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 Centralized Multipoint Supervisor Protocol
Envoy Application Programming Manual—427159-001
4-24
Intermediate Text Blocks
another block to be immediately sent without the need for line turnaround (that is,
without a receiver acknowledging each block) as is the case with normal blocking. If an
error is detected during one of the block checks, a NAK is returned only after an ETB or
ETX is received. Then, the entire message containing all of the intermediate blocks is
retransmitted.
Intermediate text blocking is used when an application is sending a block of data larger
than the communications line buffer size. In this case, the block of data must be divided
into smaller blocks that fit within the buffer size specified for the line when issuing the
ADD DEVICE command.
If intermediate text blocking is to be performed, an intermediate block length of nonzero
value must be specified for a given line either when issuing the ADD DEVICE
command or with a call to the SETMODE procedure. If a zero intermediate block length
is specified, no intermediate text blocking takes place.
Envoy provides two methods for intermediate text blocking: one for normal text, the
other for transparent text.
Normal Text With ITBs
Normal text with intermediate text blocks is indicated by a nonzero intermediate block
length and messages of the form:
message = STX-text-ITB...-text-ETB
message = STX-text-ITB...-text-ETX
(message length = 2 + text length + number of intermediate
blocks - 1)
or
message = SOH-head-STX-text-ITB...-text-ETB
message = SOH-head-STX-text-ITB...-text-ETX
(message length = 1 + heading length + 2 + text length +
number of intermediate blocks - 1)
Transparent Text With ITBs
To an application process, transparent text messages with intermediate text blocking
have the same form as transparent text without intermediate text blocking. Intermediate
text blocking for transparent text is indicated by specifying a nonzero intermediate block
length for the line.
However, upon actual transmission, if intermediate text blocking is indicated, Envoy
sends transparent text messages as blocks of ITB characters (the last block contains
fewer characters if the text length is not evenly divisible by the intermediate block
length). An ITB character is appended by Envoy to each intermediate block except the
last.
Upon receipt of transparent text, if intermediate text blocking is indicated, Envoy deletes
ITB characters occurring at the end of each intermediate block (the length of each block
received must be the same as the specified intermediate block length).