Communications Programming Concepts

DLCTOKEN Device Manager Functions

The token-ring data link control (DLCTOKEN) device manager and transport medium-use two-functional layers, medium access control (MAC) and logical link control (LLC), to maintain reliable link-level connections, guarantee data integrity, and negotiate exchanges of identification. Both connectionless (Type 1) and connection-oriented (Type 2) services are supported.

The token-ring adapter and the DLCTOKEN device handler perform the following MAC functions:

• Handling ring-insertion protocol
• Handling token detection and creation
• Encoding and decoding the serial bit-stream data
• Checking received network, group, and functional addresses
• Routing of received frames based on the LLC or MAC indicator and using the destination service access point (SAP) address if an LLC frame was received
• Generating cyclic redundancy checks (CRC)
• Handling frame delimiters, such as start or end delimiters and frame status fields.
• Handling fail-safe time outs.

DLCTOKEN performs additional MAC functions, such as:

• Framing control fields on transmit frames
• Network-addressing on transmit frames
• Routing information on transmit frames.

DLCTOKEN is also responsible for all LLC functions:

• Handling remote connection services and bridge routing, using the address-resolve and name-discovery procedures
• Sequencing of link stations on a given port
• Generating SAP addresses on transmit frames
• Generating IEEE 802.2 LLC commands and responses on transmit frames
• Recognizing and routing of received frames to the proper SAP
• Servicing IEEE 802.2 LLC commands and responses on receive frames
• Handling frame sequencing and retries
• Handling fail-safe and inactivity time outs
• Handling reliability/availability/serviceability (RAS) counters, error logs, and link traces.