Communications Programming Concepts

DLC FDDI Device Manager Functions

The data link control (DLC) fiber distributed data interface (FDDI) device manager and transport medium use two functional layers, medium access control (MAC) and logical link control (LLC), to maintain reliable link-level attachments, guarantee data integrity, negotiate exchanges of identification, and support both connection and non-connection oriented services.

The FDDI adapter and device handler are responsible for the following MAC functions:

• Handling ring-insertion protocol
• Detecting and creating tokens
• Encoding and decoding the serial bit-stream data
• Checking received network and group addresses
• Routing of received frames based on the LLC/MAC/SMT indicator and using the destination service access point (SAP) address if an LLC frame was received
• Generating frame-check sequences (FCS)
• Handling frame delimiters, such as start or end delimiters and frame-status field
• Handling fail-safe time outs
• Handling network recovery.

The FDDI Device Manager is responsible for additional MAC functions, such as:

• Framing control fields on transmit frames
• Network addressing on transmit frames
• Routing information on transmit frames
• Handling network recovery.

The FDDI Device Manager is also responsible for all LLC functions:

• Handling remote connection services 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 received frames to the proper service access point
• Servicing of IEEE 802.2 LLC commands and responses on receive frames
• Handling frame sequencing and retries
• Handling fail-safe and inactivity time outs
• Handling reliability counters, availability counters, serviceability counters, error logs, and link trace.