Re: ISDN & Stuff - Questions

Dale E. Reed Jr. ( (no email) )
Wed, 19 Aug 1998 23:56:03 -0700

John Lange wrote:
> A few questions Dale, as long as you've done this before.
> [Begin ISDN Tutorial]
> They tell me that ISDN is 2 B channels??? (not sure about this part) Is
> that 4 wires or 6? Is this more like two Digital 56 circuits but bonded
> and at 64K? Do they get 2 ip address' 1 for each channel, or just one?

ISDN is a digital technology with a limited length (around 5 cable
It includes a 16kb "D" channel that is always active between the end
and the CO switch. It also includes two "B" (barrier) channels. Each B
channel is capable of handling one: 64kb data, 56kb data, or 56kb voice
connection. Because there is basically a dedicated channel between the
switch and the device that is NOT a part of the data channels, you can
do some really cool things with it. For example, one of the most
popular features now is that the switch can alert the ISDN device of an
incoming call, and the ISDN device can drop a channel temporarily to
receive the call. Most ISDN devices have either one or two POTS
connections for this.

The DOV (Data over voice) calls I referenced is really a trick.
Switches can be configured to handle data and voice calls seperately.
Most ISDN devices can allow you to specify what type of data call to
make (64kb, 56kb, and 56kb voice). Using the last, it will tell the
switch that its initially a voice call, so that it can connect to
a "voice" or 56kb circuit. Once connected, both sides can switch to
data and away you go. ISDN calls typically take 1-3 seconds to
complete, since its all digital and there is no wait time between
the switch and the end device (the D channel is always active).

For the records, a PRI works the same way, except is has 23 B channels,
rather than just 2 (its still has a 16kb D channel, though).

> >If you can get a T1 from GTE, then you can do 56k DOV ISDN. I've done
> >that here in GTE land and it does work.
> Can I receive these calls on my PM3's with CT1 AMI & D4 or do I need a
> special circuit to the PM???

You should be able to. You'd really have to try it to find the
answer, though.

> >Sure. But ISDN is a dial technology and WILL go down.
> Got it, so dynamic ip's are the issue... Just like 33.6 dialup. So if we
> were to do this we really want a mail relay from the outside world. Also a
> conventional Mail & Web domain on a real server.

Yes. If you take a look at some of the new 3Com gear, it does
NAT on the fly with a dynamic IP and can do dial on demand w/out
an issues. Its really slick and makes the "IP" assignment game
much easier NAT brings a psuedo firewall into the picture and
can be played as more secure to business customers (IE charge
them more mone for you to do less :) ).

> >ISDN has two classes. One is the dial use, which usually has the same
> >plan like the modem dialup. THe other is the dedicated/routed which usually
> >is a nailed connection with a subnet.
> This was one consideration for this customer, but when I look at dedicated
> ISDN circuit prices, ouch, and I am getting way to little for Frame Relay.

What you can do is get the $25 metered ISDN account for the customer,
and have your PM3 dial the customer (typically a T1/PRI is not metered).
This reduces the cost for the customer and should mean more sales.
Be careful on the type of equipment you use here, since some don't
support receiving a call that good (Ascend Pipelines and Livingston
ORUs work great for this, 3Com doesn't).

-- Dale E. Reed Jr.  (       IEA Software, Inc.      |  RadiusNT, Emerald, and NT FAQs Internet Solutions for Today  |