A SIP trunk might sound like a slow-paced elephant drinking game, but it’s actually some pretty cool technology behind modern business phones systems.

Let’s take a deeper look at this important technical aspect of telecommunications. SIP – pronounced like a "sip" from a cup and an acronym for Session Initiation Protocol – is a way for companies to send voice calls over Ethernet and TCP/IP services instead of old legacy phone systems. This allows you to eliminate the duplication of physical resources in your phone network, often lower your costs, and make your phone system easier to use.

How legacy networks operate

Older PBX – or Private Branch Exchange – business phone systems slog along with analog lines and Primary Rate Interface (PRI) circuits. These allow phones to make calls to the outside world over traditional landlines, but their popularity is dwindling as newer technologies do the job better and cheaper. What we’ve got here is a classic supply and demand scenario driven by three trends:

  1. Older connections have become more expensive as they see less use.
  2. As more organizations move to Ethernet-based phone calls, and prices go up for legacy connections, need drops further.
  3. More calls are moving to mobile phones at the same time the old infrastructure becomes increasingly obsolete.

PRI’s are also more complicated than SIP lines. If your company has two locations, one in San Diego and one in Miami for example, each one would have their own PRI circuit under the old model. This means you are essentially paying for the same hardware multiple times, one in each location. Further, while calls between your different branches would be routed between your Wide Area Network (WAN), any outside calls from employee mobile phones or similar devices will be going through the Public Switched Telephone Network (PSTN) into your PRIs before reaching the phone at either branch.

Like the branches of a treeSIP Trunk Tree Illustration

What is SIP trunking? A good way to think of it is as an actual tree trunk. A multi-location company without a SIP trunk has to essentially connect a bunch of different tree branches together with wire strings. Each branch has to be tied to other branches through its own PRI, like a wire. This labor-intensive process uses a lot more wire than anyone needs just in order to keep a tree up. SIP trunking replaces all of these individual connections, using the internet as a large trunk from which all other branches spring. A SIP trunk provider connects all of a company's branches to one central communication system. 

What SIP trunking changes

With SIP trunking, your different branches are connected through a SIP line. This provides the same service as a traditional phone line, but better. The difference is that a SIP trunk runs through your data cable, carrying your voice call traffic with it. SIP trunks pile on benefits beyond old-school smiling and dialing. For example, it enables caller ID services and other modern amenities, like counting certain cellphones that are connected through the SIP as company phones. This allows workers to more easily set up call forwarding from their office phones to their mobile devices. But if you are a business owner or IT manager, you’ve got an eye on the bottom line. If you have multiple offices and ax your old PRI networks, expect to drastically reduce the amount you spend on your phone service.

In summary

To sum it up, SIP trunking replaces PRIs in a company's networks and makes better connections and modern business phone systems improvements possible. It does all this while cutting the costs associated with duplicated PRI systems by instead pushing information through a WAN that is digitally connected to the company using it. 

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