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SIP Trunk Providers

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Nextiva Office logo
 
Nextiva SIP trunking connects an enterprise PBX or IP-PBX with Nextiva's worldwide call routing infrastructure. Low-cost trunking and calling charges bring a quick ROI to this popular telephony solution.
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Nextiva SIP trunking connects an enterprise PBX or IP-PBX with Nextiva's worldwide call routing infrastructure. Low-cost trunking and calling charges bring a quick ROI to this popular telephony solution.
 
Virtual Office by 8x8 logo
 
8x8 offers SIP trunking as a standalone service. Users can also bundle 8x8 SIP trunking with Virtual Office, 8x8’s hosted PBX system, for a single-provider VoIP solution. Calls to other 8x8 sites are free with 8x8 SIP trunking.
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8x8 offers SIP trunking as a standalone service. Users can also bundle 8x8 SIP trunking with Virtual Office, 8x8’s hosted PBX system, for a single-provider VoIP solution. Calls to other 8x8 sites are free with 8x8 SIP trunking.
 
Vonage Business Solutions logo
 
Vonage Business Solutions is a cloud-based unified communication solution suitable for small and midsize companies. The solution offers a business phone system that enables businesses to connect their VoIP phone system to any internet... Read More
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Vonage Business Solutions is a cloud-based unified communication solution suitable for small and midsize companies. The solution offers a business phone system that enables businesses to connect their VoIP phone system to any internet... Read More
 
MegaPath logo
 
MegaPath is Business Voip software that works with medium to large-size businesses in any industry. The system offers companies Internet connectivity, unified communications, security services, managed networking services, and more. With... Read More
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MegaPath is Business Voip software that works with medium to large-size businesses in any industry. The system offers companies Internet connectivity, unified communications, security services, managed networking services, and more. With... Read More
 
AVOXI Core Cloud PBX logo
 
Since 2001, AVOXI has been developing call center and VoIP systems that serve the needs of businesses around the globe. With customers in 50 countries, AVOXI combines a telecom service with PBX and call center software in a hosted... Read More
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Since 2001, AVOXI has been developing call center and VoIP systems that serve the needs of businesses around the globe. With customers in 50 countries, AVOXI combines a telecom service with PBX and call center software in a hosted... Read More

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inContact Hosted Call Center logo
 
Used by contact centers around the world, inContact’s SaaS-based call center software maximizes the quality and minimizes the cost of each and every client interaction. This call center solution has all of the features your customer-focused... Read More
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Used by contact centers around the world, inContact’s SaaS-based call center software maximizes the quality and minimizes the cost of each and every client interaction. This call center solution has all of the features your customer-focused... Read More
 
ContactWorld by NewVoiceMedia logo
 
ContactWorld, created by NewVoiceMedia, is a unified communication platform for any size corporation. It offers standalone call center functionality, including automatic call distribution, predictive dialer, call recording, auto attendant,... Read More
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ContactWorld, created by NewVoiceMedia, is a unified communication platform for any size corporation. It offers standalone call center functionality, including automatic call distribution, predictive dialer, call recording, auto attendant,... Read More
 
Five9 Cloud Contact Center logo
 
Five9, an early adopter of SIP trunking, combines a wide range of network connectivity options including SIP trunks and gateways with one of the industry's most robust selection of cloud-computing solutions.
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Five9, an early adopter of SIP trunking, combines a wide range of network connectivity options including SIP trunks and gateways with one of the industry's most robust selection of cloud-computing solutions.
 
Solgari Cloud PBX logo
 
Solgari Cloud PBX is an all-in-one, fully integrated PBX solution that can be customized to meet the needs of businesses of various sizes. Features and functionality as well as users and locations can be added or removed on an as-needed... Read More
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Solgari Cloud PBX is an all-in-one, fully integrated PBX solution that can be customized to meet the needs of businesses of various sizes. Features and functionality as well as users and locations can be added or removed on an as-needed... Read More
 
SafeSoft Cloud Contact Center logo
 
Market Dialer's predictive dialing platform is a perfect fit for small and medium sized customer-centric businesses. Its efficiency boosting and scalable system has been shown to improve productivity by up to 400%.
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Market Dialer's predictive dialing platform is a perfect fit for small and medium sized customer-centric businesses. Its efficiency boosting and scalable system has been shown to improve productivity by up to 400%.

