UMTS RF Troubleshooting

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UMTS RF

Troubleshooting Guideline

U04.03

Author:

Matthias Braun

Editor:

Irfan Mahmood

Date:

6th August 2007

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Change Record

This table details the changes done to the document since the last baseline version

Date Changes Issue#

6th August 2007 Updated draft after review with following changes

• Editorial throughout the document • Added sections like HSUPA,

Inter-Freq HO, RRC connection re-establishment, 2G->3G IRAT HO

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1. Glossary of terms and abbreviations

3GPP 3G Partnership Project ACB Access Class Barring

ACK Acknowledgement

AICH Acquisition Indication Channel

ALCAP Access Link Control Application Protocol

APN Access Point Number

AM Acknowledged Mode

ARQ Automatic Repeat Request

AS Access Stratum

ATM Asynchronous Transfer Mode BCCH Broadcast Control Channel

BER Bit Error Rate

BLER Block Error Rate

BSIC Base Station Identity Code (GSM) BSS Base Station Subsystem (GSM) CAC Call Admission Control

CCPCH Common Control Physical Channel

CM Configuration Management / Connection Management

CN Core Network

CongC Congestion Control CPICH Common Pilot Channel CQI Channel Quality Indicator CRC Cyclic Redundancy Checksum

CRCI CRC Indicator

CS Circuit Switched

DAHO Database Assisted HO DBC Dynamic Bearer Control DCCH Dedicated Control Channel

DCH Dedicated Channel

DL Downlink

DRNC Drift RNC

DRX Discontinuous Reception

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ETSI European Telecommunication Standard Institute FACH Forward Access Channel

FDD Frequency Division Duplex

FM Fault Management

FP Framing Protocol

FSN First SN

FTP File Transfer Protocol

GGSN Gateway GPRS Support Node

GMM GPRS MM

GPRS General Packet Radio Services GPS Global Positioning System

GSM Global System for Mobile Communication HCS Hierarchical Cell Structure

HLR Home Location Register

HHO Hard Handover

HO Handover

H-PLMN Home PLMN

HSDPA High Speed Downlink Packet Access HS-DSCH High Speed Downlink Shared Channel HSUPA High Speed Uplink Packet Access HTTP Hyper Text Transfer Protocol H-USDPA High Speed Downlink Packet Access

HW Hardware

IE Information Element

ICMP Internet Control Message Protocol IP Internet Protocol

IRAT Inter Radio Access Technology KPI Key Performance Indicator

LA Location Area

LWS Lucent Worldwide Services

MAC Medium Access Control

MAC-hs Medium Access Control high speed

MAHO Mobile Assisted HO

MIB Master Information Block

MM Mobility Management

MMS Multi Media SMS

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MOS Mean Opinion Score MSC Mobile Switching Centre

MSS Maximum Segment Size

MNC Mobile Network Code

MT Mobile Terminating

NACK Negative ACK

NAS Non access stratum

NBAP NodeB Application Part NTP Network Time Protocol O&M Operation and Maintenance

OMC-U Operations and Maintenance Centre UMTS PCPICH Primary CPICH

PC Power Control

PCH Paging Channel

PDCP Packet Data Convergence Protocol PDP Packet Data Protocol

PDU Protocol Data Unit

PHY Physical Layer

PICH Paging Indication Channel PLMN Public Land Mobile Network

PM Performance Measurement

PPP Point to Point Protocol

PS Packet Switched

PSC Primary Scrambling Code

QE Quality Estimate

QoS Quality of Service

RA Routing Area

RAB Radio Access Bearer

RACH Random Access Channel

RAN Radio Access Network

RANAP Radio Access Network Application Part

RB Radio Bearer

RL Radio Link

RLC Radio Link Control

RLF Radio Link Failure

RF Radio Frequency

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RNC Radio Network Controller

RNSAP Radio Network Subsystem Application Part RRC Radio Resource Control

RRM Radio Resource Management

RSSI Received Signal Strength Indicator RSCP Received Signal Code Power

RTP Real Time Protocol

RTT Round Trip Time

RXLEV Receive Level (GSM)

SACK Selective ACKs

SC Scrambling Code

SCCPCH Secondary CCPCH SCH Synchronization Channel

SDU Service Data Unit

SGSN Serving GPRS Support Node SHO Soft/softer Handover

SIB System Information Broadcast SIM Subscriber Identity Module SIR Signal to Interference Ratio

SM Session Management

SMS Short Message Service

SN Sequence Number

SRB Signalling Radio Bearer

SRNC Serving RNC

TB Transport Block

TBS Transport Block Size

TCP Transmission Control Protocol TGPS Transmission Gap Pattern Sequence

TM Transparent Mode

TPC Transmit Power Control

TSSI Transmitted Signal Strength Indicator

TX Transmitted

UDP User Datagram Protocol UE User Equipment (mobile station)

UL Uplink

UM Unacknowledged Mode

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URA UTRAN Registration Area U-SIM UMTS Subscriber Identity Module UTRAN UMTS Terrestrial Radio Access Network

VT Video Telephony

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2. References

[1] TS 23122 NAS Functions related to Mobile Station (MS) in idle mode [2] TS 11.11 Specification of the SIM – ME interface

[3] TS 25304 UE Procedures in Idle Mode and Procedures for Cell Reselection in Connected Mode”

[4] GSM 03.22 Functions related to Mobile Station in idle mode and group receive mode

[5] TS 24008 Mobile radio interface layer 3 specification; Core Network Protocols – Stage3

[6] TS 25331 RRC Protocol Specification

[7] TS 25433 UTRAN Iub Interface NBAP Signalling

[8] TS 24007 Mobile radio interface signalling layer 3 specification; general aspects

[9] TS 25413 UTRAN Iu Interface RANAP Signalling [10] TS 25423 UTRAN Iur Interface RNSAP Signalling [11] TS 25214 Physical layer procedures (FDD) [12] TS 25922 Radio resource management strategies

[13] TS 25201 User Equipment (UE) Radio transmission and reception (FDD) [14] TS 25306 UE Radio Access Capabilities

[15] TS 34121 Terminal conformance specification; Radio transmission and reception (FDD)

[16] UMTS RF Translation Application Note (TAN) for HSDPA [17] UMTS RF Translation Application Note (TAN) for EDCH

[18] UMTS RF Translation Application Note (TAN) for Cell Selection and Reselection

[19] UMTS RF Translation Application Note (TAN) for Access Procedures [20] UMTS RF Translation Application Note (TAN) for Load Control [21] UMTS RF Translation Application Note (TAN) RLC

[22] UMTS RF Translation Application Note (TAN) RF Call Trace [23] UMTS RF Translation Application Note (TAN) Handover

[24] UMTS RF Translation Application Note (TAN) Inter-Frequency Handover [25] UMTS RF Translation Application Note (TAN) Inter-RAT Handover [26] UMTS RF Translation Application Note (TAN) Inter Frequency Handover [27] UMTS RF Translation Application Note (TAN) Radio Link Control [28] UMTS RF Translation Application Note (TAN) Power Control [29] Actix, http://www.actix.com

