Using a SIP Trunk

About SIP – Benefits – Configuration

For most businesses, the phones are a lifeline that connects customers, partners, prospects and staff.  It is imperative that the line be kept open or business grinds to a halt.  This is why we understand that making the move to a new communications technology can be risky and that buyers need to have a clear understanding of what to expect.  People don’t invest in new communications technologies very often so it can be hard to know exactly what information you need to understand before you commit.   If you are considering using a SIP Trunk, we hope that looking at these ABCs will help you start to develop confidence that you will make the right decision for your business.

About SIP

SIP stands for Session Initiation Protocol.  It is sometimes referred to as using SIP trunks, SIP trunking or sometimes VoIP (Voice over Internet Protocol).*  It is a means of providing voice and other unified communication services over the Internet for customers with a SIP enabled PBX, otherwise known as IP PBX systems.  Using a SIP trunk enables customers to replace traditional telephone lines or PRI (Primary Rate Interface) lines.

It’s helpful to think about the components of a business phone system.  The first main component the PBX, which handles call management and other features like voicemail and automated attendants.  The second component is the connection to the PSTN or Public Switched Telephone Network.  That is the global network that allows any phone to call any other.  Traditionally, the PBX was connected to the PSTN through traditional PRI lines provided by telecommunications carriers.  Using a SIP trunk is an alternative that leverages the data network, via the Internet to connect the PBX and the PSTN.


There are many advantages of using a SIP trunk.  Here are the ones most frequently cited by customers:

  • Cost – SIP trunking can save customers as much as 60% of their monthly telecommunications costs by eliminating expensive PRI lines.  With SIP.US, long distance to most of the US and Canada is included, reducing monthly expenditures even more.
  • Flexibility – PRI lines are purchased in groups of 23, each line enabling one concurrent call.  SIP channels, on the other hand, can be purchased in any quantity, letting users purchase (and pay for) exactly what they need.
  • Scalability – Because the number of SIP channels a customer purchases is a logical limit, not a physical one, new channels can usually be added instantly without hardware or installation services.

Configuration Considerations

There are a few things you do need to know about configuration before you start using SIP trunking.  Because SIP relies on your Internet connection, it is important to be sure you have adequate bandwidth to support the number of expected concurrent calls.  For SIP providers like SIP.US that use the G.711 voice codec, each concurrent call will use approximately 85kbps of bandwidth.

Another important configuration consideration when using a SIP trunk is Quality of Service or (QoS).   QoS is a router setting designed to prioritize voice traffic over data traffic when the two share an Internet connection.  This helps to ensure the best possible audio quality for voice.  There are inexpensive routers with robust, easy-to-configure QoS.

Using a SIP trunk is an excellent and relatively straight forward way to save your business money while increasing agility.  Hopefully these basics are a good start toward arming you with the information you need to evaluate solutions and select your SIP provider.  This blog contains even more useful information and we hope you read on.  Enjoy!

* I know it is weird to have an asterisk in a blog, but I though it was important to add that, although they are sometimes used interchangeably, SIP and VoIP are not the same thing.  They are both protocols used to achieve voice services over data connections.  All SIP uses the VoIP protocol, but VoIP can be used without SIP through other types of connections, such as MPLS.  Therefor, all SIP is VoIP, but not all VoIP is SIP.

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