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Fonality logo
 
Built on the idea that big company phone features should also be available to small- and medium- sized businesses, Fonality offers robust functionality that fits the the SMB budget. Their suite of applications is both flexible and... Read More
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Built on the idea that big company phone features should also be available to small- and medium- sized businesses, Fonality offers robust functionality that fits the the SMB budget. Their suite of applications is both flexible and... Read More
 
Answer360 logo
 
Answer360 is a powerful business VoIP phone system ideal for small and mid-sized businesses. Features include call transferring, call forwarding, auto attendants, and message delivery via email.
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Answer360 is a powerful business VoIP phone system ideal for small and mid-sized businesses. Features include call transferring, call forwarding, auto attendants, and message delivery via email.
 
UNIVERGE 3C logo
 
UNIVERGE 3C, NEC’s software-based IP-PBX, is a sophisticated platform for unified communications and collaboration. Its comprehensive functionality helped it earn the 2014 Internet Telephony Product of the Year award from technology... Read More
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UNIVERGE 3C, NEC’s software-based IP-PBX, is a sophisticated platform for unified communications and collaboration. Its comprehensive functionality helped it earn the 2014 Internet Telephony Product of the Year award from technology... Read More
 
Intermedia Hosted PBX logo
 
Intermedia Hosted PBX is a cloud-based phone system designed to meet the needs of small to mid-sized enterprises with up to 1,000 employees. Users of Intermedia Hosted PBX get a range of features, such as hunt groups to make sure... Read More
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Intermedia Hosted PBX is a cloud-based phone system designed to meet the needs of small to mid-sized enterprises with up to 1,000 employees. Users of Intermedia Hosted PBX get a range of features, such as hunt groups to make sure... Read More
 
Voice Complete logo
 
Level 3 offers both SIP trunking and Integrated Services for Digital Network (ISDN) services in a package known as Voice Complete. Businesses can use Level 3 SIP trunking to connect calls between VoIP systems and the traditional phone... Read More
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Level 3 offers both SIP trunking and Integrated Services for Digital Network (ISDN) services in a package known as Voice Complete. Businesses can use Level 3 SIP trunking to connect calls between VoIP systems and the traditional phone... Read More

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XMission Hosted PBX logo
 
XMission is an Internet service provider (ISP) that offers a cloud-based business phone system known as XMission Hosted PBX. Additionally, XMission offers SIP trunking services for businesses that want a single-vendor VoIP system.... Read More
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XMission is an Internet service provider (ISP) that offers a cloud-based business phone system known as XMission Hosted PBX. Additionally, XMission offers SIP trunking services for businesses that want a single-vendor VoIP system.... Read More
 
Broadview OfficeSuite logo
 
Broadview Networks’ OfficeSuite is a cloud-based phone system that offers a number of unified communications features. This solution is scalable, and can meet the needs of very small businesses (three or fewer employees) as well... Read More
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Broadview Networks’ OfficeSuite is a cloud-based phone system that offers a number of unified communications features. This solution is scalable, and can meet the needs of very small businesses (three or fewer employees) as well... Read More
 
ShoreTel logo
 
In addition to providing a hosted PBX service (an offering that can be found here), ShoreTel also provides an on-premise solution that offers the conferencing, collaboration, presence and mobility applications and features collectively... Read More
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In addition to providing a hosted PBX service (an offering that can be found here), ShoreTel also provides an on-premise solution that offers the conferencing, collaboration, presence and mobility applications and features collectively... Read More
 
Phone.com logo
 
Phone.com is a hosted PBX solution designed for businesses with fewer than 50 employees. It offers SIP trunking service together with PBX service for a single-provider VoIP solution. Along with basic PBX functions like extensions,... Read More
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Phone.com is a hosted PBX solution designed for businesses with fewer than 50 employees. It offers SIP trunking service together with PBX service for a single-provider VoIP solution. Along with basic PBX functions like extensions,... Read More
 
TelePacific Hosted PBX logo
 
TelePacific Communications is a provider of voice and data services that offers a cloud-based phone system known as TelePacific Hosted PBX. TelePacific also offers SIP trunking, PRI/CAS and analog services for businesses with on-premise... Read More
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TelePacific Communications is a provider of voice and data services that offers a cloud-based phone system known as TelePacific Hosted PBX. TelePacific also offers SIP trunking, PRI/CAS and analog services for businesses with on-premise... Read More
 

Buyer's Guide

by Daniel Harris,
Market Research Associate
Last Updated: April 18, 2017


SIP trunking is a network service that allows businesses to connect VoIP phone systems to the traditional phone network. While this service is generally included with “per-user” licenses for cloud-based phone systems, if you have an on-premise system you’ll most likely need a SIP provider to connect calls with it.

