What is SIP Trunking and what is a SIP trunk carrier?

SIP trunking is a method by which business phone systems can operate using an Internet connection instead of a traditional phone line.

SIP Trunking:

Costs Less

Costs Less

Scalability Icon

Scales Easier


Offers More Reliability

SIP trunking is provided by SIP providers, which are similar to traditional phone companies, except a SIP trunk carrier gives access to phone lines over the Internet (and SIP solution services are significantly less expensive – sometimes as much as 60-80% less).

Find out why Sangoma is the leader in SIP trunking for SMBs 

How Does SIP Trunking Work?

SIP trunking works with VoIP phone systems (Voice Over Internet Protocol) and is based on SIP (Session Initiation Protocol).

Sangoma Sip Trunking

SIP, which is the basis of SIP trunking, is the standard communications protocol for voice and video in a Unified Communications (UC) solution across a data network.

SIP trunking eliminates the physical connection to a phone company. There are no hardware, wiring, or circuit boxes to maintain for connection to the PSTN.

A SIP “trunk” is installed virtually over your business’s existing Internet connection, therefore replacing the need for traditional analog phone lines.

Reducing multiple phone lines into a single point of entry drastically reduces charges for incoming lines and the IT cost associated with the maintenance of those lines. (Some organizations prefer to maintain standard lines for faxes and alarms.)

Sangoma Phone SIP Trunking

SIP Trunking with Your Phone System

Many companies already use VoIP within their phone system on the Local Area Network (LAN) to connect to IP phones.

SIP trunking also uses VoIP to take advantage of shared lines, such as a company’s Internet connection, to allow more flexibility in communications.

Traditional phone systems (that aren’t already VoIP-capable) can be connected using common VoIP gateways to take advantage of SIP trunking and reap the significant cost benefits.

What is a Direct Inward Dialing Number (DID)

Direct Inward Dialing number (DID) is essentially a virtual phone number that uses the existing phone lines to route incoming calls. With direct inward dialing, callers can connect to a phone extension directly without an operator. This offers convenience for both employees and callers alike. DID offers a cost saving on its own, and is less expensive when purchased with a SIP trunk.
Traditionally, when a DID is obtained from a phone company, charges are applied for the DID, IT and maintenance services, and the hardware connecting the shared physical lines or channels. A DID provided without these infrastructure costs is more affordable.

Discover which type of SIP trunking is right for your business

Benefits of DID SIP Trunking

Cost Savings Icon

Cost Savings

The cost savings and communications benefits of DID SIP trunking are substantial. If your business is experiencing any of the following, DID SIP trunking can likely help in a big way:
  • High monthly phone bills
  • Costly charges for incoming phone lines
  • Long distance charges
  • IT and maintenance fees
  • Constraints of limited communications technology
SIP trunking allows companies to only pay for the number of lines they need as opposed to getting locked into excess analog lines or partially-used T1s and PRIs. This allows companies to make more efficient use of communications costs and reduce or eradicate wasted resources. Utilizing DID numbers makes communication even more efficient and convenient since they can be routed to multiple DID numbers without the need for a physical line for each connection.
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When your company uses SIP services, you can instantly add new channels at a fraction of the cost you’d spend upgrading hardware. Because SIP trunking uses a virtual connection, adding lines or modifying service is fast and simple.


SIP trunking with VoIP increases reliability of services by providing a level of redundancy. When system failures and emergencies occur, SIP trunking providers can reroute services to a redundant data line or forward the PBX to mobile phones to keep your business up and running.

Other Benefits of SIP Services

  • Works with most modern phones
  • Ability to transfer and use your old phone numbers
  • Affordable phone numbers for all your team members
  • Less maintenance – No longer have to maintain analog and IP infrastructure

SIP Trunking vs. PRI (Primary Rate Interface)

If you’ve been shopping around for business phone systems, you’ve probably come across the term Primary Rate Interface (PRI). You’ll often hear people compare PRI to SIP trunking, and it’s important to know the pros and cons of each before making a decision. 

PRI and SIP trunking are two different ways to “connect” your phone system to the outside world. On the most basic level, SIP trunking uses your Internet connection to make phone calls, while PRI uses a dedicated physical connection.

