ISDN PRI 23/24 Ch's

ISDN PRI 23/24 Ch's

Post by Mike Hutchin » Wed, 14 May 1997 04:00:00



I may be installing a ISDN PRI line and was wondering about which config
to use.

What are the benifits and drawbacks of using it native (23b+d) or With
Robbed bit signaling (24b).

Thanks Mike

 
 
 

ISDN PRI 23/24 Ch's

Post by Reid Simpso » Thu, 15 May 1997 04:00:00



> I may be installing a ISDN PRI line and was wondering about which
> config
> to use.

> What are the benifits and drawbacks of using it native (23b+d) or With
> Robbed bit signaling (24b).

> Thanks Mike

Let's straighten out the terms, first.

T1 is the physical layer (layer 1), which describes a medium that
contains 24 64,000 bit/sec timeslots, along with some line management
overhead (the "superframe").

Primary-rate ISDN (PRI) introduces two protocol layers on top of T1,
described by Q.921 (layer 2) and Q.931 (layer 3) to provide a call
signalling over one of the time slots (the D, or "delta", channel) for
the other 23 time slots (the B, or "bearer", channels).

Robbed-bit signalling is a different mechanism that uses 8,000 bit/sec
to carry the call signalling on each of the 24 timeslots.

The net result is that PRI B channels can carry a maximum data bandwidth
of 64000 bit/sec and robbed-bit channels can carry a maximum data
bandwidth of 56000 bit/sec. Trade off is therefore 23 calls of 64000
bit/sec vs. 24 calls of 56000 bit/sec.

Of course, availability and pricing for fixed and recurring charges may
make one more favorable over the other, so you need to weigh the
economics along with the technology. In addition, your expected usage
and/or billing model for the consumer of your T1 data services might
affect this as well. If you charge by the hour, then more calls at lower
bandwidth (robbed-bit) gives you more income. If you charge by the data
load, then you receive more income by minimizing the call signalling
load on the line (PRI).

To further compound your decision, PRI allows you to use a single D
channel to carry call signalling for several T1 lines connected to a
single piece of equipment. This is called NFAS (non-facility associated
signalling). So, 'n' T1 lines using PRI NFAS will yield 1D + (23 +
((n-1)*24)B channels.

So expansion plans and equipment costs need to be figured into your
equation as well.

Hope that wasn't too long-winded ;^)

Reid.



 
 
 

ISDN PRI 23/24 Ch's

Post by Reid Simpso » Thu, 15 May 1997 04:00:00



> I may be installing a ISDN PRI line and was wondering about which
> config
> to use.

> What are the benifits and drawbacks of using it native (23b+d) or With
> Robbed bit signaling (24b).

> Thanks Mike

Let's straighten out the terms, first.

T1 is the physical layer (layer 1), which describes a medium that
contains 24 64,000 bit/sec timeslots, along with some line management
overhead (the "superframe").

Primary-rate ISDN (PRI) introduces two protocol layers on top of T1,
described by Q.921 (layer 2) and Q.931 (layer 3) to provide a call
signalling over one of the time slots (the D, or "delta", channel) for
the other 23 time slots (the B, or "bearer", channels).

Robbed-bit signalling is a different mechanism that uses 8,000 bit/sec
to carry the call signalling on each of the 24 timeslots.

The net result is that PRI B channels can carry a maximum data bandwidth
of 64000 bit/sec and robbed-bit channels can carry a maximum data
bandwidth of 56000 bit/sec. Trade off is therefore 23 calls of 64000
bit/sec vs. 24 calls of 56000 bit/sec.

Of course, availability and pricing for fixed and recurring charges may
make one more favorable over the other, so you need to weigh the
economics along with the technology. In addition, your expected usage
and/or billing model for the consumer of your T1 data services might
affect this as well. If you charge by the hour, then more calls at lower
bandwidth (robbed-bit) gives you more income. If you charge by the data
load, then you receive more income by minimizing the call signalling
load on the line (PRI).

To further compound your decision, PRI allows you to use a single D
channel to carry call signalling for several T1 lines connected to a
single piece of equipment. This is called NFAS (non-facility associated
signalling). So, 'n' T1 lines using PRI NFAS will yield 1D + (23 +
((n-1)*24)B channels.

So expansion plans and equipment costs need to be figured into your
equation as well.

Hope that wasn't too long-winded ;^)

Reid.


 
 
 

ISDN PRI 23/24 Ch's

Post by David Lesh » Thu, 15 May 1997 04:00:00



>Let's straighten out the terms, first.
>T1 is the physical layer (layer 1), which describes a medium that
>contains 24 64,000 bit/sec timeslots, along with some line management
>overhead (the "superframe").

Not quite. That's "DS-1"...

T1 is a facility; 2 pairs of copper, with repeaters every 6000 ft.
It *carries* DS1.

Quote:>Primary-rate ISDN (PRI) introduces two protocol layers on top of T1,

.....

--

& 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

 
 
 

ISDN PRI 23/24 Ch's

Post by David Richar » Fri, 16 May 1997 04:00:00




Quote:>I may be installing a ISDN PRI line and was wondering about which config
>to use.

>What are the benifits and drawbacks of using it native (23b+d) or With
>Robbed bit signaling (24b).

They are two very different services, sold at different rates, requiring
different software interfaces on your end. Either circuit can be used for
analog or data calls.

PRI over T1 is 23 data channels of 64K, while 'channelized-T1' is 24 channels
of (generally) 56K, with the 'robbed' bits used for signalling.

Without knowing what you're using it for, what hardware you're connecting,
and what the two variations cost, there's no way to say which would work
better in your application.

Just because most dialup server hardware can work with either configuration
doesn't make them totally interchangable.
--
David Richards                             Ripco, since Nine*-Eighty-Three
My opinions are my own, IRS withstanding   Public Access in Chicago
Proud to be the 5,000th least-important    Shell/SLIP/PPP/UUCP/ISDN/Leased
usenet-abuser, by the official GSUA.      (773) 665-0065 !Free Usenet/E-Mail!

 
 
 

1. ISDN PRI D-Channel (23 or 24)

        I am having trouble bringing up the D channels on my 4700. I
have 2 ISDN PRI's from MCI. MCI does not see the D channel up. The
T1 is up (continuity), the D channel is not.

        Specifics:

        controller T1 0
        framing esf
        linecode b8zs
        pri-group timeslots 1-24
        !
        controller T1 1
        framing esf
        linecode b8zs
        pri-group timeslots 1-24
        !
        interface serial 0:23  
        (.....)

        This looks to me like channel 23 is configured as the D
channel. MCI shows the D channel is supposed to be on channel 23 of
their T1. I tried changing to "interface serial 0:24" - but that
didn't work.

        How do I specify channel 24 as the D channel?  

2. Haiku program?

3. T1<->23 or 24 BRI Equipment?

4. Best Movie/Animation Format for LARGE files

5. Didot release?

6. "Processed an NCP with a bad subfunction length, station XX (NCP 23 24)"

7. Announce DJGPP and Win 2K/XP beta testing availabbility

8. Monitoring port 23 and 24 on Cisco 2924XL-C

9. Significance of ":23" on ISDN PRI interfaces

10. Smurf amplifier attacks involving 24.6.230.169, 24.8.22.81, 24.1.13.39, 24.13.156.131, 24.8.18.47

11. So Calif Telephone Show Saturday, Feb 24, in Placentia Presby. Ch.

12. What is *Mar 16 04:26:24: wanted ',' got '-'?