ISDN phone lines

[Michael]

Does an ISDN line function as both a POTS and ISDN
line. (yes--stupid?)


The system detects the difference and switches to adapt?
(yes--stupid?)


So on an ISDN line you would still see 90vac ringing voltage from ANY
incoming call? (yes--stupid?)


Thanks.

 

[Nico Coesel]

"Michael" <newszz10@yahoo.com> wrote:

Does an ISDN line function as both a POTS and ISDN
line. (yes--stupid?)

No. An ISDN line is completely different to a POTS line.

So on an ISDN line you would still see 90vac ringing voltage from ANY
incoming call? (yes--stupid?)

No, but beware, there is 96V DC between the pairs to feed the
equipment!

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

 

[Richard H.]

Michael wrote:

Does an ISDN line function as both a POTS and ISDN
line. (yes--stupid?)

Sortof. You can buy an endpoint that can convert each channel to a POTS
port. The ISDN service knows when a POTS call vs. a data call is being
established; voice calls won't setup on a data-only endpoint &
vice-versa. (An endpoint with both is smart enough to route incoming
calls to POTS vs. data port.)

So on an ISDN line you would still see 90vac ringing voltage from ANY
incoming call? (yes--stupid?)

No. An ISDN line is not like a POTS line. It's a 2-wire always-on data
circuit. The endpoint maintains a full-time heartbeat with the telco
switch at the other end. "Calls" are established via setup commands
over the wire. Calls are tagged as voice vs. data and get routed
appropriately.

If you have a POTS port on your endpoint (to connect your phone), it
will generate the ring pattern and voltage locally.

Richard

 

[Michael]

Sortof. You can buy an endpoint that can convert each channel to a POTS
port. The ISDN service knows when a POTS call vs. a data call is being
established; voice calls won't setup on a data-only endpoint & vice-versa.
(An endpoint with both is smart enough to route incoming calls to POTS vs.
data port.)

Do most of the ISDN phone "systems" have this ability?
(I would think they ALL would have this endpoint bulit in?).

So on an ISDN line you would still see 90vac ringing voltage from ANY
incoming call? (yes--stupid?)

No. An ISDN line is not like a POTS line. It's a 2-wire always-on data
circuit. The endpoint maintains a full-time heartbeat with the telco
switch at the other end. "Calls" are established via setup commands over
the wire. Calls are tagged as voice vs. data and get routed
appropriately.

If you have a POTS port on your endpoint (to connect your phone), it will
generate the ring pattern and voltage locally.

Richard

Thanks kindly Richard.
I wanted to detect ring with a normal POTS detector at 90vac---I would
imagine they generate the same (or close).

My question was more about ISDN "systems" rather than just a single
dedicated line and certainly they're going to be backwards compatible.

This "D" channel ring stuff was scaring me.

 

[Richard H.]

Michael wrote:

Do most of the ISDN phone "systems" have this ability?
(I would think they ALL would have this endpoint bulit in?).

Yes, I'd expect so. There are a lot of possible scenarios, but if the
system is talking ISDN to the carrier and POTS to the phone sets, then yes.

I wanted to detect ring with a normal POTS detector at 90vac---I would
imagine they generate the same (or close).

Yes. On a POTS interface, they are expected to meet the standards, and
appear as a telco switch in terms of dial tone, ring patterns, voltage
levels, etc.

My question was more about ISDN "systems" rather than just a single
dedicated line and certainly they're going to be backwards compatible.

In effect, the question of whether it's ISDN upstream should be
irrelevant if the interface to you is POTS. Translating is the job of
the "system", and downstream devices should neither know nor care. In
practice, the upstream trunk could be any variety of analog line,
channelized T1/E1, ISDN PRI/BRI, or even VoIP.

FYI, many "phone systems" use digital phone sets, and the line between
the desk set and the PBX/key system is a proprietary vendor protocol,
not POTS. Your POTS ring detector won't work on these lines.

This "D" channel ring stuff was scaring me.

You'd only care about that if you were monitoring the ISDN line, not the
POTS line. That's a whole different ball game, magnitudes more complex,
requiring you to monitor and decode a digital signal.

Cheers,
Richard

 

[Nico Coesel]

"Richard H." <rh86@no.spam> wrote:

Michael wrote:
Does an ISDN line function as both a POTS and ISDN
line. (yes--stupid?)

Sortof. You can buy an endpoint that can convert each channel to a POTS
port. The ISDN service knows when a POTS call vs. a data call is being
established; voice calls won't setup on a data-only endpoint &
vice-versa. (An endpoint with both is smart enough to route incoming
calls to POTS vs. data port.)


So on an ISDN line you would still see 90vac ringing voltage from ANY
incoming call? (yes--stupid?)

No. An ISDN line is not like a POTS line. It's a 2-wire always-on data
circuit. The endpoint maintains a full-time heartbeat with the telco
switch at the other end.

