Envoy Application Programming Manual

Software Concepts
Envoy Application Programming Manual—427159-001
2-3
The Envoy Environment
The protocol procedures determine the valid message formats, the sequence in which
line operations are to be performed, and the appropriate corrective action to be taken
when a line error occurs.
Envoy currently supports the protocols shown in Table 2-1
:
An Envoy I/O process accepts application program I/O requests by way of Guardian 90
file-system procedure calls and, in turn, calls the protocol and driver procedures to
perform the desired operations. For each line that it controls, an Envoy I/O process
acquires the system buffer space necessary to complete an I/O request, remembers the
current state of the line, and returns a completion status code (and data, for input
operations) to the application process. Figure 2-1
shows the functional relationship
between an application process, the Guardian 90 file system, and an Envoy subsystem.
Table 2-1. Protocols, Line Configurations, and Concentrator Types
Protocol Line Configuration Concentrator Type
ADM-2 Multipoint supervisor Asynchronous*
Asynchronous Generalized supervisor Asynchronous
BISYNC (IBM, BSC) Multipoint (supervisor or tributary) Byte-synchronous
BISYNC (IBM, BSC,
SWIFT)
Point-to-point (primary or second-
ary)
Byte-synchronous
Burroughs Point-to-point (primary or second-
ary)
Asynchronous or Byte-
synchronous
Full Duplex Point-to-point Byte-synchronous
TINET Multipoint supervisor Asynchronous
* Envoy also supports Burroughs multipoint configurations, using either the asynchronous
or byte-synchronous concentrator. Burroughs multipoint asynchronous lines are configured
as ADM-2 lines. Burroughs multipoint byte-synchronous lines are configured the same as
regular BISYNC multipoint supervisor lines.