Overview
ISO/IEC 9314-5:1995 - "Information technology - Fibre Distributed Data Interface (FDDI) - Part 5: Hybrid Ring Control (HRC)" specifies a hybrid ring protocol that integrates packet-switched and isochronous traffic into a single FDDI frame structure called a cycle. The standard defines the HRC logical components (the Hybrid Multiplexer - H‑MUX and the Isochronous MAC - I‑MAC), the cycle format, clocking/synchronization rules, and the interfaces to existing FDDI layers (PHY, MAC, PMD) and Station Management (SMT). HRC enables FDDI-II stations to carry both regular data frames and time-sensitive streams on the same ring.
Key topics and technical requirements
- HRC architecture: Definitions and roles of H‑MUX and I‑MAC, and their relationships to P‑MAC, CS‑MUX and LLC.
- Cycle/frame structure: Cycle header, cycle control field (synchronization and sequence control), cycle programming template and cycle timing/format (document specifies parameters at 100 Mbps).
- Timing & synchronization: Rules for cycle generation, selection of a single cycle master (ranked monitor selection), ring timing adjustments and latency buffering.
- Traffic types & bandwidth management: Support for packet and multiple isochronous channels, channel definitions, wideband channel interleaving/sorting and bandwidth allocation hierarchy.
- Services and interfaces: Detailed services between PHY↔H‑MUX, H‑MUX↔MAC / P‑MAC / I‑MAC, and H‑MUX↔SMT, plus I‑MAC↔CS‑MUX interfaces for circuit-switched services.
- Operational behavior: Ring operation overview, cycle acquisition/generation/exchange processes, error recovery, state machines, timers, counters, signals and protocol variables.
- Transmission rates: Designed for operation at 100 Mbps and higher (document notes support in increments of 6.144 Mbps).
- Conformance artifacts: Symbol sets, protocol parameters, figures and state diagrams; annexes with examples (circuit‑switch services, station considerations, isochronous call control, security, bandwidth management).
Applications and who uses it
- Network equipment vendors implementing FDDI-II hardware and firmware (H‑MUX, I‑MAC, monitors).
- Systems integrators and telecommunications engineers designing networks that combine data and real‑time streams (e.g., audio/video, TDM‑like circuit services) over FDDI.
- Protocol implementers and interoperability test labs verifying conformance to FDDI hybrid operation and cycle timing.
- Organizations using legacy FDDI infrastructure that require guaranteed isochronous channels or circuit‑switched services alongside packet traffic.
Related standards
- ISO/IEC 9314 (other parts): Part 1 (PHY), Part 2 (MAC), Part 3 (PMD); referenced parts such as PHYS‑2 and MAC‑2.
- ISO 8802-2 (LLC) and other FDDI family documents referenced by ISO/IEC 9314‑5:1995.
Keywords: ISO/IEC 9314-5:1995, FDDI, Hybrid Ring Control, HRC, H‑MUX, I‑MAC, FDDI‑II, cycle, isochronous channels, cycle master, SMT, PHY, MAC, CS‑MUX.