Sorry, that's not true. Depending on the settings in the public
network, an ISDN line is put in 'standby' and needs to be activated
before use.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

 

[Richard H.]

Nico Coesel wrote:

No. An ISDN line is not like a POTS line. It's a 2-wire always-on data
circuit. The endpoint maintains a full-time heartbeat with the telco
switch at the other end.


Sorry, that's not true. Depending on the settings in the public
network, an ISDN line is put in 'standby' and needs to be activated
before use.

I presume you're referencing the "always on" point. No doubt ISDN can
be made to be a switched service; it seems to support a great many
variations. I understand it can also be made multi-drop with
addressable nodes (e.g., POS terminals).

However, in practice, I've never seen an installation implement other
than always-on. (IIRC, blowing the cobwebs out, this is the Q.921 link
signaling, which is typically kept alive regardless of upper-layer Q.931
sessions.)

In what scenario would it be beneficial to tear down the link layer?
IIRC, it takes several seconds to establish Q.921, so this wouldn't be
friendly to many voice applications.

Cheers,
Richard

 

[Nico Coesel]

"Richard H." <rh86@no.spam> wrote:

Nico Coesel wrote:
No. An ISDN line is not like a POTS line. It's a 2-wire always-on data
circuit. The endpoint maintains a full-time heartbeat with the telco
switch at the other end.


Sorry, that's not true. Depending on the settings in the public
network, an ISDN line is put in 'standby' and needs to be activated
before use.

I presume you're referencing the "always on" point. No doubt ISDN can
be made to be a switched service; it seems to support a great many
variations. I understand it can also be made multi-drop with
addressable nodes (e.g., POS terminals).

However, in practice, I've never seen an installation implement other
than always-on. (IIRC, blowing the cobwebs out, this is the Q.921 link
signaling, which is typically kept alive regardless of upper-layer Q.931
sessions.)

Over here all public network ISDN2 links are shut down after 30
seconds. Also, 99% of the connections are point to multi-point. For
instance, I have 3 telephones and a fax connected to one ISDN line
each having a different phone number.

In what scenario would it be beneficial to tear down the link layer?

Preserve power and CPU resources. An active link needs processor power
in the switch and an energy wasting signal on the S bus.

IIRC, it takes several seconds to establish Q.921, so this wouldn't be
friendly to many voice applications.

Several seconds? More like 100ms (depending on resources). Besides, on
an ISDN2 link the incoming setup message is send before layer2 is
actually initiated.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

 

[David Lesher]

"Michael" <newszz10@yahoo.com> writes:

Does an ISDN line function as both a POTS and ISDN
line. (yes--stupid?)

That Depends [tm]

The system detects the difference and switches to adapt?
(yes--stupid?)

no..

So on an ISDN line you would still see 90vac ringing voltage from ANY
incoming call? (yes--stupid?)

Not at all...


ISDN BRI {Basic Rate Interface} is a 1 pair echo-cancelled ~200Kb/s
data link. It runs 2B1Q, i.e. 4 voltage levels, so that baud rate is
half the data rate.

Of that, you have two 64Kbps "B" channels, one 16Kbps "D" channel
and another 16K worth of hidden overhead bits. No 90VRMS 20 Hz
allowed....

In some parts of the world, but not the US, there's DC parked on
the pair to run the subscriber equipment. (There may be, however,
DC superimposed to run an in-line regenerator. Don't ask-- it's
a tariff issue..)

As designed, the incoming 80 KBaud BRI hits a "NT-1" to turn that
point-point one pair, to multi-point 2 pair 160K S/T bus that would
run around your house. (w/ a third pair for -48DC power) Ma was
going to provide that NT-1 and power it. But what happened in the
US was She was forbidden to do so by the MFJ, and besides, the common
use was dialup Internet access at 64/128Kbps, and that was the sole
use, so the routers were usually built with an internal NT-1.

Note that US ISDN {"National" or NI-1, not to be confused with NT-1.}
is way different from EuroISDN, at the loop level. At the S/T bus
stage, ISTM things are about the same....but at the higher level,
it's way different Yet Again.

In any case, you plug a router/adapter/whatever name into the BRI
and depending on its features, get 2 POTS jacks to drive sets, or
an Ethernet to go to your LAN, or both. {Phone calls could pre-empt
existing data calls.}

You COULD have an exotic ISDN "phone set" with lots of neat features
[really, "lots of button sending signals back to the CO switch to
do those neat features"...] but almost no one in the US did, except
of course, me.

Where ISDN *did* shine was in Centrex business installations, esp.
spanning buildings. The fact that voice and data were just bits
meant a Centrex set could have buttons and displays just like
a local PBX offered on its fancy sets.

Is this more than you wanted to know?

Oh yes.... ISDN PRI {Primary Rate Interface vs Basic} is a horse of
a different color.. It's a DS1 1.544 mb/s data stream that offers
23B's and one 64Kb D channel. It is in WIDE use to feed PBX's, and
often is the ONLY product offered by CLEC's.




--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433