UMTS Performance Trouble Shooting and Optimization Guidelines Ericsson Retainability

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability Performance Engineering

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Introduction Purpose & Scope The intent of this document is to provide UMTS Trouble Shooting and Optimization from KPI and Counter perspectives for Ericsson (E///) Retainability and provide detailed analysis strategies for identifying reason for the KPI trends and offering guidelines for improving performance by Key Optimization techniques. The KPI/Counters described here are applicable to the Ericsson UTRAN. This document is not all inclusive and is only intended to provide a quick cook book to understand available E/// for trouble shooting and optimization best practices Guideline Document. For any information not covered here, the Ericsson product documentation (CPI/ALEX Libraries) should be referenced.

1.1. Definitions for this Document Term or Acronym

Definition

3GPP

Third Generation Partnership Project

AS

Active Set

BSIC

Base Station Identity Code

BTS

Base Transceiver Station

CN

Core Network

CPICH

Common Pilot Channel

DCH

Dedicated Channel

DL

Downlink

DPCCH

Dedicated Physical Control Channel

DPCH

Dedicated Physical Channel

DRNC

Drift Radio Network Controller

FACH

Forward Access Channel

FIFO

First In First Out

GERAN

GSM EDGE RAN

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Term or Acronym

Definition

GSM

Global System Communications

for

Mobile

HCS

Hierarchical Cell Structure

HSDPA

High Speed Data Packet Access

IAF

Intra Frequency

IE

Information Element

IEF

Inter Frequency

IFHO

Inter Frequency Handover

Inter-RAT

Inter Radio Access Technology

IRAT

Inter Radio Access Technology

Iur

Interface between two RNC’s

KPI

Key Parameter Indicator

LA

Location Area

LAI

Location Area Indicator

MO

Managed Object

NBAP Node B

Node B Application Part Logical node responsible for radio transmission and reception in one or several cells

OCNS

Orthogonal Channel Noise Simulator

PLMN

Public Land Mobile Network

RA

Routing Area

RAB

Radio Access Bearer

RAI

Routing Area Indicator

RAN

Radio Access Network

RAT

Radio Access Technology

RB

Radio Bearer

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Term or Acronym

Definition

RBS

Radio Base Station – another name for the Node B

RF

Radio Frequency

RL

Radio Link

RNC

Radio Network Controller

RRC

Radio Resource Control

RSCP

Received Signal Code Power

RSSI

Received Signal Strength Indicator

SIB

System Information Block

SIR

Signal to Interference Ratio

TRX

Transceiver

TX

Transmit

UE

User Equipment

UL

Uplink Universal Mobile Telecommunication Services UMTS Terrestrial Radio Access Network Wideband Code Division Multiple Access

UMTS UTRAN WCDMA

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Retainability Retainability is defined as the ability of a user to retain its requested service once connected for the desired duration. The metrics within the Ericsson RNC and OSS provide counters and KPI’s that describe the behaviors and experience of the subscribers on the UMTS network. This is divided up into a number of areas, CS and PS, as well as being divided on an RRC and RAB basis. The main items which affect retainability on the UMTS network include: • Handover performance (soft/softer/Iur/IRAT) and missing neighbour cell • UL/DL imbalance • Incorrect parameter settings (power, admission, release) • Congestion • Radio environment impact (corner effect, fast Ec/No drop, Pilot pollution etc) • Node Hardware failure • T1 Congestion The services which have counters for retainability are: 

CS Voice



CS Data



Video



PS Streaming



PS Interactive



HSDPA



EUL (HSUPA)

In the following sections, CS Voice, PS Interactive and HSDPA will be discussed in detail.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Troubleshooting Flowchart The following flowchart may be useful for troubleshooting the voice drop issues based on the problem areas

Flow chart in PowerPoint

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Ericsson Retainability flowchart.ppt

CS Voice RAB Retainability The metrics for CS Voice RAB Retainability are the most extensive of the UMTS Services in the Ericsson OSS. These metrics can be run on an RNC/Market level or on a cell level. The main report for identifying and troubleshooting retainability .This contains the Drop Rate and Drop Reason counters that will be discussed. For drops during the IRAT procedure, the 3G-2G Relation report can also be used to identify the IRAT Drops. The KPI for Voice is the Voice RAB Drop Rate %. This is made up of the following counters: Counter

Description

Condition

MO Class

pmNoSystemRabReleaseSp eech

Number of successful system RAB releases (Speech) referred to the Best Cell in the Active Set.

