 measure called 'Rx quality class' which varies from 0 to 7. Quality class 0 is the best and 7 is the worst. The quality classes are based on measurement of the bit error rates (BER) as measured by the error detection schemes built into the system. On a general level, voice quality of 0 with advanced codecs like EFR comes near to landline quality. Qualities of 2 and 3 have some perceptible distortions. Quality 4 has some amount END-TO-END SYSTEM PERFORMANCE MEASUREMENT of distortion. Conversation can still take place at Quality 5 levels depending on the ability of the people conversing. Quality classes 6 and 7 mean that no useful voice conversation is possible. In fact if there are too many instances of quality classes 6 and 7, system algorithms first try to hand over the call to a different cell or, in the worst case, the call may be dropped. An example of the use of quality class would be to specify '99% of the network has quality class of between 0 to 5'. Again these parameters can be measured by drive testing which gives a good idea of the location of good and bad quality areas. However, some vendors are able to collect the statistics of quality as measured by mobiles and reported to the network. Use of such statistics gives a much more accurate picture of the call quality of the network. A point to be noted is that the quality class measures the quality of the bearer and not of the service. A measure of service quality is provided in the sections on service quality. Handover Success Rate Modern wireless networks are called 'cellular' networks since they have small 'cells' each providing service in its immediate surrounding area. For the user to experience a seamless call, the user call is 'handed over' to the next cell when the user reaches the cell boundary. An extensive measurement and signalling protocol ensures that this handover is smooth and unnoticeable by users. In spite of all precautions, handovers between cells fail. Handover failure can be a major cause of quality degradation in service or may le