roaming & gsm anonymous audit report

8/11/2019 Roaming & GSM Anonymous Audit Report

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Astellia Roaming and GSM Analysis Customer Name page 1 / 66

GSM Roaming analysis

With Cigale


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Table of Contents

1 ABSTRACT ........................................................................................................................................................................5 1.1 INTRODUCTION ............................................................................................................................................................5 1.2 MAIN POINTS ...............................................................................................................................................................6

2 CIGALE ROAMING .........................................................................................................................................................7 2.1 LOCATION UPDATES .....................................................................................................................................................9

2.1.1 Roamers Networks ........................................................ ........................................................... .............................9 2.1.2 Roamers Network and Capture Cells.......................................................... ........................................................ 12 2.1.3 Reject and Failure causes per Roamers Network ...............................................................................................13 2.1.4 Roaming Capture Cells .................................................. ........................................................... ...........................14 2.1.5 Roaming Transit Cells............ ............................................................ ........................................................... .......17 2.1.6 Back subscribers................................................................................. ........................................................... .......19 2.1.7 Back subscribers with invalid Old LAC value ........................................................ ..............................................20 2.1.8 Competitors failures ....................................................... ........................................................... ...........................21

2.2 TRAFFIC .....................................................................................................................................................................22 2.2.1 Roamers networks and drop calls..................................................... ........................................................... .......22 2.2.2 Other roamers activities......................................................................................................................................25 2.2.3 Roaming traffic spots (cells)........................................... ........................................................... ...........................28

2.3 LOSS OF ROAMERS .....................................................................................................................................................29 2.4 ROAMING VIEW GIS .................................................. ........................................................... .....................................32

3 CIGALE GSM COMPLEMENTARY ANALYSIS ......................................................................................................33 3.1 CALL SETUP EFFICIENCY ............................................................................................................................................33

3.1.1 Originated call setup efficiency............................................................................................................................33 3.1.2 Terminated call setup efficiency......................................................... ........................................................... .......40

3.2 CALL DROPS ...............................................................................................................................................................44 3.3 HANDOVERS ..............................................................................................................................................................49

3.3.1 Outgoing Handovers causes.................................................................................................................................49 3.3.2 Ping-pong handovers............................................................................................................................................50 3.3.3 Asymmetric handover flows................................................................ ........................................................... .......52 3.3.4 Incoming handovers efficiency........................................................... ........................................................... .......53

3.4 TRAFFIC LOAD AND CONGESTION ...........................................................................................................................55 3.4.1 BSC_2053 Load and Congestion detailed analysis...................................... ........................................................ 56 3.4.2 BSC_2321 Load and Congestion detailed analysis...................................... ........................................................ 61

3.5 SMS...........................................................................................................................................................................63 3.5.1 SMS Originated .................................................... ........................................................... .....................................63 3.5.2 SMS Terminated ................................................... ........................................................... .....................................65

4 CONCLUSION :...............................................................................................................................................................66


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Table of Figures

Figure 1 - Astellias Top-down approach ......................................................................................................................7 Figure 2 - Subscribers classification ............................................................................................................................8 Figure 3 - Subscribers classification by IMSI................................................................................................................8 Figure 4 - Network statistics ranged by decreasing value of IMSI New (Req) .............................................................9 Figure 5 - Collected (Accept) IMSI by Network ..........................................................................................................10 Figure 6 - NC1_1 subscribers arrival cell list .............................................................................................................12 Figure 7 - Foreign_2 subscribers arrival cell list ........................................................................................................12 Figure 8 - Location Update Rejects and Failure causes ............................................................................................13 Figure 9 - Cells collecting roamers .............................................................................................................................14 Figure 10 - Roamers networks (Cell 15811)...............................................................................................................15 Figure 11 - Roamers networks (Cell 32232)...............................................................................................................15 Figure 12 - Cells retrieving roamers ...........................................................................................................................15 Figure 13 - Top 20 collecting cells..............................................................................................................................16 Figure 14 - Top 20 retrieving cells ..............................................................................................................................16 Figure 15 - Transit cells ..............................................................................................................................................17 Figure 16 - Ping-pong Location Updates between two Location Areas for cell 15001...............................................18 Figure 17 - Back subscribers ......................................................................................................................................19 Figure 18 - Back subscribers Invalid Old LAC.........................................................................................................20 Figure 19 - Competitors failures Competitor_1........................................................................................................21 Figure 20 - Competitors failures Competitor_2........................................................................................................21 Figure 21 - OC and TC traffic breakdown per network...............................................................................................22 Figure 22 - Cells dropping calls ..................................................................................................................................23 Figure 23 - Call drop rate Cell 15811 ......................................................................................................................23 Figure 24 - Details of causes for Call drop Cell 15811............................................................................................24 Figure 25 - Details of outgoing handovers Cell 15811 ............................................................................................24 Figure 26 - Roamers SMS and SS activity .................................................................................................................25 Figure 27 - Foreign_21 Mobile Roamers activity (more than 10 SMS O) ..................................................................25 Figure 28 - Roamer F21_1117 SMS activity ..............................................................................................................26 Figure 29 - Roamer F21_1117 SMS content..............................................................................................................26 Figure 30 - NC1_1 Roamers activity (more than 10 SMS O) .....................................................................................26 Figure 31 - NC1_1 Roamers SMS activity..................................................................................................................26 Figure 32 - NC1_1 Roamers SMS activity..................................................................................................................27 Figure 33 - Roamers SS activity.................................................................................................................................27 Figure 34 - Example of Supplementary Service to pre-paid subscriber .....................................................................27 Figure 35 - Example of USSD Service to pre-paid subscriber ...................................................................................28 Figure 36 - Traffic spot cells .......................................................................................................................................28 Figure 37 - Roaming Traffic compared to total traffic .................................................................................................29 Figure 38 - Loss / Recovery cells ...............................................................................................................................30 Figure 39 - Loss cells..................................................................................................................................................31 Figure 40 - Roaming View GIS...................................................................................................................................32

Figure 41 - Cigale GSM domains ...............................................................................................................................33 Figure 42 - OC Setup Inefficiency BSC Level .........................................................................................................33 Figure 43 - OC Setup Inefficiency Worst cells.........................................................................................................34 Figure 44 - OC Setup Inefficiency (Details) Cell 16336...........................................................................................35 Figure 45 - OC Setup Inefficiency (Details) Cell 12052...........................................................................................35 Figure 46 - OC Setup Inefficiency (State) Cell 16336 .............................................................................................36 Figure 47 - OC Setup Inefficiency (State) CMSRJ-NF ............................................................................................37 Figure 48 - Network topology......................................................................................................................................37 Figure 49 - OC Setup Inefficiency (Details) Cell 12053...........................................................................................38 Figure 50 - Activity in cells 12051 & 12052 After 10.30 AM ....................................................................................38 Figure 51 - Activity in cell 12053 After 10.30 AM.....................................................................................................38 Figure 52 - Activity in cells 1205x After 13.25 PM...................................................................................................39

Figure 53 - Call session with CM Service Reject cause Network Failure...................................................................39 Figure 54 - TC Setup Inefficiency BSC Level..........................................................................................................40 Figure 55 - TC Setup Inefficiency Worst cells .........................................................................................................40 Figure 56 - TC Setup Inefficiency (Details) Cell 16336 ...........................................................................................41 Figure 57 - TC Setup Inefficiency (Details) Cell 12052 ...........................................................................................42


