SIP and PRI Trunking: A Complete Guide to Phone Systems

SIP and PRI Trunking: A Complete Guide to Phone Systems

When managing business communications with the best phone systems, getting the most out of your monetary investment in services and useful features is essential. Telephone trunking, in which multiple phone conversations can be transported over long distances through a single line, is an efficient and financially sound option to consider for your company. The particular business needs of your organization will determine which system type you should invest in.

SIP Trunking

Most trunking systems have traditionally used “T1 lines” to connect a company’s phone system and its service provider. This is true for “SIP [Session Initiation Protocol] trunking,” which utilizes already installed IP-PBXs. T1 lines are the most readily available and cost-efficient telephone lines today. SIP trunking allows a business to connect with outside organizations in addition to its inter-office communications, all through a single SIP trunk line connected to a PSTN network. It most often uses the same Internet access used for data. The Internet telephone service provider supplies the SIP trunk line, and it eliminates the clunky bunches of physical phone wires once necessary with older telephone systems.

Because only three parts are needed to employ a SIP trunk line, this system is very cost-effective. The only requirements are:

  • A provider offering Internet telephone or SIP-trunking service,
  • A phone system that has a trunk side to enable SIP, and
  • An “enterprise edge device” capable of understanding and working with SIP.

With these three pieces, a business can increase its telecommunications reach, especially if an existing IP-PBX is installed.

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“PRI [Primary Rate Interface] trunking” is another option for transmitting many different voice and data communications amongst multiple locations. PRI, seen by many as an older alternative to the more modern SIP, is also based on the use of T1 lines, though telephone circuits not in place may need to be installed. Monthly rates and calling fees are often higher than with SIP. Still, PRI allows large numbers of voice lines at once (i.e., 23 at a time, compared to only 1 SIP at a given time), an attractive option for large businesses. But traditional PRI does tend to cost many enterprises more due to its older technology and equipment needs. It also does not include new popular features available with SIP, like IM-call screening and third-party interfacing.

The size of your business, the scope of its telecommunications needs, and budget flexibility should be all factor into a decision regarding whether to use traditional PRI or new SIP trunking technology. No matter which you choose, both options will increase your company’s productivity and ability to interact internally and with outside clients.

SIP and PRI in Action

SIP and PRI trunking are popular choices for businesses looking to expand their telecommunication capabilities with unified communications. Here are a few real-world scenarios where SIP and PRI technologies can be implemented:

Small Business

A small business with a limited budget may benefit from a communication solution with SIP trunking as it is more cost-effective. With SIP trunking, a small business can access a full range of advanced telephony features such as call waiting, voicemail, and conferencing. Since the system is based on an internet connection, it is more flexible and can easily be scaled up or down to meet changing business needs.

Medium-sized Business

A medium-sized business with multiple locations and many employees would benefit from PRI trunking. This technology provides more bandwidth and capacity for multiple voice and data communications. The PRI trunking system can connect different locations and can easily be expanded as the business grows. A medium-sized business can save on long-distance calling costs by combining all of its sites into a single phone system.

Call Centers

A call center that handles a large volume of calls every day requires a robust telecommunication system. SIP trunking can connect call centers to the public switched telephone network (PSTN) and provide advanced features like auto-attendant, call recording, and call queuing. SIP trunking is a cost-effective solution that can be easily scaled up or down to meet changing business needs. Call centers can also use PRI trunking to connect multiple locations and provide additional capacity for their communication needs.

Large Enterprises

Large enterprises with thousands of employees require a reliable and scalable communication system. PRI trunking can connect multiple locations and provide additional voice and data communications capacity. Large enterprises can also use SIP trunking to provide advanced call features and a more flexible solution. With SIP trunking, large enterprises can easily connect their existing phone system to the PSTN network and quickly scale up or down to meet their changing business needs.

The best communications system suited for your business with SIP and PRI will depend on your specific needs and budget. Regardless of your chosen approach, you can be sure that these solutions will help you increase productivity and efficiency while improving internal and external communication with clients.

SIP Vendor Selection Checklist

Here are a few things to consider when evaluating which system is the best fit for your unique needs:


Choosing and upgrading a SIP trunking system that can grow with your business is essential. Look for a provider that can quickly scale up or down the number of channels you need as your business evolves.

Quality of Service

Consider the level of voice quality your business requires. If you need high-quality, reliable voice service, choose a SIP provider that offers Quality of Service (QoS) guarantees.

Network Reliability

Ensure the PBX provider with SIP trunking has a reliable network with multiple redundancy options. This ensures that your business stays up and running even during network outages.

Support Network

Consider the level of support you need from your SIP provider. Look for a provider with a support team that is available 24/7 and can quickly respond to any issues that arise.

Price Comparison

Compare pricing from different providers and ensure you're getting a competitive rate for the services you need.

Product Integration

If you have an existing phone system, ensure the SIP trunking system you choose can easily integrate.

By considering these factors, businesses can choose the SIP trunking system that best meets their unique needs, ensuring high-quality voice service and reliable communications. Compare the best phone systems software with SIP and PRI capabilities to determine your business's next move. 

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