atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telecom Service & Providers PRI VS DID Trunking

I need some help in deciding between a PRI or DID Trunking.

We have a location where we are tearing out the PBX and installing a Cisco IP phone system. The office consist of 8 total lines. (2 DID's, 1 main, 1 hunt, 1 fax, 1 vault and 2 for 911).

What makes more sense? PRI or DID Trunking? Any experience in this area out there?

DID trunking is inbound-only, so if you installed DID trunks, they couldn't be used to make outbound calls. You would need to have another set of trunks to handle outbound calling. Trunks via a PRI work in both directions on a call-by-call basis, so they can handle all system traffic both into and out of the system. The use of a PRI is the most logical choice.

It sure doesn't make much sense to use DID anymore. It also doesn't make much sense to tear out a PBX and replace it with Cisco, but that's another topic althgether.

Troy, What is a vault?

Not to mention PRI set-up time is faster in the network and you get instant return messages.

Why is this important? Because some carriers DONT charge for long distance if the call is under 6 seconds. This becomes important when you are doing a call center with outbound dialers.

Plus a PRI allows you more versatility, like Ed said.

Analog DID does not support CID, either...

Ed, I am confused by your comment. I thought you said in another pst that you use DID in your office, and it is great.

I think that the confusion was caused by my comment that it doesn't make sense to use DID anymore. What I intended to imply was that it doesn't make sense to use stand-alone DID 'trunks' that are dedicated for this purpose only. That's the understanding that I got from the original post.

Yes, my company has DID service delivered via a PRI in my office. PRI channels allow DID calls to arrive over the same circuit that an outgoing call might use (commonly referred to as "both way" trunks, although technically a misnomer).

It all depends upon what's needed of the PRI at the time and what trunks are available. That's what is nice about PRIs: Traffic dictates how trunks are managed (automatically) instead of a fixed "incoming-outgoing" structure that would be set up with standard trunks. PRI trunks change their purpose (direction) on a per-call basis.

With 23 channels on a standard PRI available, any one of them can handle an outgoing call OR an incoming call to a DID number. It's referred to as "call by call" service. The constant handshaking process that goes on between the phone system and the serving CO determines how each trunk's purpose is determined for each call.

To delve more deeply: The 24th channel of a T1 circuit that's delivering a PRI (the "D" channel), communicates between the CO and the phone system. It's sort of a "modem line" between them, so to speak. This is to determine what's expected of the other 23 channels ("B" channels). The B channels will individually process calls however they are told via information exchanged over the "D" channel. This occurs on a real-time basis.

Oh, and for all intensive purposes: ALL incoming calls to PRI trunks are effectively DID calls. It's up to the end-user's system installer to determine where these calls are routed.

PRI's are the way to go...Like Ed said you get all your trunks 2-way did..so the customer makes out in the end..due to the fact if business changes and there is a program with more outgoing calling they are all set..same with incoming. Plus around this part of the country all the carriers are making sweet deals on PRI vs DSS..guess they like selling them more also.
Just my 2 cents worth

Must be a bank application… Vaults require a standalone dedicated dial tone circuit just like elevators in many states.

Yeah, but that vault line should be plain ol' copper, as should the 911 lines. But, maybe their pockets are "deeper" than mine! John C. (Not Garand)