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[30] Ethereal, documentation and download at www.ethereal.com [31] tcptrace, documentation and download at www.tcptrace.org [32] Tardis2000, www.kaska.demon.co.uk/tardis.htm

[33] UMTS RF Optimization Guidelines available at

http://rfcoresupport.wh.lucent.com/RFCoreSupportWebPage/guidelines.htm [34] UMTS RF Engineering Guidelines available at

http://rfcoresupport.wh.lucent.com/RFCoreSupportWebPage/guidelines.htm [35] UMTS Cluster Optimisation Guideline

[36] TS 25322 RLC protocol specification

[37] TS 21905 Vocabulary for 3GPP Specifications

[38] Cygwin available at http://public.planetmirror.com/pub/cygwin [39] DR TCP available at http://www2.kansas.net/drtcp.asp

[40] TS 25323 Packet Data Convergence Protocol (PDCP) Specification [41] Network Performance Engineering LWS Europe

http://npe.de.lucent.com/AL/arca/index.cfm

[42] Performance Measurements Definitions Manual (PMDM) for U04.03 available at http://ns.uk.lucent.com/ctip/gsmnav/gsmsysdoc/mnode/webdocs/libfiles/pmd mindex.htm [43] NDP homepage http://ge1884ndp01.de.lucent.com:7779/portal/page?_pageid=35,31210&_d ad=portal&_schema=PORTAL

[44] Parameter consistency checks http://mobility.ih.lucent.com/~caateam/ [45] Multi-vendor PM database system http://135.246.63.129/pm_db/login.php [46] UMTS IRAT Optimization Guidelines

http://rfcoresupport.wh.lucent.com/RFCoreSupportWebPage/guidelines.htm [47] TR 26975 Performance characterisation of the AMR speech codec Report [48] ITU-T J.144 Objective perceptual video quality measurement techniques

for digital cable television in the presence of a full reference [49] RF Optimisation and Analysis Tool Suit

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3. About this document

3.1. Introduction

The UMTS RF Troubleshooting Guideline is the base document for the UMTS optimisation process and is used for the identification, classification and resolution of problems, failures or performance degradations that might be observed during the optimisation activity.

This document covers the following items:

• _{Drive test data analysis (Uu traces and 2G/3G scanner measurements)} • Network interface tracing analysis (e.g. Iu, Iur and Iub interface tracing) • PM KPI analysis

• _{End-to-end performance analysis}

Furthermore this guideline is cross correlating the observed occurrences to the corresponding UTRAN parameter, PM counters and KPIs of the UTRAN and/or CN and gives references.

Last but not least this document is used as a specification for writing queries that automatically identify and classify failures and problems from network interface traces and drive test data. For more information see [41].

3.2. Content

There are five main chapters in this document:

• Chapter “About this document” is providing an introduction and an overview of the UMTS RF Troubleshooting Guideline.

• Chapter “Description of the optimisation process” is providing a short overview of the UMTS optimisation process as covered by the UMTS RF Troubleshooting Guideline.

• Chapter “Call setup” is listing all problems that might occur at the call establishment phase.

• Chapter “Call reliability” is describing failures and problems that might occur after call establishment; examples are dropped calls, radio link failures or handover problems.

• Chapter “Call quality” is dealing with quality problems as perceived by the UMTS subscriber.

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3.3. How to read

The main analysis chapters are subdivided into subsections that are describing the particular problems and failures step by step. Basis for the structure is the UMTS call handling. The subsections are structured as follows:

• _{In the first part, the problem and when applicable corresponding} UTRAN parameter are described and listed; this part has the subtitle “concept”.

• In the second part called “failure symptoms, identification and fixes for improvement” there are – if applicable – three tables:

o The first table is specifying the trigger points for the identification in the network interface trace or in the drive test data including the type of traces necessary for problem identification (e.g. Uu trace, 3G scanner measurements or TCP/IP protocol interface trace)

o The second table is listing the PM KPIs as retrieved by the UTRAN or CN PM system

o The third table is listing the corresponding parameter(s)

3.4. UTRAN/CN release and vendor dependency

This document is a “living” document and is updated on a regular basis based on the experience coming from the different projects.

This version of the UMTS RF Troubleshooting Guideline is supporting ex-Lucent equipment only. However it is geared towards supporting multi-vendor equipment so long as they follow 3GPP mandated procedures. Whenever a new UTRAN or CN network release is available certain tables and descriptions have to be updated while others parameters are project dependent and hence no particular value is assigned to them.

3.5. Intended audience

This document is directed to system engineers, network planners, RF optimisation engineers and all engineers that are going to analyse network with the aim of optimising a UMTS network.

3.6. Disclaimer - what is not covered

This document is not covering Element Management Layer activities. As a consequence this Guideline cannot be used for troubleshooting maintenance task issues. This document does not support how to trace and to operate measurements instruments and tools. For more details check the corresponding reference documentation.

Currently the Fault Management (FM) analysis is also not covered in this guideline, but might be added in later releases.

This guideline is only shortly covering RF network planning and dimensioning issues; these topics are covered in more details in [33] and [34].

Core Network specific problems are only covered in this guideline in the way to explain how to identify these kind of problems during the analysis. The question of the root cause and how to overcome this problem is not part of the UMTS RF Troubleshooting Guideline.

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4. Description of the optimisation process

The different fields of UMTS RF optimisation can be summarised by the following items:

• FM audit and analysis

• RF design audit and optimisation (see [33] and [34] for a detailed description)

• _{CM audit and optimisation} • PM audit and optimisation • Drive testing and investigation • Network interface tracing and analysis • Lab investigation and optimisation

These fields of UMTS optimisation are displayed in Figure 1 in yellow below.

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Pre-requisite before starting with a performance verification and optimisation is that

• _{The FM analysis shows no severe alarms that might influence the} performance measurements as retrieved by the PM statistic or drive test data

• _{The RF design audit and optimisation has been finished for the region} to be optimised

In case, one or both pre-requisites are not fulfilled starting with the performance investigation and troubleshooting does not make much sense. For troubleshooting and optimizing new clusters, the Drive test and interfaces’ traces would be more relevant than PMs that may get skewed because of small number of users.

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5. Call setup

One main user perception of a UMTS network is the success of setting-up a UMTS call. This section is describing all kind of failures and problems that might occur during the call establishment phase. The different phases during the call setup are covered step-by-step in the following subsections of this chapter.

5.1. Call setup – RRC connection establishment

5.1.1. PLMN/cell selection and reselection 5.1.1.1. Concept

The UE in idle mode has to perform the following tasks: • PLMN selection and reselection

• _{Cell selection and reselection} • Location registration

The whole procedure is visualised in Figure 2 below and will be explained in detail in the following subsections:

Figure 2: PLMN (re-)selection and cell (re-) selection process

If the UE is in CELL_FACH, CELL_PCH or URA_PCH the UE also performs cell reselections; however possible failures that may occur are covered in the subsection regarding failures on RACH (subsection 5.1.3) and FACH (subsection 5.1.6). In the following it is assumed that the UE is in idle mode.

