What is SIP Trunking? A Mystery Exposed | Flowroute Blog

What is SIP Trunking? A Mystery Exposed

Posted on June 5, 2013 by Andrea Mocherman

You’ve been tasked with the responsibility of upgrading your business’s communication suite. Your first instinct is to google your options, and by doing so you’ve opened a giant nest of confusing acronyms. You’re not alone, and this wouldn’t be the first time someone has gone down this path. Let’s get you started off on the right foot by focusing on SIP Trunking.

I’ll start off with “SIP“. SIP is an acronym for Session Initiated Protocol, which is an industry (IETF) standard signaling protocol that introduces and manages digital connections. The protocol is used to initiate interactive user sessions over an internet connection. It’s used in quite a lot of digital communications including IMs, Skype, and just so happens to be the backbone of VoIP.

The second part of this term, “trunking“, refers to the telecom term “trunk“. A trunk is a circuit that carries a number of calls (also referred to as channels) at a time. You may recognize these acronyms, ISDN BRIs, PRIs, T1s, or E1s, the legacy versions of a trunk, which companies have paid an arm and leg for.

“SIP Trunking” is a connection between a private and a public domain. Let’s talk about domains.

There are private and public domains. A private domain refers to a part of the network connected to your PBX or unified communications server (typically everything you are responsible for). Public domain refers to the part of the network which allows access into the PSTN / PLMN. This is usually the responsibility of your internet telephone service provider (ITSP).

Putting all these concepts together, we have the complete SIP Trunking package – A VoIP connection between your PBX (private domain) and your telephone provider (public domain). It’s a modern day alternative to offering traditional legacy trunks. SIP trunking is what allows your VoIP calls to leave your local area network and reach your friends, family, and business connections.

SIP trunking benefits in a nutshell:

  • Cost savings. Your company can eliminate the need for PSTN gateways, out-dated and costly legacy trunks. We’re talking about a typical savings of 30-70% on your monthly phone bill.
  • Flexibility. Since this is IP-based, you can run your PBXs virtually anywhere and not have to worry about physical connectivity in most cases. This allows you to skirt around hardware limitations of legacy systems.
  • Scalability. You can ramp up your voice channels as needed, and much faster than installing a new T1/E1.
  • Stronger security. SIP can be much more secure than TDM when implemented correctly.
  • Easy integration. Getting setup with a PBX nowadays is a breeze. You have many options when it comes to ITSPs (more on choosing the right provider here) and the interop process is usually only a few clicks away.

What you need to take advantage of SIP trunking:

  • Own a PBX. Some common setups are software-based solutions, which can be installed on a server at your business location, at a datacenter, or you can choose to have it hosted in the cloud. There are also legacy physical PBX solutions, which your company may already own.
  • A SIP gateway. This feature is included with most software based PBX solutions. If you have a legacy system you will need to get gateway card or appliance to convert the SIP stream to a TDM stream.
  • An ITSP. Without this you’ll just be making calls internally, to yourself or your friends that are connected to your IP-PBX. Which is fun if you want to re-create a digital version of red cup telephones.

Resources for additional research:

Hopefully you’re now able to switch tabs back over to your Google results with more confidence. Once you settle on a SIP-capable PBX, the next big step will be to make sure you choose the right provider. Here’s a great article to read before shopping for your ITSP.

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