These modules provide "ports" to which ISDN service subscribers are connected
A port is a logical concept here, an access module is a phusical equipment item.

Actually, the access modules are circuit packs (or cards, whatever) installed, say, in a remote (a remote is an outdoor/indoor subscriber concentration unit) or in a line concentration module (a module in a host automatic telephone exchange).
Here's how it ticks:
<ISDN access module>
||||.... (quad [4-wire]loops)
<[M]DF> ([Main] Distribution Frame)
<ISDN port> <ditto> <ditto>
|| (xcriber line, could be quad too)
(operator side ends here)
<NT-1>
<TE-1> <TE-2> ( for ISDN terminals)
|||| ||||
ISDN ISDN
Term. Term.

I'm too sleepy to look for relevant links, sorry :)


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Note added at 2003-10-22 00:30:40 (GMT)
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physical, of course :)

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Note added at 2003-10-22 00:32:13 (GMT)
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physical, of course :)