T1<->23 or 24 BRI Equipment?

T1<->23 or 24 BRI Equipment?

Post by Bob Am » Sun, 02 Oct 1994 02:37:39



What is available to connect two remote offices via T1?

Ideally, I'd like to use a T1 on each end and provide:

*) Intercom service,
*) TCP/IP traffic (Ethernet),
*) (One/Several?) ISDN S/T or U lines.  I'd like to be able to use
   ISDN phones on one end and on the other end connect to the
   Intercom system or to the LD Company via POTS or ISDN.  Or to
   use, say, a Waverunner on one side and get thru the T1 to the
   main office, and then routed into the Ethernet on the other side.
*) Anything else ISDN provides, like FAX.

Do I need a PBX for all of this?  Certainly some kind of switch-like
routing seems necessary.

Perhaps just a device which converts T1 into 24 ISDN B channels,
and looks like an ISDN switch and provides, say, some S/T jacks.

How much traffic can fit on an S/T?  For example, can I put all 24 B
channels on the S/T bus concurrently without degradation or failure?
(I doubt it)

Bob Ames
UNIX & Telecom Administrator
Creative Computer Solutions

 
 
 

T1<->23 or 24 BRI Equipment?

Post by Fred R. Goldste » Wed, 05 Oct 1994 00:54:48



> What is available to connect two remote offices via T1?

Good question, actually, but one that opens up so many options!  (It
gives us consultants a good living.)

Quote:> Ideally, I'd like to use a T1 on each end and provide:
> *) Intercom service,

What do the two offices have for telephone service now?  If there are
PBXs, then tie lines via the T1 will do it.  Even without a PBX, there
are ways to derive voice channels from a T1, to mate different types
of telephone system.

Quote:> *) TCP/IP traffic (Ethernet),
> *) (One/Several?) ISDN S/T or U lines.  I'd like to be able to use
>    ISDN phones on one end and on the other end connect to the
>    Intercom system or to the LD Company via POTS or ISDN.  Or to
>    use, say, a Waverunner on one side and get thru the T1 to the
>    main office, and then routed into the Ethernet on the other side.
> *) Anything else ISDN provides, like FAX.
> Do I need a PBX for all of this?  Certainly some kind of switch-like
> routing seems necessary.

Several types of equipment terminate a T1.  A few examples:

* A PBX.  These typically handle 64 kbps data calls (period) too.
* A Data Service Unit.  This takes all of the bandwidth and makes
  it into one fat data channel.  Fractional-T1 DSUs operate on a
  subset of the 24 channels, as you specify.
* A channel bank.  This is a static (configure by plugging in cards)
  multiplexor.  Option cards of all sorts are available.  Each of
  the 24 channels is picked up by one card or another.
* A nodal processor.  This is like a fancy channel bank with software
  configurability, multi-T1 networking, etc.  Overkill for two sites
  but worth it for larger networks.
* A drop-and-insert mux.  This generally lets you pick off a couple of
  data channels (n*64k) while feeding the remaining channels into a PBX,
  Fractional-compatible Data Service Unit or whatever.

Quote:> How much traffic can fit on an S/T?  For example, can I put all 24 B
> channels on the S/T bus concurrently without degradation or failure?
> (I doubt it)

The ISDN Basic Rate S/T bus handles exactly two B channels (one BRI).
T1 is a different animal.

One common way to go: Get a T1 to your long-distance company.
Designate some channels for access to their network ("WATS"-style
services.)  Run others into a Fractional T1 for your site-to-site
needs (data, maybe some voice, etc.).  They can deliver ISDN Primary
Rate using one D channel and however many B channels you designate
(the rest used for "FT1" or individual-channel services).

If you have an ISDN system at one end and want for some odd reason to
remote a Basic Rate channel, you can use a channel bank equipped with
Adtran's BR1TE cards.  These take 3 channels and map 2B+D onto them.
They fit into standard D4-family banks so you can mix and match, or
use 8 to fill a T1.  That's a common way to deliver "virtual ISDN".