What SIP trunking is & how it improves communication

What is SIP trunking? Session Initiation Protocol explained

SIP trunking is a means of operating phone systems over the internet, instead of using a traditional phone line. As a main component of modern CPaaS platforms, SIP trunking allows businesses to communicate more efficiently with employees and customers. If you're new to the industry, understanding SIP trunking fundamentals will help you effectively scale your business communications.

Using SIP trunking, businesses and individuals can place and receive calls from multiple different clients or handsets, all of which share the same dedicated internet communications channel, the "trunk", and all of which use the same protocol, SIP, to connect, maintain, and disconnect calls.

In this guide

• What is SIP?
• How does SIP trunking work?
• SIP vs. PRI: Key differences
• SIP trunking provider comparison
• Key features and benefits
• Getting started with Telnyx

What is SIP?

SIP stands for Session Initiation Protocol and is a standard which describes how phone systems can establish calls, maintain the connection between phone systems so that voice and data can be transmitted when a call is active, and terminate the connection when the call ends. SIP trunks do not require any hardware installations or servicing from telecom operators, so they can be set up, scaled, and configured much more easily than legacy PRI systems.

How SIP trunking works with VoIP and PBX

SIP and Voice over Internet Protocol (VoIP) are both protocols that describe voice and data communications carried out over the internet. VoIP is an umbrella term that encompasses many different protocols for voice communications, including voice calls. SIP is a protocol that describes how VoIP calls are established, maintained, and disconnected. As such, SIP is a subprotocol that enables VoIP. For a deeper dive, check out our SIP vs. VoIP guide.

A Private Branch Exchange (PBX) is a business telephone system that switches calls between multiple users on the same connection, usually within the same organization or enterprise. Businesses use a PBX to provide a single phone line for their business, instead of leasing multiple Public Switched Telephone Network (PSTN) lines for their multiple users or staff.

An organization's PBX must have a connection to the PSTN in order to make and receive calls outside the organization. This connection can take the form of a PRI circuit, or, more commonly, a SIP trunk. A PBX can be implemented as an on-premise piece of physical equipment (an on-premise PBX), or a cloud-based hosted PBX or virtual PBX managed by an external SIP trunk provider.

SIP trunks vs. SIP channels

In SIP trunking terminology, there is often confusion between SIP trunks and SIP channels. Channels are often referred to as SIP lines, as they operate just like a traditional phone line that can handle one incoming or outgoing call at a time. As such, SIP trunking capacity can be increased by adding more channels.

Unlike traditional PSTN-based telephony or PRI implementations, channels can be added without any additional infrastructure or configuration. This means that SIP trunking is much more scalable than traditional business telephone systems.

SIP vs. PRI: The key differences

The main difference between SIP and PRI is that SIP is an internet communications protocol, whereas PRI is a voice technology based on physical phone lines. SIP trunks do not require any hardware installations or servicing from telecom operators, so they can be set up, scaled, and configured much more easily than PRI systems. Because of these efficiencies, SIP trunking is often much cheaper than using PRI for business telephony.

"Quality SIP trunking demands that your provider take measures to combat latency, jitter, and packet loss. In order to address these issues, your SIP trunk provider needs to have its own private network to carry the traffic themselves and eliminate the public internet where possible."

— David Casem, Co-Founder & CEO, Telnyx (INCOMPAS Member Profile)

SIP trunking provider comparison

When evaluating SIP trunking providers, consider factors like global coverage, pricing model, scalability, and integration capabilities. Here's how leading providers compare:

Note: Pricing and coverage may vary. Telnyx is highlighted as a recommended option due to its private global network infrastructure, which reduces latency and improves call quality compared to cloud-only providers.

Key features and benefits of SIP trunking

Common SIP trunking use cases

SIP trunking supports a wide variety of business communications scenarios. Whether you're building a contact center solution or creating custom IVR call flows, SIP trunking provides the foundational connectivity you need.

• Enterprise unified communications: Connect distributed offices with a single, unified communications platform
• Contact centers: Handle high call volumes with elastic scaling and intelligent routing
• Remote workforces: Enable employees to make and receive calls from anywhere
• Voice AI applications: Power conversational AI with low-latency voice infrastructure

Industry solutions powered by SIP trunking

Modern SIP trunking integrates seamlessly with industry-specific solutions. For healthcare organizations requiring HIPAA-compliant communications, visit our healthcare solutions page. Financial services firms needing secure, compliant voice infrastructure can explore our financial services solutions.

Getting started with Telnyx SIP trunking

Setting up SIP trunking with Telnyx is straightforward. Our Elastic SIP Trunking service offers businesses pay-as-you-go SIP trunking with no minimum commitments. This allows for easy scaling—add or remove channels dynamically based on current demand.

Telnyx has introduced advanced redundancy and failover mechanisms, ensuring that SIP services remain reliable even during network disruptions. Additionally, businesses can configure call failover policies, adding more resiliency to their voice communications.

For step-by-step setup instructions, visit our SIP trunk configuration guide in the Telnyx Help Center. You'll also find configuration guides for popular PBX systems including FreePBX, Asterisk, 3CX, Cisco, and Avaya.

Why choose Telnyx for SIP trunking

Telnyx operates a private global IP network specifically designed for real-time communications. Unlike providers who rely solely on the public internet, our infrastructure minimizes latency, jitter, and packet loss—delivering carrier-grade call quality worldwide.

With Telnyx SIP trunking, users can count on carrier-grade quality and low-latency communications. Our Mission Control portal and APIs allow you to build your own scalable solution with highly configurable features for better control over all elements of your calls, including cost.

Ready to get started? Sign up for a free Telnyx account and set up your first SIP trunk in minutes. Contact our team of experts to learn how you can leverage Telnyx SIP trunking for your business.

Related resources

• SIP trunking architecture: What is it, and how does it work?
• Understanding SIP trunk channels and how they work
• SIP trunking and DID: Everything you need to know
• HD SIP: Smarter voice, smarter calls, AI ready

Got SIP trunking questions or tips? Join the Telnyx subreddit. https://www.reddit.com/r/Telnyx/