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Description of the NAS part during PLMN/cell selection and reselection

The NAS part is described in [1] and depends mainly on the information stored on the U-SIM [2].

After power-on the UE starts with the initial cell search procedure and tries to decode the network information as broadcasted by the 2G or 3G cells on the BCCH. The UE is either selecting the best suitable cell (in terms of the cell selection criteria, see below) of its H-PLMN and starts with the location registration procedure or otherwise when the H-PLMN is not available the UE is selecting a non-forbidden PLMN, camping on the best suitable cell and starts with the location registration procedure.

In case there is no suitable cell of a non-forbidden network (no roaming agreement, lack of coverage, SIM locked in the HLR etc.) the mobile enters the “Limited Service” state. In this state the UE is only allowed to initiate emergency calls in case it detects any PLMN coverage.

Description of the AS part during PLMN/cell selection and reselection

The AS part is defined in [3] (for UMTS) and [4] (for GSM). Optimisation approach is to ensure that the UE camps on the best suitable cell (in terms of RF conditions, traffic distribution assumptions etc.) to setup a call. The process can be configured by O&M parameters as explained below:

In case ACB is used the UE is selecting a non-barred cell based on either cell information stored on the U-SIM or after doing the initial cell search.

Prerequisite for the cell selection (and also cell reselection) are that the following criteria are fulfilled:

For UMTS: Squal = Qqualmeas - Qqualmin > 0 AND

Srxlev = Qrxlevmeas – Qrxlevmin - Pcompensation > 0

For GSM: Srxlev = Qrxlevmeas – Qrxlevmin - Pcompensation > 0

The different terms in the formula are defined as follows:

Qqualmeas is the measured cell quality value. The quality of the received signal expressed in CPICH

Ec/N0 (dB) for FDD cells. Not applicable for TDD cells or GSM cells.

Qrxlevmeas is cell RX level value. This is received signal, CPICH RSCP for FDD cells (dBm),

P-CCPCH RSCP for TDD cells (dBm) and RXLEV for GSM cells (dBm)

Pcompensation is the defined as Max(UE_TXPWR_MAX_RACH – P_MAX, 0) (UMTS),

Max(MS_TXPWR_MAX_CCH – P, 0) (GSM)

UE_TXPWR_MAX_RACH is the maximum allowed power for the RACH and P_MAX is the maximum power for the given mobile power class.

The different O&M parameters of the formula above are listed in Table 1 below:

Parameter Description

Qqualmin Minimum required quality level in the cell (dB). Not applicable for TDD cells or

GSM cells, broadcasted via SIB3 and SIB4

Qrxlevmin Minimum required RX level in the cell (dBm), broadcasted via SIB3 and SIB4

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Remark

The current formulas can only be used in case HCS is not deployed.

Furthermore while camping the UE shall start to perform inter-RAT measurements if Squal <= SSearchRAT, otherwise not. SSearchRAT is a configurable

UMTS parameter broadcasted on SIB3/SIB4. However note that to avoid ping ponging between UMTS and GSM the following condition should be fulfilled: FDD_Qmin > Qqualmin + SsearchRAT

If the above condition is not satisfied, a UE will move from GSM to UMTS and immediately start monitoring neighboring GSM cells again, an undesirable condition. Furthermore frequent re-selections between UMTS and GSM can cause mobile terminating call failure in case the PLMN pages the current network while the UE is in the process of registering with the other network. In a similar way the criterion for UMTS Interfrequency measurements is defined; for this parameter Sintersearch is used and is broadcasted on SIB3/SIB4.

The UE can only reselect one of the 2G or 3G cells that are defined in the reselection list that are broadcasted via SIB11/SIB12 on the BCCH.

For cell reselection the target cell has to fulfill the same criteria as specified for the cell selection case. The UE ranks the cells according to the cell ranking criteria Rs (serving cell) and Rn (neighbour cell). The UE will reselect the best

GSM or UMTS cell of the ranking list if at least Treselection (UMTS parameter) has elapsed when camping on the cell. For UMTS network without HCS the following formulas are used (both for GSM and UMTS cells):

Rs = Qmeas,s + Qhysts

Rn = Qmeas,n - Qoffsets,n

For UMTS Qmeas is based either on RSCP or Ec/No measurements of the

server/neighbour cell depending on the setting of the UTRAN parameter configuring the selection and reselection quality measure. Qhysts is an hysteresis

to avoid ping-pong effects, Qoffsets,n is an offset defined on a per-neighbour

definition (for both GSM and UMTS neighbours).

The reselection process using the mentioned parameters (Qoffsets,n = 0) is

visualised in Figure 3 below:

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Table 2 below is listing the main parameters configuring the cell reselection process in case no HCS is used:

cellSelAndResQualMeas Parameter defining whether CPICH or RSCP measurement shall be used for UMTS measurements

sIB3Treselection Time hysteresis for the cell reselection

sIB3RAT.sSearchRAT UMTS parameter broadcasted via the SIB3/SIB4 defining whether or not to start with inter-RAT measurements (setting of SSearchRAT)

sIB3SInterSearch UMTS parameter broadcasted via the SIB3/SIB4 defining whether or not to start with UMTS interfrequency measurements (setting of Sintersearch)

sIB3Qhyst1, sIB3Qhyst2 Hysteresis to avoid ping-pong effects (RSCP, Ec/No hysteresis)

outFDDAdjCells.cellOffset UMTS parameter broadcasted via the SIB11/SIB12 defining an offset on a per neighbour basis

Table 2: Most important parameter used for cell reselection, non HCS

Description of the Location Registration part during PLMN/cell selection and reselection

The Location Registration procedure is initiated by the UE by sending MM/GMM Direct Transfer messages. For these kinds of failures see subsection 5.3.1. The cell selection and reselection process and its translations are covered in more details in [18].

5.1.1.2. Failure symptoms, identification and fixes for improvement

A failure of the PLMN selection/reselection during a drive test can be easily identified when the screen of the drive test mobile is showing “Limited Service” and the MNC of the selected cell is different from the H-PLMN. The root cause might be a network outage due to NodeB, RNC or any particular network interface like Iub or Iu (see also subsection 6.4.5 and 6.8) or when the test van is driven out of the coverage footprint of the (GSM and UMTS) network. In that case the drive test route should be checked.

When the PM counters of the CN are showing a high rejection rate due to missing national roaming it may be caused by an interface problem to or an outage in the roaming networks be it UMTS or GSM.

Another problem might be ACB on one or several of the surrounding GSM and/or UMTS cells. Information regarding Access Class Barring is broadcasted via SIB3 or SIB4 [6]. ACB is used during the integration of cells see [35] for details.

