SIP Trunks & Trunking Explained

SIP Trunking

What is a SIP trunk?

A SIP trunk is a new technology that allows a business to replace it's existing analogue or digital telephone lines with a data connection. Once connected a business can continue to operate in the same manor as before with no changes to it's telephone call handling. SIP Trunk calls are carried by both VoIP (Voice over Internet Protocol) and the traditional telephone network.

What are the benefits of SIP Trunks?

SIP trunks are able to provide a business with many benefits, the most common, and perhaps the most important of which includes a reduction in on-going phone costs. SIP trunks are provided at a lower rental charges than other standard analogue or digital telephone lines plus have the added benefit off routing calls off the traditional phone network providing telephone call savings, particularly if businesses operate across different sites as these calls are often provided free.

SIP trunking also has the benefit of being able to operate without geographic telephone number constraints, area telephone number codes able to function freely in any location where a data connection is available.

Connecting to SIP Trunks

The important areas that need to be considered when making a business connection to SIP trunks can be listed as follows-

Can your existing business phone system support the SIP trunking standard? Many newer phone systems are likely to have capability for SIP Trunks with the simple addition of a software license or a hardware module. f however your phone system does not support SIP trunks, there is another tested solution, namely a SIP convertor. The convertor unit will allow you to add your SIP trunks by acting as an interface between the existing business phone system trunk ports and the newer SIP trunk data circuit.

How important is the actual quality of the telephone call to your business? SIP trunking can be delivered at lower cost if you decide on sharing an existing standard data connection to route calls over the public Internet network, however as the connection is shared SLA’s (service level agreements) are unlikely to apply from the SIP trunking supplier and call quality can not be guaranteed as calls are beyond the routing control of the supplier. If call quality is paramount then a dedicated xDSL voice link should be provided. This will link your business into the MPLS data backbone, bypassing the public Internet service which will then guarantee suitable bandwidth and therefore call quality or QoS (Quality of Service).

Business should also consider the maximum simultaneous number of calls, both inbound and outbound? If you are replacing an existing number of standard trunks than you may have the answer to this question, however if you do not then calculations need to be made to ensure that the SIP trunking circuit that is provided can provide enough bandwidth to carry the calls required for your business phone system. As a rough guide, one SIP trunk call will require around 32K of bandwidth.  

Resiliance should also be considered when considering a SIP trunk solution. A business may wish to install a secondary data circuit to carry calls in the event of problems with a service provider or with problems caused by fibre of copper line breakages within or external to the building, but this also applies with traditional voice telephone lines as well.

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