Communications Programming Concepts

DLCSDLC Device Manager Functions

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.