A report on Repeat Call Rates as a Key Performance Indicator used to improve the Network's Quality of Service. This report was prepared during my internship at Bharti Airtel Limited, India.

1. 2018
Using Repeat Call Data as a
Key Performance Indicator
in Mobile Network
Management to Improve
Network Quality of Service
A REPORT BY ANANT JAIN

2. INDEX
Acknowledgement..............................................................................................1
About Bharti Airtel .............................................................................................2
Research.………………………………………………………………………………………………………….4
Introduction........................................................................................................5
How do we measure network quality?................................................................5
What are Network Key Performance Indicators? ................................................5
Why are these KPIs important? .............................................................................5
Some commonly used 3G KPIs by Bharti Airtel....................................................6
Some commonly used 4G Voice KPIs by Bharti Airtel ..........................................7
What is Customer Perception?............................................................................8
Why is Customer Perception Important?...............................................................8
What is Repeat Call Rate?...................................................................................8
Why is RCR Needed?...........................................................................................9
Values Retrieved During RCR Data Collection....................................................10
• Apache Calcite……………………………………………………………………………..10
How is RCR Data Prepared? ..............................................................................11
What are the Major Factors which affect RCR? ................................................12
• Network Outage
• Handover Success Rate
• Dual Seizure
• Codec Negotiation
What is done with this collected Data?.............................................................16
Post RCR Improvements………………………………………………………………………………….16
Changes Suggested in Data Retrieval Process………………………………………………….18
Conclusion……………………………………………………………………………………………………...19
Appendix………………………………………………………………………………………………………..19
References And Readings….…………………………………………………………………………….20

3. 1

4. 2
About Bharti Airtel
Bharti Airtel Limited is a leading global telecommunications company with operations in 17
countries across Asia and Africa. The company ranks amongst the top 3 mobile service providers
globally in terms of subscribers.
It is not only the leading telecom operator in India, but also offers a portfolio of services in India
including voice and data solutions over fixed, wireless and internet platform, DTH, enterprise
services, including national & international long-distance services to carriers.
Along with offering a host of services, Airtel contributes towards making Earth a better place by
generating employment, building infrastructure, supporting the underprivileged and enabling
digital India.
Airtel has made a profound impact on the lives of millions of people, by helping farmers through
a program known as “ IFFCO Kisan Sanchar Limited (IKSL)”, establishing Kisan call centres ,
Promoting Health and Education Awareness, working with self-help groups and Empowering
digital education in Bihar.
On 10 April 2012, Airtel became the first telecom operator in India to launch 4G services via TD-
LTE technology in Kolkata. Under ‘Project Leap’, Airtel became the first telecom operator to
launch 4G mobile services in Leh-Ladakh, India in 2017.
Launched in November 2015, “Project Leap”, is Airtel’s aspirational nationwide network
transformation program to build a future ready network by committing an investment of over 8.766
billion USD, over three years.
Airtel recently launched India’s first Open Network, setting a new benchmark for transparency in
the industry by making the entire network information including coverage, site details and signal
strength available to customers.
With an annual turnover of 13.8 billion USD, around 180000 network towers (as of July,2018),
over 336700 base stations, 288 Million customers in over 7800 towns and over 785000
villages,95.3% Mobile Population Coverage and a customer market share of 23.39% in India,
Airtel has repeatedly emerged as the industry leader year after year.
This is one of the major factors that its operations are supported by 60000+ leading partners and
vendors globally such as Ericsson, Huawei, Nokia Siemens Network(NSN), Cisco, ZTE and
Alcatel Lucent to name a few.