Common problems of the cell selection/reselection procedure are non-optimised configuration of the corresponding UTRAN parameter. As a consequence the call will be setup on a non-optimal cell or a non-optimal RAN so the call-setup might fail during the RACH procedure (subsection 5.1.3), the paging procedure (subsection 5.1.2) or during the call setup procedure (subsection 5.2). A consistency check of the parameters listed in Table 1 and Table 2 might help to find parameter misconfiguration. Parameter Qoffsets,n used for optimisation of a

per-cell basis should be reviewed.

In case of poor 3G coverage and low call setup success rate the parameter SSearchRAT might be set to a lower value so the UE will start earlier with inter-RAT

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measurements. Also the cell offsets for the GSM cells can be adapted to prefer call setup on the 2G layer.

Another problem arises when different LA codes are defined for the GSM and UMTS networks and the Inter-RAT reselection criterion is met. This is in particular the case for subscribers inside a building where the UMTS coverage is not as strong compared to the GSM coverage, but the preference is on the UMTS network. As a consequence it is recommended to assign the same LA codes to GSM and UMTS cells that are providing coverage to the same area to avoid LAU ping-pong.

Table 3 below is listing the identification techniques of PLMN/cell (re-)selection failures in drive test traces and scanner measurements:

Problem Trace Trigger

Wrong PLMN selected

Uu Any occurrence of the MNC of the cell the UE is camping on is different from the MNC of the H-PLMN

ACB Uu Any occurrence of IE “Access Class Barred” = TRUE in SIB3/SIB4

Call setup on non-optimal cell

Uu, 3G scanner

The call is setup via RRCConnectionSetup message on a cell that is not on the x best cell listed by the 3G scanner within y dB window.

Call setup on non-optimal RAN technology

Uu, 2G/3G scanner

The RXLEV of the best measured 2G cell is within a x dB window (or even better) for y seconds compared to the RSCP of the cell the UE is camping on when sending the RRC Connection Request or Cell Update message on RACH

Ping-pong LU between 2G / 3G

Uu There are two consecutive LUs between 2G and 3G within x seconds and the LA codes for the cells are different.

Table 3: Identification of PLMN/cell (re-)selection failures in traces Cell selection and reselection failures cannot be detected via PMs because the process is within the UE. Failures during the Location Registration procedure are identified via CN PMs and covered in subsection 5.3.1.

5.1.2. Failures on the AICH, PICH and PCH 5.1.2.1. Concept

The UTRAN might initiate the paging procedure because of the following events:

• _{The UTRAN is receiving a paging request from the CN via RANAP} • The UE has an established PDP context, but the UE is in URA_PCH or

Cell_PCH mode and downlink PS data are scheduled to be delivered in the downlink

If the UE is in idle, URA_PCH or CELL_PCH modes and the UE is receiving a Paging Indication on the PICH from the NodeB; then the UE is starting to monitor the PCH to receive the paging (“Paging Type 1”). In case the UE is in connected mode and is paged, then the UTRAN is sending the paging via DCCH (“Paging Type 2”).

The CN might perform a repetition of paging process in case the UE has not answered within a certain period in time. In addition the RNC might trigger the repetition of the UE paging in the UTRAN. The repetition timers of the RNC and CN have to be set accordantly.

In the following it is assumed that the UE is not in connected mode so it has received a Paging Type 1.

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After the UE has successfully decoded the paging on the PCH it sends a RACH Preamble using the open loop power control algorithm. When the NodeB receives the RACH Preamble it answers by sending an indication on the AICH, the reception of the AICH is answered by the UE by sending a RRC Connection Request/Cell Update/URA Update message using the RACH (so called RACH Message Part). Upon successful decoding the NodeB forwards the RACH Message Part to the RNC. RACH failures are covered in subsection 5.1.3. The RNC sends back (on the FACH) the RRC Connection Setup/Cell Update Confirm/URA Update Confirm message (successful case). FACH failures are covered in subsection 5.1.6.

5.1.2.2. Failure symptoms, identification and fixes for improvement Failures on the PCH, PICH and AICH are most likely due to

• Non-optimal power settings of the PICH, AICH or PCH

• _{Poor radio conditions in terms of low RSCP or Ec/No because of e.g.} pilot pollution (subsection 6.4.1), poor RF coverage (subsection 6.4.5), camping on a non-optimal cell (see subsection 5.1.1) etc.

• _{Congestion on the PCH}

Table 4 below is listing the main UTRAN parameters configuring the PICH, PCH and AICH:

pICHPower UTRAN parameter defining the power settings of the PICH pCHPower UTRAN parameter defining the power settings of the PCH aICHPower UTRAN parameter defining the power settings of the AICH CN_PCH_Timer1 _{Timeout when the CN will reinitiate the paging}

tPageRep Timeout when the RNC will reinitiate the paging

CN_PCH_Max Maximum number of paging repetitions by the CN

nUtranPageRep Maximum number of paging repetitions by the RNC

Table 4: Parameter used for configuring the PICH, AICH and PCH

The paging itself is sent on the PCH that is a PHY channel on Uu. The drive test equipment can record paging requests. However analysing drive test logs is not a good way to investigate paging problems because paging that is not received by the UE can only be detected via parallel Iub tracing.

A better approach for analysing call setup problems due to paging failures is to use PM counters of the UTRAN and the CN.

If the UE is in URA_PCH or CELL_PCH mode, the RRC connection is maintained via the common physical channels (subsection 6.6). When the UE cannot be reached via paging the UTRAN may decide to drop the RRC connection.

1

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Figure 4: Dropped RRC connection due to unsuccessful paging Congestion on the PCH is also indicated by the UTRAN PM system. A solution of lowering the paging load might be to separate the FACH and PCH on the SCCPCH by introducing an additional SCCPCH. In addition creating smaller Location Areas / Routing Areas will also lower the paging load.

Failures on the AICH or PICH (PHY channels, no corresponding Transport channels) can be detected only indirectly because standard drive test tools do not record these messages that are sent only on the Uu interface. Increasing the power settings of the particular Physical Channels will reduce the failure rate. In addition “normal” RF optimisation for areas with low Ec/No will improve the situation.

Table 5 below is listing of how failures on the PICH/AICH/PCH can be identified in interface traces:

RRC drop due to unsuccessful paging

Iub and Iu Cross correlation Iu and Iub trace: any occurrence where a UE page is recorded on Iub, there is no Cell Update recorded on Iub within x seconds and the RNC is sending back within y seconds an Iu Release Request message with cause “Release due to UTRAN generated reason” (UE is either in URA_PCH or CELL_PCH mode)

Unsuccessful paging Iub Any occurrence where a UE is paged and recorded on the Iub and there is no answer by the UE on UL CCCH also recorded on the Iub within x seconds

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Table 5: Identification of PICH/PCH/AICH failures in traces

Table 6 below is listing the identification possibilities using KPIs/Counters retrieved by the CN and/or UTRAN PM system.

