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
Software Concepts
Envoy Application Programming Manual—427159-001
2-22
Line-Error Handling
the station’s poll and select addresses. The tributary’s READ completes when the
station is either polled or selected or when an error occurs.
Line-Error Handling
During data transmission, certain error conditions can be expected to occur from time to
time. The occurrence of an error condition causes Envoy to attempt recovery on behalf
of the application process. Examples of these error conditions are:
•
BCC error when receiving
•
NAK received when transmitting
•
Incorrect ACK received when transmitting
Each separate error causes Envoy to perform a predefined sequence of operations when
attempting recovery. For example, if text is being received and a BCC error is detected,
Envoy responds to the incoming message with a NAK control sequence and waits for the
message to be retransmitted. Likewise, if a NAK control sequence is received when a
message is transmitted, Envoy resends the message. Recovery operations such as these
are invisible to the application process. To detect cases where line conditions prevent the
successful transmission of data and to detect a failed remote station, the following
parameters are specified for each line when the device is added (and can be changed
with a call to the SETMODE procedure):
•
Timeout
This specifies a maximum time period that Envoy allows for a line operation
initiated by a call to a file-system procedure to complete.
•
Retry Count
This specifies the maximum number of times an operation that failed due to a line
error or timeout should be retried. (Note that not all operations are retried.)
The total time period allowed for a line operation to complete is a function of the
timeout period, the retry count, and the specific operation being performed. For
example, when receiving operations with the BISYNC protocol (such as when a receiver
waits for a line bid or waits for a message), the total timeout period is the product of
retry count multiplied by the timeout period. For sending operations (such as, line bid or
send data), the total timeout period is the same as the configured timeout period.
The responses by Envoy to specific line errors and timeouts are described with each
protocol.