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
BISYNC Point-To-Point Protocol
Envoy Application Programming Manual—427159-001
3-15
ID Exchange
ID Exchange
When performing an ID exchange, the application process must format the ID in its
buffer by appending the appropriate control characters:
•
An ID exchange message from the caller is indicated by a message having the
following form:
message = ID—ENQ
(message length = 1 + ID length)
•
An ID exchange message from the called station is indicated by a message having
the following form:
message = ID—ACK0 (caller’s ID okay)
message = ID—WACK (caller’s ID okay, wait before sending)
(message length = 2 + ID length)
ACK0 = DLE ,
"0" (DLE = %020)
WACK = DLE , ";"
message = ID—NAK (caller’s ID not okay)
(message length = 1 + ID length)
An ID consists of up to 16 noncontrol characters.
BCC Calculation
Block-check characters (BCCs) are computed by Envoy using the Consultative
Committee International Telephone and Telegraph (CCITT) polynomial, the cyclic
redundancy check (CRC-16) polynomial, or the longitudinal redundancy check (LRC).
Envoy adds BCC on output and checks BCC on input for messages that start with an
SOH or an STX and that end with an ETB or an ETX. Normally, only the characters
after the initial SOH or STX are included in the BCC calculation; the SOH and STX
characters themselves are excluded from the BCC calculation for most protocols.
SWIFT Variant of BCC
The SWIFT variant of BCC includes the initial STX characters (after a block starting
with SOH) in the BCC calculation. Therefore, a specific message format must be
followed when using SWIFT communication:
•
Single block:
SOH—head—STX—text—ETX
•
Multiple blocks:
SOH—head—STX—text—ETB (initial block)
STX—text—ETB (intermediate blocks)
STX—text—ETX (final block)