What is SIP trunking? We explain the concept!

SIP trunking is a term that often comes up when talking about phones. But what are SIP trunks? How does SIP work, and how can your company benefit from the technology? We explain the concept and benefits of the technology.

What is SIP?

SIP stands for Session Initiated Protocol. It is the protocol that enables services for telephony and VoIP. The latter is also called IP telephony, broadband telephony, and Internet telephony. A SIP trunk is a virtual telephone line that allows you to make and receive calls over the Internet. A SIP trunk can control both voice and video calls and chat messages.


You can compare this to calling over the traditional, analogue telephone network, called PSTN (Public Switched Telephone Network). It is a network made up of copper wires that requires that you have a physical connection between two points to make a telephone call. For a long time, it was the backbone of all telecommunications.


But that is coming to an end. Instead, the demand for digital telephony services and cloud-based telephony solutions, SIP trunking, IP telephony, and cloud PBX is constantly increasing.


Read more: What’s the difference between VoIP and SIP?

What are SIP sessions and SIP phones?

A so-called SIP session is simply a call or a session via a SIP trunk. With SIP, you can establish sessions between two parties, a recipient and a sender. You can also park and forward calls and add more participants during the session.


A SIP phone is the same as a VoIP phone or a softphone – just different names of phones to make VoIP calls. SIP phones can be both software and hardware-based. A SIP phone as hardware works much like a regular phone but can receive and make calls over the Internet instead of the traditional phone network. Software-based SIP phones allow computers to function as telephones.

How SIP trunking works

A SIP protocol is text-based and similar to an HTTP protocol. SIP is the industry standard for communicating via voice and video over the Internet or an intranet. SIP uses VoIP to send information over the Internet. Here, a SIP trunk line is used instead of a traditional telephone line, whether you’re calling your colleague in another office or video chatting with someone internally.


When you get an incoming call, it is routed through your current telephone system using signal information that lets your phone know where the call is to be sent.


With SIP trunks, you can call anyone over the Internet – whether they use VoIP or PSTN. SIP trunking works in conjunction with a SIP-compatible PBX. It thus replaces the traditional copper wires.


A SIP trunk can handle multiple SIP channels/SIP lines, and each SIP channel operates a call, just like a traditional telephone line. With old-fashioned physical telephone lines, it was a time-consuming and complex task to increase the number of companies' telephone lines. A SIP trunk can handle unlimited channels, meaning you only need one SIP trunk. How many SIP channels you need depends on the number of calls within the company.


Guide  SIP trunk for your company – a complete guide  Get your guide here!


What do you need to use SIP trunking?

All you need is a connection in the form of an internet subscription and a SIP-compatible PBX where the traffic can be sent. Most new PBXs are SIP compliant, but if you have an older PBX designed for the traditional telephone network, you will need to upgrade to an IP PBX.

Benefits of using SIP trunking

A significant advantage of SIP trunking is that it is future-proof. The Internet will remain in 100 years, even though it may be designed differently. Regardless, it will be possible to connect calls similarly for a long time.


SIP trunking is also a robust and secure technology. No one wants a call to be interrupted, whether a phone call or a video conference. Should the connection be down, you can use SIP trunking to ensure that your calls are redirected automatically after a few seconds of interruption. 

Reduced costs

There are many benefits to calling via the Internet instead of the analogue telephone network. Perhaps the most obvious difference that attracts many is the reduced costs SIP can offer. Here are some reasons why you can reduce the cost of telephony: 


  • Lower initial costs – setting up SIP trunking is cheaper than using the traditional analogue network.
  • Lower call costs – you can call for free between your connected offices.
  • Reduced number of fixed subscriptions.
  • You don’t have to pay for maintenance for a specific operator's wiring.
  • Lower monthly line and DID (Digital Inward Dialing) rent as you do not have to pay to switch to more lines.
  • With SIP trunking, you can use local numbers and toll-free numbers to the same SIP trunk.
  • You only need to maintain one network as SIP trunking uses your existing data network. You can thus reduce the resources you had to manage the PSTN network.

Vad är en SIP-trunk? 2

Improved flexibility

SIP trunking is a scalable solution that allows you to be flexible. Is your most intense period around Christmas and New Year? Then you can choose to scale up when you know the call traffic will be heavier and then remove the extra lines during the low season. Remember that if you want to add more telephone lines, installing it takes a long time if you use the traditional telephone network.


With SIP trunking, you can quickly add more trunks and channels with DID (Direct Inward Dial) – it usually only takes a few minutes. Since SIP trunking enables DID, everyone in the office can have their own SIP line. And, it is also no problem if you move your office or open new ones – you can still use the same number.


Want to know more?

Telavox can help you with everything related to SIP, VOIP, mobile telephony, and PBX services. Feel free to book a complimentary demo and learn more about the possibilities!


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