ultivendor solution, the statistics from different vendors' equipment are collected into a special reporting tool to give an idea of the performance of the system as a whole. Network element counters have not been standardised, SO both the amount of counters available and their trigger points differ widely among vendors. For example, for 2G GSM radio systems one vendor has only about fifty counters available to the user while another has close to a thousand. When using such counters from a different vendor, the user has to be aware of the differences in counter availability as well as their trigger points. In a typical multivendor scenario it is not unusual to have different values reported for the same KPI depending on the sub-system used for the reporting. Network statistics gives a far more accurate and comprehensive picture of network performance since it includes all geographical area covered. Network statistics are collected automatically by the system and hence no special costs are associated with the measurement. The disadvantage of network statistics is that precise geographical information is missing. The problem can be localised down to cell level, and in some vendors' cases to distance from the cell antenna (based on timing advance). Also, user experience tests like MOS or the future video call-quality tests cannot be performed using network statistics. The best solution for testing networks is to use a combination of both the tools. A typical application would be to use statistics to spot problems and localise them to cell level, and then use a drive test to get the details of the problem. Appendix E Erlang B Tables Nezha Larhissi Nokia Networks An Erlang B or C table presents the estimated traffic to be handled by a certain num- ber of TCHs according to a certain blocking probability. Since Erlang C admits queuing, more traffic can be handled for the same TCH/Probability combination than by Erlang B. However, in GSM standard, we use Erlang B tables with a common probability of usually 2% blocking. T