[asterisk-users] Benefit of PRI vs SIP trunk calls

[Joel Maslak]

On Thu, Jan 6, 2011 at 7:06 AM, Jim Dickenson <dickenson at cfmc.com> wrote:
> Are there reasons to prefer the use of PRI over SIP or SIP over PRI?

Assuming you are talking to connect a PBX to the PSTN...

PRI advantages:

1. Relatively little equipment between the PTSN and the PBX.  Less to
break or go wrong.

2. Simple to set up.  No need for QoS, routing, authentication, etc.
Of course if you only know IP, SIP is easier, but if you learn both,
ISDN is easier.

3. If compared to SIP over internet, PRI has guaranteed quality.
Granted, SIP *can* have just as good (and better) quality, just not
guaranteed if done over the internet (it can be guaranteed over a
private circuit).

4. Less latency/delay so there is less "talk-over".

5. FAX, high speed modem, TTY, etc, pass-through actually works.  (it
*can* work over SIP, but Asterisk just isn't quite there yet)

I run the PBX for my organization which has about 160 extensions.  I
wouldn't even think of doing anything but PRI for the main lines
because (A) for our size organization where we are located, we're
talking a couple hundred dollars a month difference between PRI and
SIP in cost so it's nearly break-even in cost which means cost
difference isn't a huge motivator, (B) it supports FAX, modems, and
TTYs - perfectly, (C) Quality is 100% consistent.  In addition, the
reliability is good enough that I'm willing to use it for 911.

Of course if this installation wasn't in downtown Denver, where ISDN
PRI is very cheap (a full CLEC 23-channel ISDN PRI costs roughly what
6 or 7 ILEC POTS lines cost), then SIP would be interested.

SIP advantages:

1. Cheap (at least SIP-over-internet)

2. Easy and quick to scale if you have bandwidth.

3. Great for disaster recovery if using SIP over internet

4. Very cheap to get "local" numbers from all around the world.

5. If using SIP over internet, easy to compare providers