Table 6: PM KPIs/Counters for PICH/PCH/AICH failures

5.1.3. Random Access Procedure 5.1.3.1. Concept

The RACH Access Procedure is used when attaching to the network, setting up a call, answering to a page or performing a LA Update/RA Update. The RACH procedure has been successfully performed when the RACH Message Part is received by the RNC upon successful decoding at the NodeB.

The RACH is transmitted on the PHY in two separated parts: first a certain number of RACH Preambles are sent. The power of the first RACH Preamble is relatively low and calculated using Open Loop Power Control. Each of the following RACH Preambles are transmitted with an increased power level till an ACK is received on the AICH. This is the case when received preamble power exceeds the parameter “physicalRACHPreambleThreshold”.

Then the UE transmits the RRC Connection Request (Cell Update, URA Update) message in the RACH Message Part. Figure 5 below illustrates the transmission of several RACH Preambles in different Ramping Cycles and only after the reception of an ACK on AICH, the transmission of the RACH message part:

PM system

Counter / KPI KPI Name / Description

RNC VS.MM.RRCConnDrop.UTRANPagingFailure Counting the number of RRC drops due to

UTRAN Paging failures

UtranCell VS.MM.PagAttDiscard.ProcessorLoad This measurement provides the number of

paging attempts discarded by the RNC TPU due to processor load

RNC VS.MM.PagAttRec This measurement provides the number of

paging attempts received by the RNC 3G-SGSN (MM.SuccPsPagingProcIu + SuccPsPagingRepititionsIu) /

(MM.AttPsPagingProcIu + AttPsPagingRepititionsIu)*100

KPI ”Paging success rate”. Paging success rate defines the rate of successful paging in the packet network.

3G-MSC VS.succFirstPageReqs The measurement provides the number of

successful page responses from MS. The attempt and success counts are used to monitor the paging performance.

RNC VS.ChannelOccupRatePCH Provides the channel occupancy rate for the

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Figure 5: RACH procedure with RACH Preambles and Message Part When the UE is sending the RRC Connection Request message for the first time, it resets its internal counter V300 to 1 and starting its internal guard timer T300 (to UTRAN parameter t300); if the UE has already sent one or several RRC Connection Request messages before, counter V300 is incremented by one and guard timer T300 is restarted. Upon reception of the RRC Connection Request message at the RNC, PM counter RRC.AttConnEstab.<per establishment cause> is incremented by one2. Upon expiry of timer T300 the UE may start again by sending RACH Preambles depending on the status of counter V300. If V300 <= N300 (configured by UTRAN parameter n300), the UE increments V300 by one, resets T300 and sends the RACH Preamble again. If V300 > N300, the UE stops sending on the RACH and stays in idle mode [6]. For the Cell Update and URA Update procedure V302 and T302 are used, the corresponding PM counters are named VS.MM.CellUpdateReq.<per establishment cause>. Figure 6 below is showing as an example the Cell Update procedure:

Figure 6: Cell Update procedure supervised by T302 and V302

2

“<per establishment cause>” is a placeholder for e.g. OrigConvCall, OrigStrmCall etc. A full list is available in [42].

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Failures in the RACH procedure occur if either the RACH Preamble or the RACH Message Part cannot be decoded.

Possible reasons for these decoding problems are: • Non optimal RACH power settings

• Non optimal RACH counter/timer settings • RACH congestion

• Non optimal setting of physicalRACHPreambleThreshold & RACH search Window

• Poor radio conditions in terms of low RSCP or Ec/No because of e.g. pilot pollution (subsection 6.4.1), poor RF coverage (subsection 6.4.5), camping on a non-optimal cell (see subsection 5.1.1) etc.

In the following only the RACH specific issues are covered, for the other (common) RF issues see the corresponding subsections.

Table 7 below is listing the main UTRAN parameters configuring the RACH:

constantVal Used by UE to calculate Initial Preamble Power

PowerRampStep Determines the power increment between two successive RACH

Preambles

maxRetranPreamble Determines the maximum number of preambles allowed within one Power Ramping Cycle

physicalRACHPreambleThres hold

The threshold for preamble detection. The ratio between received preamble power during the preamble period and interference level shall be above this threshold in order to be acknowledged. SIB3MAXAllowedULTXPower,

SIB4MAXAllowedULTXPower

These parameters define the maximum allowed power the UE may use when accessing the cell on PRACH in idle mode

mMax Determine the maximum number of power ramping cycles allowed

t300 UE guard timer that is supervising the RRC Connection Setup

procedure when the UE is waiting for the RRC Connection Setup message

n300 Defines the number of times the UE is allowed to send the same

RRC Connection Request message

t302 UE guard timer that is supervising the Cell/URA Update procedure

when the UE is waiting for the Cell Update Confirm/ URA Update Confirm message

n302 Defines the number of times the UE is allowed to send the same

Cell Update/ URA Update message

Table 7: Parameter used for configuring the RACH For a complete list of RACH parameters see also [19].

The RACH Preambles may only be recorded in internal UE or NodeB traces, but not by “normal” drive test tools. In most cases only a statistic about the PHY

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and MAC procedure of the RACH is listed in the drive test logs e.g. number of RACH Preambles sent, last transmitted power etc3.

Possible congestion on the RACH could be detected by supervision of PM UTRAN counters (Table 9 below).

The RACH performance can be improved by changing of the power settings and/or changing of the timer/counter as listed in Table 7.

Table 8 below is listing the identification possibilities for network interface traces, Table 9 below is listing the identification possibilities using KPIs retrieved by the UTRAN PM system.

RACH message lost

Uu, Iub Cross-correlation Uu/Iub trace: RACH Message Part (RRC Connection Request, Cell Update or URA Update) is recorded on the Uu, but not recorded on the Iub interface.

Table 8: Identification of RACH failures in traces

PM system

UtranCell VS.RACHcongestion This measurement provides the percentage of

time that the RACH is in congested state. UtranCell VS.RACHTransBlock.Good / (VS.RACHTransBlock.Bad

+ VS.RACHTransBlock.Good) * 100

KPI “RACH transport block good CRC rate” is the percentage of RACH Transport Blocks with good CRC.

UtranCell VS.ChannelOccupRateRACH This measurement provides the channel

occupancy rates for Radio Access Channel. Table 9: PM KPIs for RACH failures

More RACH related PM KPIs are available in [19].

5.1.4. Call Admission Control (CAC) 5.1.4.1. Concept

The Call Admission Control (CAC) procedure is used in order to admit or deny the establishment of the RRC connection to avoid an overload of the UMTS system. The CAC thresholds can be defined for uplink and downlink load separately. The CAC algorithms and the corresponding parameter are described in detail in [20].

The CAC is started after the RNC receives the RRC Connection Request message on RACH and executes CAC before setting up the RL on NBAP (see Figure 7 below):

3

Note: It might be that in the drive test logs a RRCConnectionRequest message is listed, but the RACH message part is never transmitted via the air interface in case the RACH preamble has already failed.