We’ll explain what SIP trunking is, why you need it, and the primary considerations that you should factor in when deciding on a provider.

Here's what we'll cover:

What Is the Session Initiation Protocol (SIP)?
What Is a SIP Trunk
Benefits of SIP Trunking
Features of SIP Trunking Service
Important Considerations for Buyers

What Is the Session Initiation Protocol (SIP)?

Imagine the Internet as a vast network of roads and highways. On it are many types of vehicles, delivering various-sized packages (or packets, to use the technical term) containing a variety of information at a wide range of speeds. Most Internet users only ever see the contents of the vehicles traveling on the roads.

But like real roadways, the Internet has many layers below the surface. These lower layers support—and determine the quality of—the layers above them. Each layer has its own specific set of languages used to communicate within that layer. These languages are called “protocols.”

One of the lowest layers supporting the Internet is called the link layer. Within the link layer, link layer protocols organize groups of local connections into large networks. At the top, just under the surface, is the application layer. The application layer determines the quality of the “road surface” directly above it. SIP is a protocol that operates within the application layer.

Different application layer protocols are used to create different surfaces. The Internet has a wide variety of road surfaces, some favoring certain types of traffic over others: Compare a heavily loaded truck slowly climbing the rough road surface of a hill to a sports car zipping down smooth concrete. Some surfaces work better for certain purposes.

VoIP—phone conversations over the Internet—are one very particular type of traffic. They require audio to be delivered consistently with minimal delay. SIP is an application layer protocol designed to provide a very certain type of road surface for this special traffic. SIP initiates the sessions (or connections) that prepare the network to best meet the specific needs of a real-time audio connection over the Internet. 

We offer a fuller explanation in our article on the SIP protocol.

What Is a SIP Trunk?

We’ve mentioned that SIP trunking is a network service. It’s necessary because VoIP calls travel over the internet rather than the traditional phone network. This means that you need some way to connect calls between the internet and the traditional phone network, as otherwise you’d only be able to call other users with VoIP.

SIP trunking is the solution to this problem.

A SIP trunk isn’t a phone “line.” Instead, you connect to your SIP provider’s network using your internet connection. Your SIP provider utilizes specialized technologies to create a bridge between the internet and the traditional phone network, thereby connecting calls between these networks.

In some cases, you can get SIP trunking from the same company that provides your internet service, but in other cases you may need to use separate providers for SIP trunking service and internet service.

If you don’t have SIP trunking, you won’t be able to do much with a business VoIP phone system aside from admiring the server hardware. And while the traditional phone network is dying in the United States, it’s alive and well across the globe, so the need for SIP trunking isn’t going to disappear anytime soon.

Benefits of SIP Trunking

SIP trunking can cut costs in the following ways:

Lower trunking costs. Combined voice and data connections have traditionally been provided by telecoms in the form of Integrated Services Digital Network (ISDN) lines, also known as trunks. ISDN trunks come with fixed quantities of lines per trunk (for example, T1 trunks have 23 lines each). If a business needs even one additional line, it must purchase another entire trunk—meaning businesses often pay for unused capacity. SIP trunks are comprised of bandwidth, a flexible commodity, and their capacity can be increased on the fly.

Lower equipment expenses. Offices without SIP trunks use media gateways to translate between the analog PSTN and the office’s internal digital traffic. Offices using SIP trunks don’t need this expensive piece of equipment because their traffic bypasses the PSTN. A SIP trunk also makes it more practical for an office to use a cloud-based phone system rather than purchasing and maintaining an in-office hardware version.

Lower calling charges. Traditionally, and under many existing calling plans, charges are calculated based on the physical length of the PSTN line required to complete a call. Calls made via SIP trunks bypass most of the PSTN and so avoid many long-distance charges.

SIP providers also frequently offer better rates on international calls than traditional phone service providers, and most importantly, intra-office calls and calls between branch offices are frequently free when connected via SIP trunking.

