With advancements in technology, many businesses and enterprises have switched to SIP trunking for better communication purposes. However, most multi-site businesses initially had a network for voice, the other for data, and connection to the internet before availing a SIP trunk service. 

The voice network used to be controlled by a PBX (private branch exchange) which uses PRI (primary rate interface) to connect to the PSTN (public switched telephone network). LAN is used to connect everyone via a firewall to the internet and in most cases to a private data network.

The complexity increases with each new branch location. However, today’s advanced IP networks and implementation of SIP trunking eliminates PRIs, most of the PBX, vendors, and the entire network while still maintaining high-quality calls and resiliency.

In this article, you will be learning about what is SIP trunking, how it works, its benefits and the cost associated with it. Also, see how SIP trunking compares to VoIP and things to consider before making the switch. 

What is SIP Trunking?

Session Initiated Protocol (SIP) trunking is a telephone service delivered via the internet. While SIP trunks can be delivered by other means, the internet is the most common delivery method. It is important to know that SIP trunks are provided by an ITSP (Internet Telephony Service Provider) instead of the traditional phone company. 

A SIP trunk service helps organizations to increase productivity in their workplace. With a single IP PBX, all network management, maintenance, and configurations can be accomplished with fewer resources from a centralized command center. It can also enable other technologies like unified communications which enhances collaboration for greater productivity and flexibility. 

In SIP trunking, the voice becomes an application that can then be virtualized. It has its bandwidth which helps to accommodate demand and business continuity, and disaster recovery planning is simplified because of it.

Benefits of SIP Trunking

A SIP trunk is a virtual equivalent to a traditional business phone line. It is the use of voice to facilitate the connection of private branch exchange to the internet. On the other hand, traditional voice services require a physical interface such as a digital PRI circuit. 

With SIP trunks, IP based data networks are leveraged to deliver audio, video, and rich media services. The separation from the physical circuit enables SIP based voice services to be delivered very dynamically. Moreover, the SIP trunking service hit its limit only by the amount of bandwidth available on the wide-area network connection.

benefits of sip trunking infographic

1. Cost Savings

One of the main benefits of SIP trunking service is the cost savings. The amount of SIP trunking cost savings depends on the distribution of the organization and the number of PSTN trunks currently in use. Also, very beneficial for small companies as it will help to cut down call costs dramatically.

2. Integration with the cloud

SIP trunking allows the integration of a unified communications strategy into a centralized platform. SIP trunking supports the cloud strategy and collaboration of different companies or organizations. 

3. Ease of Communication

Implementation of several SIP trunk services allows your communication to be more resilient. Also, in the case of an emergency, you can easily switch between any of the SIP trunks and it is easy to move or divert fixed lines anywhere. Also, in case of failures, calls easily route to other phone lines. 

4. Flexibility

SIP trunking is extremely versatile, easy to scale up or down, and the ability to add trunks as needed can be done depending on volumes of calls. 

5. Easy Mobility

SIP trunking is not bound to a particular location and comes with easy mobility. So, users can conveniently change offices without informing the clients or customers. 

6. Number of Channels

While using SIP trunks, you can easily choose the number of channels as per your requirement. 

7. Eliminate VoIP gateways

Since all phone calls come in via IP while using SIP trunks, it eliminates the need to buy and manage VoIP gateways. 

How Does SIP Trunking Work?

SIP trunking carries your calls over data or the internet connection. The process looks like you make a call, and it goes through the PBX. At this stage at PBX assuming it has reached its capacity, if you got the SIP function on there, this is an extension. It means that PBX would take the call from the SIP trunk.

Then, it comes through your service provider, and from there, it delivers the call to the person you are calling. Now let’s assume you are calling somebody within your company who is using SIP but based in another location. In such a scenario, you make a call and it goes through PBX. 

Then it goes through the SIP trunk and comes through your service provider. At this stage, the service provider recognizes that the call you are making is to another SIP user. Then the service provider would take the call and deliver to their SIP. Then from their SIP, it goes through the PBX and the call gets delivered.

