Overview
ISO/IEC 13871:1995 - Information technology - Private telecommunications networks - Digital channel aggregation - specifies procedures for combining multiple 56 kbit/s or 64 kbit/s digital channels into higher‑bandwidth, bi‑directional connections between Channel Aggregation Units (CAUs). The standard focuses on maintaining bit‑sequence integrity, synchronisation and optional dynamic bandwidth variation across public and private networks (including ISDN). It defines the frame structure, information messaging and error‑monitoring needed for aggregated bearer services, while leaving call‑control signalling and electrical physical layer details to other standards.
Key topics and requirements
- Channel aggregation concept: inverse multiplexing of multiple switched/unswitched bearer channels (56/64 kbit/s) into a single aggregated service.
- Channel Aggregation Unit (CAU): functions and interface behaviour required to support aggregation.
- Frame structure and alignment: inclusion of Frame Alignment Word (FAW), Frame Count (FC), information channel (IC) framing and overall multiframe alignment.
- CRC4 error control: CRC computation, encoding/decoding, enabling/disabling and error monitoring procedures.
- Information Channel (IC): continuous 16‑octet messages for parameter negotiation, synchronisation and control.
- Dynamic bandwidth procedures: call setup, adding/deleting bandwidth during a call, delay equalization and collision resolution.
- Operational modes: transparent mode operation and interactions between aggregating and non‑aggregating units.
- Procedures and state machines: detailed state diagrams, timers and message/event handling (annex D informational).
- Annex material: RMULT/SUBMULT values for bearer rates, manufacturer identifiers, phone number length extension and state machine descriptions.
Practical applications
ISO/IEC 13871 supports use cases that need aggregated, reliable digital throughput over multiple narrowband channels:
- LAN interconnection over leased lines or ISDN trunks
- Bulk file transfer and image transfer where higher aggregate throughput is required
- Video conferencing or multimedia sessions that demand synchronized bandwidth
- Legacy ISDN/PRI/BRI optimization where channel bonding enhances throughput without new physical interfaces
Who should use this standard
- Telecom equipment manufacturers designing CAUs, inverse multiplexers or ISDN bonding devices
- Network architects and integrators deploying private network links that combine multiple B‑channels
- Firmware/software developers implementing aggregation protocols, frame alignment and CRC procedures
- Standards and compliance engineers ensuring interoperability with public ISDN and private networks
Related standards (reference)
- ITU‑T H.244 (synchronized aggregation of ISDN‑B channels)
- ITU‑T G.704, H.221, H.320
- ISO/IEC 11571 (numbering/sub‑addressing for private ISDNs)
Keywords: ISO/IEC 13871, digital channel aggregation, Channel Aggregation Unit, 56 kbit/s, 64 kbit/s, ISDN, inverse multiplexing, CRC4, frame alignment, H.244.
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