ISDN PRI - How many DIDs ?

I came across some web info about assigning 40-100 DIDs in a single PRI trunk. I was looking at telco supplied Pri trunks and have always thought that you can only assign up to 23/30 B's and 1 D channel.

how is this possible? Is this where NFAS plays a role?

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Comments

pitviper

Don’t think if it as 1:1 relationship; you can have 23/30 concurrent calls (inbound and outbound combined). The “path” is determined by the available B-channels at the time of setup. I always get a block of (at least) 100 continuous numbers as it typically costs less than $5/month for the entire block.

So say we have an office with 60 or so phones and a single PRI – We can assign a DID to each phone (even though we only have 23 physical paths) because it’s unlikely that everyone will be on the phone at the same time.

Check this out if you really want to learn about telecom traffic prediction:

http://en.wikipedia.org/wiki/Erlang_unit

tokhss

Ok. that makes sense.. same concept of standard over capping data lines..i didnt know you can do that with voice lines.

chmorin

It is a similar concept. Some people think of a PRI as 24 POTS lines, which it a misleading way of thinking. With a digital PRI you have the ability to assign many many DID's into the location, the only limiting factor (that I have had to deal with) is concurrent calls between RBS and other signaling methods.

Sounds like you have it figured out now, I just wanted to chime in

tokhss

Hey Pit.. who do you purchase your pri trunks from ? as in which provider.

pitviper

tokhss wrote: »

Hey Pit.. who do you purchase your pri trunks from ? as in which provider.

Mostly ONE Com (recently bought out by EarthLink) and Verizon - I’ve done ports from just about every carrier in the north east though.

tokhss

company is called ONE Com ? as in one.com or onecom.com or ?

pitviper

One Communications

. Their footprint is mostly east coast I believe.

pitviper

PRI cost = local loop + port (just like a standard data t-1, usually around $400-$500/month around here), plus DID blocks ($5/month for 100 DIDs).

tokhss

Thanks!