The results of the main KPIs for voice tests achieved by operators with the split per the aggregation type are presented in Figure 1.
Fig. 1. Results of main KPIs for voice tests
Telekom Srbija had the best success rate (above 99%) with Telnor in second and Vip mobile a bit further behind. The shortest average call setup time was equal in Telekom Srbija and Telenor (1.45s). The best average speech quality (MOS - Mean Opinion Score) was achieved by Telenor with 4.49 score (scale from 1 to 5).
The results in Small Cities were very similar in terms of operator relative scoring as in Large Cities. Call success rate achieved by all operators was on a very similar level. Telekom Srbija had the shortest call setup time. Highest speech quality was achieved by Telenor (4.50 score).
The Call Success Rate on roads was much lower in general than in cities, with Telekom Srbija having the best result. Vip mobile had the shortest call setup time (1.73s) and achieved the highest speech quality (4.34 out of 5).
In Table 1, voice failed calls and dropped calls scores for all three operators, in different aggregations, are shown.
In Large Cities all operators achieved good results. Telekom Srbija and Telenor had below 1% of failed calls.
Telenor had the lowest percentage of dropped calls, only 0.17%. Vip mobile and Telenor were behind with results respectively 0.23% and 0.29%.
In Small Cities, all operators met the minimum expected call success rate - less than 3% of both failed and dropped calls. Telenor had the best result, 0.25% of failed calls.
The percentage of dropped calls in Small Cities was very low for all three mobile operators.
The results on Roads were worse than within the cities. Vip mobile had the highest percentage of failed calls (over 6%).
The dropped calls rate of Telekom Srbija and Vip mobile were close to each other. The highest percentage of dropped calls was achieved in Telenor network and was equal to 1.46%.
Table 1. Voice Failed Calls and Dropped Calls
Figure 2 below presents average call setup time values for all three operators in different aggregations.
Fig. 2. Average call setup time values
Results achieved by all operators in Large and Small Cities were on very good, similar level. On Roads Vip Mobile and Telekom Srbija achieved same level of results, 1.73 and 1.75 respectively. Telenor behind the competitors (1.91s).
Distribution of call setup time duration in Large Cities for all three mobile operators is presented in Figure 3.
Fig. 3. Distribution of call setup time duration in Large Cities
Figure 4 below presents average MOS values for all three operators in different aggregations.
Fig. 4. Average MOS values
There is a variety of speech coding methods allowing transmission of the speech effectively. The use of codecs is determined by the quality of radio signal, available network technology and capacity of the network. Codecs offering the best speech quality require good radio conditions, reasonable radio resources and support of the codec by the network and mobile devices at both ends of the connection. In cases where the capacity of the network is limited, mobile operators use codecs with more efficient compression of the speech, but also providing worse speech quality. The distribution of the codecs used has a direct influence on the voice quality represented by MOS value (from 1 to 5, the best being 5). The EVS (Enhanced Voice Services) codec offers the best speech quality and was used by operators throughout all aggregations to the biggest extend.
Telenor achieved the best speech quality in Large and Small Cities, with competitors slightly behind. Results on Roads slightly worse than in other aggregations, nevertheless on very good level for all operators.