What is SIP Trunking?

Until 2017 most of the relevant telephone network (PSTN) providers in Europe (e.g. Deutsche Telekom, Swisscom and BT) will switch their services to Voice over IP telephony. As a result, the traditional landlines are being switched off already today. Even new ISDN lines, are only ISDN on the final meter to the user. Internally, the ISDN signals are translated to SIP and RTP via gateways. In most other European countries, there are no analoge provider lines available anymore.

A detailed list of all the benefits of VoIP can be found here. With a change to IP telephony your company will benefit instantly. Voice over IP, is often used with the terms SIP trunk or SIP trunking. Those trunks can be used individually, as a replacement for traditional PSTN lines, or in combination with with those. Furthermore, there are more and more companies offering VoIP related services, and this way increasing the number of available SIP trunks. This way it is easily possible to choose the right trunking product needed in your company.

If you want to make full use of your IP phone system and not just use VoIP within your local network (LAN), a SIP Trunk is a good alternative (or addition) to your existing ISDN BRI or PRI lines.

A SIP Trunk is usually provided by an internet service provider (ISP). Unlike a PTSN provider, the lines provided are not physical wires, but a service provided over the internet. The SIP Trunk Provider provides phone numbers and lines, usually at better rates than the traditional providers and with more flexibility and shorter contract durations.

For instance, SIP trunks are very flexible when it comes to the number of available channels. While ISDN BRI only offered two channels per line or thirty channels per line with E1/T1, SIP trunks are (within the limitations of the trunking provider) almost completely flexible when it comes to the number of available voice channels. Additionally, the booking of additional channels is often only one click in the providers web interface. Even trunks with up to 1000 numbers, which have so far only been known from costly ISDN E1/T1 lines, are now available for everybody.

Further, in most cases the contract duration is much shorter as with PSTN. In most cases, contracts for internet telephony can be cancelled or changed on a monthly basis.

One frequently used reason for not moving to VoIP is the porting of phone numbers. In case of Voice over IP, there is no problem to keep your “old” phone number. Most VoIP providers offer number porting as a free service. Also, if your company moves to a new location, your number (or SIP trunk) can be kept without any changes as there is no physical binding to the location.

To deploy SIP Trunking you need an IP PBX, a SIP Trunk and an adequately dimensioned internet connection.


Common questions about IP Phone Systems, PBX and VoIP