What Is SIP Trunking? How It Works, Benefits & How to Get Started

Business communication has moved far beyond traditional phone lines. Modern companies rely on internet-based tools that offer more flexibility, lower costs, and advanced features. 

And one of the most effective options is SIP (Session Initiation Protocol) trunking. 

This guide explains what SIP trunking is, how it works, the benefits (plus potential drawbacks) for your business, and the steps to get started.

What Is SIP Trunking?

Session Initiation Protocol (SIP) trunking is a way to deliver voice and multimedia communications over the internet instead of traditional phone lines. Using SIP, an application-layer protocol, it sets up, manages, and ends communication sessions between two or more endpoints—helping businesses cut costs, increase flexibility, and modernize their phone systems.

The term “trunking” refers to the consolidation of multiple communication channels or lines into a single, logical connection, known as a “trunk.” SIP trunks provide Voice over Internet Protocol (VoIP) connectivity between an on-premises phone system and the public switched telephone network, also known as PSTN.

If your office already has a PBX for internal calls, SIP trunks give it the connection it needs to make and receive calls with the outside world through the internet.

Is SIP trunking for everyone?

A SIP trunking provider is an affordable option for many small businesses, but it may not be suitable for everyone. 

For most companies with stable internet, it eliminates the need for physical lines and makes it easy to add or modify phone service without disruptions or new hardware. SIP trunking technology lets companies upgrade their PBX to an all-digital phone system. SIP service providers like Nextiva are known for their flexibility and cost-effectiveness, especially for businesses with high call volumes.

However, since it relies on your internet connection, businesses with poor bandwidth, unreliable connectivity, or strict regulatory requirements may run into issues.  

Another thing is that SIP trunking is a more technical solution for business voice functionality. It operates similarly to HTTP, which is the basis of browsing web pages online. SIP was adopted by the open-source community and served as a catalyst for business phone services. Additionally, SIP’s capabilities extend beyond phone service to include broader messaging functions.

Just like a traditional phone line subscription from a landline provider, SIP trunking is provided by an SIP provider. An excellent SIP trunking service lets you use your existing PBX equipment to transition into an internet-powered telephone network.

Plus, you can also use an SIP phone as part of your unified communication system. You can synchronize all your communication channels in real time. This way, you’ll enhance productivity, collaboration, and efficiency across your company.

Now that you know what is SIP trunking, let’s see who its best for.

Who can benefit from SIP trunking?

SIP trunking is a valuable solution for businesses of all sizes, particularly those with:

• High call volume: SIP trunking can significantly reduce communication costs for businesses with frequent calls.
• A need for scalability: Businesses with fluctuating call needs can easily adjust their SIP channel.
• A desire for advanced features: SIP trunking unlocks a range of features that can improve communication efficiency.

If you’re still unsure about SIP trunking, Jake from Nextiva gives a great explanation in this 2-minute video:

How Does Session Initiation Protocol (SIP) Trunking Work?

SIP trunking works as an intermediary between your business phone system and the Internet Telephony Service Provider (ITSP). The diagram below shows how calls flow from a SIP phone (VoIP) in a business to the outside world:

SIP trunking replaces traditional phone lines with a virtual connection, allowing your business to make and receive calls using your existing internet connection. It acts as an intermediary between your on-premises phone system and the Internet Telephony Service Provider (ITSP) that delivers your service.

Think of it this way: Traditionally, businesses relied on physical phone lines to connect calls. SIP trunking bypasses these lines by converting voice calls into digital data packets that travel over your internet network. This eliminates the need for expensive installations and clunky hardware.

Direct inward dialing (DID) numbers: Enhancing flexibility

Direct-inward dial (DID) and SIP trunking go hand-in-hand.

DID numbers are a helpful feature you can use with SIP trunking. They provide a cost-effective way to assign specific phone numbers to employees or departments within your company.

