Dialing from BRI to PRI

Posted on 2005-04-01
Medium Priority
Last Modified: 2010-03-17
We have ISDN at our remote offices and clients for failover in case one of the PVC's goes down.  All of these connections from the remote offices are terminating to us on a single ISDN circuit.  The problem is that we can only support 2 concurrent dialin because all ISDN connections are Basic Rate.  

WHat is involved in switching the circuit that the clients dialin to to a primary rate, so everyone can dial up at one simultaneously?  I am assuming that we would have 23 spids (I've never worked on this)?   Would the cost of a PRI ISDN line (used occasionally onlly for backup) compare to say a full T1?  Suggestions?
Question by:cdesimone
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LVL 40

Expert Comment

ID: 13688082
No..  Primary Rate ISDN does not use SPIDs for its connections...  You essentially would be purchasing a full T1, which is what Primary Rate really is...  23 B channels and 1 D channel = T1 or 1.544 Mbps...

There are lots of T1 flavors around, depending on your location.  Make sure you do your research, and don't buy into those who try to sell you a fractional T1 with Bursting...  No matter what the sales people tell you, it is not a Full T1...

LVL 40

Expert Comment

ID: 13688126
Forgot..  the cost will depend on your location, but I can get a Full T1 in Ohio for under $500 / month..

Remember that a BRI ISDN is what you would normally use as a backup, as it is only on when you need it...  Therefore the very reduced charges over the monthly period.  What is your primary connection?  Have you considered getting Cable or DSL as a backup?  Then you could install something like what I have, a dual wan router to handle both connections...  I have a Xincom that does the job for me...


Author Comment

ID: 13698193
Thx for the replies.

We have the remote offices dialing to one spid, so once the two B-channels have a call, nobody else can dial in.  What I am asking is what could we do to make our current setup accept multiple isdn calls if the main line went down.  

I did notice that cisco has instructions for BRI to PRI connectivity.  How could this be implemented to provide for us to have more resilent backup confuguration.  

It just wouldn't be practical to redo all connections to DSL or cable unless we are absolutely out of options.
LVL 79

Accepted Solution

lrmoore earned 500 total points
ID: 13700119
Your PRI would have one phone number and support up to 11 multilink BRI lines (using both 64k channels for each link, or 22 of 23 PRI channels). Basically same as having just one SPID. Provider usually has something like a (700) + number for the remotes to dial into.
You would need a PRI Network module for your core router (in this case it is not the same as a generic T1, so you can't use a plain T1 WIC)
Just remember, that the PRI has long-distance and maybe even per-packet charges in addition to the monthly loop charge. The monthly $500 fee might look nice up front, but you could get hit with a bill for several $thousand if you have too much usage.

I've you already have the investment in the Cisco gear and BRI lines, it won't be difficult to upgrade the main site to a PRI.

Author Comment

ID: 13703566
I talked to bellsouth and pacbell about this and they said the same thing.  I was quoted 700 a month for unlimited usage.  Thanks for the headsup on the long distance fee.  

We have 16 lines that will dial in, so we'll just determine who needs one B channel, and who needs to multilink the B-channels.  

Good to have two ppl saying the same thing


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