Overview
ISO/IEC 8877:1992 specifies the physical connector and contact assignments for ISDN Basic Access interfaces located at the S and T reference points. The standard defines an 8‑pole plug and jack, the required contact/pair assignments used between Terminal Equipment (TE) and Network Termination (NT) devices (including NT1 and NT2), and minimum requirements for ISDN basic access cords. It references and requires conformance with CCITT Recommendation I.430 for signalling, impedance and termination behavior.
Key topics and technical requirements
- Connector type: 8‑pole plug and jack (plug/jack mechanical and contact specifications illustrated in the standard).
- Contact/pair assignments: Wire pairs connect contact pairs 1‑2, 3‑6, 4‑5 and 7‑8. Contact numbering and TX/RX assignment follow I.430; the mapping at TE and NT ends results in the same conductor being connected to the same contact number in jacks at both ends of interface cables.
- Cabling roles: Defines three physical cable types - connecting cords, extension cords and interface cables - and their intended use in point‑to‑point and passive bus topologies.
- Cord length & electrical limits (from I.430 extract):
- Standard TE connecting cord maximum length: 10 m.
- For cords ≤ 7 m: pair capacitance < 300 pF; characteristic impedance > 75 Ω at 96 kHz; crosstalk loss > 60 dB at 96 kHz (with 100 Ω terminations); conductor resistance limits; cords terminated at both ends in plugs.
- For cords > 7 m (up to 10 m): capacitance allowance up to 350 pF; other limits apply.
- Termination resistors: For point‑to‑point wiring, terminating resistors must be located in or at the jack and connected across contact pairs 4‑5 and 3‑6; for passive bus, resistors may be at bus ends.
- Powering options (informative): Optional powering methods include phantom powering over transmit/receive pairs, power on optional pair 7‑8, and optional use of pair 1‑2 for power (powering rules and limits are defined in I.430, section 9). Use of power on 1‑2 supports TE‑to‑TE arrangements via crossover adapters.
Applications and practical use
- Standardizes the physical interface for ISDN Basic Access on customer premises wiring and equipment connections.
- Used when installing or manufacturing:
- ISDN terminal equipment (TE), network terminations (NT1/NT2), and PABX interfaces.
- Wall jacks, user‑premises wiring (interface cables), connecting and extension cords.
- Crossover adapters for TE‑to‑TE connections and installers planning passive bus vs point‑to‑point topologies.
- Ensures interoperability, correct termination, and signal/power behavior between vendors and installers.
Who should use this standard
- Telecom equipment manufacturers and hardware designers
- Network planners and installers for ISDN installations
- Cabling and premises wiring contractors
- Compliance and test labs validating ISDN interfaces
Related standards
- CCITT Recommendation I.430 (detailed ISDN Basic Access requirements referenced throughout)
- IEC 603‑7 (connector specifications for low‑frequency connectors)