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Figure 58 - TC Setup Inefficiency (State) CLCMD-CC............................................................................................42 Figure 59 - CLCMD-CC Message flow protocol decode .........................................................................................43 Figure 60 - Drop Call rate BSC level .......................................................................................................................44 Figure 61 - Drop Call rate Worst cells (more than 1000 established calls) .............................................................44 Figure 62 - BSS Drop Call rate Cell 32161..............................................................................................................45 Figure 63 - Outgoing Handover Details Cell 32161.................................................................................................46 Figure 64 - BSS Drop Call rate Cell 15241..............................................................................................................46 Figure 65 - Outgoing Handover Details Cell 15241.................................................................................................47 Figure 66 - BSS Drop Call rate Cell 1208................................................................................................................48 Figure 67 - Outgoing Handover Details Cell 1208...................................................................................................48 Figure 68 - Outgoing Handover Details BSC Level.................................................................................................49 Figure 69 - Ping-pong Handover By cell couples ....................................................................................................50 Figure 70 - Outgoing Handover Cell 1190...............................................................................................................51 Figure 71 - Asymmetric handover flow .......................................................................................................................52 Figure 72 - Handover efficiency definition ..................................................................................................................53 Figure 73 - Incoming handover efficiency rate (response) .........................................................................................53 Figure 74 - Details of non response for incoming handovers Cell 3066 .................................................................54 Figure 75 - Load and Congestion BSC level ...........................................................................................................55 Figure 76 - Load and Congestion BSC_2053 Worst cells (TCH Congestion)......................................................56 Figure 77 - OC Setup Inefficiency Cell 16336 .........................................................................................................57 Figure 78 - OC Setup Inefficiency (details) Cell 16336 ...........................................................................................57 Figure 79 - OC Setup Inefficiency (state) Cell 16336..............................................................................................58 Figure 80 - CLREQ-NRRA Message flow protocol decode.....................................................................................58 Figure 81 - Load and Congestion BSC_2053 Worst cells (HO Saturation) .........................................................59 Figure 82 - Details of non response for incoming handovers Cell 3066 .................................................................60 Figure 83 - Load and Congestion BSC_2321 Worst cells (HO Saturation) .........................................................61 Figure 84 - Details of non response for incoming handovers Cell 12111 ...............................................................62 Figure 85 - SMS Originated Efficiency .......................................................................................................................63 Figure 86 - SMS Originated Efficiency Details of inefficiency .................................................................................64 Figure 87 - SMS Originated Efficiency Details of inefficiency per SMS Center ......................................................64 Figure 88 - SMS Terminated Efficiency......................................................................................................................65 Figure 89 - SMS Terminated Efficiency Details of inefficiency................................................................................65


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1 Abstract1.1 Introduction

Astellia has committed to provide a sample analysis report based on data captured on Customers network.The purpose of this analysis was to determine the quality of Customers GSM network using Astellias Cigale GSMengine as well as perform a Roaming performance assessment of the network using Cigale Roaming module.

This analysis is performed based on data captured from January 19 th to January 23 rd.

During this trial, Customer has provided access to capture of 5 BSC (8 A interface signalling Time Slots each) and4 MAP interface links (one signalling TS each).

Capture was performed continuously during 120 hours starting on Thursday January 19 th at 0.00 AM until MondayJanuary 23 rd at 23.59 PM.

The captured areas consist in BSC_2050 (Area 1), BSC_2053 (Area 2), BSC_2059 (Area 3), BSC_2321 (Airport)and BSC_2577 (Neighbouring Country 1 Border).

As a result of these 120 hours of continuous capture, a total of about 17.3 GB of signalling raw data was retrieved.This data was post processed with Astellias Cigale Engine in order to obtain the following:

1. Input data for roaming module (aggregated over the 120 hours of capture)2. Cigale View Database providing KPIs (daily database)

Additionally, a Cigale Roaming processing was performed in order to extract information specific to inboundroamers. This post processing includes Astellias value added feature providing information on the loss of roamers.

For the GSM analysis sample, the data from Friday 20 th January is used.For the Roaming analysis 5 days aggregated data is used.

Note:

When performing the post processing in Singapore, it was noticed that a mis-configuration had been done onthe time slot switching with Manta. Indeed, at the end of the processing, Cigale warned that two TS werecarrying the same information. This was not seen when presenting the data to Customer on January 19 th.These TS belong to BSC_2577 (Country Border).Several calls have thus been disregarded by Cigale engine due to incomplete call flow (only part of thesignalling messages seen due to missing one signalling TS).As a consequence, some statistics obtained on BSC_2577 (especially GSM KPIs) may not be pertinent due tothis mis-configuration.

Note:

Only part of Cigale GSM / Cigale Roamings capabilities are presented in this sample analysis report.The points presented herein have been selected to highlight the most important issues revealed by the analysisand cover Customers expectations expressed by email on February 2 nd .


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2 Cigale RoamingThe purpose of Cigale Roaming analysis is to bring to Customer key information to increase their revenuegeneration through a better understanding of roaming activity on their network.

Cigale Roaming allows to: Identify roaming capture zones, Define roaming traffic spots and mobility within the network, Identify areas where radio coverage is poor and where roamers are lost, Study the behaviour of roamers per IMSI and network of origin, Analyse roamers problems at cell, BSC or LAC levels, Generate reports (for example daily reports) Provide information on the last visited network for Customers subscribers coming back from abroad.

Information delivered by Cigale Roaming module can be analysed at different levels:

Figure 1 - Astellias Top-down approach

Cigale Roaming module provides statistical information of roamers location update efficiency.For this purpose, different categories of roamers are defined:

Collected: Roamers coming directly from a foreign network (their last location update registration wasabroad);

Retrieved: Roamers coming from a competitive network (previous location update registration performedon a competitors network)

New: Is the union of Collected and Retrieved roamers; Transit: Roamers moving within Customers network (previously registered on Customers network); All: Is the union of New and Transit roamers.

Additionally, a category for Customers subscribers is defined: Back: Customers subscribers coming back from another network (either abroad or Customers

competitors)

Information on these categories (Collected, Retrieved, New, Transit, All, Back) is provided: For the number of different roamers (or subscribers): IMSI For the total number of procedures: Total


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For example 50 different users (IMSI=50) could generate a total of 200 procedures.The IMSI information provides a better subscriber view of roaming activity.

These categories can be represented using the following drawings:

Figure 2 - Subscribers classification

Figure 3 - Subscribers classification by IMSI

During the capture period, the same subscriber can belong to several categories: Collected if coming from a foreign network, Transit when moving within Customers network Retrieved if coming back to Customers network from a competitor.


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2.1 Location updates2.1.1 Roamers Networks

Cigale Roaming provide the following information per network: IMSI New (Req): the number of different NEW roamers that performed a location updating request; IMSI New (Acc): the number of different NEW roamers that received a location updating accept; %IN(Acc): the percentage of NEW roamers accepted location updates; %IN(PLMNna): the percentage of NEW roamers rejected location updates for cause PLMN Not Allowed; %IN(other): the percentage of NEW roamers rejected location updates for other cause than PLMN

Not Allowed; IMSI Coll (Req): the number of different COLLECTED roamers that performed a location update request

(when coming from another country than Customers country); IMSI Coll (Acc): the number of different COLLECTED roamers that received a location updating accept

(when coming from another country than Customers country); IMSI Retr (Req): the number of different RETRIEVED roamers that performed a location update request

(when coming from a competitors network such as Competitor_1, Competitor_2 ); IMSI Retr (Acc): the number of different RETRIEVED roamers that received a location updating accept

(when coming from a competitors network such as Competitor_1, Competitor_2 ).

The table below presents these statistics sorted by decreasing value of IMSI New (Req).

