Specifications

Chapter 1. Introduction 7
Channels and control unit links can be attached to the Fibre Channel switch in any
combination, depending on configuration requirements and available resources in the Fibre
Channel switch.
Sharing a control unit through a Fibre Channel switch means that communication from a
number of channels to the control unit can take place over one switch to CU link (in the case
where a control unit has only one link to the Fibre Channel switch), or over multiple link
interfaces (in the case where a control unit has more than one link to the Fibre Channel
switch).
Just one Fibre Channel link is attached to a FICON channel in a FICON switched
point-to-point configuration, but from the FC switch (FICON Director) that FICON channel can
communicate with a number of FICON CUs on different FC switch ports. Once at the control
unit, the same control unit and device addressing capability exists as for a point-to-point
configuration. However, the communication and addressing capability is increased for the
channel when the channel is connected to a FC switch with the ability to use the domain and
port address portion of the 24-bit N_Port address (8 bits for the domain and 8 bits for the port)
to access multiple control units.
Figure 1-3 Switched point-to-point configuration
The communication path between a channel and a control unit is composed of two different
parts: 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
FC links, or interconnection of two FC links connected by a FC switch that provides the
physical transmission path between a channel and a control unit.
A FICON (FC-SB-2) logical path is the relationship established between a channel image and
a control unit image for communication during execution of an I/O operation and presentation
of status.
FICON
Channel
FC
Switch
Control Unit
FICON Port
F i b r e C h a n n e l
FC Links FC Links
Server Fabric Storage
FICON
Channel
Control Unit
FICON Port
Fabric Login (FLOGI)
Determine fabric connection
(Point-to-Point or Switched)
Processor
Channel Image
Channel N_Port
zSeries and 9672 G5/G6 Configuration Definition - Path Addressing
Storage Unit
CU Image
CU N_Port
1-Byte Link Address (Port @)