ISDN-oriented Modular Interface explained

ISDN-oriented Modular Interface (IOM) is a system architecture and its bus for communication between various VLSI ICs for the lower layers (ref. OSI model) of ISDN. It was developed by Siemens (today: Infineon), current revision is IOM-2. Its purpose is to enable modularity. Second sources are AMD, Alcatel, Plessey.

IOM-2 is a 4-wire serial, full-duplex link. 2 operation modes are available: line card mode and terminal mode; which differ only in number and purpose of the channels. Signals are:

• DCL (data clock, 16 kHz * N, where N = number of channels)
• FSC (frame sync, 8 kHz)
• DU (data upstream)
• DD (data downstream)

References

• Book: 1991 . ICs for Communications, IOM–2 Interface Reference Guide . Siemens AG . Order Number B115-H6397-X-X-7600.
• Book: 1994 . ICs for Communications, ISDN Subscriber Access Controller for Terminals, ISAC–STE, PSB2186 User's Manual . Siemens AG.
• Book: Georg, Otfried . 2000 . Telekommunikationstechnik . Springer . 978-3-540-66845-9 . (in German, p. 278ff give an overview and some application examples)