AR20001119 Astellia Preliminary Voice Auditreport RA

This document is the property of Astellia and can not be reproduced in any form or conveyed to a third party without the prior written permission of Astellia. All trademarks, service marks, registered trademarks or registered service marks mentioned in this document are the property of their respective owners.

Astellia Audit December 2011

Preliminary Voice performance report

A and IuCS interfaces: focus on call drop

Order acknowledgement: AR20001119

This document is the property of Astellia and can not be reproduced in any form or conveyed to a third party without the prior written permission of Astellia. All trademarks, service marks, registered trademarks or registered service marks mentioned in this document are the property of their respective owners.

Written by Reviewed by

Name Yann LE GAL / Jerme JAMIN Eric GATEL

Company ASTELLIA ASTELLIA

Job title Telecom Engineer Consulting Project Manager

Date 13/12/2011 13/12/2011

Signature

Recipients

Telenor

- Peter FEKETE

- Lszl TOBIAS

- Bela NAGY

Astellia :

- Jerme JAMIN

- Yann LE GAL

- Jean-Pierre THOMAS

- Enrico BASSO

- Eric GATEL

Releases

Release Date Author Purpose

A 13/12/2011 Yann LE GAL Jrme JAMIN

Creation

Astellia Voice audit report Page: 3 / 33

Model: AuditReport - Release: B AR20001119_Astellia_Preliminary Voice auditreport_RA

1. TABLE OF CONTENTS

1. TABLE OF CONTENTS ............................................................................................................................. 3 2. INTRODUCTION......................................................................................................................................... 4 3. VOICE SERVICE PERFORMANCE ........................................................................................................... 5

3.1. 3G VOICE CALL DROP (IUCS) ....................................................................................................... 5 3.1.1. VOICE CALL DROP METRICS (IUCS) ..................................................................................... 5 3.1.2. VOICE CALL DROP NETWORK (IUCS) ................................................................................... 6 3.1.3. VOICE CALL DROP DETAIL OF CAUSES (IUCS) ...................................................................... 7

3.2. 2G VOICE CALL DROP ................................................................................................................. 15 3.2.1. VOICE CALL DROP METRICS (A) ....................................................................................... 15 3.2.2. VOICE CALL DROP NETWORK (A) ...................................................................................... 16 3.2.3. VOICE CALL DROP DETAIL OF CAUSES (A) ......................................................................... 17

3.3. HANDOVERS ................................................................................................................................. 24 3.3.1. 3G-2G HO EFFICIENCY NETWORK (IUCS) ........................................................................... 24



2. INTRODUCTION

TELENOR HUNGARY has selected Astellia to perform an E2E audit in order to evaluate the quality of performances of its both 2G &nd 3G networks. Objective of this audit is to assist TELENOR HUNGARY in improving its 3G, 2G and 2.5G network after the swap to ZTE. Despite good results providing by ZTE OSS counters, Telenor is now facing an increase of the customer complaints This first preliminary report focuses on the call drop part, based on A and IuCS interfaces,. An additional analysis for handovers is also included in this report. This audit is based on the analysis of raw data captured through Astellia probe on A and IuCS interfaces, for the BSC ZBSC51 and RNC ZRNC11.

Schedule for the capture phase was the following:

Site Node name Capture Begin Capture End Duration Comments

Budapest ZBSC51 ZRNC11

25/11/2011 17:00

27/11/2011 23:59

55H

Capture of A and IuCS 76GB of signalling raw data was retrieved



3. VOICE SERVICE PERFORMANCE

3.1. 3G VOICE CALL DROP (IUCS)

3.1.1. VOICE CALL DROP METRICS (IUCS)

0.44% of the established calls are dropped due to NSS reason. Around 1.6% of the subscribers have a call drop rate higher than 1% due to NSS inefficiency.

0.23% of the established calls are dropped due to BSS reason. 0.91 % of the subscribers have a call drop rate higher than 1% due to BSS inefficiency.