The higher layer (RRC) initiates the transmission of the RACH message. In case of a lower layer failure ro deliver preamble it is up to the higher layer re-initiate the whole RACH procedure again (means in the RRC decoding another RACH Message would be listed).

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Figure 7: CAC executed after reception of RACH Message Part If the defined load thresholds for CAC are exceeded the RRC connection establishment request is denied and a RRC Connection Reject message with cause “Congestion” is sent back to the UE.

The only optimisation approach in case of CAC rejections is to optimise the RF environment in terms of pilot pollution, neighbour list optimisation etc. In addition it should be verified that the CAC thresholds are set correctly.

Table 10 below is listing the main parameters configuring CAC:

thrCAC2UL Specifies the load threshold for UL call admission of a non-emergency RRC connection request.

thrCAC2DL Specifies the load threshold for DL call admission of a non-emergency RRC connection request when HSDPA is disabled.

thrCAC2DLHS DPA

Specifies the load threshold for DL call admission of a non-emergency RRC connection request when HSDPA is enabled.

Table 10: Parameter configuring CAC

CAC failures can only be identified in a reliable manner via PM counters or internal traces. Reason is that the RRC Connection Reject message with cause “Congestion” might also be sent in case of missing resources during the RL setup procedure (subsection 5.1.5) or also for other failures.

RRC Connection Reject

Uu or Iub After the UE sends a RRC Connection Request message the RNC replies with RRC Connection Reject message with cause “Congestion” .

Table 11: Identification of RRC Connection Reject due to Congestion or missing resources

For CAC related PM KPIs see [20] however the main PM counter is given below:

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PM system

Counter / KPI Name / Description

UtranCell RRC.FailConnEstab.CAC This measurement provides the number of failed RRC connection establishment with cause “Call Admission Control” (CAC). Table 12: PM Counter for CAC failures

5.1.5. Radio Link Setup 5.1.5.1. Concept

The Radio Link Setup procedure is initiated in two cases:

• During the call establishment phase after the CAC is granted the RNC requests the NodeB to allocate resources through the NBAP Radio Link Setup message.

• In case of soft handover when allocating resources on a new NodeB Note that after the Radio Link Setup on NBAP the RNC should initiate the establishment of the AAL2 bearer over the Iub interface using ALCAP (ALCAP Establishment Request and ALCAP Establishment Confirm). Problems on ALCAP could be due to ATM configuration and are outside the scope of this document. ATM synchronisation problems are not expected at this stage of the call because of the already successful NBAP procedure.

The same is valid for the synchronisation between NodeB and RNC via the DCH-FP over AAL2 bearer.

Figure 8: Initial RRC Setup Steps after successful CAC

The NBAP Radio Link Setup procedure may fail and the NodeB sends back the Radio Link Setup Failure message.

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According to [7] the failure causes can be classified as follows: • _{Radio Network Layer Cause}

• Transport Layer Cause • _{Protocol Cause} • Miscellaneous Cause

Each category has many subcauses like “Transport Resources unavailable”, “NodeB Resources unavailable” or ”Semantic error” etc. 3GPP has defined a variety of failure causes. Here one major reason for NodeB resources problem can be UCU capacity shortage, while transport resources issue can point to the backhaul bandwidth limitation.

Table 13 below is listing the identification possibilities for network interface traces, Table 14 is listing the identification possibilities using KPIs retrieved by the UTRAN PM system.

For identification of failures during the Radio Link Setup procedure Iub traces are mandatory. Reason is that on Uu only the RRC Connection Reject message is available with only two possible failure causes (“congestion” and “unspecified”), see also subsection 5.1.4.

Radio Link Setup I Uu, Iub Cross-correlation Uu/Iub trace: Any occurrence of the NBAP Radio Link Setup Failure message on Iub and RRC Connection Reject with cause “unspecified” or “congestion” on Iub/Uu

Radio Link Setup II Iub Any occurrence of the NBAP Radio Link Setup Failure message on Iub Table 13: Identification of failures in the Radio Link Setup

PM system

UtranCell RRC.FailConnEstab.RLSetupFailure/RRC.AttConnEstab.sum*100 Failed RRC Connection

Establishment Rate due to RL Setup failures

UtranCell RLM.SuccRLSetupIub / RLM.AttRLSetupIub*100 Radio link setup success rate on

Iub UtranCell (RLM.FailRLSetupIub.NodeBRes.CSV + RLM.FailRLSetupIub.NodeBRes.CSD

+ RLM.FailRLSetupIub.NodeBRes.PSD) / RLM.AttRLSetupIub*100

Radio link setup failure rate on Iub NodeB resource

UtranCell (RLM.FailRLSetupIub.TransRes.CSV + RLM.FailRLSetupIub.TransRes.CSD + RLM.FailRLSetupIub.TransRes.PSD) / RLM.AttRLSetupIub*100

Radio link setup failure rate on Iub transport resource

RNC (RLM.AttRLSetupIur – RLM.FailRLSetupIur.sum) / RLM.AttRLSetupIur * 100 Radio link setup success rate on Iur

Table 14: PM KPIs for Radio Link Setup failures

5.1.6. Call setup failures on the FACH 5.1.6.1. Concept

This subsection is covering only call setup related failures on FACH; for failures in CELL_FACH mode see subsection 6.7.

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It is assumed that the RACH Message Part has been successfully received, the CAC has been granted and the RL are established. In this case the RNC sends back either the RRC Connection Setup, Cell Update Confirm or URA Update Confirm message on FACH (successful case).

The RNC sends the FACH message, resets counter V30001 and starts its guard timer T30001. When the RNC receives the answer by the UE (RRC Connection Setup Complete, UTRAN Mobility Information Confirm, Radio Bearer Reconfiguration Complete, … ) before T30001 expires, the RNC stops T30001. If the RNC does not receive the message before T30001 expires, the RNC may resend the FACH message depending on the status of counter V30001. If V30001<= N30001 (maximum number of retries), the RNC increments V30001 by one, resets timer T30001 and sends the FACH message again. If V30001 > N30001, the RNC will stop sending FACHs to the UE and will release the reserved resources on NBAP and ALCAP. Note that the RNC will not send any failure message on the Uu.

The whole procedure is visualised in Figure 9 below:

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Table 15 below is listing the parameters configuring the FACH:

fACHTrafPower UTRAN parameter defining the power settings of the FACH data part fACHSigPower UTRAN parameter defining the power settings of the FACH control part uERRCConnectionSetupRes

ponseTimer

UTRAN parameter defining setting of T30001 maxRRCConnSetupRetries UTRAN parameter defining setting of N30001

Table 15: Parameter used for configuring the FACH 5.1.6.2. Failure symptoms, identification and fixes for improvement

There are the following possible reasons for failures on FACH:

• _{Non optimal UTRAN parameter settings (e.g. FACH signalling and} traffic power)

• Call setup not done on an optimal cell (subsection 5.1.1)

• The FACH message is not successfully decoded due to poor FACH coverage

• The message on the FACH is successfully decoded by the UE, but afterwards the RNC cannot successfully decode the answer sent by the UE (UE is already in CELL_DCH mode, see also subsection 5.2) Failures on the FACH can be indicated by UTRAN PM statistics, Iub and Uu traces. On Uu FACH failures cannot be directly observed because there is no corresponding failure message sent.

