The ultimate guide to
SIP Trunking

The days of the traditional phone system are numbered, with digital-based telephony emerging as the future of business communication. And with good reason as businesses are leveraging these new technologies and realizing the benefits including cost savings, increased reliability and call quality and flexibility.  

The technology behind digital-based telephony is SIP Trunking which allows businesses to make and receive phone calls and other forms of digital communication, over the internet instead of traditional phone lines. SIP Trunking is fast becoming essential to businesses as the traditional phone system, the Public Switched Telephone Network (PSTN) which runs on copper and ISDN lines, is rapidly moving online with cloud-based solutions.  
In this guide we’ll cover: 

  • What is SIP Trunking 
  • How does SIP Trunking work?
  • Benefits of SIP Trunking?
  • SIP Trunking / VOIP
  • What is the future of SIP Trunking?
  • How Pure IP can help 

What is SIP Trunking?

SIP (Session Initiation Protocol) Trunking is a technology that connects a Private Branch Exchange (PBX) to the internet, enabling businesses to make and receive phone calls through an internet connection. In SIP Trunking the ‘trunk’ is the virtual phone line that allows you to make calls to anyone with a phone number over the internet.  
SIP Trunking replaces traditional phone lines by utilizing Voice over Internet Protocol (VoIP) technology to transmit voice data over an internet connection. With SIP Trunking, businesses can make and receive calls to any phone number, whether it's a traditional landline or another VoIP phone. 
SIP Trunking is a flexible solution for businesses of all sizes, from small startups to large enterprises. It allows businesses to easily scale up or down their phone services as needed without the need for additional hardware or infrastructure. This makes SIP Trunking an ideal solution for businesses that experience fluctuations in call volume or need to expand their phone services rapidly. 

How does SIP Trunking work?

SIP Trunks work to connect a company’s current phone system, which is either an IP enabled PBX or a Media Gateway (typically a more traditional PBX), to the internet. The PBX system is responsible for managing and routing incoming and outgoing calls and the SIP Trunk connects that PBX to the internet through VoIP. 

They are made up of these key components: 

  • Channels: The digital version of the traditional phone line. Each SIP channel allows one outbound call and one inbound call simultaneously. SIP channels can be added or removed virtually which means there is no wiring required. 
  • Trunks: Usually, companies will have multiple SIP lines which are bundled into trunks. The trunk works as a conduit between the company phone connection and it’s Internet Telephony Service Provider. It facilities inbound and outbound calls between the corporate network and other phone and data networks.  
  • SIP protocol: SIP (Session Initiation Protocol) is a signaling protocol used to initiate, maintain, and terminate real-time sessions that involve video, voice, messaging, and other communications applications and services. 

To set up a SIP Trunk, a business needs to work with a SIP Trunk provider, who will provide the necessary software and hardware to connect the PBX system to the internet. Once the SIP Trunk is established, the business can make and receive calls over the internet just like they would with traditional phone lines. 
The SIP Trunk provider typically charges a monthly fee for the service, which is based on the number of channels or concurrent calls the business needs. This makes SIP Trunking a cost-effective solution for businesses that need to make a high volume of calls. 

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What are the benefits of SIP Trunking?

SIP Trunking offers a number of benefits for businesses, including: 


With SIP Trunking, businesses can make and receive calls from anywhere in the world, as long as they have an internet connection. This allows businesses to easily set up remote offices or work from home arrangements without the need for additional hardware or infrastructure. And with the hybrid working patterns common across the workforce today, the flexibility enabled through SIP Trunking is crucial to support the modern workforce. 

Cost Savings 

SIP Trunking can help businesses save money on their phone services. By utilizing VoIP technology, businesses can avoid the high costs associated with traditional phone lines, such as line rental fees, long-distance charges, and per-minute charges. Additionally, SIP Trunking allows businesses to make and receive calls from anywhere in the world, eliminating the need for expensive international calling plans. 


SIP Trunking is a scalable solution for businesses that need to expand their phone services quickly. Unlike traditional phone lines, which require additional hardware and infrastructure to add new phone lines, SIP Trunking allows businesses to fluctuate as needed without the need for additional equipment. 

Call Quality 

With traditional phone services, issues like telephone pole maintenance and inclement weather could cause interruptions with an analog phone line. SIP Trunking allows for calls to be rerouted to bypass network issues. Also, SIP Trunks are designed with ample bandwidth for high-quality calls to ensure issues like echo and drop-outs are minimized.  

Call Reliability 

SIP Trunking is a reliable solution for businesses that need to ensure their phone services are always available. SIP Trunking providers typically offer redundant systems and failover capabilities, ensuring that businesses can make and receive calls even in the event of an outage or system failure. 


Your SIP provider should have specific protocols in place ensuring the security of your SIP Trunk solution. Look for a SIP Trunking provider with a strong track record of providing a secure and reliable service with a strong security policy. And also consider features like multi-level authentication and data encryption to keep calls and data safe from attacks.   

What is the difference between SIP Trunking and VoIP?

Voice Over Internet Protocol (VoIP) is an industry term that is limited to voice calls that are made over the internet, instead of through analog phone lines. SIP is a broader term and whilst it uses VoIP technology for voice calls, it supports other multimedia services like video, messaging and conferencing calling.  

What is the future for SIP Trunking?

With PSTN and ISDN shutdowns happening worldwide, SIP Trunking is poised to become the main method of voice calling. But as cloud technology advances and the telecommunications industry continues to evolve, it's important to consider what the future holds for SIP Trunking.  

The global SIP Trunking market is expected to grow at a compound annual growth rate of 10.5% by 2026. That growth is being driven by the increasing demand for cloud-based communication solutions and the need for businesses to reduce their communication costs.  

We also expect market growth to continue based on the integration of SIP Trunking with other communication technologies such as Unified Communications as a Service (UCaaS) and Contact Center as a Service (CCaaS). By integrating these technologies, businesses can create a seamless communication experience for their employees and customers. For example, employees can use the same interface for voice, video, and messaging, while customers can reach businesses through multiple channels such as voice, email, chat, and social media. 

We can also expect to see more advanced features being added to SIP Trunking. For example, artificial intelligence and machine learning can be used to improve call quality, identify and block spam calls, and provide personalized experiences for customers. Features such as real-time call analytics, call recording, and speech-to-text transcription can provide businesses with valuable insights into their communication activities. 

How can Pure-IP help you with SIP Trunking?

Pure IP is an agnostic managed services provider which means we can add voice to your unified communications platform of choice, whether that be Microsoft Teams, Zoom, Webex, Azure, Contact Centre or a traditional PBX. All our services are underpinned by cloud-based SIP technology and rich in integration capabilities, to support any hybrid/remote working set-up.

We also use SIP technology for our SIP Connect service which connects analog and on-premises devices to the cloud environment. SIP Connect works by creating a single SIP endpoint in the Pure IP voice network to which SIP registered devices, such as video conferencing units and Analogue Telephone Adapters (ATAs) can be connected to consolidate services. 

Benefits of SIP Connect include:

  • Consolidate your services and management
  • Extend the life of your legacy systems
  • Gain centralized visibility over physical devices
  • Provide a unified user experience
  • Integrate your services
  • Port number ranges without having to order a new number for your legacy device, such as a fax machine
  • Provide added flexibility to relocate physical devices 
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