More details about the inefficiency causes are provided below in the report.



3.1.2. VOICE CALL DROP NETWORK (IUCS) This graph displays the call drop rate. On the left Y-axis you have the call drop rate and on the right Y-axis you can see the number of CS voice calls.

The call drop efficiency is good. During the busiest periods of the day the call drop rate is around 0.8% if we dont take User causes into account. The main source of drop inefficiency is due to NSS/CN causes and more details about the causes are provided on the next pages.



3.1.3. VOICE CALL DROP DETAIL OF CAUSES (IUCS) This graph displays the call drop causes. On the left Y-axis you have the percentage of RNS call drop causes and on the right Y-axis you can see the number of established calls.

The Call Drop due to RNS causes is lower than 0.3%. This value is constant during the whole day. The two main causes are Failure in the Radio Interface Procedure and Radio Connection With UE Lost.



This graph displays the call drop causes. On the left Y-axis you have the percentage of CN call drop causes and on the right Y-axis you can see the number of established calls.

The Call Drop due to NSS/CN causes is around 0.4%. This value is constant during the whole day. The two main causes are Destination Out Of order



This graph displays the top 40 cells with highest call drop rates. On the left Y-axis you have the percentage of call drop causes and on the right Y-axis you can see the number of established calls (filter > 50 occurrences).

The worst cell is the SAI 2902 with around 15.5% of call drop rate. Its interesting to investigate each cell in order to understand high call drop rates.



Radio Connection with UE lost This graph displays the 40 cells having highest cause radio connection with UE lost drop rate. On the left Y-axis you have the call drop rate and on the right Y-axis you can see the number of established calls (>50 occurrences).

When the mobile goes out of radio coverage the connection is released with this cause. No specific cell is concerned.



CLREQ Radio Interface Failure (RIF) This graph displays the 40 cells having highest cause radio interface failure drop rate (RIF). On the left Y-axis you have the call drop rate and on the right Y-axis you can see the number of established calls (>50 occurrences).

If we focus on the Failure in the Radio interface procedure, we can see the following call flow showing the loss of the radio link during the call.



When the radio connection is not good enough to maintain the communication, the node B when one single radio link is available will release the connection with the Mobile. No specific cell is concerned.



DISC_F Destination Out Of Order (DOOO) o In the first 2 lines, the calling party (A: +362093021) calls the number B: 204981185 with a failure end.

The customer A is in the cell 4852 and the Customer B in the cell 3961

The call drops at 18h:26min 28s 529ms with the loss of the radio link for A (Failure in the Radio interface, cause investigated in previous chapter) and the cause Destination out of order for B

Call flow for A Call flow for B



o In the last 2 lines, the calling party A has changed of cell; the customer A is now in cell 4853 and the calls is a success. So bad radio quality is responsible of such a message for the mobile A. For B this cause is the consequence of the loss of the radio link for the side party.

This cause is generated when a radio problem on the other side during the call.



3.2. 2G VOICE CALL DROP

3.2.1. VOICE CALL DROP METRICS (A)

0.3% of the established calls are dropped due to BSS reason. Around 1% of the subscribers have a call drop rate higher than 1% due to BSS inefficiency.

0.57% of the established calls are dropped due to NSS reason. 1.87% of the subscribers have a call drop rate higher than 1% due to NSS inefficiency.

The call drop rate is very low and more details about the inefficiency causes are provided below in the report.



3.2.2. VOICE CALL DROP NETWORK (A) This graph displays the call drop rate. On the left Y-axis you have the call drop rate and on the right Y-axis you can see the number of established calls.

The call drop efficiency is good. During the busiest periods of the day the call drop rate is lower than 1.5%. The main source of drop inefficiency is due to NSS causes and more details about the causes are provided on the next page.



3.2.3. VOICE CALL DROP DETAIL OF CAUSES (A) This graph displays the call drop causes. On the left Y-axis you have the percentage of call drop causes and on the right Y-axis you can see the number of established calls.