Figure 4 - Network statistics ranged by decreasing value of IMSI New (Req)

It can be noted that during the observation period (120 hours), roamers from 459 networks have tried to register onCustomers network. We can also see that competitors from Customer are properly rejected with cause PLMN NotAllowed.

Networks with the highest number of roamers trying to register on Customer are from (for networks with more than600 roamers trying to register):

Neighbouring Country 1 (NC1_1, NC1_2 and NC1_3), which is not surprising considering the fact that aBSC covering the border between Customers country and Neighbouring Country 1 is part of the capture,

Foreign_1, Foreign_2, Foreign_3, Foreign_4


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However, we can notice for Foreign_1 that some roamers are accepted (24.9%) and others are rejected with causePLMN Not Allowed (18.35%). This also applies to several other networks.Such behaviour is not the best. Indeed, PLMN NA cause should only be used for Customers competitors. Whenreceiving PLMN Not Allowed, the mobile station will store Customers network within its SIM card into the list offorbidden PLMNs. It will never try again to select automatically Customer when roaming.

This is the reason why other reject causes like Roaming Not Allowed in the Location Area (RNAILA) or LocationArea Not Allowed (LANA) are preferably to be used with foreign networks. With these reject causes, the mobilestation will keep Customers rejected Location Area in its volatile memory. Then, the mobile may either try to selectanother network (if rejected with RNAILA) or stay under Customer radio coverage (if rejected with LANA).

ACTION FLAG: Roamers coming from operators others than Customers direct competitors should not be rejectedwith PLMN NA cause. Other reject causes such as Roaming Not Allowed in this Location Area or Location AreaNot Allowed should be used.

Assuming the fact that if subscribers are from a network are 100% rejected with PLMN Not Allowed cause thiscorresponds to lack of roaming agreements, Cigale Roaming allows to identify with which operators Customer doesnot have roaming agreements:

Foreign_29 : 251 subscribers Foreign_46 : 171 subscribers Foreign_49 : 161 subscribers Foreign_51 : 153 subscribers Foreign_53 :122 subscribers Foreign_59 : 110 subscribers Foreign_63 : 105 subscribers Foreign_64 : 105 subscribers

ACTION FLAG: it may be interesting for Customer to obtain roaming agreement with these operators as they canprovide some revenue increase.

Location Update information can also be displayed as a bar-graph, for example here for the top 20 networks.

By Imsi, Top 20 Collected (Accept) from network

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Figure 5 - Collected (Accept) IMSI by Network


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Since the number of Collected subscribers is more important than the number of Retrieved ones, we can confirmthat roaming some entry points (such as airports, borders) are captured. This document will later on describewhere roamers are collected and retrieved in the monitored area (cell information).

The first 10 collected networks are the following (successful registration): NC1_1 Neighbouring Country 1 NC1_2 Neighbouring Country 1 NC1_3 Neighbouring Country 1 Foreign_2 Foreign_3 Foreign_4 Foreign_9 Foreign_7 Foreign_3 Foreign_8 Foreign_12

We can also notice that for these 20 first networks, the ratio New / (Collected + Retrieved) is always lower than 1

which indicates that some roamers have been detected as both Collected and Retrieved roamers. This may beeither due to problems to connect to their network (HLR) or due to loss of coverage while under Customersnetwork.


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2.1.2 Roamers Network and Capture Cells

Using Astellias Cigale Roaming module, it is possible to identify where subscribers from a particular network aretrying to register on Customers network.

For example, below is displayed cells in which NC1_1s roamers are registering (cells are sorted by decreasingIMSI New (Acc) values).

Figure 6 - NC1_1 subscribers arrival cell list

In this particular case, we notice that most subscribers try to register in cells from BSC_2577 (border withNeighboring Country 1) but also that some of them are arriving thru cells from BSC_2321 (Airport).

If the same information is displayed for Foreign_2, we can notice that most subscribers are registering in cells fromBSC_2321 (Airport) and in particular, cell 15811.

Figure 7 - Foreign_2 subscribers arrival cell list


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2.1.3 Reject and Failure causes per Roamers Network

Cigale Roaming module provides detailed information on Location Updating Reject and Failure causes.

The following information is available per network:

NewIMSI_LUnu: the number of different new roamers that performed a location updating request; NewIMSI_LUac: the number of different new roamers that received a location updating accept; NewIMSI_LUrj_NF: the number of different new roamers that received a location updating reject with

cause Network Failure; NewIMSI_LUrj_PLMNna: the number of different new roamers that received a location updating reject with

cause PLMN Not Allowed; NewIMSI_LUrj_IUH: the number of different new roamers that received a location updating reject with

cause IMSI Unknown in HLR; NewIMSI_LUrj_RNAILA: the number of different new roamers that received a location updating reject with

cause Roaming Not Allowed In this Location Area; NewIMSI_ClRq_RImf: the number of different new roamers that had a location updating failure

because of a Clear Request message with causes Radio Interface Failure andRadio Interface Message Failure;

NewIMSI_Pb_xx: the number of different new roamers that had a location updating failurebecause of another message / cause than the previous ones.

The screenshot below presents (for part of the networks) the breakdown of Location Updates failure causes.

Figure 8 - Location Update Rejects and Failure causes


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Apart from the fact that PLMN Not Allowed cause seems to be abusively used in Customers network (asmentioned in section 2.1.1), we can notice the following:

Several subscribers from NC1_2 (155), Foreign_1 (49), Foreign_20 (35) and Foreign_22 (89) are rejectedwith cause Network Failure,

Some subscribers from several operators are rejected with cause Roaming Not Allowed in this LocationArea. This probably corresponds to roamers without roaming option.

Several roamers (from several networks) encounter radio problems during the location registrationprocedure.

Some roamers are rejected with cause IMSI Unknown in HLR. This may correspond to new subscribers forwhich the subscription information has not yet been written in the HLR or subscribers for which thesubscription has been terminated.

For the case of Registration Failure due to Network Failure, the use of Activity Analysis does not allow to identifyspecific HLR or time window where subscriber are not able to register on Customers network (only NC1_2 andForeign_22 have been investigated).

2.1.4 Roaming Capture Cells

Cigale Roaming information can be provided directly at a cell level, to identify roamers capture spots.

To identify roamers entry points within the monitored area, it is interesting to sort the data by decreasing number ofcollected roamers (as defined before, a collected roamer is coming directly from a foreign network). This isillustrated by the picture below.

Figure 9 - Cells collecting roamers

From this table, we can identify that cells 32232 (BSC_2577), 15811 (BSC_2321), 32128 (BSC_2577), 15001(BSC_2321) and 15814 (BSC_2321) are the cells collecting the highest number of roamers (between 900 and1900).These cells are probably located on main roads at the country border and in the airport.


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It is also possible to display the details per network (cf. below). This view allows the identification, per cell, of whichnetwork new roamers belong to.

Taking the example of cell 15811, we can notice that, by decreasing number of collected roamers, these arecoming from Foreign_2, Foreign_4, Foreign_6, Foreign_1, Foreign_9

Figure 10 - Roamers networks (Cell 15811)

For cell 32232, we can see that in this case, most of the roamers are coming from the Neighbouring Country 1.Only 2 roamers are coming from either Foreign_108 or Foreign_2.

Figure 11 - Roamers networks (Cell 32232)

Another category of capture cells consist in identifying cells with the highest number of retrieved roamers. Thesecells will indicate where Customer has a better coverage than its competitors.

To illustrate this, the picture hereafter sorts the number of retrieved new roamers by decreasing values for each cell(more than 300 retrieved roamers).

