SIP Trunking Popularity Grows

What is SIP Trunking?

What has typically been used to make a phone call, or carry voice traffic, is called the Public Switched Telephone Network (PSTN). PSTN traffic includes, Analog, ISDN BRI, E1 or t1 lines. But with the advent of VoIP (Voice over Internet Protocol) telephony is moving from PSTN to much more modern and flexible Session Internet Protocol trunks or SIP trunks.

All the large telecom providers are in the process of phasing out the old PSTN functionality, and are moving customers to IP. Most businesses are moving to a SIP trunk which will also include a phone system upgrade.

By 2018 Verizon will phase out ISDN in the U.S. In the UK, ISDN lines are down to less than 3 million lines, from 4.7 million lines in 2007 and the trend is growing. By 2017 major telcos such as BT, KPN, France Télécom, Deutsche Telekom and Telecom Italia will no longer offer ISDN lines.

As a result, Session Initiation Protocol (SIP) trunking has increased by 62 percent in 2015 from the prior year, taking place mostly in North America. More and more businesses are deploying the technology to access the benefits it offers.

In an article by Pejman Roshan on, he explains why more businesses are turning to SIP trunking. The Software Advice report revealed 69 percent of IT decision-makers in the survey have already adopted SIP trunking in their organization, and 73 percent said they are “very” or “extremely satisfied” with the audio quality of calls connected by their SIP providers.
Below we explain what SIP trunks are, their advantages and how you can make the switch.

What are SIP trunks?

Session Initiation Protocol (SIP) trunking is the use of voice over IP (VoIP) to facilitate the connection of a private branch exchange (PBX) to the Internet. It is particularly popular for companies that are still using an older analog system and the PSTN, to get the benefit of VoIP without having to replace their entire PBX system. By simply installing a Gateway to translate analog data to VoIP, and a SIP trunk to carry that data over the Internet, companies can see a costs savings as well as increase in features such as access to more phone numbers or DID’s.

Benefits of SIP Trunking

So what if you’re not financially ready to invest in a VoIP PBX?

You’ve still got options.

VoIP Service providers most commonly offer SIP Trunking in order to allow you to make VoIP calls using your phone system – either analog or VoIP.

Electing to take advantage of SIP Trunking affords the opportunity for smart and cost effective solutions such as only requiring one connection for both data and voice.

Some of the other benefits of switching to a SIP trunk also include:

Combine Data/Voice & Video

One of the most significant advantages of SIP trunking is its ability to combine data, voice and video in a single line, eliminating the need for separate lines of physical media. The result is reduced overall cost and enhanced reliability for these services.

Lower Monthly Line & DID Costs

Adding lines of SIP Trunks is much cheaper than it is to add analog lines and the DID’s cost less as well.

Lower Phone Bills

Since calls are being routed over the Internet, call charges are much lower than routing through a PSTN. Some providers even offer unlimited long distance.

Better Customer Service

You get more access to geographic and international numbers than you would with a PSTN. You can easily add numbers to your SIP and terminate them on your VoIP PBX. Giving your customers more local numbers to call you instead of only offering toll-free or long distance calls, will increase customer satisfaction.

Take Your Numbers Wherever You Go

SIP trunks are not tied to a location, so it’s easy to move offices without having to change your company phone number.

No More Calls to the Phone Company for New Lines

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. 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.)

Easily Upgrade to a Modern VoIP PBX

With a SIP trunk you are one step closer to moving your entire telecom over to VoIP. Modern VoIP PBX systems give businesses increased productivity, mobility, and are easier to maintain. Connecting a VoIP PBX to SIP trunks is much easier than via the PSTN.

Better Flexibility

It is easy to add channels to your SIP trunk to deal with a higher call load. Your provider can easily add channels, and often this can be done immediately. With a PSTN it can take days or even months to add lines and then the hardware on the analog PBX system will need to be upgraded as well which can take a lot of time and money.

Add One Channel at a Time

With SIP trunks, you can choose just the amount of channels that you need. With ISDN/T1, you often have to choose to add either 15 or 30 lines adding more expense to your overall telecom cost.

Security and Network Providers

As SIP trunks are exposed to the Internet, it is very important that the SIP trunk has a well secured network as well as an anti-fraud system. A secure network will have encryption that keeps others from listening into your channel. With an anti-fraud system in place, your provider will be able to constantly scan & monitor your trunk for illegal calls made by criminals using your trunk channel.

Upgrading Internet Connectivity

Once you have selected your SIP trunk provider, consider a dedicated Internet line for the SIP trunk. Most firewalls are able to handle multiple WAN connections, and, considering the low cost of an Internet line in most places, a separate VoIP connection will be the most reliable way to ensure the quality of your VoIP calls.

Bandwidth Needed

To prepare your company for SIP Trunking, you need to assess the usage rates of your business communications. Specifically, you should consider how many people are on the phone at the same time during your busiest hours. The answer to this question will determine how many channels you will need. Remember, SIP trunks allow for quick and easy scaling, so you may add or remove channels as needed, if you under or over estimate. You can also decide which method to purchase SIP services. Some organizations may benefit purchasing a set number of trunks while others would benefit from a set number of minutes.

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

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

(number of concurrent calls at your company’s peak) x 85kilobits per second = bandwidth in Megabits per second (Mbps) needed for calls

QOS (Quality of Service)

Equally important to bandwidth is QoS. 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.

Upgrading Your Old Analog PBX to a VoIP PBX

If you are looking at moving from PSTN lines to SIP trunk, you are most likely also using an old, outdated, analog PBX system. Experts have coined the term ‘dinosaur’ for this old relic because it is inflexible, difficult to manage and upgrade, and typically expensive to maintain.

Although it is possible to buy a gateway that allows an analog PBX system to talk to the SIP trunks, why not upgrade to a modern VoIP PBX and leverage the flexibility and modern features IP telephony can bring? This allows you to take advantage of the cost savings, easy management, and productivity increases that a VoIP PBX offers. You can choose from a VoIP hosted PBX (most popular), or install an in-house VoIP PBX system.

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