5. 3
With over 17000 people in its workforce, Airtel’s primary aim is to achieve customer satisfaction
at the ground level and connect with as many people as possible.
With 18000 exclusive contact center agents across 31 cities to serve their customers, around 34
Mn customer queries are addressed per month, which eventually results in 0.016 complaints per
customer(as of March 31st, 2017).
Online, through www.airtel.in, Airtel receives over 0.9 Mn hits per day with an average time spent
per visit of almost 6 minutes and around 0.8 million customers.
It can clearly be understood by these statistics that Airtel’s primary focus is to serve its customers
the best, which is the reason that Airtel has been the most celebrated mobile telecom operator in
India.
__________________________________________________________________
(BHARTI AIRTEL LIMITED INDIA SUSTAINABILITY REPORT 2017)
www.airtel.in

6. 4
RESEARCH
During my internship at Airtel, my aim was to research about the KPIs used by Airtel for Network
Enhancement and how they improve the customer’s perception about the network.
My work consisted of numerous tasks like collecting data, researching on it, identifying the key
issues and formulating reports.
I commenced this research by learning about call flow of 2G,3G and 4G network architecture. This
was followed by learning about the technologies like international network management and
geolocation used by Bharti Airtel’s Network Operations Centre (NOC) located in Manesar,
Haryana, India.
I then learned about how call drop data is recorded into Airtel’s servers and how monthly billing
reports are generated. This enabled me to work further on RCR data.
Following that, I worked on the data collection process and KPIs used to improve customer
perception about the network.
My research also contained suggestions to improve the data collection process to make it more
efficient. By achieving this, the customer satisfaction at Airtel could be improved further.

7. 5
Introduction
Major companies all over the world use KPIs for service enhancements, to generate real-time
reports and improve its QoS. Mobile network operators and telecommunication firms also use
specific KPIs for network optimization and complaint resolution.
Repeat Call Rate is a KPI used by Bharti Airtel Limited, which is the only telecom operator in
India to collect and use this data as a KPI. This KPI is used to improve customer perception of the
network.
How do we measure network quality?
As the name suggests, “Quality of Service (QoS) refers to the capability of a network to provide
better service to selected network traffic over various technologies.” “The primary goal of QoS is
to provide priority including dedicated bandwidth, controlled jitter and latency (required by some
real-time and interactive traffic), and improved loss characteristics.”1
What are Network Key Performance Indicators?
Key Performance Indicators are values that organizations record and use to improve the Quality
of Service (QOS) and increase efficiency.
Network operators also use this data to optimize their network.
These operators may consider numerous factors which affect the network.
If the KPI is not within the set threshold range, the operator may decide to implement some changes
to improve the network QoS.
Why are these KPI important?
KPIs are necessary for most of the organizations because they provide the companies with basic
functioning data about how the services provided by them are performing in the real world.
Any organization may collect different number of KPIs according to their own requirements and
use the data as per their own evaluation.
1
http://docwiki.cisco.com/wiki/Quality_of_Service_Networking

8. 6
Some commonly used 3G KPIs by Bharti Airtel:
S. No KPI
Average
Threshold
(Airtel)
Measuring
Units Hour
1
Cells with network availability
(Redundant Network Access) 99% Percentage
BBH [Busy Bouncing
Hour]
2
BCR [Benchmark Call Drop Rate] (100-
Call Setup Success Rate) <1% Percentage BBH
3 DCR [Dropped Call Rate] <0.9% Percentage BBH
4 IFHO Success Rate >93% Percentage BBH
5 RxQual (0-5) >96% Percentage BBH
7 Frame Loss Rate <=1% Percentage BBH
8 Location Update Success Rate >=97% Percentage CS NBH
9 Paging Success Rate >=95% Percentage CS NBH
10 POI Congestion <=0.005 24 Hrs
11 CoPC (Complaints/1000 Customer) <4
12 Resolved Within SLA (HVS) >90%
13 % of Repeat and Reopen Complaints <2% Percentage

