What is SIP Trunking?

We’ve heard the question a lot: What is SIP Trunking?  In order to really understand SIP Trunking we have to understand the basics of SIP, how the Telephone system works, and where SIP Trunking fits into the larger picture.  This page is going to give you a high level overview of where SIP Trunking fits into the larger picture.

Quick Overview

At the end of the day, the final goal for your business phone system is to connect your employees to the Public Switched Telephone Network (PSTN); the existing network for reaching all phones around the world by dialing a 10 digit number.

The actual connection to the PSTN is handled by service providers around the world, so you have to connect your business to a service provider that has a connection to the PSTN.

Traditionally that connection would be to a Telephony Service Provider (Like AT&T, Verizon, and Windstream) via PRIs, Analog Lines, or Dynamically Integrated Services Lines.

Lastly you have to connect all of your different employees to that connection, so that they can communicate with each other and with the outside world.  In most cases this is where a bunch of phones connected to a Key System or PBX comes into play – a piece of hardware that manages the call routing of your employees.

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Your employees all use phones, connected through a Key System/PBX.  Your business is then connected to your service provider (using pri/analog lines) which has connections to the PSTN.  This is the general setup for your business phone system.

SIP Trunking Replaces…

SIP Trunking replaces the old style connection to your telephone service provider.  Rather than using a dedicated circuit for your phone calls, you connect your PBX/Key System to the public internet (there are some alternatives to this using a private connection, but that’s outside the scope of this post).

So how does your PBX communicate with the public internet?  That’s where SIP comes into play.

What is SIP?

SIP stands for Session Initiation Protocol – a set of rules that the IETF has decided on, that determines how a connection between two end points is setup, managed, and terminated over an IP based network. (Look for our ultimate guide to SIP coming out later this year)

The first major thing to understand about SIP is that it is designed to traverse an IP Network – therefor any type of SIP Trunking or SIP communication will go over an IP Based Network.  The two IP networks that everyone is familiar with are your internal LAN at your office and the public internet.

In order for your PBX/Key System to use the public internet it must be SIP capable.  Older style PBX/Key Systems are not compatible – and will require either an upgrade, replacement, or purchase of additional equipment.  In order to allow your phone system to communicate via SIP Trunking you have several options, you can: add a SIP capable module to your legacy PBX system, purchase an IP-PBX with SIP Capabilities,  purchase an ATA device, Session Border Controller (SBC), or other Media Gateway device that works as a translator between your old analog system and the SIP trunks coming in over your internet.

Buying SIP Trunks

Not all SIP Trunking services are created equally! In general, most of the SIP Trunk providers out there are going to give you the same type of service and quality of sound. You want to make sure, however, that you’re looking for a provider with redundancy, scalable packages, and a trial to test the service out.

It’s important that if there is some sort of disaster at the Provider’s location, that your SIP Trunks don’t go down.  You want to make sure that your SIP Trunk provider can grow with you as your business grows.  Lastly, ask for a free trial!  Make sure you can test your internet connection and hardware with the service provider before you sign on the dotted line.

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