What is Sip Trunking and how does it work?

By Jane Sheeba / April 23, 2015

What is Sip Trunking and how does it work?

SIP trunking is basically a VoIP, or Voice over Internet Protocol based on the Session Initiation Protocol (SIP). ITSPs (Internet Telephony Service Providers) use it to provide telephone services and unified communication like instant messaging, data sharing, desktop sharing, audio, and video and web conferencing to customers with private branch exchange and unified communication facilities.

What Is SIP Trunking?

SIP trunking is a kind of standard communication system for voice and video that allows organizations to use VoIP instead of conventional phone lines.  The VoIP systems use the internet rather than phone lines for calling purposes. VoIP Users can also call numbers having conventional phone lines but if both parties have SIP then the call takes place entirely over the internet.

SIP Providers

The aforementioned activities can take place on an organization’s private or even public internet connection through a SIP provider. SIP Trunking is a powerful and flexible solution that allows SMBs to decrease business communication costs and resources, while retaining a truly remarkable quality of service at the same time. SIP providers also known as ITSPs provide the Public Switched Telephone Network (PSTN) services based on a “per minute” pricing model. 

How Does SIP Trunking Work?

SIP trunking relies completely on internet services and because of it Voice becomes just another data service delivered through a data network. SIP trunking basically consists of three parts:-

  • An ITSP
  • An enterprise edge component which could either be a firewall having SIP support or an edge device connected to the firewall.
  • A PBX or a private branch exchange. It is the key feature of SIP trunking that converts ordinary voice calls to VoIP calls.

It requires a public network, irrespective of whether it is a video call, voice call or video conferencing. That is the main function of the SIP providers who help in transporting and terminating SIP calls.

An important element of SIP trunking is the Session Border Control (SBC). It is a device placed on the border between the public network provided by telephony service providers and the organization’s private network. It acts as a traffic cop of SIP trunking as it checks every session passing between the networks and determines where it should be routed.

Before deploying SIP trunking systems, the enterprise or the organization must be aware of the effect it will have on the network bandwidth and the challenges that may arise.

Benefits and advantages of SIP Trunking

SIP trunking has recently gained popularity not just because it is the next best thing but because it is extremely beneficial for enterprises as it simplifies communications and network, enables new services and reduces expenses considerably. The countless benefits of SIP trunking have made it all the more significant in the fast developing communications industry. Some of the major benefits of SIP trunking are:-

Better economy and cost effective

As a result of SIP trunking, business enterprises save a fair amount of money. Studies show that they save nearly 20-60% as compared to old conventional phone lines. Also, SIP trunking allows cheaper long distance calls as a result of which they become almost equivalent to local calls.

SIP trunking can be tweaked to suit a business’s needs-during peak business seasons they can scale up calling capacity or scale it down during slow seasons. They can setup what they need and then expand as the business grows. The company pays for only the lines they need as opposed to paying for the excess analog lines which are not needed.

Easy maintenance

SIP trunks are virtual; therefore they do not need expensive installations of circuits and termination points. There is no physical connection to a phone company, hence there are no wires, circuit boxes, or hardware and multiple phone lines are reduced to a single point of entry.


SIP trunks are more dependable than conventional phone lines. If the system fails, the SIP providers can reroute the services to make sure there is no disruption of services (for SIP lines visit Amcom). If the customer is working remotely or if the line is busy and the customer is away, the calls are routed to his mobile phone, thus avoiding missed calls.

More services

A large number of services like voice calls, video conferencing, recording calls, maintaining address books are available.

Unifying the network

It allows the company to merge its voice and data networks into a unified single network connection.

Optimum utilization of bandwidth

It helps to maximize the company’s current Internet bandwidth by adding the voice traffic to your existing service.

ROI is almost instantaneous

It provides the fastest ROI of all.

Switching over to SIP trunking is one of the smartest moves a company can make in the field of technology. Introducing this has a tremendous impact on how people work, collaborate and communicate now and in the future and marks the transformation from old PSTN connection to Internet.

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About the author

Jane Sheeba

is an entrepreneur and online business consultant. She shares her wellness tips at Slick Wellness. If you are into starting/running an online business and want success with life and business go here.

1 comment
john - April 25, 2015

Thanks for the post, i had known VOIP but not about SIP. Now i can understand something.

Kind Regards

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