Envoy Application Programming Manual
Table Of Contents
- What’s New in This Manual
- About This Manual
- 1 Application Programming With Envoy
- 7 ADM-2 Multipoint Supervisor Protocol
- 8 TINET Multipoint Supervisor Protocol
- 9 Burroughs Point-To-Point Protocol
- 10 Asynchronous Line Supervisor Protocol
- A ASCII Character Set
- B ASCII to EBCDIC Code Conversion
- C File-System Procedures
- D Statistics Messages
- E S-Series Changes to Envoy
- NonStop™ Himalaya S-Series Server Architecture
- G-Series Migration Considerations
- CBSENSEON and CFSENSEON Modifiers
- LEOTRESYN and NOLEOTRESYN Modifiers
- Treatment of Characters After the Termination Character
- Number of SYN Characters
- DTR Drop
- Reporting of Parity Error
- Half-Duplex Support for Asynchronous Lines
- Controller Replacement
- SYSGEN and COUP
- Unit Numbers
- FDX Line Changes
- No Support for Auto-Call Unit
- Glossary
- Index
Envoy Application Programming Manual—427159-001
2-1
2
Software Concepts
This section describes the software concepts that apply to an Envoy data
communications environment.
Topics described in this section include the following:
•
Synchronization and Timing on page 2-1
•
Software Environment on page 2-1
•
Line Configurations on page 2-11
•
Point-to-Point Operation on page 2-12
•
Multipoint Operation on page 2-15
•
Line-Error Handling on page 2-22
•
Programming Considerations for NonStop™ Himalaya Servers on page 2-23
Synchronization and Timing
For data to be passed back and forth between two stations in a data communications
environment, the stations must first establish and then maintain synchronization with
one another.
In an asynchronous environment, the stations synchronize with one another by means of
a start and stop bit attached to every character that passes over the line. The
asynchronous controller at each end of the line automatically generates (on output) and
strips (on input) the start and stop bits.
In a byte-synchronous environment, the stations synchronize with one another by means
of synchronous idle (SYN) control characters. SYN is an actual character in the ASCII
or EBCDIC character set. Each transmission comprises one or more variable-length
blocks of control characters and data. Each block begins with a sequence of two or more
SYN characters. In long blocks, the byte-synchronous controller automatically inserts
additional SYN characters at regular intervals to maintain synchronization throughout
the transmission.
The asynchronous and byte-synchronous protocols use control characters to define the
nature of each transmission.
Software Environment
Subsystems running in the NonStop™ Kernel, such as Envoy, use a single data-
communications ServerNet wide area network (SWAN) concentrator rather than the
communications controllers used by D-series. The SWAN concentrator connects bit-
synchronous, byte-synchronous, and asynchronous devices to Compaq NonStop™
Himalaya S-series servers.