9. 7
Some commonly used 4G Voice KPIs by Bharti Airtel:
S.
No
KPI Average Threshold (Airtel)
Measuring
Units
Hour
1 Radio Network >99.91% Percentage 24 Hrs
2 CCSR >98.5% Percentage 24 Hrs
3 E UTRAN Session >98.5% Percentage 24 Hrs
4 PS Drop Call Rate <0.5% Percentage 24 Hrs
5 PS Handover >=96% Percentage 24 Hrs
6 % of Cells with PS >=95% Percentage CDBH(Call Drop Busy Hour)
7 PS BLER % <=1% Percentage 24 Hrs
8 UL PLR % <=1% Percentage 24 Hrs
9 DL PLR% <=1% Percentage 24 Hrs
10 DL Latency <=25ms ms CDBH(Call Drop Busy Hour)
11 E-UTRAN Average >=8% Percentage 24 Hrs
12 Detached Subs NBH
The KPIs mentioned above usually provide the core required data for network improvement,
however Bharti Airtel has established a new KPI, known as Repeat Call Rate which provides a
realistic insight into the network performance. This KPI can be used to increase customer
perception.
As it can be observed by the KPI data, Airtel’s primary focus is to measure the customer perception
and improve it’s QoS

10. 8
What is Customer Perception?
Customer Perception is the measurement of the quality of service(QoS) perceived by the user in
real time. Customer Perception is also a measurement of how satisfied the consumer is with the
network.
Why is Customer Perception Important?
Bharti Airtel’s key objective is to improve customer’s satisfaction by improving the network. To
achieve this, Airtel works with the actual data about how it’s network is perceived, and Customer
Perception data is used for this purpose.
What is Repeat Call Rate?
The Repeat Call Rate is a key KPI which measures the number of repeat calls.
When a user equipment (mobile device) [say UE1] disconnects with another user equipment [say
UE2] during or after a connected call, and UE1 calls UE2 again within 60 seconds of
disconnection, the call is counted as a repeat call.
Bharti Airtel Limited, India uses this collected RCR Data to improve and optimize its network.

11. 9
Why is RCR Needed?
Even with hundreds of KPIs available for network evaluation, it wasn’t possible to obtain the real
customer perception. This is because these KPIs only indicated network performance and missed
out on a very important aspect; what the customer felt about the network.
Even after working on, and suggesting improvements based on conventional KPIs like Network
Outages, Erroneous Session Release, etc. There was no way of correlating the number of
complaints, the customers actual perception and the network performance.
For instance, if the data of network outage was procured, it didn’t indicate the number of users
facing issues due to it.
As Airtel’s primary goal is customer satisfaction, with the aim of reducing customer complaints,
it has developed a new KPI, known as Repeat Call Rate.
RCR is a critical KPI. If a consumer is facing difficulties due to network complications and they
make the call again immediately after disconnection, it can be inferred that the call is urgent, and
crucial data about real customer perception is obtained.
Obtaining data about real customer perception is of utmost importance to Airtel, because the
changes to the network have a direct impact on this, and customer satisfaction can be achieved at
the ground level by driving down the number of complaints and reducing issues like muted voice,
latency, etc.

12. 10
Values Retrieved During RCR Data Collection
RCR Data Collection isn’t limited to just the number of repeat calls.
Various data associated with the repeat call is recorded into the database so that detailed reports
can be generated related to network and related issues at a later stage.
At Airtel, this data is retrieved in the following format:
Cell id
RCR
count
Network
(2G,3G,4G)
Hour
LAC (Location Area
Code)
Home Circle ID Load Date
46936 3 4G 20 165 101 7/9/2018
3793 5 3G 16 555 121 8/9/2018
**Invalid Data Used. Only for representative purposes.
The framework used for data retrieval is Apache Calcite and the platform used was Apache
Superset.
Apache Calcite
“Apache Calcite is an open source framework for building databases and data management
systems. It includes a SQL parser, an API for building expressions in relational algebra, and
a query planning engine. As a framework, Calcite does not store its own data or metadata, but
instead allows external data and metadata to be accessed by means of plug-ins.
Several other Apache projects use Calcite. Hive uses Calcite for cost-based query optimization”*2.
The commands used were:
select * from daily_rcrtable
where call_start_date=‘2018-06-07’
and trai_cirlceid=‘105’
2
https://en.wikipedia.org/wiki/Apache_Calcite

13. 11
* USING BACL END SQL QUERY IN SUPERSET
How is RCR Data Prepared?
Airtel has predefined algorithms which segregate user data and records it in the database which is
later used for bill generation and resolution of issues. This data is used to formulate the RCR data.
When an Airtel customer has made repeat calls to the same user within a period of 60 seconds,
these predefined algorithms identify this data as RCR data, extract all the relevant data of this call
and finally insert it into the RCR Database.

