one or more control units and/or images (logical control units). This forms a Cascaded
FICON topology (see the following figure). The Cascaded FICON Directors topology is only supported
by IBM zSeries processors.
XP Disk Array Mainframe Host Attachment and Operations Guide 31