Around 0.3% of the inefficiency is due to the causes Radio Interface Failure (RIF) and Radio Interface Message Failure (RIMF), in other words due to bad radio condition (classified as BSS inefficiency). It is also important to note than 0.3% of the established calls are dropped due to the cause Destination Out Of Order (classified as NSS inefficiency) and 0.5% of the established calls are dropped due to the cause Normal Unspecified (classified as a NSS inefficiency).



CLREQ Radio Interface Failure (RIF) and Radio Interface Message Failure (RIMF) This graph displays the 20 cells having highest radio call drop rate (RIF & RIMF). On the left Y-axis you have the call drop rate and on the right Y-axis you can see the number of established calls.

The highlighted cells above have an important call drop rate and we recommend checking the global radio condition for these cells. Deeper Abis investigations could be useful to understand the issue. Analysing Outgoing handover causes, Astellia KPI could help to focus on the radio problem.



Here are more details about radio condition based on Outgoing handover causes:

Causes of outgoing handover

Cell Nb of established calls Drops RIF+RIMF(%) UQ US DQ DS BC Possible radio

problem

dujvatanq8_3512_15498 2139 2,9453 2,69% 2,78% 0,15% 0,38% 94,00% /

kvolwest3_3511_7823 721 2,91262 2,52% 9,63% 5,45% 6,85% 75,54% Radio signal strength

in both ways

dujvatan3_3512_15493 882 2,60771 1,46% 1,01% 1,34% 2,10% 94,09% /

kvolwest1_3511_7821 603 2,32172 5,94% 20,18% 8,66% 4,85% 60,37% Uplink strength

problem

biatorbag2_3511_21012 1249 2,08167 1,34% 2,77% 1,07% 6,66% 88,16% Downlink strength

problem

ormezo2_3511_1882 518 1,5444 1,73% 1,15% 0,93% 2,18% 94,00% /

rokales1_3511_7471 1050 1,2381 7,16% 8,84% 4,27% 10,24% 69,49% Radio Quality and Strength problem

dujvaros2_3512_15112 725 1,10345 5,23% 7,53% 7,81% 6,13% 73,28% Quality problem in

both ways

kikoto7_3512_7947 646 0,928793 7,40% 10,91% 4,46% 1,44% 75,80% Uplink way problem

bfokwest3_3511_5793 761 0,919842 4,45% 7,80% 3,67% 8,74% 75,31% Radio strength

problem in both ways

soroksmil2_3512_7322 563 0,888099 1,49% 2,38% 11,38% 6,60% 78,12% Downlink problem

erdeszak1_3511_61181 571 0,875657 3,16% 2,03% 4,97% 14,15% 75,69% Downlink strength

problem

menyecsk2_3511_6812 916 0,873362 1,35% 0,40% 2,04% 0,78% 95,42% /

borstesc1_3511_41471 581 0,860585 1,34% 0,93% 1,48% 2,58% 93,67% /

szhalwat3_3512_61233 2114 0,851466 4,37% 2,47% 4,52% 7,82% 80,43% Quality problem in

both ways

szoborpar1_3511_3381 707 0,848656 8,36% 2,30% 8,72% 8,83% 71,74% Quality problem in

both ways

budaors3_3511_21153 1071 0,840336 3,32% 2,06% 1,62% 4,26% 88,71% /

highwayq8_3511_1828 601 0,831947 1,04% 3,17% 0,86% 3,10% 91,78% /

m7m02_3511_41972 970 0,824742 2,64% 2,80% 4,89% 11,38% 78,29% Downlink strength

problem

harbor3_3511_7563 981 0,815494 1,48% 10,47% 5,55% 9,06% 73,44% Radio strength

problem



DISC_F Normal Unspecified (Nu) During the conversation phase a disconnect message associated with the cause Normal Unspecified is sent from the MSC site. The following pie show the state when the disconnect message is sent:

Here are some established calls CDRs which have been dropped with the cause Normal Unspecified:

Most of the case this cause appears for terminating established calls (82%).