SIP trunking also has a number of technological advantages:

More communications options. A SIP trunk extends, in a virtual sense, an office’s internal network to the outside world—letting remote offices, mobile employees and customers worldwide interact as if they were in the same building. Click-to-call website options for customers, application sharing and simple call transferring for work-at-home or abroad employees, for example, can all be done more easily with SIP trunks.

Meanwhile, SIP client apps can facilitate communication via a mobile device over an Internet connection, with capabilities such as voicemail, SMS messaging and more.

Features of SIP Trunking Service

The following table shows some common features of SIP trunking service:

Bursting Traditionally, if you needed more calling capacity on your phone lines, your provider took a month or longer to deliver it. SIP providers, on the other hand, can scale capacity up and down in as little as 24 hours, a vital cost-saving feature for businesses with fluctuating call volume.
Port sharing If you have multiple sites, and one site maxes out its number of simultaneous calls, you can connect calls via open ports at one of your other sites. Again, this is a vital cost-saver for call centers.
Disaster recovery In case of a service outage at one of your sites, your SIP provider can forward calls made to critical phone numbers.
911 and E.911 support Your SIP provider can support 911 calls by providing location information with the call. Without E.911 support, VoIP isn’t compatible with emergency services.
MPLS support Multi-protocol label switching is a networking technology that allows information to be routed within a network using path labels rather than the network protocols we discussed above. This offers performance, reliability and security benefits, and some businesses prefer to have SIP trunks delivered over MPLS. You’ll need to make sure your provider offers both MPLS and SIP trunking services, however.

Important Considerations for Buyers

Phone system deployment type. Whether you have an on-premise or cloud-based system is the most important factor affecting your approach to SIP trunking. Businesses with cloud systems may not even need a separate SIP provider.

In most cases, SIP trunking is included with “unlimited” user licenses for cloud systems. The vendor generally doesn’t even mention that SIP trunking is included, given the complex nature of the service. Other cloud vendors provide “metered” SIP trunking - i.e., SIP trunking service priced using per-minute rates. If you have an on-premise phone system, however, you’ll need to search for a SIP provider, as generally vendors of on-premise systems don’t offer SIP trunking.

Phone system brand. Different phone system vendors have implemented the SIP protocol in their systems in different ways. This means that not all SIP providers will be compatible with your specific brand of phone system. Check with your phone system vendor, as many list the SIP providers that their systems support. You also need to ask your SIP provider about support for specific features and devices such as FAX machines.

Connection type. A SIP trunk can be provided over most any high-speed Internet connection. The cheapest option uses an existing broadband Internet connection from a standard Internet service provider (ISP), and simply has the ITSP service share it. Call quality and capacity may be reduced because both data and voice are sharing the connection. A more expensive—but better—option is to lease a line from an ITSP and dedicate it solely to your SIP traffic. Giving your SIP traffic its own line helps improve call quality and reliability. Not all SIP providers offer internet service, but many partner with ISPs.

Quality of service and service level agreements. Quality of Service (QoS) and Service Level Agreements (SLAs) are common components of the contracts businesses sign with their ITSP. The QoS agreement defines (in technical terms regarding IP traffic’s delay, jitter and packet loss) the acceptable average quality of a voice call. The SLA, on the other hand, describes exactly how much "downtime" a service provider is allowed, what constitutes downtime and how quickly network issues must be resolved.

Trial period. ITSPs recognize that it can be difficult for a business to commit to a new phone system without experiencing it firsthand. For this reason, many now offer full or limited trial periods. The trials can be adopted on a small scale to make sure everything is functioning as expected before making the switch. Make sure to test any devices such as FAX machines that are connected to the phone network as well as the actual features of your phones.

911 dialing. The FCC has mandated that all “interconnected” VoIP services provide functionality to connect 911 calls to the appropriate local emergency services authority. But not all ITSPs fall under this mandate. If a business plans to eliminate their PSTN service entirely, then this needs to be considered. Maintaining a single PSTN line for emergencies is a viable option.

Firewall and security. If not properly managed, SIP trunks can expose an office network to external privacy and security threats. Traditionally, offices have used standard firewalls to keep out unwanted IP traffic, but SIP traffic does not always travel smoothly through firewalls. Other security options, like Virtual Private Networks (VPNs) and session border controllers, are increasingly common.

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