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Communications Programming Concepts
Synchronous data link control
(SDLC) is split between a physical adapter with its associated device handler
and a data link control (DLC) component. The synchronous data link
control (DLCSDLC) device manager is responsible for functions that
include:
- Sequencing information
frames
- Creating address and control
for transmit frames
- Servicing control for
receive frames
- Handling repoll and
inactivity time outs
- Generating frame-rejects
- Handling transmit windows
- Handling reliability
counters, availability counters, serviceability counters, error logs, and link
traces.
The device handler and adapter are
jointly responsible for the remaining SDLC functions:
- Recognizing station
addresses
- Encoding and decoding
non-return-to-zero (inverted) recording (NRZI) and non-return-to-zero (NRZ)
- Inserting and deleting 0
bits
- Generating and checking
frame-check sequences
- Generating and checking
flags and pads
- Filling interframe time
- Handling line-attachment
protocols, such as RS-232C, X.21, and Smartmodem
- Handling fail-safe time outs
- Handling autoresponse for
nonproductive supervisory command frames.
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