Here’s how it works:

• Your ITSP assigns you multiple phone numbers, each linked to a specific SIP extension within your PBX system.
• Incoming calls with a specific DID number automatically route to the designated extension, eliminating the need for a receptionist or auto-attendant.
• The beauty of SIP trunking with DID is the elimination of separate phone lines for each number. You only pay for the service itself, reducing infrastructure costs.

Using DID numbers with SIP trunking, you can enhance call management for various departments like customer service, sales, or even individual employees, improving overall communication efficiency.

Benefits of SIP Trunking

Here are the benefits of a SIP trunk.

1) Cost savings and efficiency

With a traditional phone line, you may be paying for extra features you aren’t using, equipment maintenance, and high charges for long-distance and international calls.

With SIP trunking, you’ll experience simplified pricing, usually charged per user or per minute (if you want). This comes with the extra benefit of predictability in your recurring expenses.

You get the choice between metered and unmetered SIP trunk plans. 

2) Virtual presence

SIP creates a unified virtual presence. It allows individuals and businesses to choose when and how they would like to be available.

For example, calls and messages can be forwarded to your assistant if you’re in a meeting or routed to a smartphone if you’re on a business trip.

Thanks to SIP, you’ll have centralized communication. We all communicate in more than one way: multiple devices at home, just as many (or more) at work, texts, video chat, etc. SIP grants users one “address” for all these devices and applications.

As a result, your interactions remain frictionless, no matter where you are.

3) Room for growth and scalability

When you’re looking to grow your company, your business needs will change, and you need your technology to grow with you. 

With SIP trunking, you’ll combine your communications across channels and multiple offices into a single network. Your call volume or the number of concurrent calls will likely increase as your company grows. 

There is no need for new IP infrastructure or waiting to speak to a customer service agent just to add new phone lines! With SIP trunking, you can do all of that on your own, on demand.

4) Reliable technology

Traditional telephony service can be disrupted due to phone failures, bad weather, or a damaged telephone pole.

Luckily, SIP trunking with VoIP boasts higher reliability. This means that you can keep using your phone even if it fails. Calls can be routed to other lines, offices, or mobile devices.

Drawbacks of SIP trunking

While SIP trunking offers many advantages over traditional telephony services, it also has some potential drawbacks:

1) Dependence on internet connectivity

SIP trunking relies on your internet connection to transmit voice call into digital data. If your internet goes down, your phone system will be inoperable. This can be a major issue for businesses that depend heavily on reliable phone communications.

How to overcome it: Implement redundant internet connections from different providers, or use a backup like 4G/5G cellular data to ensure continual internet connectivity.

2) Quality of Service (QoS) issues

Since voice data travels over the public internet, latency, jitter, and packet loss can degrade call quality if the internet connection is not correctly optimized for real-time communications.

How to overcome it: Implement QoS prioritization policies on your network equipment to prioritize voice data. Use a dedicated internet connection for SIP trunking traffic.

3) Security vulnerabilities

SIP communications are transmitted as data packets, making them vulnerable to interception and hacking if not correctly secured.

How to overcome it: Use encrypted SIP trunks, enable security features like firewall protections, authentication, and data encryption, and implement robust cybersecurity practices.

4) Power dependency

Unlike traditional analog phones that derive power from the telephone line, SIP phone systems require power.

How to overcome it: Deploy a backup battery or generator for SIP phones. Consider keeping analog phone lines for emergency use.

PRI vs. SIP Trunking vs. VoIP

While Primary Rate Interface (PRI), SIP Trunking, and VoIP are related technologies used in voice communication, they differ in their capabilities and implementation. 

Here’s a side-by-side comparison:

• PRI uses traditional phone lines, making it inflexible, costly to scale, and potentially obsolete.
• SIP trunking uses the internet to connect your business phone system to the public telephone network, providing cost savings, scalability, mobility, and advanced features.
• VoIP is the broader technology of making calls over the internet. SIP trunking is one method of delivering VoIP calls, using the SIP protocol to set up and manage those calls.

