StorageTek Host Software Component 6.0, System Programmer'S Manual

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Chapter 2. Host Software Component Functions 79
1st ed., 6/30/04 - 312579601
How Communications Services are Set or Changed
Communications services are set or changed by the Communications Path (COMMPath)
command and control statement. This command specifies host, communication method,
LMU paths and VTAM path name for the associated host. The communication path
definitions can be modified at any time during library operation without terminating the
HSC.
The COMMPath command and control statement sets up a table of definitions for the host
that is executing the command. Each host’s table must contain a list of path definitions for
itself and a separate list for each defined host. Therefore, on each host, the command must
be issued once to define the paths for itself, once to define the paths for a second host,
once to define the paths for a third host, and so on, until all hosts are defined.
For example, the library is operating in an environment with three hosts: Host 0, Host 1,
and Host 2. The COMMPath command must be issued three times on each host. The table
of definitions for Host0 must contain a list of paths for Host 0, a list for Host 1, and a list
for Host 2. The same is true for Host 1 and Host 2.
For one host to communicate with another, they must have matching entries in their
respective lists of defined paths. The highest-performance method that is common to two
hosts is selected as the current method of communications between the two. A host can
use one method of communications with a second host, and a different method of
communications with a third host.
Figure 9 illustrates how different communication methods can be used between multiple
hosts.
C26184
CDS
COMMUNICATIONS
LMU
COMMUNICATIONS
HOST 0
METHODS
VTAM
CDS
HOST 1
METHODS
LMU
CDS
HOST 2
METHODS
VTAM
LMU
CDS
VTAM
COMMUNICATIONS
EACH PAIR OF HOSTS COMMUNICATE USING THE
HIGHEST PERFORMANCE METHOD DEFINED TO BOTH
Figure 8. HSC Communication Methods Between Multiple Hosts