Another situation is when you’re making a call to somebody who is not using SIP but using VoIP which will be then a fully hosted solution. In such a case, you will make a call and go through the PBX. It comes through your SIP, goes to the service provider but this time, it goes to the router that they have on their site. From that router, it will be sent.

How Much Does SIP Trunking Cost?

The cost of SIP trunking depends on a variety of factors. The price of SIP trunking is based on subscription, calling rates, add-on costs, and setup fees.

  • Subscription: It is about the price per DID number or the SIP channel
  • Call Rates: SIP trunking price also depends on the cost per call done or per minute rate for all the outbound calls
  • Add-on Fees: This includes extra fees for add on features such as call recording
  • Setup and Installation: One-time expense for setup and installation. However, most of the providers are now not charging this fee

It is important to understand that the calling rates majorly determine the cost for SIP calling since it depends on country to country. Calling rates are determined based on origination and termination country for the call. 

Moreover, the rates are constantly changing per minute during the call. However, you can expect a setup fee anywhere around $0-$150 and monthly costs anywhere between $25-$50 per trunk most of the time.

SIP Trunking Vs VoIP

It is important to understand the difference between SIP trunking and VoIP which will provide you better clarity regarding their specifications and usage.

  • No. of Sessions: VoIP calls are simply those calls that are made over the internet which can only handle one type of session. But, SIP is a protocol meant to make those calls and can connect multimedia sessions.
  • Transfer of Data: Moreover, VoIP is restricted or limited to transferring the voice data over the internet. But the SIP trunk can easily transfer multimedia data in the form of packets that include voice, text, or video.
  • Infrastructure: VoIP requires a computer to operate it’s software whereas SIP equipment can operate separately and does not require any computer
  • Security: SIP trunking is more secure as compared to VoIP since in SIP, you can get a direct connection to your network provider providing an extra layer of security.

Things to Consider Before Switching to SIP Trunking

It is important to cross-check and evaluate a lot of things before switching to SIP trunking or basically SIP trunks. This will ensure that you have satisfied the requirement to integrate SIP trunking within your business ecosystem and do not face any technical issues or difficulties.

Things to Consider Before Switching to SIP Trunking Infographic

Internet Bandwidth

It is important to know that the amount of bandwidth necessary to support SIP trunking depends. It is based on the voice codec used by the SIP provider. So, do check what is the internet bandwidth you are getting from the ISP before switching to SIP trunking. 

Analyzing the number of concurrent calls to support

Analyze the number of concurrent calls you will be supporting as this will help in determining the number of SIP channels and the required bandwidth. 

IP enabled PBX

IP enabled PBX does not require any additional hardware to use SIP. If your PBX is not IP enabled, then you may require additional hardware i.e. an inexpensive converter device called an ATA (analog telephony adapter) to use SIP. 

Selecting the Best SIP Trunk Provider

Selecting the best SIP trunk service provider as per your requirements is a crucial step. However, there are certain factors that you may consider while choosing the best SIP trunk provider based on your needs.

  • Secure and risk-free: While choosing the best SIP trunk provider, it is important to confirm that the SIP trunk has a well-secured network. Moreover, an anti-fraud system should monitor the system and protect against call scams or frauds.
  • Network: It is important to know whether the service provider is running its network or reselling SIP Trunks from other providers. Always prefer those service providers who have the ownership and control over their network and service.
  • Cost comparison: Make sure to do market research and look for competitive rates, but also to ensure that you are getting great quality service regarding SIP trunk.
  • Porting of numbers: Cross-check with the service provider whether all the existing numbers can be ported.
  • Tech Support:  Check with the service provider regarding tech support provided by them in case of technical difficulties or assistance. Also, to check them regarding their availability.


To conclude, SIP trunking plays a very important role in the world of business communications. SIP trunks provides businesses with a comprehensive communication solution that improves processes. Moreover, it comes with a lot of advantages such as connecting multiple offices and better engaging remote employees with user-friendly communication.  

Thus, many businesses are using this technology of SIP trunking which is helping them improve their workflow within and outside the organization while also increasing productivity among employees.