Table 16 below is listing the identification of FACH failures on Iub, Table 17 the corresponding PM KPIs:

Lost FACH message

Iub and Uu

Cross-correlation Uu/Iub trace: one or more FACH messages are recorded on the Iub, but not on the Uu interface

FACH Failure Uu or Iub Any occurrence of a Cell Update/URA Update message and within x seconds there is a RRC Connection Release message with specified cause other than “normal event” sent back by the RNC

Table 16: Identification of failures on the FACH

PM system

UtranCell RRC.FailConnEstab.SetupIncomplete /

RRC.AttConnEstab.sum*100

Failed RRC connection Establishment Rate timeout

UtranCell VS.PercentageFACHOccupancy Occupancy rate on FACH

Table 17: PM KPIs for failures on the FACH

5.1.7. RRC Connection Reject message with specified cause “unspecified” The UE might receive a rejection when trying to establish a RRC Connection with specified cause “unspecified”.

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Possible reasons for that failure message are problems in the Radio Link Setup procedure, protocol errors or problems when sending the FACH etc. Table 18 below is listing how to identify this kind of error in Uu logs:

RRC Connection Reject with cause unspecified

Uu Any occurrence of an RRC Connection Reject message with specified cause “unspecified”.

Table 18: RRC Connection Reject – unspecified

There are no specific PM counters for that case; instead other PM counters with the name RRC.FailConnEstab.<different rejection causes> are used.

5.2. Call setup – failures during the call setup phase

5.2.1. Concept

At this point in time the UE is in the transition phase to either CELL_FACH or CELL_DCH mode. The next message will already be sent in the new mode (as an example next message to be sent by the UE is RRC Connection Setup Complete or UTRAN Mobility Information Confirm).

When transiting to the CELL_DCH mode there is the possibility that the UE is already in soft/softer handover mode when sending this message. This is the case if

• _{The UE is allowed to report the measurements of more than one NodeB} in the RRC Connection Request / Cell Update message

• The UE is supporting this feature

• The measurement of more than one cell is reported in RRC Connection Request / Cell Update message

• The RNC is then directing the UE to soft/softer HO via RRC Connection Setup, Cell Update Confirm or URA Update Confirm message

Table 19 below is listing the parameters that are important for the call setup phase:

measQty.maxNoReport edCellsOnRACH

Defines the maximum number of cells the UE may report on RACH

addThresholdSHO Defines the hysteresis used at call setup to add neighbour cells to the Active Set Table 19: Parameter important for the call setup phase

For more details about the translations see [23].

If the call is setup in an area where several NodeBs are providing marginal coverage and it is not possible to add the radio legs quickly, there is a big likelihood that the call setup will fail. When the call is not setup in soft/softer HO mode the UE has to wait for the reception of the Measurement Control messageand time-to-trigger before sending Measurement Report 1a etc. 5.2.2. Failure symptoms, identification and fixes for improvement

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• _{Non optimal handover parameter configuring the call setup in soft/softer} handover mode

• _{Non optimal power settings}

• Poor radio conditions in terms of low RSCP or Ec/No because of e.g. pilot pollution (subsection 6.4.1), poor RF coverage (subsection 6.4.5), camping on a non-optimal cell resulting in non-optimal reselection list (see subsection 5.1.1) etc.

There are no specific PM counters available that can be used to identify issues during the call setup phase because at this point the UE is already in CELL_DCH/CELL_FACH mode so a drop of the RRC connection cannot be differentiated from an RRC drop occurred in a later stage of the call. Also the drop might occur only a very short time later, but the root cause for the failure is one of the issues mentioned above.

Nevertheless it is possible to identify issues in network interface traces as listed in Table 20 below:

Call setup on a non-optimal cell

Uu, 3G scanner

The call is setup via RRCConnectionSetup message on a cell and at the same time the 3G scanner is reporting at least x cells that are within a y dB window compared to the best measured cell.

Not best cells in AS at call setup

Uu, 3G scanner

The number of cells in the Active Set is smaller than max AS size, but one neighbouring cell is within xdB window compared to the Ec/No of the best cell in the Active Set

Drop of RRC connection at call setup

Uu The call is dropped within x seconds after sending the RRC Connection Request or Cell/URA Update

Call Setup not in soft/softer HO mode

Uu, 3G scanner

The call is setup in non soft/softer HO mode (# of SCs in RRC Connection Setup message is 1), the assigned SC is under the best x SCs measured by the 3G scanner, and these SCs are within y dB window as measured by the 3G scanner

Table 20: Identification of call setup in traces

5.3. Call setup – Core Network failures

After establishment of the RRC connection the UE and the CN exchange Direct Transfer messages so the UE can GPRS attach to the PS network, perform a Location or Routing Area Update or initiate a data, voice or VT call. LAU/RAU involve just the mobility management procedures while the Call setup also includes call control and session management protocols for CS and PS calls respectively.

The following subsections are summarising possible failures that might occur during these procedures. The subsections are grouped by the following three different protocols:

• Mobility Management (MM) and GPRS Mobility Management (GMM) • _{Call Control (CC)}

• Session Management (SM)

The three protocols are sublayer protocols of the Connection Management (CM); these protocols are specified in [5] and [8]. CM failures causes like “CM

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Service Reject Cause” is mapped on the Reject Cause of the Mobility Management IE [5].

Note that (almost) any failure in this subsection is not UTRAN related because Direct Transfer messages are transparent to the UTRAN4. Any of the failures can be easily detected by the corresponding failure messages.

Because the protocols are transparent to the UTRAN all PM KPIs are defined within the CN entities e.g. SGSN / GGSN, 3G-MSC, … basis.

5.3.1. Mobility Management failures 5.3.1.1. Concept

The main function of the mobility management is to support the mobility of user terminals, such as informing the network of its present location and providing user identity confidentiality. A mobility management context in the SGSN or 3G-MSC is a prerequisite for the initialisation of voice, data or VT services.

For the root cause analysis please review the timer settings supervising the mobility management protocols as specified in [5] chapter 11.2. The settings of these timers are specified and not configurable. In addition Mobility Management failures might be due to missing roaming agreement, locked SIM card, CN problems like authentication not possible due to inaccessible HLR database etc.