Feature	PRI	SIP Trunking	VoIP
Technology	Traditional phone lines	Internet Protocol (IP)	Internet Protocol (IP)
Scalability	Limited, requires additional physical lines	Highly scalable, no physical line limitations	Highly scalable, no physical line limitations
Cost	Higher costs for maintenance and scaling	Lower costs, no physical line expenses	Lower costs, no physical line expenses
Mobility	Limited to physical locations	Supports remote workers and mobility	Supports remote workers and mobility
Features	Basic voice calling	Depends on the specific protocol used (e.g., SIP)	Advanced features like video conferencing, integration with business apps
Flexibility	Rigid, aging technology	Flexible, adaptable to changing needs	Flexible, adaptable to changing needs
Future-proof	May become obsolete as telecom providers phase out support	Future-proof as it uses IP networks	Future-proof as it uses IP networks

For modern businesses, SIP trunking and VoIP solutions are generally more future-proof, cost-effective, and feature-rich compared to the aging PRI technology.

How to Get Started With a SIP Trunking Service

Transitioning to a SIP trunking service is straightforward but requires some key steps. 

Here’s what you’ll typically need to make the switch to SIP trunking:

• Reliable Internet connection: Since calls travel over your internet, a stable and high-speed connection is crucial for clear call quality.
• SIP-compatible PBX system: Your PBX acts as the brain of your phone system. Ensure it’s compatible with SIP technology, or you may need an upgrade. Your SIP trunk provider might offer hosted PBX solutions, eliminating the need for on-premise hardware.
• VoIP phones or softphones: For making and receiving calls, you’ll need phones that work with SIP technology (VoIP phones). Alternatively, if you prefer to keep your existing phones, SIP adapters can convert them for use with any VoIP call.
• Network connection: While voice calls travel over the internet, your phones themselves might still require a separate network connection for features like internal calls and intercom functionality.

Here’s how to get started:

• Assess your needs: Determine how many concurrent calls you need to support, decide if you want to keep your existing phone numbers, and consider any advanced calling features like auto-attendant, video conferencing, or call recording that are must-haves.
• Choose a SIP provider: With your requirements in mind, research reputable SIP providers that can support those needs at a reasonable cost. Make sure they’re compatible with your current PBX system or offer a hosted PBX solution. Also, check their uptime guarantees and customer support offerings.
• Prepare your network: Before making the switch, prepare your network infrastructure. Ensure your internet has enough bandwidth for VoIP calling and configure your router/firewall to allow the necessary SIP traffic. Setting up a dedicated voice VLAN or QoS rules to prioritize voice packets is recommended.
• Port your numbers (if applicable): If you’re keeping your existing phone numbers, you’ll need to request number porting from your current provider to the new SIP provider, which can take 1-3 weeks typically.
• Configure your system: Once the numbers are ported, configure the SIP trunk connection between your PBX and new provider, program your numbers, calling rules, auto attendant, and other settings, and thoroughly test inbound and outbound calling.
• Train your staff: Make sure to properly train your staff on using any new phone system features and provide instructions for things like making external calls through the new system.

With our plans, we give you all of the above control and power over your cloud PBX — and more. We also have an award-winning customer service team to help you with anything you may need along the way.

Move to the Cloud with Nextiva SIP Trunking

SIP trunking is engineered for cloud-based communications to revolutionize how businesses provide redundant voice and multimedia communications. IT leaders are tasked with replacing obsolete analog systems with cloud-hosted ones for lower cost, greater scalability, and stronger business continuity.

This modern approach replaces traditional phone lines, allowing businesses to make and receive phone calls, conduct video conferences, and send messages from a centralized location.

With Nextiva SIP trunking, your business can scale its communication capabilities without breaking the bank. Get your customized quote today — and mix and match solutions to meet your needs.

SIP Trunking FAQs