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
Large Cities:
All operators achieved excellent session success rates. A1 with the shortest call setup time and Telekom with the highest average MOS.
Medium Cities:
Similarly to the Large Cities, all operators achieved excellent session success rates. A1 took the lead in the shortest average call setup time and Telenor with the slightly higher MOS than Telekom Srbija and A1.
Small Cities:
Again, all operators achieved excellent session success rates. And again, A1 with the shortest average call setup time, Telenor with the highest average MOS, Telekom and A1 almost at pair.
Roads:
Success rates were lower on the Rural Roads compared to the Highways and Main Roads for all three operators. A1 almost at pair in the session success rates with Telekom Srbija, Telenor slightly behind.
Trains:
The session success rates are much lower than in other aggregations mainly due to the tunnels and mountainous areas which lead to the weak coverage. Telenor with the best session success rate with Telekom Srbija and A1 right behind.
Hot Spots:
Like in Large Cities, all operators achieved excellent session success rates. Overall, A1 had the shortest Call Setup Time. Telekom Srbija and Telenor with the MOS values almost at pair and A1 slightly behind the competitors
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. Telenor with lack of failed calls.
Telekom with the lowest dropped calls rate 0.13%, A1 with the second best result 0.20% and Telenor last with 0.46%
In Medium Cities, all operators with perfect call success rate, Telekom without any failed call.
A1 had the lowest percentage of dropped calls, only 0.13%. Telenor slightly behind with 0.19% and Telekom Srbija last with 0.45%.
In Small Cities, all operators met the excellent call success rate, A1 without any failed call.
The percentage of dropped calls in Small Cities was very low for all three mobile operators.
On the Highways, A1 and Telekom without any failed call, Telenor with 0.32% only
Telekom Srbija had the lowest dropped calls rate – 0.32%, with A1 behind 0.48% and Telenor last 0.64%
On Main Roads, all operators achieved good results. A1 and Telekom Srbija had below 1% of failed calls.
All operators with above 1% of dropped call, Telenor with the highest – 1.46%
On the Rural Roads, all operators with high call setup failure rate. Telenor with the highest 1.83% of failed calls, Telekom second and A1 with the best 1.57%
In term of dropped calls, Telenor with the highest dropped calls rate – 3.57%, A1 with the Second worst result with 2.56%, Telekom with the lowest 2.28%
Trains aggregation is the most challenging to maintain coverage and keep connection. All operators with the high failed calls rate of over 10%
Telekom and Telenor with the highest dropped calls rates, exceeding 3%, A1 with the lowest 2.21%
Hot Spots showed perfect success rates for all three operators, none failed call recorded.
The excellent connection maintenance resulted in the lack of any dropped session.
Figure 2 below presents average call setup time values for all three operators in different aggregations.
Fig. 2. Average call setup time values
A1 is clearly ahead the competitors in terms of Call Setup Time in all eight aggregations. Telekom Srbija most often with second best result, Telenor almost at pair with Telekom Srbija.
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.
All operators achieved similar speech quality results (MOS). Results on Roads slightly worse than in other aggregations, nevertheless on very good level for all operators.