PRI (Primary Rate Interface)

Uses Traditional Phone lines

SIP Trunking

Uses existing Internet connection
PRI Pros:
  • Quality of Service is guaranteed with Primary Rate Interface
  • Works with older phones that aren’t compatible with VoIP

PRI Cons:
  • Primary Rate Interface is typically more expensive than SIP carriers
  • Connections are physical and new lines have to be installed when your company grows
  • Requires in-house IT staff to maintain
SIP Services Pros:
  • Usually more cost-effective for businesses than Primary Rate Interface (PRI)
  • Scales quickly and service can easily be modified with SIP Carriers
  • Connections are virtual, so no physical lines

SIP Services Cons:
  • Quality of Service is not guaranteed, as Internet
    connections can introduce lag and delay if not configured correctly or there is insufficient bandwidth
  • Does not work natively with older analog or digital

Sangoma’s SIP trunking services were rated #1 in customer satisfaction

SIP Trunking vs. VoIP

SIP is a protocol that helps enable VoIP phone systems. So, while the two terms can seem like different services, they actually work to accomplish the same goal. VoIP systems and SIP services both work – to run your business phone system over your Internet connection and internal data network. Check out our VoIP Basics page to learn more about how VoIP works and how it can benefit your business.

Questions to Ask When Switching to SIP Trunking

To prepare your company for SIP trunking, you first need to consider a few questions.

How many people are on the phone at the same time during your busiest hours?

That will determine how many channels you will need. SIP trunks allow for quick and easy scaling, so you may add or remove channels as needed if you under or overestimate.

Will your call volume remain fairly consistent from week to week, or will it fluctuate?

With SIP trunking, you can purchase channels. When call volume increases, Concurrency Bursting allows you to burst beyond the number of channels you have. This is explained more on our SIP trunking pricing page.

Will you need to scale or add new users relatively quickly?

This is an important factor, particularly when deciding between on-premise and hosted phone systems. Click here to learn more about hosted vs. on-premise options.

What to look for when selecting a SIP trunk carrier?

Is Your Network Ready for SIP Trunking?

Network considerations that must be examined include total available bandwidth, Quality of Service, and firewalls. Upgrading your Internet connection may be necessary to ensure sufficient bandwidth to carry a new phone system on top of typical Internet usage for your company.

Quality of Service (QoS):
Equally important to bandwidth is Quality of Service. QoS prioritizes your voice traffic and ensures that your phone calls are going to get the bandwidth needed, regardless of what else is happening on the network. The vast majority of business grade network routers will provide QoS for your network.

A firewall is critical to maintain security both within a LAN and Wide Area Network (WAN). Though firewalls are a critical component to any business network, they must be configured correctly to work well with SIP trunking.

For safety, it is essential to add Enhanced 911 (E911). E911 is a feature of the 911 emergency-calling systems that places VoIP emergency callers with the appropriate resources by associating a physical address with the calling party’s telephone number.

Network Bandwidth Equation

Use the following simple equation to determine the necessary bandwidth to support your calls:

(number of concurrent calls at your company’s peak)


100 kilobits per second


bandwidth in Megabits per second (Mbps) needed for calls


SIP Trunking Pricing

SIP trunking pricing varies depending on how many channels you need. Per channel pricing, also known as “channelized”, is great for businesses that prefer a set, predictable monthly phone bill.

To see how much SIP trunking costs, check out our SIP trunking pricing page.

Wholesale SIP Trunking

Are you a carrier, service provider, or enterprise with large call volumes? 
Wholesale SIP trunking from VoIP Innovations, a Sangoma Company, may be right for you. With advanced value-added features like e911 and SMS/MMS, wholesale SIP trunks offer a competitive advantage to businesses who use a large number of trunks or who plan to resell as a service. 
In fact, industry analysts Frost & Sullivan call Sangoma’s carrier services the “modern approach to wholesale SIP trunking.” Download the free whitepaper to discover why!

How Can Sangoma Help You With SIP Trunking?

Now that you can answer, “What is SIP Trunking?”, we invite you to learn more about SIP solutions, DID SIP, SIP trunk carriers and more.

SIP Trunking by SIPStation

SIPStation is your VoIP Connection to the world. SIP trunking is easy to maintain and configure, can reduce costs, is reliable, provides business continuity, can be set up quickly and allows customers to consolidate infrastructure.

How Does SIP Trunking Work?

Still unclear about how SIP trunking works? A SIP trunk is the virtual version of an analog phone line. Learn more about how SIP trunking works from our Customer Success Team.

How Much Does SIP Trunking Cost?

SIPStation’s SIP trunking costs are ideal for businesses that prefer a set, predictable monthly phone bill. Learn more about SIP trunking pricing and plan features.

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