ISDN-NT1+2ab /w Annex A Modem

[hufaunder]

From the answer of a previous post I learned that there is Annex A and
Annex B. A modem for Annex B (in my case one from the US) will not work
on Annex A. The setup I currently have looks like this: ISDN connection
goes to an ADSL splitter. One part goes out to a ADSL modem for ISDN
which then is connected to a PC via USB. The other output goes to the
ISDN box that has two S-Bus and 2 a/b outputs.

What comes out from the splitter to the modem must be connected to an
Annex B modem (ADSL over ISDN). The question now is, could I connect an
Annex A modem (ADSL over POTS) to one of the a/b ports on the ISDN box
and connect to the internet?

I assume the provider does not really care what you have POTS or ISDN.
It is the telecommunication company that puts the ADSL signal in the
appropriate frequency range depending on if you have POTS or ISDN. If
this is correct then the above suggestion is unlikely to work.

On the other hand maybe neither the telecommunication company nor the
ISP cares and they send the signal always at the ADSL signal always in
the same frequency (above the 140kHz or so for ISDN). In that case
maybe there is a solution?

Any input is appreciated.

Thanks

 

[Dennis Ferguson]

Annex B. A modem for Annex B (in my case one from the US) will not work
on Annex A. The setup I currently have looks like this: ISDN connection
goes to an ADSL splitter. One part goes out to a ADSL modem for ISDN
which then is connected to a PC via USB. The other output goes to the
ISDN box that has two S-Bus and 2 a/b outputs.

What comes out from the splitter to the modem must be connected to an
Annex B modem (ADSL over ISDN). The question now is, could I connect an
Annex A modem (ADSL over POTS) to one of the a/b ports on the ISDN box
and connect to the internet?

You might be better off calling these "ADSL and ISDN", or "ADSL and POTS".
There is one ADSL signal and one ISDN (or POTS) signal on the line.
They share the copper wire pair but are otherwise entirely separate. The
difference between Annex A & B is only that, since ISDN takes up more
"space" on the pair than POTS, the ADSL signal that shares with ISDN
needs to be adjusted to take up less space on the pair.

When you insert the splitter the ADSL signal (without the ISDN) comes
out one port of the splitter while the ISDN signal (without the ADSL) comes
out the other. There is hence no ADSL on the ISDN side of the splitter,
so plugging an ADSL modem into anything on the ISDN side of the splitter
won't do any good at all.

Dennis Ferguson

 

[NoNeedToKnow]

I assume the provider does not really care what you have POTS or ISDN.

Since there are Annex A and Annex B standards, it is pretty clear that
the provider *would* care whether you have POTS or ISDN, because they
are unlikely to offer both (one of the past suggestions was that if
there was a mix of these, crosstalk would stop some connections from
working - whether correct or not I don't know) as they'd have to
have two types of equipment, and there'd be scope for not having the
right spares, or using incompatible kit (perhaps with dire results!)

It is the telecommunication company that puts the ADSL signal in the
appropriate frequency range depending on if you have POTS or ISDN.
If this is correct then the above suggestion is unlikely to work.

Correct. So you might be best getting something 'locally' rather than
trying to use something incompatible, and jumping through hoops to get
it connected whilst never having a chance of it working...