External telephone lines provide the fixed network voice connections between you and the outside world. You really need to get it right first time because insufficient telephone lines may have your customers complaining about the engaged tone – worse still they may decide to call a competitor because they “can’t get through”. Your staff may also complain that they can’t “get an outside line”.
It is important to know how many external telephone lines you will need to connect to your new telephone system, this should be how many external lines/trunks you need to service the volume of telephone calls you are likely to make or receive at peak times. Make sure you consider future business growth and think about how many lines you would need in five years’ time.
There are 3 main types of telephone line you can consider and there is little difference between the call tariffs and line rental charges, but there is a big difference in terms of functionality and reliability. You may need to use all three or at least two of the line types for your business requirements and summarised below are the key points for consideration.
PSTN Lines _ public switched telephone network
This is the most basic type of telephone line available, it provides good service levels in terms of response times to faults and very good speech quality. You would use a PSTN line to support any of the following devices or services:
- Broadband internet access
- Fax machine connection
- Intruder or Fire alarm systems
- Emergency lift telephones
- Analogue dial up modems
- Remote access for maintenance support
- Franking machines
With a PSTN line it is only possible to have a single telephone number per line. This can be restrictive if you are planning to have multiple incoming call numbers for departments or want individual direct dial numbers to increase the efficiency of your incoming call handling.
ISDN Lines _ integrated services digital network
ISDN lines offer the very highest level of resilience and quality available for connection to the telephone network. You can take advantage of supplementary features such as the ability to transfer incoming calls back out from your site to any external telephone number, you can also have additional numbering options for incoming calls known as DDI (direct dialling inwards) ranges.
There are two types of ISDN line available:
ISDN2. These are generally connected to phone systems with less than 8 external lines. ISDN2 lines are delivered in pairs so you can only operate with an even number of individual line rentals. They are powered from the local exchange with no power connection “on premises” required to operate them.
ISDN30. This option is available if you have a requirement for 8 telephone lines or more. ISDN30 lines are presented on a single connection which can be upgraded to provide up to 30 telephone lines without the need for any additional cabling or engineering site visits. ISDN30 lines require power to be provided locally “on-premises”.
VOIP _ voice over internet protocol
A VOIP service connection allows you to make and receive telephone calls via the Internet as opposed to the telephone network. It offers a very high degree of flexibility with regard to numbering options. You can choose to have any UK STD code as your incoming number irrespective of your geographic location. This can prove very useful for some businesses when relocating “out of area” as you can take your fixed line telephone with you anywhere.
The voice quality of speech via SIP trunks is very slightly lower than with ISDN lines and is a similar quality to a UK mobile telephone call. The quality of service level is also slightly lower because the response options to faults are traditionally slower with Internet providers than with telephone line providers.
Related Article – Do you need an onsite or offsite telephone system?