It clearly appears most of the failed procedure are established calls towards T-Mobile subscribers and more particularly for terminating call procedure.

To investigate this cause some Core CS investigations could be useful and Astellia recommends checking the ISUP efficiency by switches couples between T-Mobile and Telenor.



Here is the associated flow chart:



DISC_F Destination Out Of Order (DOOO) During the conversation phase a disconnect message associated with the cause Destination Out Of Order is sent from the MSC site. Here is an end to end procedure based on the A interfaces capture:

It was possible to match the outgoing and terminating procedures thanks to a specific feature implemented on your network illustrated below:

For terminating call procedures, the setup message contains the MSISDN of the calling and the called parties.



Here are the flow charts of the analyzed end to end case: Calling party: Called party:

In this example, during the conversation phase the calling party lost the radio coverage (failure with the cause RIF). The MSC released to procedure on the called site with the associated cause Destination Out Of Order. This cause is classified in the NSS inefficiency and based on standard the associated cause should be Normal Clearing.

The call is connected and the

communication phase begins

The call is dropped with the cause RIF on the calling party

and DOOO on the called party



3.3. HANDOVERS

3.3.1. 3G-2G HO EFFICIENCY NETWORK (IUCS) The 3G/2G HO efficiency can be divided into 2 phases.

This graph displays the 3G-2G HO failure rate.



3.3.1.1. During the preparation phase With a decreasing filter on the Preparation Failure rate per 3G cell and for a number of relocation procedures> 10. We find a lot of cells with high rate of Preparation Failure



The first column shows us rates of failure higher than 30%. With the associated Call Flow, we can find that the first time this procedure of preparation is not successfully achieved but this procedure can be repeated and the second time, the mobile ends its communication in 2G. An interruption of around 2s during the communication can be estimated.



The most concerned couple SAI 3G/Cell 2G are the following



So some couples have a high failure rate. The main cause is RANAP ReLOCation Preparation FAILure , cause: RADio RelocationFailureInTargetCNRNCorTargetSystem for 90%.

This cause is mainly due to a lack of resources on the target 2G Radio system



With a multi interface analysis Iucs/A (see next page), we can find that with a focus on preparation phase with problem of RelocationFailureInTargetCNRNCorTargetSystem

During the 3G to 2G mobility, we can see a handover failure on the A interface with the cause NO RADIO RESOURCE AVAILABLE o GSM resources are not available for the 3G call

So the mobile cant go to the 2G, a handover failure is sent to the CN with the cause nor resource available The mobile must continue its communication on 3G but the Core Networks sends a DISCONNECT with the cause Normal clearing

o This is a abnormal behaviour as the call is drop with a normal message-cause



But Abnormal message is sent by the Core Networks to end

the Call

After the HO failure due to a lack of GSM resources, the

relocation preparation failure is sent



The number of HO is quite important in Telenors networks. An interruption during the call can be suspected (An interruption of around 2s during the communication can be estimated) and this high number needs explanation, bad radio threshold? Bad radio coverage? (Iub analysis could help for better understanding) We have around 0.9% of failure during the preparation phase. Most of the problems during the preparation Phase are due to a lack of GSM resources. The Call drop rate must be impacted by the couple Disconnect- Normal Clearing sends to drop the call when mobility fails. Investigation is needed with the vendor to understand such behaviour.

3.3.1.2. During the completion phase



The most concerned couple of cells are the following

The main cause of failure for the Completion phase is RANAP ReLOCation CANcel , cause: MISCellaneous UnspecifiedFailure



We observe around 0.7 % of failure during the Completion phase. Most of the problem is due to the cause unspecified. Additional investigation on UTRAN/IUB is needed.

Documents

AR20001119 Astellia Preliminary Voice Auditreport RA