Figure 12 - Cells retrieving roamers

Cells 15241 and 15378 are retrieving more than 300 roamers from competitors networks.


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Another possibility to quickly identify capture cells is to use a graphical display of the data as shown in the next twopictures for collected and retrieved roamers respectively.

Figure 13 - Top 20 collecting cells

Figure 14 - Top 20 retrieving cells


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2.1.5 Roaming Transit Cells

More information can be displayed for roamers in transit within Customers network. This includes: IMSI Tran (Req): the number of roamers performing a location updating request, when moving towards a

new LAC within Customers network (while they are already registered on Customers

network); IMSI Tran (Acc): the number of roamers that received a location updating accept, when moving towards anew LAC within Customers network (while they are already registered on Customersnetwork);

%IT (Acc): the percentage of accepted location updates for in transit roamers; Tot Tran (Req): the total number of location updating requests performed by roamers in transit; Tot Tran (Acc): the total number of location updating accepts received by roamers in transit; %TT (Acc): the percentage of accepted location updates attempts from in transit roamers.

The picture below illustrates the transit points for roamers within Customers network.

Figure 15 - Transit cells

We can see that cells 11084, 15001, 11665, 1234 and 5205 are the most important transit points in the monitoredarea with more than 2000 roamers in transit. These cells should be at the boundary of two Location Areas of thenetwork. These cells are important to optimize and maintain available since they are the main points for roamersmobility in Customers network.

We can also notice that for cell 15001 the total number of Location Update procedures is very high compared to thetotal number of roamers (2882 roamers have generated 4211 procedures).

Using Activity Analysis (refer to next page screenshot), it is possible to identify that some subscribers areperforming mobility between LAC 20602 and LAC 20802 from Customers network. The two LACs probably belongto different MSC since there is a MAP Cancel Location procedure triggered when moving from one LAC to theother.In fact, roamer NC1_3_6451 generates 34 Location Update procedures on cell 15001 between 11.57.42 and

12.11.59 on Saturday January 21st

.ACTION FLAG: In order to decrease the number of ping-pong Location Updating procedures between LAC 20602and its neighbours (LAC 20802 at least), it may be interesting to increase the parameterCELL_RESELECT_HYSTERESIS on cells at the border of LAC 20602 such as cell 15001. Indeed, this parameteris a margin on the field level (in dB) to avoid leaving the cell on which a subscriber just arrived (as long as the fieldlevel on any other cell is not higher by at least CELL_RESELECT_HYSTERESIS dB, the mobile will not performreselection). Other radio parameters may apply for cell reselection, but CELL_RESELECT_HYSTERESIS mostlyserves in case of change of Location Area.


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Figure 16 - Ping-pong Location Updates between two Location Areas for cell 15001


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2.1.6 Back subscribers

Back subscribers are Customers subscribers coming from abroad. They can be easily identified thanks to the OldMCC / Old MNC value stored in the SIM card and provided during the location updating procedure.

The following information is available:

IMSI Back (Req): the number of Customers subscribers performing a location updating request whencoming back from an other network than the monitored network; IMSI Back (Acc): the number of Customers subscribers that received a location updating accept when

coming back from an other network than the monitored network.

The following picture can be used to identify from which countries Customers subscribers are coming from abroad.

Figure 17 - Back subscribers

Network 00000 represents bad old LAC information for Customers subscribers. It could be for new subscribers(LAC unknown in the SIM card) or because a previous Location Update was rejected for a subscriber with an old

handset.

We can see that most of Customers subscribers are coming back from Neighbouring Country 1 (not surprisingconsidering the fact that the border with this country is monitored), Foreign_1, Foreign_45, Foreign_75,Foreign_23

ACTION FLAG: It may be useful to check if outbound roaming is done to Customers preferred partners networks.


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2.1.7 Back subscribers with invalid Old LAC value

The Old LAC value sent during the location updating procedure can be used to identify another category ofsubscribers.In the case the Old LAC value provided is an invalid value (0, 65534 or 65535), it means that Customerssubscribers had a failure on their previous location update attempt.IMSI Back (iol) information may then indicate areas where Customers subscribers come back after having had aradio coverage problem.

The following information can be used: IMSI Back (iol) HPLMN: the number of Customers subscribers performing a location updating request

that indicate Customers as Old PLMN information but with a non-valid value forthe previous registered LAC (iol = invalid old LAC).

Figure 18 - Back subscribers Invalid Old LAC

Main cells that seem to have radio coverage issues since more than 2000 subscribers from Customer haveperformed a Location Updating procedure with an invalid old LAC are neighbours from cells 5282, 5032, 11102 and11084 and also possibly these cells themselves.

ACTION FLAG: The possible corrective actions to enhance Customers radio coverage in these cells anddepending on their geographical location could be:

Modification of radio parameters, Change (tilt) of antenna, New site,


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2.1.8 Competitors failures

Thanks to Cigale Roaming, it is possible to get information on competitors failures (mainly radio coverageproblems) by using cells on which they try to perform location updates on Customers network.

As already seen previously, the reject cause for these subscribers should be PLMN NA which prevents them to tryto select Customers network automatically.

The pictures below provide a list of the main cells for which competitors subscribers are trying to register onCustomers network.

Figure 19 - Competitors failures Competitor_1

Figure 20 - Competitors failures Competitor_2

We can notice that several competitors subscribers try to register in cells 32232, 32231, 5509

ACTION FLAG: It should be noted here that roamers on the competitors network will encounter the samecoverage issues as competitors home subscribers and it may thus be interesting for Customer to take actions toretrieve these roamers (or even capture then from the very beginning) on these cells.

Additionally, such information on competitors network radio coverage might be used for marketing purposes forexample towards business accounts (companies) identified in the area where competitors coverage is not asefficient as Customers.


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2.2 Traffic

Cigale Roaming module provides statistical information on roamers activity.The following categories are defined:

Calls: Mobile originating calls for speech (VOC), mobile originating calls for data (DOC), mobile

originating emergency calls (EC), mobile terminating calls for speech (VTC), mobile terminatingcalls for data (DTC); SMS: SMS-Mobile Originating (SMS-MO), SMS-Mobile terminating (SMS-MT); SS: Supplementary Services (SS-MO).

2.2.1 Roamers networks and drop calls

Cigale Roaming module follows the activity of roamers and provides traffic information per network.

Among all the available data, it is possible to focus on: IMSI nb: The number of different roamers having traffic activity (calls, SMS and SS); Call Init: The number of all call attempts (OC and TC for speech and data and emergency calls)

initiated; Call Traff: The total duration (in hour) of all connected calls; Call %Ring: The percentage of initiated calls that reach the alerting phase; Call %Com: The percentage of initiated calls that are connected and reach the conversation phase; Call %Drop: The percentage of connected calls which are dropped (abnormal release); Call Avg: The average duration (in seconds) of connected calls; VOC Traff: The total duration (in hours) of connected Voice Originating Calls; VOC %Drop: The percentage of connected Voice Originating Calls which are dropped (abnormal

release); VOC Avg: The average duration (in seconds) of connected Voice Originating Calls; VTC Traff: The total duration (in hours) of connected Voice Terminating Calls; VTC %Drop: The percentage of connected Voice Terminating Calls which are dropped (abnormal

release); VTC Avg: The average duration (in seconds) of connected Voice Terminating Calls;

The next snapshot provides the traffic repartition between Originated and Terminated calls for each network.

We can notice that the first networks with the highest roaming traffic are Foreign_1, NC1_2, NC1_1 and Foreign_3with each more 62 hours of communication. Subscribers from NC1_1 have the highest number of calls.The average call duration for these networks is between 90 and 193 seconds for these networks.

