RE: [SLUG] ISDN Question

From: Ian C. Blenke (icblenke@nks.net)
Date: Thu Oct 10 2002 - 12:19:58 EDT


On Wed, 2002-10-09 at 15:44, Mikes work account wrote:
> Mark,
>
> When I did this years ago, I used a router to accomplish this task. At the
> time I programmed the router to do what I wanted.
>
> Michael C. Rock
> Systems Analyst
> Registered Linux User # 287973
>
> "The time has come the Walrus said to speak of many things,,,"
> "Christians give up what they cannot keep,,to gain what they cannot lose"
>
> -----Original Message-----
> From: slug@lists.nks.net [mailto:slug@lists.nks.net]On Behalf Of Mark
> Sent: Wednesday, October 09, 2002 3:14 PM
> To: slug@nks.net
> Subject: [SLUG] ISDN Question
>
>
>
> Anyone with some knowledge of ISDN please email me as that I have a few
> questions as to how one multiplexes into a two channel ISDN line.
> Specifically if I have 2 phones and a computer, how would I do that.
> Thanks.
>
> ------------------------------------------------------------------------
> | Mark Bishop (mark@bish.net) | Computer Engineer |
> | 813-253-2197 | Network Engineer |
> | http://bish.net | Embedded Programmer |

The wire coming into your house is known as an ISDN Basic Rate Interface
(BRI) "U" loop (2B1Q). You plug the outside line into your Network
Termination (NT1) device. This NT1 device is typically integrated into
the customer's Terminal Adapter (TA). This TA is usually ISDN router,
which usually provides one or two RJ11 POTS line jacks and a 10/100
Ethernet RJ45 data jack for your network.

<IGNORE>
You might read about "ST" bus equipment behind the NT1 termination
device. This was an idea to provide independent data endpoints with
unique Terminal IDs (TIDs) on customer prem. As this never really caught
on (and IP over Ethernet did), this stuff simply isn't used - so ignore
it.
</IGNORE>

You need a BRI U-loop ISDN TA (NT1U) Router that has two POTS phone
jacks and (potentially) an Ethernet interface.

ISDN BRI lines consist of three channels: 2B+D. That's two Bearer
channels (64k DS0) and a "Data" channel (16k) for Q.931 call signalling
to the switch. All call signalling for incoming/outgoing lines goes over
the D-channel, so your ISDN TA knows when to drop data channels and ring
the appropriate POTS line.

As for the Ethernet interface - you can do synchronous-PPP over a serial
port if your TA and provider support V120, however most modern ISDN TA
Router hardware replaces such cheap (and generally frustrating) gear.
Motorola made an old Bitsurfer TA that worked this way years ago (I
still have one in my closet ;)

As for transport: multilink PPP (MPPP) is typically used now to "bond"
the two channels into one apparent data stream. This is the same trick
used today to run data simultaneously over multiple dialup modems - only
over a 64k DS0 clear channels instead of nasty V.90 max
56k-down/33.6k-up modem connections.

Did this help at all? I can get into further detail if anyone is
interested.

- Ian C. Blenke <icblenke@nks.net>



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