Overview
ISO 2628:1973 - "Basic mode control procedures - Complements" is an ISO International Standard that extends the digital basic-mode control procedures defined in ISO/R 1745 and ISO 2111. Published in 1973, it provides complementary guidance for data communication systems on recovery, abort and interrupt procedures, and multiple-station selection in master/slave and control-station environments. The standard is primarily concerned with control procedures, character supervisory sequences and practical mechanisms (timers, counters) to protect information transfer on data links.
Key topics and technical requirements
- Scope and relationship: Complements ISO/R 1745 and ISO 2111; references CCITT Recommendation V.24 for interface functions and characteristics.
- Recovery procedures: System-level guidelines for error detection and recovery. Addresses recovery responsibilities for control, master and slave stations and links these functions to the standard’s phase diagrams.
- Timers and counters: Defines timer types (no numeric values are prescribed) used to detect failures and trigger recovery:
- Timer A - No-response timer (protection against invalid response or no response).
- Timer B - Receive timer (protects against non-recognition of block-terminating characters).
- Timer C - No-activity timer for switched lines (facilitates disconnection procedures).
- Timer D - No-activity timer for non-switched lines (system-wide inactivity time-out).
- Abort procedures: Master-initiated procedures to stop a transmission safely:
- Block abort - Terminate a block unusually (e.g., ENQ/DLE ENQ sequence), with guidance on retransmit and block-numbering concerns.
- Station abort - Master returns to control mode or neutral between blocks or during a block.
- Interrupt procedures: Slave-initiated means to request immediate cessation:
- Block interrupt - Slave replies EOT to indicate negative acknowledgement and end of transmission.
- Station interrupt - Slave sends a special control sequence (DLE