14. 12
What are the Major Factors which affect RCR?
Network Outage
When a User Equipment tries to latch to a failed cell (say due to a power failure or some other
issues), it will latch to the nearest available working cell. This working cell might be at a farther
distance than the failed cell.
Due to this increased distance between the latched cell and the user equipment, call quality might
drop and the user might face issues like muted voice. To rectify the issue, the user might disconnect
the call via regular session release, or the call might drop itself. In any of these cases, the user will
call again to complete his/her conversation, and this data will be recorded in the RCR data, thus
increasing the RCR data collected along with reduced Customer Satisfaction.
*Network Outage
A higher number of outage cells corresponds to a higher number of customer complaints.
Handover Success Rate
The Handover Success Rate(HOSR) is a measure of the successful handovers over the network.
If the user equipment moves during a connected call from the coverage area of one cell to another
cell, the call is handed over to the other cell in co-ordination with the BTS.

15. 13
If this handover fails due to some reason (say network outage), the call will be disconnected. The
user will call again, thus increasing the RCR Data and impacting the customer’s perception.
*Handover Success Rate
A higher Handover Success Rate corresponds to a lower number of customer complaints.
Dual Seizure
The Handover Success Rate(HOSR) is a measure of the successful handovers over the network.
“The condition that occurs when, in both-way operation, two exchanges attempt to seize the same
circuit at approximately the same time.” It is also known as Call Collision.3
3
http://www.atis.org/glossary/definition.aspx?id=7470

16. 14
*Dual Seizure
Dual Seizure increases the number of Repeat Calls, thus impacting customer perception.
Codec Negotiation
When a call is made, the analog signal is converted into digital signal using a codec via a
modulator. This digital signal is converted back to analog audio using a decoder at the receiver’s
end.
“Codecs are the algorithms which used to convert the analog audio signal to digitally
encoded version. There are simply a lot of codecs are introduced for different purposes.
Those different codec types differentiate in the outcome quality, the bandwidth
requirements and compatibility with the services.”
Some of the Codecs used are:
• G,711(PCM)
• Adaptive Multi-Rate Codec Type (AMR)
• Adaptive Multi-Rate Wideband Codec Type (AMR-WB) [Used by Bharti Airtel]
• GSM Full Rate Codec Type (GSM-FR)
• GSM Enhanced Full Rate Codec Type (GSM-EFR)
• GSM Half Rate Codec Type (GSM-HR)

17. 15
Tandem Free Operations (TFO) and Transcoder Free Operations (TrFO)
*TC: Traffic Channel (3, References and Readings)
If codec negotiation fails due to some reason (say Demodulator Malfunctioning), the call would
not be heard successfully on the user’s equipment. The user will call again to rectify the issue, thus
increasing RCR Data.
Higher level of successful codec negotiations lead to lesser number of repeat calls.