We can see that for most of the networks, the ratio of calls reaching the ringing state is above 60% (above 78% ifwe exclude Neighbouring Country 1 operators) whereas the ratio of calls reaching the connected state is between30% and 56%.

Figure 21 - OC and TC traffic breakdown per network


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It is also possible to verify on which cells the call drop rate or number of calls dropped is important.By sorting the data by number of calls dropped in a cell (Call Drop End), we obtain the view presented below:

Figure 22 - Cells dropping calls

We here notice that cells 15811, 33705, 1170, 1160, 15001, 15002, 15812, 15334, 15335, 1400 and 15814 aredropping more than 20 calls (between 3% and 15% of the calls terminated in these cells).

ACTION FLAG: Several of these cells have been identified as capture cells (either Collected or Retrieved). It maybe interesting to perform radio optimisation of these cells in order to retain roamers in Customers network.

Causes of drop calls in cell 15811:Using the Cigale View database, it is possible to assess the quality of cell 15811 for all the subscribers (homesubscribers or roamers) in this cell. In particular, we can display the drop call rate for cell 15811 (see below).

Figure 23 - Call drop rate Cell 15811

We can notice here that the total drop call rate is about 4%, similar to the one for roamers, and mostly due to BSSoriginated Clear Request messages. If we drill down, we can display the details of the causes for drop calls in cell

15811 and in particular, we can notice that the main cause is a Clear Request message with cause Radio InterfaceFailure (85% of the failures).


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Figure 24 - Details of causes for Call drop Cell 15811

When looking at the outgoing handover causes, we can notice (see below) that there are many Downlink Strength(DLS) and Uplink Quality (ULQ) with the main neighbours (15812, 11711, 11084 and 11746).

Figure 25 - Details of outgoing handovers Cell 15811

ACTION FLAG: This could be linked to defaults and signal losses in the transmit path (antenna, duplexer,feeder). If Uplink Power Control is active, a check of the target value should be done.


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2.2.2 Other roamers activities

Cigale Roaming offers complementary roaming traffic information for SMS and other procedures: SMS O: The number of SMS Mobile Originating attempts; SMS O Time: The total duration (in hours) of SMS MO attempts; SMS O %Eff: The percentage of successful SMS MO attempts; SMS T: The number of SMS Mobile Terminating attempts; SMS T Time: The total duration (in hours) of SMS MT attempts; SMS T %Eff: The percentage of successful SMS MT attempts; SS: The number of Supplementary Service (Mobile Originating) attempts; SS %Eff: The percentage of successful Supplementary Service attempts; IMSI Att: The number of location updating requests for IMSI attach for roamers already registered

in the observed location areas; IMSI Att %Eff: The percentage of accepted location updating requests for IMSI attach; IMSI Det: The number of IMSI detach messages received for roamers.

Figure 26 - Roamers SMS and SS activity

We can notice that roamers from Foreign_2 are sending a lot of SMS with around 3000 SMS sent other 5 days andmore than 4000 SMS received (but this also includes welcome messages).The Originated SMS efficiency is quite high for most networks except for NC1_1 (49.6%), Foreign_21 (30%) andNC1_3 (54%). However, for these networks, the Terminated SMS efficiency is above 90%.

In the case of Foreign_21, thanks to Activity Analysis, we can identify that this is mainly due to one roamer who hastried to send 582 SMS without success! (see below)

Figure 27 - Foreign_21 Mobile Roamers activity (more than 10 SMS O)

This roamer (IMSI = F21_1117) tries to send an SMS on January 21 st at 18.18.21. This SMS is rejected with causeNetwork Out of Order and his mobile then tries to send the SMS every 40 seconds (see below).His mobile considers the failure as temporary and tries again and again to send the SMS.


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Figure 28 - Roamer F21_1117 SMS activity

Figure 29 - Roamer F21_1117 SMS content

In the case of NC1_1, thanks to Activity Analysis, we can identify that this affects several subscribers (see below).These subscribers are however able to receive SMS.

Figure 30 - NC1_1 Roamers activity (more than 10 SMS O)

When checking on the Activity of these subscribers, we can notice that this corresponds to subscribers who are notallowed to send SMS: the SMS is rejected with cause Call Bared.

Figure 31 - NC1_1 Roamers SMS activity


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Figure 32 - NC1_1 Roamers SMS activity

It is also possible to focus on Supplementary Services. When sorting the same data as previously but bydecreasing values of Supplementary Services, we obtain the following table:

Figure 33 - Roamers SS activity

Roamers from Neighbouring Country 1 and Foreign_4 networks are those using the most supplementary services.The efficiency on supplementary services is between 84% and 100% for networks with more than 100Supplementary Service activities.

Thanks to Activity Analysis, it is possible to see the detailed activity of roamers. For example, if we take one roamerfrom Foreign_4, we get:

Figure 34 - Example of Supplementary Service to pre-paid subscriber


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This roamer sends an SMS, then checks his balance using a Supplementary Service to know his credit by diallingthe service code *#10#. He does not use traffic channel but only SDCCH resources for the request and theresponse.

Taking one roamer from NC1_1, we obtain the following activity:

Figure 35 - Example of USSD Service to pre-paid subscriber

This roamer uses a USSD call-back mechanism to call a number. He first dials a USSD string which contains thecall back service code (*120*) and then receives a message Call setup in progress. Please wait for call back and

then receives an incoming call.This USSD call-back service is provided by the home network of the roamers and allows them to reduce the cost oftheir calls when roaming by transforming an outgoing call into an incoming call which is cheaper when roaming.

ACTION FLAG: Due to the increase of the number of value-added services provided by networks throughSupplementary Services, it is recommended to ensure that SDCCH resources are correctly dimensioned.

2.2.3 Roaming traffic spots (cells)

Roaming traffic data can be displayed directly at the cell level. This allows an easy identification of roaming trafficspots as shown on the picture below.

Figure 36 - Traffic spot cells

We can see that cells 15814, 33705 and 15812 are the cells with the highest roaming traffic (more than 60 hours).At the cell level a new parameter is available:

Call %Roam: The percentage of roaming traffic within the total cell traffic (all connected calls, all users).

We can see that for the aforementioned cells, the roaming traffic represents 12.3% to 35.2% of the total traffic ofthe cell.


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If the data is sorted by roaming traffic ratio, we notice that cells 15295, 15334, 15814 and 15852 have the highestroaming traffic with more than 30% of the total traffic.

Figure 37 - Roaming Traffic compared to total traffic

ACTION FLAG: Except for cell 15814, none of the aforementioned cells have been identified as roaming capturecells. It is possible that roamers have already been captured before arriving in these cells.

ACTION FLAG: Cells with high roaming traffic should be monitored regularly in order to ensure quality(registration, call establishment, call quality, capacity ) as these cells will generate a lot of revenues.

2.3 Loss of roamersWith the Loss of Roamers (LOR) option, Cigale Roaming performs a correlation between A interface activity(including the cell value) and MAP CANCEL_LOCATION messages.

This allows the identification of cells where roamers are leaving the monitored VLR area ( Loss ) or coming backinto the monitored area ( Recovery ).

