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Xpander VoIP Blog

SIP Trunk vs PRI

Posted September 06, 2009

SIP trunk vs PRI is a key comparison that many businesses are making.  In the past, the PRI or Primary Rate ISDN line has been the gold standard in business phone service, that also came along with a gold price and a long-term agreement.  For this reason, you will never see a real small business (1 – 10 employees) with a PRI, it just doesn’t make alot of sense cost-wise and rarely does a small business have enough of a need for the features that a PRI offers to absorb the cost.  That being said, you will find a PRI at virtually every company that has upwards of 20 staff members in one location. 

Key PRI features:
- DID (Direct Inward Dial) phone numbers that are pointed directly at an extension, allowing for callers to be routed to specific people, voice menus, or voice mail boxes.
- Digital call service allows for the outgoing caller ID for each person to be set to the same number every time, eliminating the traditional phone service dilemna where line 1 is in use and a call has to be made from line 2 which will then show the world the caller ID of line 2 instead of line 1.  The digital service of a PRI allows for the entire company to show the main advertised phone number on every call.

In a nut shell a PRI allows for companies to easily route callers to different employees, departments such as sales or support, voice menus, or even voice mail boxes.  This kind of a task would be very messy to try to accomplish using POTS, or plain old telephone service, due to the fact that you cannot have a phone number without a POTS line attached to it whereas with a PRI you can have each phone number following it’s own rule and sending callers through any open trunk available on the PRI.  The phone number being married down to the copper line is no more. 

Enter SIP trunk service, and things only get better!  SIP trunk service does EVERYTHING a PRI does along with some very powerful advantages:
1. SIP trunks can be ordered and provisioned one at a time.  PRI service is delivered over a T1 copper pair which means you are forced to buy 23 trunks at a time.  This means when you step up into a PRI you need to buy a minimum of 23 trunks worth of service, and once you’ve grown enough to use all 23 trunks, you will be forced to get another PRI and another 23 trunks of service.  The ability to add one trunk at a time disappears in the PRI world; however this is not true with SIP trunks.  With SIP trunks you can buy 1 at a time, always based on the true number of simultaneous calls you want your business to be able to handle.

2. SIP trunks are not installed on site physically, they are provisioned over existing IP networks and delivered across a WAN.  PRI service is delivered over a T1 copper pair which must physically be brought into the suite.  This gives SIP trunk service tremendous advantages such as the ability to ring to phones across multiple geographic locations at the same time.  You can have a customer service staff that works purely from home dispersed across the country, or IN another country, and they can all receive calls that come in on your customer service number!  Think about it, if a company with a PRI loses electricity due to a major storm then they will lose their phone system until the electricity comes back on.  SIP trunks are not physically installed on site which means calls can seamlessly route to other locations without missing a single call. 

SIP trunk service has now become the gold standard in business phone service and it comes along with better pricing, and the ability to order one at a time, on demand.  This allows for even 2 and 3 phone companies to have the same service levels as fortune 1000 companies; while allowing fortune 1000 companies to save boatloads of cash for services that are more flexible, scalable, and redundant.  At this point the SIP trunk is here to stay for as long as we can see into the future!


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