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Understanding the Basics of SIP Trunking

Running a successful business requires a solid communication strategy that prioritizes customers. Bad customer experiences can cost the global economy a total of $3.7 trillion, and poor call quality is responsible for a sizable portion of lost sales. From dropped calls to grainy sound quality and the inability to adapt operations to customers’ preferred hours, analog phone systems heavily restrict your business’s potential growth and can create poor customer experiences. 

Stakeholders throughout your organization are likely aware of just how problematic analog phone systems can be as they actively look for options to stand out for superior, versatile calling. Two solutions that will rise to the top are SIP trunking and VoIP.

Before selecting the right choice, it’s important to know exactly how SIP trunking works, where it differs from analog and VoIP systems, and what implementation will look like. With this knowledge, you can compare SIP trunking providers to find the best fit for your organization.

Before SIP Trunking, There Were Analog Phone Systems

Many businesses today still rely on older analog Public Switched Telephone Network (PSTN) systems. These setups use copper lines to create a direct connection between two speakers—or in the case of businesses reaching out to customers with cell phones, from copper landlines in the office to the customer’s service provider’s network center. 

Each call moves through several semi-analog processes to reach its destination. Users dial a number on their phone set, and the request is converted to electrical signals and sent to the terminal. The signal moves from terminal to terminal until it reaches a central office’s cable system. Once the signal completes the long distance to the recipient’s phone line, the electrical signal switches back to audio. 

The PSTN itself is comprised of centralized switches across the network that push the call onward from point to point. However, there are several points of failure running through analog calls, and quality can suffer enormously if your network isn’t robust enough. Long-distance calls are far more resource intensive and (as a result) more expensive. Increasing the size of a legacy phone line network is also costly, and the system is very reliant on hardware. 

These analog phone systems aren’t yet obsolete. Many businesses still rely on them, and they can hold your company back if you feel like you have to stick with the hardware you invested in.

What Is SIP Trunking?

SIP trunking effectively “digitizes” your PSTN so you can use modern calling and multimedia technologies via your existing phone network. Landline systems have a PBX (private branch exchange), which you can still utilize while modernizing your system. Via SIP trunking, you can make both PSTN-based and VoIP calls by using your physical PBX to make digitized calls and a hosted PBX to access more typical VoIP capabilities.  

SIP trunking gives you the best of both worlds by enabling VoIP-to-PSTN functionality. Your in-office business hardware has two main hubs:

  • Wireless devices like cell phones and laptops that connect to your wireless router, which connects to the on-site servers
  • Wired devices like phones and computers with apps that connect to the server

Both hubs connect to the LAN, and SIP trunking can send call and web conferencing data to a router, which sends it to a VoIP provider and PSTN phone system.

SIP trunking can use your hardware or virtual hardware so your team can make voice calls, conference calls, video calls, and other essential forms of communication. Your employees can automatically use the PSTN-based system, the internet, or both based on the particulars of the call and which option the prearranged settings determine is best. 

Some unique advantages of SIP trunking are: 

  • Compared to analog telephony
    • You can integrate your communication system with omnichannel SaaS and UCaaS.
    • Digital phone systems include add-on features that you can pick and choose between based on your company’s needs.
    • Call quality improves when operating over the internet.
    • You can scale your operations more easily and enable WFH options.
  • Compared to solely VoIP
    • You can switch between PSTN and internet-based telephony—if the internet goes down, your business can’t operate as efficiently.
    • You can choose the features you need rather than bulky packages that may offer extraneous (and costly) add-ons.
    • Your PSTN and past investments don’t go to waste.

Other common beneficial features of SIP trunking include toll-free numbers, free domestic calls, metered international calls, and improved security. Because it uses dual networks, you can create backup networks and routing options so your phones are covered for both phone line and internet outages. 

What to Consider When Purchasing a SIP Trunking Solution

There are several key factors to consider when opting for SIP trunking and small business VoIP solutions.


If your business isn’t up and running at a critical time, day or night, it’s important to know that provider support is available 24/7.

Backup and Redundancy

Ensure that your SIP provider has several redundancy provisions so that all call traffic can be rerouted to a backup network if one part goes down.

Bandwidth Needs

Because SIP works over an internet connection, businesses must consider all the hardware connected to that network, including phones, laptops, desktops, and tablets. Determine how much bandwidth you’ll need, and make sure the provider can accommodate your volumes.


A good SIP provider should walk you through their equipment and setup options. These options might include updating your PBX or key system to be SIP compatible. They should also supply a SIP gateway. Choose a provider that operates with recognized, professional, name-brand equipment.


Security is critical to a SIP trunking solution, and firewalls are essential when businesses are interacting with the public internet. Read contracts in detail to ensure that the SIP provider offers full liability in instances of denial of service attacks, data loss, and toll fraud.

Network Design

Engage a provider who will create a personalized, fast, reliable, and secure solution for your business.

Converting from a PSTN to SIP

When moving from an analog PSTN setup to SIP trunking, half the work is already done because your hardware is in place. SIP trunking can route multiple calls through a single line (rather than the analog one-to-one requirement), so you don’t even have to readjust many of your existing physical goods. 

Follow these six simple steps to convert from a PSTN to a SIP trunking service provider: 

  1. Audit your company’s communication needs. Determine your calling metrics and current network capabilities, but also consider options like web conferencing and video calls. 
  2. Research and compare multiple service providers to find one that aligns with your business-critical feature demands, growth plans, and budget.
  3. Negotiate with a SIP trunking service provider to create your agreement. Ideally, they should help your organization develop an installation, number porting, and implementation plan to minimize business interruptions throughout the entire process. 
  4. Reevaluate company policies and processes. SIP trunking does far more than upgrade your phone systems. Form committees of key cross-departmental stakeholders who can evaluate which features and benefits can be better utilized. Then, start making iterative changes in your operations to take full advantage of SIP trunking.

Benefits of SIP Trunking

Businesses that deploy a cloud-based solution can expect several benefits of SIP trunking, which include revenue savings, increased productivity, scalability, and business continuity.

Reduced Cost

SIP trunking is a less expensive voice solution, especially compared to traditional PSTN. Without the cost of installing and maintaining fixed copper wire networks, SIP trunking offers a much higher ROI.

Increased Productivity

Most systems with unified communications features offer unique personal mobility options to increase productivity. Employees can reroute calls to their mobile or home phones while maintaining the appearance of being on their business line.

Other features associated with unified communications include unified messaging, voice, and video conferencing applications.


SIP increases scalability by allowing your business to add capacity quickly and easily. Service providers sell PSTN lines in bunches. Increasing capacity requires a physical installation, which can take days to schedule and adds cost.

SIP allows customers to add channels virtually and, in many cases, far more quickly than traditional PSTN systems. Some ISTPs offer a bursting option, which allows temporary use of additional calling capacity without adding extra channels permanently.

Easier Maintenance and Disaster Recovery

With traditional phone systems, there are telephone sets, wires, and cables to maintain. Some of these components sit outside and are subject to wear and tear. When service goes down, repairmen search through a long trail of often difficult-to-access service points to find the problem.

With SIP trunking, points of failure are limited to computers, routers, and software. Repairs can be completed quickly and often remotely.

See How SIP Trunking Can Reduce Costs and Increase Productivity for Your Business

SIP trunking isn’t just a middle-ground approach between analog PSTN and VoIP options. Instead, it’s an option that offers both possibilities and results in much more secure business communications. At SIP.US, we provide clients with seamless transitions to SIP phone services and VoIP SIP trunks. Get started on implementing a practical business decision to see the advantages professional SIP trunking services can offer your organization.

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