UtranCell

pmNoNormalRabReleaseSpe ech

Number of successful normal RAB releases (Speech) referred to the Best Cell in the Active Set.

This counter is only increased due to a RANAP Iu Release Command or RAB Assignment Request message with “release cause” = anything except ’Normal Release’, ’Successful Relocation’, ’Resource Optimisation Relocation’, ’User Inactivity’ or ’release-due-toUE-generated- signalingconnection-release’. This counter is incremented for the best cell in the Active Set in the SRNC. This counter is only increased due to a RANAP Iu Release Command or RAB Assignment Request message with “release cause” = ’Normal Release’, ’Successful Relocation’, ’Resource Optimisation Relocation’, ’User Inactivity’ or ’release-due-to-UE-generated signaling- connection-release’. This counter is incremented for the best cell in the Active Set in the SRNC.

UtranCell

The KPI is defined in T-PIM shows the percentage of system/abnormal RAB releases over the total number of RABs. It is defined as follows: VoiceRABDr opRate (%)  100 * [1 

pmNoNormalRabReleaseSpeech ] pmNoSystemRabReleaseSpeech  pmNoNormalRabReleaseSpeech

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

In the Ericsson RNC, there are also counters that breakdown some of the RF Drop Reasons (Other than IRAT) to aid the troubleshooting of issues. The counters for Voice Drop reasons are: Counter

Description

Condition

MO Class

pmNoSysRelSpeechSoHo

Number of system disconnects of a speech call for the best cell in the active set due to Soft Handover action. Number of system disconnects of a speech call for the best cell in the active set due to unknown measured cell (missing neighbor relation). Number of system disconnects of a speech call for the best cell in the active set due to lost UL synch.

Network initiated call release of speech calls due to inability to include a non-valid or valid cell in the active set. The counter shall be incremented for the best cell in the active set prior to the call release. Note: This counter is only incremented in the SRNC.

UtranCell

Network initiated call release of speech calls due to inability to include a non-valid cell in the active set. The counter shall be incremented for the best cell in the active set prior to the call release.

UtranCell

Incremented if the timer dchRcLostT expires and the RAB type is a CS Conversational Speech 12.2 Kbps RAB. Note that the counter is applicable for CS Speech RAB and for Multi- RAB, that is, the counter will be stepped if the released RAB is a multi-RAB including a CS Conversational speech RAB Note: This counter is only incremented in the SRNC. The counter is increased when a UE using the speech service is released due to cell congestion. The counter is increased in CRNC for nondrifting UEs for the one cell with congestion.

UtranCell

pmNoSysRelSpeechNeighbr

pmNoSysRelSpeechUlSynch

pmNoOfTermSpeechCong

Number of speech Radio Connections served by this RNC terminated due to congestion

UtranCell

The counters for Soft Handover and Neighbours can be used to determine the drops caused by Radio Link Addition failure (SHO Failure). This is typically due to site issues or T1 issues causing a failure to add a Radio Link on this SHO leg.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

These counters can be used in conjunction with the IRAT Drop calculation to determine the breakdown of drops on the RNC/Market or Region level. The IRAT Drops are given by the following formula:

IRAT Drops (c) = pmNoAttOutIratHoSpeech -pmNoSuccessOutIratHoSpeechpmNoFailOutIratHoSpeechReturnOldChPhyChFail -pmNoFailOutIratHoSpeechReturnOldChNotPhyChFailNoFailOutIratHoSpeechUeRejection

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

The raw counter descriptions for these are below. Counter

Description

Condition

MO Class

pmNoAttOutIratHoSpeech

Number of attempted outgoing (to GSM) inter-RAT handover for ’Conversational speech RAB’. The counter is stepped for the best cell in the active set but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is not stepped. Number of successful outgoing (to GSM) inter-RAT handover for ’Conversational speech RAB’. The counter is stepped for the best cell in the active set but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is not stepped. Number of failed outgoing (to GSM) inter-RAT handover due to physical channel failure, where the UE returns to the present Active Set for ’Conversational speech RAB’. The counter is stepped for the best cell in

The counter is increased when RNC sends "HANDOVER FROM UTRAN COMMAND". This counter will only be incremented in the SRNC.

