The Basics of Getting Started with SIP Trunking

Posted on May 29, 2020

Session Initiation Protocol or SIP trunking is a telephone service delivered most commonly via the internet. SIP trunks are provided by internet telephony service providers (ITSP) instead of the traditional phone company. There are several reasons why businesses should consider switching to SIP trunks. Cost savings is one of the main reasons driving the switch to SIP trunking over the past few years, along with increased scalability and flexibility. Companies can easily save around 50% of the cost of legacy telephony using SIP trunking, as well as easily scale up or down as needs change. To start using SIP trunking you’ll need the following things:

  • Solid internet connection
  • Telephone system capable of using SIP trunks
  • Router that can prioritize SIP trunking
  • Service from an ITSP

Make sure you have a solid internet connection

The type of internet connection you’ll need depends on the amount of traffic you want to pass through and the service providers in your area. A T1 is a digital circuit that has a speed of 1.5 megabits per second. That is relatively slow by today’s standards, but the T1 has some advantages. The main advantage of the T1 is that it’s a dedicated connection. Unlike cable and DSL, the T1 service provider guarantees that you’ll always have the 1.5-megabit speed. T1 is also synchronous so the upload speed is the same as the download speed.

Another option is a Digital Subscriber Line (DSL) that’s generally provided by the local telephone company. DSL speeds vary depending on how far you’re located from the phone company’s equipment and how much you want to pay for DSL. Download speeds can range between 3 to 20 megabits per second. Unlike a T1, DSL is asynchronous, so the upload speed is not the same as the download speed. When you use DSL you may have a 10 megabit download speed, but your upload speed will be typically less than one megabit. If you consider DSL for SIP trunking, remember that the upload speed is just as important as the download speed.

A third option is cable internet. Cable speeds are typically faster than DSL with download speeds that can reach 100 megabits. If a cable internet connection is available in your area, it may provide the best service for the price. There are other internet options available in some areas, but a T1, DSL or cable connection are the most common.

Choose a telephone system capable of using SIP trunks

Next you’ll need to have a phone system that’s capable of receiving SIP trunking. You may also use a SIP-to-analog gateway for older telephone systems. A SIP gateway is a device that will break SIP trunking into individual lines that replicate Plain Old Telephone Service (POTS) lines. The gateway will allow you to keep an existing phone system that will not natively accept SIP trunks. This may save money on an upgrade, but you’ll lose a lot of the flexibility of SIP trunking by using the gateway. You will want to get a phone system that’s capable of integrating directly with SIP trunks in order to optimize their advantages.

Make sure your router can prioritize voice traffic

Routers act as your gateway to the internet. Your router directs traffic to and from your network to the internet. When you’re moving to SIP trunks routers are one area where you don’t want to go cheap. Invest in a higher end router with plenty of processing power and can provide quality of service (QoS). QoS is the ability to provide a different priority to different applications. For example, users for data flows, or to guarantee a certain level of performance to a data flow. When you are using SIP trunking it is critical that the voice traffic going to the internet is prioritized over all other traffic. If your email arrives a second late it’s not a big deal, but if a voice packet arrives one second late your conversation has just become garbled. Your router should be properly configured using QoS so that all voice traffic gets priority over everything else. This will ensure that your conversations remain smooth and clear. Setting up and configuring your router is just as important as buying a quality router.

Select an ITSP with a proven record of world class service

The ITSP you choose for SIP trunking will in effect become your phone company. If someone calls you from another business, once they dial your number, their telephone company will connect to your ITSP. Your ITSP will send a call to your IP address over the internet and your router will identify the incoming traffic as a SIP call and then send it to your phone system. Your phone system will then recognize the number that was dialed and send it to the proper phone or phones.

Let’s walk through the process in reverse to see what happens when you make an outgoing call. First you dial the number on your telephone, and it’s processed through your phone system. Your phone system takes your analog voice and converts it to digital packets designed to be sent across the network. These packets are getting sent to your router which has been configured to prioritize all voice traffic coming from and going to the phone system. The router takes the voice packet and marks it to be sent to your ITSP via the internet. The packet is then routed over the Internet to the ITSP. The ITSP then can connect to the public switched telephone network (PSTN) which then links the call to the proper landline or cell phone.

Learn more about SIP trunking and how to get started.

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