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 Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-18
Normal Text With ITBs
No Need for Line Turnaround
Intermediate text blocking allows individual (or intermediate) blocks to be checked for
errors and then another block to be sent immediately without the need for line
turnaround (that is, without the 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 an ETX is received and the entire message containing all
the intermediate blocks is retransmitted. Intermediate text blocking is used when an
application is sending a block of data that is 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 set for the communications 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 having the following 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 + of
intermediate blocks - 1)
Here, the application process must embed ITB (%37) characters at the end of each
intermediate block except the last. The message must be terminated with an ETB or an
ETX character. The intermediate block length must be specified as a value equal to or
greater than the longest intermediate text block to be transmitted.
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 intermediate blocks of intermediate block length
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.