The results of the main KPIs for voice tests achieved by operators, split per aggregation type are presented in Figure 1.
Fig. 1. Results of main KPIs for voice tests
Big Cities:
Telekom Srbija achieved 100% of the session success rate, the other two operators achieved slightly smaller values of the session success rate.. Telekom Srbija achieved the shortest call setup time. All operators achieved almost the same, nearly the highest average MOS.
Medium Cities:
A1 Srbija and Yettel achieved excellent session success rates, Telekom Srbija was slightly behind A1 Srbija took the lead in the shortest average call setup time. All operators achieved almost the same, nearly the highest average MOS.
Small Cities:
Telekom Srbija and Yettel achieved excellent session success rates, A1 Srbija achieved a smaller success rate, lower by almost 0.5%. A1 Srbija had the shortest average call setup time. All operators achieved almost the same , nearly the highest average MOS.
Highways:
Success rates are at an excellent level for all three operators. Telekom Srbija had the shortest call setup time, and A1 Srbija was slightly behind. All operators achieved almost the same, nearly the highest average MOS.
Main Roads:
The maximum value of the session success rates was achieved by A1 Srbija. Telekom Sbija and Yettel were behind. A1 Srbija was with the shortest average call setup time, Yettel came second and Telekom Srbija was the last. Yettel and A1 Srbija almost equal with MOS results, followed by Telekom Srbija.
Rural Roads:
The maximum value of the session success rates was achieved by A1 Srbija. The minimum value of the session success rates was achieved by Telekom Srbija. Yettel was in the middle. As expected, in the rural areas the average MOS values are lower than in other aggregations. A1 Srbija had a higher average MOS and the shortest call setup time compared to the competitors.
Voice failed calls and dropped calls scores are shown for all three operators, in different aggregations.
In Big Cities all operators achieved good results. Telekom Srbija with no failed calls.
Telekom Srbija with no dropped calls. A1 Srbija and Yettel recorded one drop each.
In Medium Cities, all operators with perfect call success rate, with a single failed call. A1 Srbija and Yettel equal, with 1 failed call each, Telekom Srbija with 2.
A1 Srbija and Yettel with no dropped calls. Telekom Srbija with one dropped call.
In Small Cities, all operators met an excellent call success rate. Telekom Srbija and Yettel without any failed calls.
No dropped calls occurred for any of the operators in Small Cities aggregation.
On the Highways, all three operators without any failed calls this year.
A1 Srbija without any dropped calls. Yettel with 2 dropped calls on Highways, Telekom Srbija with one dropped call.
On Main Roads, all operators achieved good results. A1 Srbija with the least number of failed calls.
All operators with less than 1% of dropped calls, Yettel with the highest rate at 0.84%
On the Rural Roads, all operators with poor call setup success rates. A1 Srbija with least failed calls among the three operators.
In terms of dropped calls, Yettel with the highest dropped calls rate – 2.35%, A1 Srbija with 1.18%, Telekom Srbija with least dropped calls - at 0.82% rate.
Figure 2 below presents average call setup time values for all three operators in different aggregations.
Fig. 2. Average call setup time values
Telekom Srbija and A1 Srbija are ahead of Yettel in Cities and on Highways. On the Main Roads and Rural Roads, Telekom Srbija with the longest average Call Setup time, where A1 Srbija again with the shortest Call Setup Time, followed by Yettel.
Distribution of call setup time duration in Big Cities for all three mobile operators is presented in Figure 3.
Fig. 3. Distribution of call setup time duration in Big 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.
Telekom Srbija achieved the best speech quality in Big Cities and Small Cities, while A1 Srbija had the best result in Medium Cities. Results on Roads was slightly worse than in other aggregations, nevertheless at a very good level for all operators. On Highways, Telekom Srbija had the best average MOS and A1 Srbija showed the best average MOS on Main Roads and Rural Roads. Yettel was slightly behind the competitors in all aggregations, except for the Main Roads, where Telekom Srbija had poorer result than Yettel.
The results of the main KPIs for voice tests achieved by operators, split per aggregation type are presented in Figure 5.
Fig. 5. Results of main KPIs for voice tests
Trains:
Telekom Srbija had the best Call setup success rate on trains, Yettel followed with second-best result and A1 Srbija was right behind. Overall, the Call setup success rates were lower than in other aggregations, mainly due to the tunnels and mountainous areas.
Hot Spots:
Like in Big Cities, all operators achieved excellent Call setup success rates. Overall, Telekom Srbija had the shortest Call Setup Time with A1 Srbija right behind, followed by Yettel. MOS result were almost equal for all three operators.
Voice failed calls and dropped calls scores are shown for all three operators, in different aggregations below.
All three operators had high failed calls rate on trains. Trains aggregation is the most challenging for service accessibility and reliability.
Yettel had the highest dropped calls rates, exceeding 5%, Telekom Srbija had the lowest rate at 3.09% and A1 Srbija was right behind, with 3.66%.
Hot Spots showed perfect success rates for all three operators, with one failed call recorded for A1 Srbija.
The excellent connection maintenance resulted in the absence of any dropped session for Yettel this year, while Telekom Srbija and A1 Srbija recorded one drop each.
Figure 6 below presents average call setup time values for all three operators in different aggregations.
Fig. 6. Average call setup time values
A1 Srbija had a slightly better average call setup time than the other two operators, on Trains aggregation. In the Hot Spots aggregations, Telekom Srbija had the best result, almost equal as A1 Srbija, followed by Yettel.
Figure 7 below presents average MOS values for all three operators in different aggregations.
Fig. 7. Average MOS values
In Hot Spots areas, MOS results were almost equal for all three operators, with Telekom Srbija at 4.69, A1 Srbija at 4.68 and Yettel at 4.67. Results on Trains were poorer than in other aggregations, due to the demanding mountainous areas, which resulted in lower MOS values, where A1 Srbija had the best result at 4.25, Telekom Srbija was second- best at 4.18, followed by Yettel at 4.12.