18. 16
What is done with this collected Data?
Since Bharti Airtel values the privacy of its customers, the data retrieved is split into respective
fields automatically with the help of Apache Calcite and individual customer’s data is not
displayed to the data analyst.
When RCR data is collected, the following actions are performed at MAPA(Management Audit
and Performance Analysis) Centre, Bharti Airtel, Gurgaon, Haryana, India:
1. CELL-Location Area Code (CELL-LAC) is isolated for cells with high RCR.
2. The radio and core KPIs of those specific cells are obtained from the database.
3. From these KPIs, the persistent issues are identified, like High Congestion, Paging
Congestion, Handover Success Rate, Dual Seizure, Codec Negotiation, etc.
• High Congestion: The reduced quality of service that occurs when a network node
or link is carrying more data than it can handle is known as High Network
congestion.
• Handover Success Rate: HOSR is the rate of successful connection between two or
more user equipments.
• Dual Seizure: When two users call each other at the same time, the channel is
blocked, and this scenario is known as Dual Seizure.
4. Improvements are suggested
5. Weekly reports (FI) are generated and impact measured.
6. Formal report generated for documentation purposes.
Post RCR Improvements
Network Rating as Mean Opinion Score
“Mean Opinion Score (MOS) is a measure used in the domain of Quality of
Experience and telecommunications engineering, representing overall quality of a stimulus or
system. It is the arithmetic mean over all individual “values on a predefined scale that a subject
assigns to his opinion of the performance of a system quality”.”4
4
https://en.wikipedia.org/wiki/Mean_opinion_score

19. 17
According to the telecom standards, any MOS ranging from 4 and above till 5, exhibits an efficient
network.
The RCR Data Collection was put in place at Bharti Airtel Limited, India in February 2017.
The MOS of its’ pan-India operations was calculated at 3.7 before this change was implemented.
After the RCR collection was implemented for a few months, and new suggested changes in effect
post its review, the MOS has increased to a score of 4.2, which is a drastic improvement in the
telecom industry.
CUSTOMER SATISFACTION SCALE ACCORDING TO MOS:
5
Since the implementation of RCR data collection and further network optimization, the complete
network has been optimized for more efficiency, eventually resulting in lesser mute calls, less
call drops, lower latency and jitter and thus, an improvement in Customer’s voice perception.
5
https://github.com/chanon-m/Measure-Call-Quality

20. 18
Changes Suggested in Data Retrieval Process
During my Internship at Bharti Airtel, I suggested some improvements for RCR Data Collection
Process.
These improvements did not only make the process faster and efficient, but also indirectly helped
in improving the Customer’s Perception.
Some of the changes and suggestions were:
• Using a front-end druid framework which employs JSON Queries in back-end, instead of
using SQL Queries via Apache Calcite. By this, more data could be incorporated in the
reports generated because of reduced limitations on Superset’s editor.
• Generating weekly reports of the repeat cells with most RCR count.
• Segregating the Weekday and Weekend data and reviewing it as the call usage varies
accordingly.
These changes, if incorporated, can give us a better overview of the network and its issues, and
provide us with data quicker enabling the operator to implement the required changes faster.
* USING FRONT END JSON QUERY AS SUGGESTED

21. 19
Conclusion
By the findings shown in this report, it can be clearly demonstrated that the adoption of Repeat
Call Rate as a Key Performance Indicator at Airtel has led to a better network, with a higher Mean
Opinion Score, reduced Customer Complaints and an Improved Customer Perception.
Since the adoption of RCR as a KPI, the call quality has improved drastically, which has led to
better profits as well.
Thus, it can be concluded that Using RCR data as a KPI in Mobile Network Management has
helped in improve Network QoS.
Appendix
Key Terms
KPI: Key Performance Indicators
RCR: Repeat Call Rate
QoS: Quality of Service
MTTC: Mean Time to Close
SQL: Structured Query Language
TRAI: Telecom Regulatory Authority of India
BCR: Block Call Rate
DCR: Drop Call Rate

22. 20
References and Readings
1. Measuring and improving network Performance-A whitepaper from Ericsson, Facebook
and XL Axiata: https://info.internet.org/en/wp-
content/uploads/sites/4/2016/07/10734295_270843076447514_1952370192_n.pdf
2. VOICE OVER LTE(Nokia Siemens Networks, Finland) - Miikka Poikselka, Harri
Holma, Jukka Hongisto, Juha Kallio and Antti Toskala
3. Different mechanisms for feedback-based control of operating modes and TFO/TrFO by
Avsar Asan (Technikum Wien – Telecommunication and Internet Studies)
Made By:
Anant Jain
anant.j2409@gmail.com