Information provided by Cigale Roaming includes: Tot LossWoLUnETL: the number of times a Cancel Location is received in less than 5 minutes

(threshold parameter value) after an A interface activity of the roamer otherthan Location Update;

IMSI LossWoLUnETL: the number of different roamers considered as lost; AvgET LossWoLUnETL: the average duration between the last A interface activity and a Cancel

Location, with the application of the 5 minutes threshold for the Lossdetection;

Tot RecETR: the number of times A interface activity is detected in less than 5 minutes(threshold parameter value) after a Cancel Location of the roamer;

IMSI RecETR: the number of different roamers considered as Recovered; AvgET RecETR: the average duration between a Cancel Location and a new A interface

activity, with the application of the 5 minutes threshold for the Recoverydetection;

Tot Collected: the number of times a Recovered roamer is also considered as a Collectedroamer. It indicates that the roamer had left Customers network for a foreignnetwork;

Tot Retrieved: the number of times a Recovered roamer is also considered as a Retrievedroamer. It indicates that the roamer had left Customers network for acompetitive network;

Tot Transit: the number of times a Recovered roamer is also considered as a Transitroamer. It indicated the roamer had moved into another VLR area ofCustomers network.


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The snapshot below shows the breakdown of roamers lost per cell sorted by decreasing number of IMSI lost within5 minutes of last activity (other than Location Update) on A interface.

Figure 38 - Loss / Recovery cells

We can notice that cells 15814, 32232, 33705, 15001 and 15811 are the cells loosing the highest number ofroamers with more than 500 roamers lost over the 120 hours of capture.

These roamers are lost within 2 minutes of their last activity seen on the A interface (activity other than a locationupdate), which indicate that they are probably lost in these cells or their immediate neighbours.


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A complimentary filtering can also be done in order to keep cells that have more Total Retrieved than TotalCollected or Total Transit, which means that these cells are not at a country border or at a VLR border and thusshould be real cells where roamers are lost from Customers network.

Figure 39 - Loss cells

We can see that cells 32127, 15378, 15241 and 5509 are the 4 main Loss Cells with respectively 101, 82, 73 and72 roamers lost (as counted by IMSI LossWoLUnETL).

ACTION FLAG: It can be noted that except for cells 15241 and 15378 that have been identified as cells Retrievingroamers, the other cells have not been identified as capture cells or traffic spots.


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2.4 Roaming View GIS

Cigale Roaming also offers that capability to display KPIs on a GIS.This can be very useful when wanting to get a geographical representation of a KPI, for example cells loosingroamers. The simple pre-requisite to be able to display any KPI generated by Cigale Roaming on the map is to

have the position and coverage area of all the cells. A map background can also be integrated.Below is an example of the use of Roaming View GIS showing the repartition of lost roamers per cell.Please note that this is based on randomly generated data.

Figure 40 - Roaming View GIS


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3 Cigale GSM complementary analysisCigale GSM completes and enriches the operational data supplied by the GSM network equipment. Cigale can beused both for optimisation campaigns and (in a more permanent way) as a QoS and Network Performancemonitoring tool.

It allows to: Measure and visualize overall QoS at various level (network, MSC, BSC, cell); Calculate call establishment inefficiency rates and differentiate inefficiency causes on call and BSC levels; Detect traffic free cells (derived from the BTS clock, blocked TS); Detect handover failures (wrong declaration of neighbourhood, inter-BSC handovers) and separating the

causes of handovers; Calculate drop call rates on cell and BSC levels, and separate their causes between different problems:

radio, BSS system, NSS and IO problems (interferences, coverage holes); Detect congestion (radio, A interface, network); Display SMS efficiency with related causes;

This information can be displayed using Astellias Cigale View module as part of different fields of investigation asshown below.

Figure 41 - Cigale GSM domains

This section presents a complementary study from Cigale main domains: call setup, call drops, handovers, trafficand SMS.

3.1 Call setup efficiency

3.1.1 Originated call setup efficiency

At the BSC level, the Originated Call Setup efficiency shows a global inefficiency between 2 to 6% for inefficienciesattributed to either the NSS or BSS.

Figure 42 - OC Setup Inefficiency BSC Level


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It can be noticed that the User Inefficiency accounts for around 9% in the total inefficiency. This includes caseswhere the calling party cancels his call before the Alerting, Progress or Setup message. It also includes caseswhere the called party is already engaged.

When the inefficiency is displayed for the cells with a significant number of calls (more than 1000 calls, limited tothe 10 worst cells), we can identify the cells with the worst efficiency in the monitored area (see below).

Figure 43 - OC Setup Inefficiency Worst cells

Cigale View also allows displaying the breakdown of inefficiency causes.

Thanks to this capability, it is possible to identify (see below screenshots) that: The main cause of inefficiency for cell 16336 is No Radio Resource Available (BSS inefficiency) The main cause of inefficiency for cells 12052 and 12051 is due to CM Service Reject, cause Network

Failure (NSS inefficiency) The main cause of inefficiency for cell 16335 is No Radio Resource Available (BSS inefficiency) The main cause of inefficiency for cell 32162 is No Radio Resource Available (BSS inefficiency). However,

this cell is part of BSC_2577 for which there has been a capture mis-configuration The main cause of inefficiency for cell 1170 is No Radio Resource Available (BSS inefficiency)


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Figure 44 - OC Setup Inefficiency (Details) Cell 16336



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Case of cells 16336, 16335 and 1170:All these failures occur in the state OC_ASS_QI_1, meaning that the call has been already queued due to the lackof TCH and is then released as no TCH is freed before expiration of the queuing timer.

Figure 46 - OC Setup Inefficiency (State) Cell 16336

ACTION FLAG: The configuration of cells for which there is a high inefficiency due to No Radio ResourceAvailable should be verified in order to ensure that no TS are blocked or TRX are failed. This behaviour could alsobe due to TCH being reserved for GPRS only. Eventually, the site capacity should be increased in order to be ableto handle the traffic requested.


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Case of cells 12052 and 12051:We have identified that for these two cells the main inefficiency is due to the Core Network sending a CM ServiceReject message. Furthermore, thanks to the details of states provided by Cigale, it is possible to identify that thisoccurs straight after the CM Service Request and affects only these two cells (see below).

Figure 47 - OC Setup Inefficiency (State) CMSRJ-NF

Using Cigale capability to identify the network topology, we can notice that cells 12051 and 12052 appear twice: Linked to BSC_2321 (LAC 20602) Linked to an unknown BSC (LAC 20402). The BSC is unknown as not part of the monitored area, but is

seen thru the handover messages.

Figure 48 - Network topology

We can also notice that this site has a third cell (cell 12053). This last cell does not suffer from the same behaviour(see below for details of inefficiency).


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As the cells from this site are associated to two different BSC, we can conclude that there has been a networkreconfiguration on January 20 th and that the site 1205x has been moved to BSC_2321 during that day.

This can be confirmed thanks to the troubleshooting database using Activity Analysis and we can notice that noactivity occurs on these 3 cells before 10.30 AM. We can also identify in the database that the CM Service Rejectmessage with cause Network Failure seen on cells 12051 and 12052 only happens between 10.30 AM and 13.25

PM, time after which all three cells of the site are working properly. In fact, only incoming handovers are acceptedon these two cells. Location Updates are also rejected with cause Network Failure.

Also, thanks to the protocol decode capability from Activity Analysis, it is possible to display and decode themessages exchanged during such a session.

Figure 50 - Activity in cells 12051 & 12052 After 10.30 AM

Figure 51 - Activity in cell 12053 After 10.30 AM


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3.1.2 Terminated call setup efficiency

At the BSC level, the Terminated Call Setup efficiency shows a global inefficiency between 0.6 to 3.6% forinefficiencies attributed to either the NSS or BSS.

Figure 54 - TC Setup Inefficiency BSC Level

When the inefficiency is displayed at the cell level, we can identify the cells with the worst efficiency in themonitored area (see below, limited to 10 worst cells).