The failure messages are retrieved from [5] chapter 9.2 (MM/CM) and 9.4 (GMM). Table 21 below is listing the Mobility Management failures as they can be retrieved by interface traces:

MM Authentication Reject

Uu or Iub or Iu Any occurrence of a MM Authentication reject message sent by the CN e.g. because of not-allowed national/international roaming

CM Service Reject Uu or Iub or Iu Any occurrence of a CM Service reject message sent by the CN; the reject cause will give an indication of the occurred failure.

CM Service Abort Uu or Iub or Iu Any occurrence of a CM Service abort message sent by the UE. This message is sent by the mobile station to the network to request the abortion of the first MM connection establishment in progress and the release of the RR connection.

MM Abort Uu or Iub or Iu Any occurrence of a MM Abort message sent by the CN. This message is sent by the network to the mobile station to initiate the abortion of all MM connections and to indicate the reason for the abortion. The rejection cause will give an indication about the occurred failure.

MM Location

Updating Reject

Uu or Iub or Iu Any occurrence of a MM Location updating reject message sent by the CN. The specified rejection cause will indicate the reason for the failure e.g. IMSI unknown in the HLR, illegal MS/ME, roaming not allowed etc.

GMM Attach Reject Uu or Iub or Iu Any occurrence of a GMM Attach Reject message sent by the CN The specified rejection cause will indicate the reason for the failure e.g. protocol error, wrong or incorrect IE format etc.

4

Exception: there might be the case that due to a bad RF environment the direct transfer messages cannot be delivered to the other entity because the RLC layer is not able to deliver the corresponding message also after RLC retransmissions, RLC resets etc. It is up to the corresponding higher layer (e.g. CC, GMM, MM or SM) to react accordantly of the discarded message.

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GMM Authentication and Ciphering Failure

Uu or Iub or Iu Any occurrence of a GMM Authentication and Ciphering Failure message sent by the UE. The specified rejection cause will indicate the reason for the failure e.g. a sync failure.

GMM Authentication and Ciphering Reject

Uu or Iub or Iu Any occurrence of a GMM Authentication and Ciphering Reject message sent by the CN.

GMM Routing Area Update Reject

Uu or Iub or Iu Any occurrence of a GMM Routing area update reject message sent by the CN. The specified rejection cause will indicate the reason for the failure e.g. protocol error, wrong or incorrect IE format etc. GMM Service Reject Uu or Iub or Iu Any occurrence of a GMM Service reject message sent by the CN

Table 21: Identification of Mobility Management failures in interface traces

Table 22 below is listing the PM KPIs of the Mobility Management as they can be retrieved by the PM system of the 3G-MSC and SGSN:

PM system

Counter / KPI KPI Name / Description SGSN (MM.AttGprsAttach.U – MM.SuccGprsAttach.U) /

MM.AttGprsAttach.U * 100

GPRS attach failure rate SGSN (attAuthInSgsn – succAuthInSgsn) / attAuthInSgsn * 100 Authentication failure rate

SGSN (MM.AttGprsDetachSgsn.U –

MM.SuccGprsDetachSgsn.U) / MM.AttGprsDetachSgsn.U * 100

SGSN initiated GPRS detach failure rate

3G-MSC (attInterVLRLocationUpdates +

attIntraVLRLocationUpdates) / (succInterVLRLocationUpdates + succIntraVLRLocationUpdates) * 100

Location Update Success Rate

SGSN MM.SuccInterSgsnRaUpdate.U /

MM.AttInterSgsnRaUpdate.U * 100

Inter SGSN routing area update success rate

SGSN MM.SuccIntraSgsnRaUpdate.U /

MM.AttIntraSgsnRaUpdate.U * 100

Intra SGSN routing area update success rate

3G-MSC VS.mobileOrigAttRejected The counter is incremented for a mobile

origination attempt that MSC for reasons other than system resource overload related.

3G-MSC VS.mobileTermAttRejected The counter is incremented for a mobile

termination attempt that is rejected by the MSC for reasons other than system resource overload related.

Table 22: PM KPIs/Counters for (GPRS) Mobility Management failures 5.3.2. Call Control failures

5.3.2.1. Concept

This subsection describes failures on the Call Control (CC) protocol. The CC protocol is responsible for CS call establishment and clearing procedures, call information phase procedures etc. CC procedures can only be performed if a MM context has been established between the UE and the CN (subsection 5.3.1).

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Table 23 below is listing the CC failures as they can be retrieved by interface traces [5]; note that the specified cause might depend on the 3G-MSC/UE vendors:

Ubnormal CC

Disconnect

Uu or Iub or Iu

Any occurrence of a CC Disconnect message (either UE or CN initiated) with specified cause other than “normal event”

Ubnormal CC

Release

Uu or Iub or Iu

Any occurrence of a CC Release / Release Complete message (either UE or CN initiated) with specified cause other than “normal event”

Table 23: Identification of CC failures in interface traces

Table 24 below is listing the PM KPIs of the CC failures as they can be retrieved by the PM system of the 3G-MSC:

PM system

Counter / KPI5 KPI Name / Description 3G-MSC NoCCDisconnectUbnormalEvent / NoCCDisconnects * 100 Ubnormal CC Disconnect Rate

3G-MSC NoCCReleaseUbnormalEvent / NoCCReleases * 100 Ubnormal CC Release Rate

Table 24: PM KPIs for CC failures

Depending on the specified failure cause the failure might be due to missing resources (e.g. “requested circuit/channel not available”), drive test configuration issue (e.g. “User busy”) or protocol failure.

For the root cause analysis please check the timer settings supervising the CC protocol in [5] chapter 11.3. The settings of these timers are not configurable. 5.3.3. Session Management failures

5.3.3.1. Concept

The main function of SM is to support the PDP context handling of the PS services. The SM comprises procedures for identified PDP context activation, deactivation and modification. SM procedures for identified access can only be performed if a GMM context has been established between the UE and the CN (subsection 5.3.1).

The failure messages are retrieved from [5]. Table 25 below is listing the SM failures as they can be retrieved by interface traces:

SM Activate PDP Context Reject

Uu or Iub or Iu Any occurrence of a SM Activate PDP Context Reject message sent by the CN. The specified rejection cause is giving an indication of the type of failure e.g. protocol error, missing or faulty APN, lack of resources etc.

SM Activate Secondary PDP Context Reject

Uu or Iub or Iu Any occurrence of a SM Activate Secondary PDP Context Reject message sent by the CN. The specified rejection cause is giving an indication of the type of failure e.g.

5

UMTS RF Troubleshooting

UMTS RF

Troubleshooting Guideline

U04.03

Author:

Editor:

Date:

Table of Contents

Change Record

1. Glossary of terms and abbreviations

2. References

3. About this document

3.1. Introduction

3.2. Content

3.3. How to read

3.4.

UTRAN/CN release and vendor dependency

3.5. Intended audience

3.6. Disclaimer - what is not covered

4. Description of the optimisation process

5. Call setup

5.1. Call setup – RRC connection establishment

5.2. Call setup – failures during the call setup phase

5.3. Call setup – Core Network failures