NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/dcom/isdn/992

Internet Message Format | 1992-12-16 | 2.1 KB

Path: sparky!uunet!pipex!doc.ic.ac.uk!uknet!axion!galadriel!pjw
From: [e-mail] (Peter Willis)
Newsgroups: comp.dcom.isdn
Subject: Re: The ISDN network
Message-ID: <[e-mail]>
Date: 16 Dec 92 12:59:54 GMT
References: <[e-mail]>
Organization: Data and Business Comms, BT Labs, Martlesham, Ipswich, UK.
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   A Terminal Adaptor (TA) should be able to tell if an incoming call is
analogue or digital data by the Bearer Capability (BC) indicated in the incoming
setup message. If the incoming call has come from a modem or fax then this
will be indicated by the BC being 3.1KHz audio, if the incoming call has
come from a digital data device then this will be indicated by the BC being
unrestricted digital information. The TA should then be `intelligent' enough
to route an incoming `analogue' ISDN call to an analogue port and a
digital `incoming' ISDN call to a digital (e.g. V.24) port.
   There's also a bit to identify the call as having originated from the PSTN
rather than the ISDN. The tricky bit is telling if an incoming call from
the PSTN is from a telephone, fax or modem  (It can't be done yet !).

   A problem does exist in determining what type of device you are calling
for outgoing calls. However not many people call a fax machine by accident
on the PSTN, you can't tell from the phone number if the device is a fax, modem
or telephone. People normally decide who they want to call, how they want to
communicate then look up the right number in some form of directory. The same
could be done for ISDN.
   Each terminal (TA or TE) attached to an ISDN S-Bus can be given an
individual number (Multiple Subscriber Number the standards call it). Then
you publish you have a FAX on a, TA on b, X.25 on c etc.
   Alternatively you could try using the HLC (Higher Layer Compatibility)
and LLC (Lower Layer Compatibility) fields.
   This all depends on the ISDN CPE manufactuers having implemented MSN, BC,
LLC, HLC in their CPE and the PTTs providing these features in their ISDNs.

Peter Willis,
[e-mail]