Overview
ISO/IEC 14165-122:2005+A1:2008 (FC-AL-2) - Information technology - Fibre Channel - Part 122: Arbitrated loop-2 - defines enhancements to the Fibre Channel Physical and Signalling Interface (FC-PH) to support arbitrated loop communication (FC-AL) among two or more Ports without using a Fabric topology. The consolidated (CSV) edition 1.1 combines the original 2005 publication and Amendment 1 (2008). This standard targets signalling, addressing, and protocol behavior specific to loop topologies within Fibre Channel storage and data networks.
Key topics and technical requirements
ISO/IEC 14165-122 covers the following technical areas and requirements:
- Loop signalling and enhancements to FC-PH to enable direct port-to-port communication in an Arbitrated Loop (FC-AL-2).
- Addressing (AL_PA): definition and management of Arbitrated Loop Physical Addresses, valid/special AL_PA values and flags.
- Ordered sets and primitive signals: ARB (arbitrate), OPN (open), CLS (close), MRK (mark), LIP (loop initialization), LPB/LPE (bypass/enable), and replicate/open variants.
- L_Port operation and state machines: L_Port State Machine (LPSM), state transitions, histories, and detailed operational behavior.
- Loop initialization procedures: initialization sequences, timers, master/slave behaviors, and AL_PA assignment.
- Flow and credit management: BB_Credit and Available_BB_Credit handling per loop circuit for reliable data transfer.
- Duplex and replicate modes: full/half duplex, dynamic half-duplex (DHD) operation, and replicate broadcast/ selective replicate modes.
- Timing, timeouts, and error recovery: timing parameters, loop timeouts and error-handling expectations.
- Buffer and elasticity management (Annex A): elasticity buffer implementation and clock skew management.
- Informative annexes with examples for L_Port state machines, DHD, access unfairness and performance considerations.
Applications and who uses it
FC-AL-2 is primarily relevant to:
- Storage hardware designers (HBA, disk array controllers) implementing Fibre Channel Arbitrated Loop topologies.
- Firmware and driver developers responsible for L_Port behavior, loop initialization and signal handling.
- System integrators and SAN architects who manage legacy FC-AL deployments or mixed topologies.
- Conformance and interoperability test labs validating loop behavior, AL_PA assignment, BB_Credit handling and L_Port state transitions.
- Technical authors and standards compliance teams documenting Fibre Channel implementations.
Keywords: ISO/IEC 14165-122, FC-AL-2, Fibre Channel, Arbitrated Loop, AL_PA, L_Port, BB_Credit, loop initialization, FC-PH.
Related standards
- ISO/IEC 14165-111 (FC-PH) - Fibre Channel Physical and Signalling Interface: FC-AL-2 provides signalling enhancements and relationship details relative to FC-PH.
