What is SIP Trunking?

What is SIP Trunking?

SIP trunking is provided by SIP providers, which are similar to traditional phone companies, except SIP providers give access to phone lines over the internet (and SIP service is significantly less expensive – sometimes as much as 75% less).

  • Costs less – Saves money on your business phone system
  • Scales easier – Makes it easy to scale your operation quickly

Many companies use VoIP within their phone system on the Local Area Network (LAN) to connect to IP phones.

SIP trunking also uses VoIP to take advantage of shared lines, such as a company’s internet connection, to allow more flexibility in communications.

SIP Trunking – How it Works

SIP (and SIP trunking) is the standard communications protocol for voice and video in a Unified Communications (UC) solution across a data network.

SIP Trunking eliminates the physical connection to a phone company. There is no hardware, wiring, or gateways to maintain for connection to the PSTN (phone service provider).

A SIP “trunk” is installed virtually over your business’s existing internet connection, therefore replacing the need for traditional analog phone lines.

Reducing multiple phone lines into a single point of entry has a huge impact to reduce charges for incoming lines and the IT cost associated with the maintenance of those lines.

Please note:  Many companies still need analog lines for things like fax machines and alarms.   In those cases gateways and dedicated PRI trunks will be needed.

Benefits of SIP Trunking

Cost Savings

Cost savings is probably the biggest advantage of SIP Trunking and they can be substantial. SIP trunking can:

  • Lower a company’s monthly phone bills
  • Reduce a company’s IT and maintenance fees
  • Remove constraints on the telecommunications technology

SIP trunking allows companies to only pay for the number of lines they need as opposed to getting locked into excess analog lines or partially-used T1s and PRIs. The savings are realized by purchasing only the necessary number of channels needed. This allows companies to make more efficient use of communications costs and reduce wasted resources.


Because SIP trunking uses a virtual connection, adding lines or modifying service is relatively simple.


SIP trunking with VoIP allows a company telecom group to set up and expanded quickly.

Support costs

Less maintenance – Your IT group no longer had to maintain analog and IP infrastructure

SIP Trunking vs. PRI

Basically, PRI and SIP trunking are two different ways to “connect” your phone system to the outside world. On the most basic level, SIP Trunking uses your internet connection to make phone calls, while PRI uses a dedicated physical connection.

Pros – PRI:

  • Quality of Service is guaranteed
  • It works with older phones that aren’t compatible with VoIP

Pros – SIP

  • Usually more cost-effective for businesses
  • Scalability – quickly and easily modify  service
  • Connections are virtual, so no physical connection

Cons – PRI

  • Typically more expensive than SIP
  • Connections are physical and new lines have to be installed when your company grows
  • Require in-house IT staff to maintenance

Cons – SIP

  • Quality of Service is not guaranteed, as internet connections can introduce lag and delay if not configured correctly or there is insufficient bandwidth.
  • Does not work easily with older analog technology deployed at a business location