What is tested

Voice call testing is done on O2, Orange, T-Mobile, and Vodafone GSM 2G networks on selected Roads, Motorways and at various locations within selected Cities. The tests are carried out by automated test equipment mounted in vehicles. Calls are 90 seconds long followed by a 30 second no-call period. The measures gathered during these tests and subsequently displayed on the comparison map are as follows:

• When you try to make a call on your mobile and the call is set up and closed down in a controlled manner i.e. ended by one of the people on the call, then that call is referred to as a 'Successful call'. On the website, this is indicated by a large green circle.
  
• When you try to make a call on your mobile and either the set up of that call on the mobile network is unsuccessful, or after successfully setting up a call on a mobile network, that call cuts off before the end of the call, then that is referred to as an 'Unsuccessful call'. On the website, this is indicated by a large red circle.
  
• When a test call is being made, the audio quality of that call is measured and if it is of acceptable or better in quality, then this is referred to as 'Good Voice Quality'. On the website, this is indicated by a small green circle.
  
• When a test call is being made, the audio quality of that call is measured and if it is unacceptable or worse in quality, then this is referred to as 'Poor Voice Quality'. This could indicate breaks in the call, echo, crackling on the line, silence or robotic voice symptoms. On the website, this is indicated by a small red circle.