Figure 55 - TC Setup Inefficiency Worst cells


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We can notice that the main worst cells in terms of terminated calls are those already highlighted thru theoriginated call setup analysis: cells 16336, 12052, 12051, 16335, 1170 and 32162.

When displaying the breakdown of inefficiency causes, we can identify the main cause of failing to establish theterminated calls (see below screenshots):

The main cause of inefficiency for cell 16336 is No Radio Resource Available (BSS inefficiency) The main cause of inefficiency for cells 12052 and 12051 is due to a Clear Command message with cause

Call Control (NSS inefficiency) The main cause of inefficiency for cell 16335 is No Radio Resource Available (BSS inefficiency) The main cause of inefficiency for cell 1170 is No Radio Resource Available (BSS inefficiency) The main cause of inefficiency for cell 32162 is No Radio Resource Available (BSS inefficiency). However,

this cell is part of BSC_2577 for which there has been a capture mis-configuration

Figure 56 - TC Setup Inefficiency (Details) Cell 16336


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Thanks to the protocol decode feature from Activity Analysis, it is possible to display the full message flow of sucha session (see below).

Figure 59 - CLCMD-CC Message flow protocol decode

The same analysis and conclusions can be given as for the Originated Call Setup inefficiency. Refer to chapter3.1.1 for details.


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We can notice that the main cause of drop call is BSS originated, i.e. radio problems.Out of the 10 top worst cells, 7 belong to BSC_2577 (Country border).

Cell 32161:Thanks to Cigale Views drill down capabilities, it is possible to investigate on the main BSS call drop causes.

Figure 62 - BSS Drop Call rate Cell 32161

We notice here that the main causes are Radio failures (Clear Request, either Radio Interface Failure or RadioInterface Message Failure) which represent about 11.8% of the drop calls. The other cause of drop call is receptionof a Clear Request message with cause Equipment Failure.

For this cell, the OC and TC Setup inefficiency do not bring valuable information on what could be the reasons ofthe drop calls.


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However, when looking at the Outgoing HO, we can notice that most of the handovers are performed towards cell32066 and mainly due to Downlink Strength (40%) and Uplink Quality (30%).

Figure 63 - Outgoing Handover Details Cell 32161

ACTION FLAG: This could be linked to defaults and signal losses in the transmit path (antenna, duplexer,feeder). If Uplink Power Control is active, a check of the target value should be done.

Cell 15241:Thanks to Cigale Views drill down capabilities, it is possible to investigate on the main BSS call drop causes.



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We notice here that the main cause of drop is Clear Request message with cause Radio Interface Failure whichrepresents about 7.8% of the drop calls. For this cell, the OC and TC setup inefficiency do not help to identify thecause of drop call.

When looking at the Outgoing HO KPI, we can notice that the main reason for performing an outgoing handoverfrom this cell is Downlink Strength. A standard behaviour should be Better Cell.


ACTION FLAG: Astellia would like to recommend Customer to verify the Handover Margin set for cell 15241.Astellia would also like to recommend Customer to check for defaults and signal losses in the transmit path(antenna, duplexer, feeder).


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Cell 1208:The main BSS call drop causes are given below.


We notice here that the main cause of drop is Clear Request message with cause Radio Interface Failure whichrepresents about 7.8% of the drop calls. We can also notice that there are about 0.5% of drops due to a ClearRequest message during outgoing Inter-BSC handover phase.

If we display the Outgoing HO statistics, we obtain the picture below:



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We can notice that there are several handovers performed towards cells 1079 and 1215 (more than 2000 HO),however, this does not correspond to ping-pong handover as Cigale has only detected respectively 77 and 54 ping-pong HO towards these cells (a ping-pong handover for cell B is defined as if a mobile performs a handover fromcell A to cell B, stays less than 10 seconds in cell B and then performs a handover into cell A).

We can also notice that about 42% of the handovers performed to cell 3066 are done with cause Downlink Quality.This cell belongs to another BSC (BSC_2053).

ACTION FLAG: Astellia would like to recommend Customer to optimize the Handover Margin set for the cellcouple 1208-3066. As well, coverage at the overlap of cell 1208 and 3066 should be optimized in order to reducethe amount of handovers due to Downlink Quality

3.3 Handovers3.3.1 Outgoing Handovers causes

Cigale can provide a breakdown of Outgoing handover causes for each Network Element within the monitoredarea.

Below is provided the breakdown at the BSC level.

Figure 68 - Outgoing Handover Details BSC Level

We can notice that the main cause of outgoing handover is Better Cell. However, BSC_2577 shows a high rate ofhandovers due to Downlink Strength (about 31%).

Examples of analysis on the outgoing handovers can be found in the section on drop calls (refer to chapter 3.2).


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3.3.2 Ping-pong handoversWhen a mobile performs a handover from Cell A to Cell B, remains on Cell B less than 10 seconds (customizableprocessing parameter) and finally returns to Cell A, this last handover is counted as a Ping-Pong handover(HoPPG) from Cell B to Cell A.

Cigale View allows display of statistics on Ping-Pong handovers for all cell couples. Below is the representation ofthe top cells having more than 20 Ping-Pong handovers. It is provided as a graph and tabulated data.

Figure 69 - Ping-pong Handover By cell couples

We can notice that the cell couple 1190 1180 has a high number of ping-pong handovers (more than 2500handovers).


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If we display the outgoing handover causes (see below) we can see that most of the handovers leaving cell 1190towards cell 1180 are done with cause Better Cell (70%). The same can be seen the other way round.

Figure 70 - Outgoing Handover Cell 1190

ACTION FLAG: Astellia recommends Customer to optimize handover parameters (such as HO margins) to avoidsuch Ping-Pong handovers between these cells).


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3.3.4 Incoming handovers efficiency

As inter-BSC handovers require exchange of messages on A interface between MSC and BSC, Cigale can provideinformation on efficiency of these handovers, especially on response and success rate.This is illustrated by the figure below.

Figure 72 - Handover efficiency definition

The following graph presents the 15 worst cells in term of response rate (cells are sorted by increasing responserate).

Figure 73 - Incoming handover efficiency rate (response)

It can be noticed that for several cells with significant number of incoming handovers (more than 500), theresponse rate remains lower than 75%.

Indeed, for cells 3066, 12111, 12053, 12113 and 1252, the response rate varies from 35% to 75%, meaning thatonly 35% to 75% of the incoming handovers are successful.

OriginBSS

TargetBSS

MSC

( 1 ) H a

n d o v

e r R e

q u i r e

d ( 2 ) H a n d o v e r R e q u e s t

( 3 ) H a n d o v e r R e q u e s t A c k ( 4 ) H

a n d o v

e r C o

m m a n d ( 5 ) H a n d o v e r D e t e c t

( 6 ) H a n d o v e r C o m p l e t e ( 7 ) C l e a r

C o m m

a n d ( H

o_ S u

c c )

Response rate

Success rate

(4) / (1)

(7) / (4)

(3) / (2)

(6) / (3)

Outgoing IncomingOriginBSS

TargetBSS

MSC

( 1 ) H a

n d o v

e r R e

q u i r e

d ( 2 ) H a n d o v e r R e q u e s t

( 3 ) H a n d o v e r R e q u e s t A c k ( 4 ) H

a n d o v

e r C o

m m a n d ( 5 ) H a n d o v e r D e t e c t

( 6 ) H a n d o v e r C o m p l e t e ( 7 ) C l e a r

C o m m

a n d ( H

o_ S u

c c )

Response rate

Success rate

(4) / (1)

(7) / (4)

(3) / (2)

(6) / (3)

Outgoing Incoming


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3.4 Traffic Load and Congestion

Cigale has the capability to know what the allocated resources are at any given time. This allows to calculate trafficin Erlang but also to provide the maximum number of allocated TCH reached during the capture.

