SIP Trunking Explained

A SIP (Session Initiation Protocol) trunk is a system that enables corporations using a set up PBX to implement real-time communications like VoIP. By connecting any SIP trunk to a central traditional PSTN (public switched telephone network) telephone system, organizations may communicate over IP outside the business. In addition, companies are able to substitute traditional fixed PSTN lines with an IP telephone system connected externally via a SIP trunking service, thereby making an individual channel for media components which include voice, video and digital information. For that reason, a SIP trunking service usually delivers increased price savings plus enhanced dependability.

How SIP Trunking Operates

SIP trunking mixes connections for digital data along with speech right into a single line. By becoming a converter between an older telephone system and a business’ internet connection, a good SIP trunking system allows the data network to carry voice traffic. SIP trunking features ordinarily incorporate local and long-distance calling, E911, directory listing and caller ID, which all blend perfectly into a company’s pre-existing telephone system.

Here’s a hypothetical demonstration of how SIP trunking performs in the average business: A San Francisco-based salesman places a long-distance telephone call to a customer located in New York City employing a dialing prefix and the local-area number. The phone call either originates being a IP call or is transformed into one prior to it leaves the office and then travels most of the way over the IP network of the system supplier, subsequently falls down again to the PSTN as soon as it gets to its end of contract point. Given that a substantial portion of the phone call journeyed within the IP network at no additional cost instead of within the PSTN, the service provider like Allstream in Canada can (and will) ask for merely a percentage of what the standard fee would be with no IP connection.

3 Basic Elements of SIP Trunking


An IP-based PBX talks with all endpoints over an IP system. In addition, it changes calls amongst VoIP users on local lines while enabling every end users to readily share numerous external phone lines. The typical IP PBX may additionally switch calls from a VoIP user and a traditional-telephone individual, as well as amongst a pair of traditional-telephone users in the same way which a traditional PBX does.


The function of any ITSP (internet telephony solution provider) is always to guarantee connectivity to the PSTN from an IP network for cellular and permanent transmission devices. Additionally it carries IP calls through an exclusive IP network or public Internet.

Border element

The border element makes it possible for connectivity between an organization IP network, the PSTN and an external IP-carrier network. The border element could be a SIP-capable firewall or a SIP-enabling edge device linked to the firewall software, or it may be a switch to transfer calls directly into and out of the PSTN. Border elements tend to be managed by the service provider.

Note that a service supplier may include SIP trunking as a possible component of an IP-phone-system offer; it should just be separated into hybrid options should there be a need to keep some locations over a standard TDM (time-division multiplexing) system, which will connect to the entire IP infrastructure by means of various border components as well as a SIP trunking service.

Advantages of Sip Trunking

A SIP trunking service benefits corporations just by:

  • Reducing the necessity to get pricey (and less suitable) TDM-gateway equipment facilities or desktop gear
  • Cutting down the need to acquire gear, just like managed-media entrance devices, to interface between IP voice and the PSTN
  • Lowering month-to-month expenditures, given that merely one connection for info plus voice is needed
  • Removing the need for PRI (primary rate interface)/BRI (basic rate interface) connections, reducing telephone costs
  • Permitting businesses to contract out their PSTN connectivity to some alternative party, decreasing long-distance charges
  • Delivering points of presence in several U.S. areas to ensure that companies can establish local telephone numbers rather than counting on a 1-800 phone number
  • Accessing the benefits of a hosted VoIP platform, while not discarding present investments in a classic telephone system

Common Sip Implementation Problems

Whenever corporations try to combine hardware from different suppliers inside of a single IT atmosphere, complications may happen. Numerous equipments dependent upon the SIP protocol are definitely no different. That’s why corporations ought to determine guidelines intended for interfacing a PBX implementation with an ITSP to lessen incompatibilities.

SIP trunking may also cause security dangers. Luckily, SIP-server and -proxy systems can control the circulation involving SIP traffic, allowing any IT manager to make sure correct routing, employ confirmation and validation policies and minimize threats.

As for quality, corporations would probably be wise to establish quality-of-service contracts to their providers prior to signing the contract. Fortunately, steps such as the suitable provisioning of connections along with prioritizing audio traffic might help stop slowdowns and enable for proper scaling. What’s more, a network-monitoring solution can help look for a real-time traffic route designed for greater value and dependability.

Author Bio:

Patrick McTosh has deeply immersed himself into the IT world over the past decade. From his early days tinkering on his own sites, to his Computer Science Engineering days at McGill University, Patrick has had his own successes as a small business owner and freelancer, and now passes on his success to other small business owners as a consultant.

(Don't worry, we won't spam you)