6100 BSC Programming Manual

Features of the 6100 BSC Product
FEATURES OF THE 6100 BSC PRODUCT
The BSC protocol module runs in a Line Interface Unit (LIU) on
a 6100 communication subsystem. It is downloaded from a disk
file to the LIU, either when the system is cold-loaded or by
operator request. A single copy of BSC controls one data
communication line. (If you use the MULTI option in SYSGEN,
one copy of CP6100 can control multiple lines, but each line
has its own Line Interface Unit and copy of BSC.)
The part of the LIU in which the protocol runs is called the
Communications Line Interface Processor, or CLIP.
Applications use the line by making file management calls. Some
calls, like OPEN, are handled by the I/O process; others convey
instructions to the protocol module. Each request of the second
type is encoded in a WRITEREAD call; the "write" part of the call
delivers the request to the LIU, and the "read" part carries the
response message back to the application. Figure 1-1 lists the
requests an application can make to BSC.
NOTE
The figure does not show requests that are issued only by
Tandem-supplied software. Nor does it show requests that,
if issued by the application, have no effect. Because these
requests may still be reflected on the output from a trace,
Section 3 includes a list of their function codes.
Notice that some requests have the same names as GUARDIAN file
system calls. For example, the GUARDIAN SETMODE call is
different from the BSC SETMODE request. To avoid ambiguity,
this book uses call or request to qualify each name. (Thus a
WRITEREAD call is a GUARDIAN call--which has some request
encoded in it--while a WRITEREAD request is a specific
function for the protocol module.)
Also notice that some requests perform a variety of functions.
In some cases, you specify the function you want performed;
in other cases, the function depends on the state of the line.
Section 3 of this book describes each request in detail.
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