Several counters are also incremented when a subscriber is refused a channel due to lack of resources: When the mobile is queued in; When the assignment procedure fails (full queue or maximum waiting time reached); When the mobile tries to perform an inter-BSS handover and no TCH are available.

The snapshot below provides these statistics at the BSC level.

Figure 75 - Load and Congestion BSC level

It can be noted that: On BSC_2050, the A interface CIC resources margin (delta between white and purple dots) is the smallest, BSC_2321 shows a high level of saturation on Handover (about 13%). BSC_2053 shows about 1% of TCH Congestion, associated to a Queuing Rate of about 5% and 5% of HO

saturation.

ACTION FLAG: Traffic evolution (increase) on BSC_2050 should be monitored in order not to saturate CICcapacity on this A interface.

BSC_2321 and BSC_2053 performance is analysed hereafter.


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3.4.1 BSC_2053 Load and Congestion detailed analysis

TCH Congestion

When displaying the 5 worst cells in terms of TCH congestion, we can notice that several cells are highlycongested (refer to figure below):

Cell 16336: 72.4% of TCH congestion (92.7% of Queuing), maximum 5 resources used at the same time Cell 16335: 14.8% of TCH congestion (25.3% of Queuing), maximum 6 resources used at the same time Cell 1170: 9.1% of TCH congestion (30.2% of Queuing), maximum 29 resources used at the same time Cell 1400: 4.5% of TCH congestion (25.2% of Queuing), maximum 28 resources used at the same time

Figure 76 - Load and Congestion BSC_2053 Worst cells (TCH Congestion)

If we have a look to the Call Setup Efficiency for Cell 16336, we can notice (see below) that for this cell, there areabout 830 calls that cannot be established due to reasons associated to the BSS.


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Figure 77 - OC Setup Inefficiency Cell 16336

When drilling down and displaying the details of inefficiency (see below), we notice that most of these unsuccessfulcalls are due to the cause No Radio Resource Available.

Figure 78 - OC Setup Inefficiency (details) Cell 16336

All these failures occur in the state OC_ASS_QI_1, meaning that the call has been already queued due to the lackof TCH and is then released as no TCH is freed before expiration of the queuing timer.


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Figure 79 - OC Setup Inefficiency (state) Cell 16336

Thanks to the protocol decode feature from Activity Analysis, it is possible to display the full message flow of sucha session (see below). We can notice the Queuing Indication shortly after the Assignment Request and then 5seconds later the Clear Request message with cause No Radio Resource Available.

Figure 80 - CLREQ-NRRA Message flow protocol decode

The same behaviour can be observed for cells 16335, 1170 and 1400.

ACTION FLAG: As cells 16336, 16335 show a low number of maximum resources available at the same time, theirconfiguration should be verified in order to ensure that no TS are blocked or TRX are failed. This behaviour couldalso be due to TCH being reserved for GPRS only.


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ACTION FLAG: Capacity of these cells could be extended in order to decrease the congestion rate and increasethe call setup efficiency.

HO Saturation

When displaying the 5 worst cells in terms of Handover Saturation, we can notice that several cells are highlysaturated (refer to figure below):

Cell 3066: 65% of HO Saturation (37.8% of Queuing), 2.5% of TCH Congestion Cell 5509: 26.7% of HO Saturation (24.4% of Queuing) Cell 1252: 24% of HO Saturation (4.4% of Queuing) Cell 5508: 8.2% of HO Saturation (3.8% of Queuing)

Figure 81 - Load and Congestion BSC_2053 Worst cells (HO Saturation)

We can remember that cells 3066, 5509 and 1252 have been seen in the incoming handover efficiency analysis ashaving a low response due to Handover Failure with cause No Radio Resources Available (see chapter 3.3.4).


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Figure 82 - Details of non response for incoming handovers Cell 3066

ACTION FLAG: In order to decrease the number of handover failures due to No Radio Resource Available, it maybe interested to extend the capacity of the sites showing a high HO Saturation rate.


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Figure 84 - Details of non response for incoming handovers Cell 12111

ACTION FLAG: In order to decrease the number of handover failures due to No Radio Resource Available, it maybe interested to extend the capacity of the sites showing a high HO Saturation rate.


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3.5 SMS

Cigale View is able to provide information on SMS-MO (Mobile Originated) and SMS-MT (Mobile Terminated)procedures.As well, it is possible to differentiate between SUBMIT and COMMAND for SMS-MO and between DELIVER and

STATUS_REPORT for SMS-MT.

3.5.1 SMS Originated

The screenshot below shows the SMS Originated efficiency for the 5 BSC that were monitored.

Figure 85 - SMS Originated Efficiency

It can be noticed that the efficiency is rather low (slightly above 80%) for all the BSC.

A detailed analysis shows that the main inefficiency cause is RP_MT_ERROR message with cause RP_SMTR(Short Message Transfer Rejected) as shown below.


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Figure 86 - SMS Originated Efficiency Details of inefficiency

According to the GSM specification, the cause Short Message Transfer Rejected indicates that the equipmentsending this cause does not wish to accept this short message, although it could have accepted the short messagesince the equipment sending this cause is neither busy nor incompatible .

Using the capability of Cigale to provide statistics per SMS Centre, we can identify that the failures with cause

Short Message Transfer Rejected (RP_SMTR) is mostly affecting the SMS Centre +xxabcd9120.

Figure 87 - SMS Originated Efficiency Details of inefficiency per SMS Center

ACTION FLAG: Astellia would like to recommend Customer to check and increase the capacity of SMS-C+xxabcd9120 as it seems to be congested.

In this case (SMTR), the subscriber gets Message not sent information on his phone and needs to send it againas it is kept by his mobile.


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3.5.2 SMS Terminated

The screenshot below shows the SMS Terminated efficiency for the 5 BSC that were monitored.

Figure 88 - SMS Terminated Efficiency

It can be noticed that the efficiency is around 90% for all the BSC.

A detailed analysis shows that the main inefficiency cause is RP_MO_ERROR message with cause RP_MT_MCE(Memory Capacity Exceeded) as shown below. This means that the subscribers SIM card is full and the SMScannot be delivered to his mobile device. This can then be more considered as a user failure rather than a networkproblem

Figure 89 - SMS Terminated Efficiency Details of inefficiency


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4 Conclusion :During the analysis of the data captured over 120 hours on 5 BSC, it was possible to identify the following points(full details and explanations can be found in the core text of this report).

The roaming analysis has pointed out that:

1. PLMN Not Allowed cause is abusively used for Location Update Reject: A better cause should be Roaming Not Allowed in the Location Area or Location Area Not Allowed

as this could allow better classification or roamers rejection.2. Roaming agreements :

Customer does not seem to have roaming agreements with several operators from whichnumerous subscribers are trying to register on Customers network. Among those are Foreign_29,Foreign_46, Foreign_49, Foreign_51, Foreign_53 networks (respectively 251, 171, 161, 153, 122subscribers for the 5 days of monitoring).

3. Cells at LAC boundary : Some of these cells are suffering from ping-pong handovers between the two LACs: for example

cell 15001 and its neighbour in LAC 20802. An increase of Cell_Reselect_Hysteresis parameter should help reduce the number of these ping-

pong handovers. Cells at LAC boundary are important to maintain as they are the main points for roamers mobility.

4. Several good capture and / or traffic spot cells are suffering from Loss of Roamers and / or Drop Calls: For example, although

roaming & gsm anonymous audit report

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