GsmRelati on

pmNoSuccessOutIratHoSpeech

pmNoFailOutIratHoSpeechReturn OldChPhyChFail

The trigger is when IU RELEASE COMMAND is received with cause ’Normal release’ or ’Successful relocation’ and based on the CS RAB state. This counter will only be incremented in the SRNC.

The trigger is the reception of "HANDOVER FROM UTRAN FAILURE" with Inter-RAT handover failure cause=Physical Channel Failure and based on the CS RAB state. This counter will only be incremented in the SRNC.

GsmRelati on

GsmRelati on

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Counter

pmNoFailOutIratHoSpeechReturn OldChNotPhyChFail

pmNoFailOutIratHoSpeechUeReje ction

Description the active set but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is not stepped Number of failed outgoing (to GSM) inter-RAT handover due to reasons other than physical channel failure, where the UE returns to the present Active Set for ’Conversational speech RAB’. The counter is stepped for the best cell in the active set but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is not stepped Number of failed outgoing (to GSM) inter-RAT handover, rejected by UE, for ’Conversational speech RAB’. The counter is stepped for the best cell in the active set but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is

Condition

MO Class

The trigger is when "HANDOVER FROM UTRAN FAILURE" is received with interRAT handover failure cause=any other cause apart from Physical channel failure or configuration unacceptable, and based on the CS RAB state. This counter will only be incremented in the SRNC.

GsmRelati on

The trigger is when "HANDOVER FROM UTRAN FAILURE" is received with interRAT handover failure cause=configuratio n unacceptable, and based on the CS RAB state. This counter will only be incremented in the SRNC

GsmRelati on

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Counter

Description not stepped

Condition

MO Class

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Drop Breakdown These metrics can be used to determine the breakdown of drops on an RNC, Market or Region level and can be shown as follows.

The “Other Drops” shown in the chart represent the drop causes which cannot be tagged with a specific reason for the drop. This represents: Other Drops = Total Voice Drops – Voice Drops with a defined Reason This chart provides an overview of the areas to concentrate the performance analysis for the network.

MOU Per Drop The other metric which is important to monitor is the MOU Per Drop (MPD). This gives a measure of the Customer Experience on the network. This is given by: MOU Per Drop = Minutes of Use [Derived from Erlangs] / Total Number of Voice Dropped Calls

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

As expected, as the drop rate decreases, the MPD will increase.

Iur Drops When more than one RNC is used to serve a particular area, drops may occur when the user travels between the area served by one RNC to the area served by the 2 nd RNC over the Iur boundary. These can be seen in the retainability Iur report which can be broken down by Iur Link MO. This metric uses the same counter names as the Drop Rate metric but on an Iur MO.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

As can be seen from the graph above, the Iur Drop Rate is higher than the overall RNC Drop Rate and the number of samples is much lower.

Other Metrics/Counters Other counters which are included in the report which may be useful in troubleshooting on an RNC level are: Counter

Description

Condition

MO Class

pmNoReleaseDchRcLostT

Number of overall release triggered by dchRcLostT expiry

When the RBS detects loss of UL synchronization for an RL Set in a Radio Connection it will send the Radio Link failure Indication message to the RNC. If all RLs have failed the timer dchRcsLost is started. When the timer expires the Radio Connection is considered lost and the counter is increased. The counter is never incremented in relation to a successful or a failed

Rcs

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Counter

pmNORlcErrors

Description

Number of RLC unrecoverable error (UTRAN) for UEs on FACH or DCH

Condition Cell_DCH to IDLE Transition. However, this does not apply to cases when RCS failure is the actual trigger of CELL_DCH to idle transition An RLC unrecoverable error in RNC L2 initiates the IU Release procedure. The counter is increased. NOTE: The counter is not stepped for L2 errors in the UE. The UE shall send Cell Update with ’RLC Error’ in that case.

MO Class

Rcs

These counters are active in the Radio Connection Supervision (RCS) Subsystem.

Drops Due to Missing Neighbours (Invalid Neighbours) When analysis is completed for Missing Neighbours for a cell, both the WNCS/GPEH Missing Neighbour tool and Drive Test Coverage analysis should be used. Existing neighbours should also be optimized using the RL Addition counters in the 3G-3G Report. The following steps are a suggestion for troubleshooting (Effect on the surrounding sites must also be taken into account): 1. Ensure that during the period the missing neighbours were pegged that surrounding sites were not off air creating a coverage hole and false missing relations. 2. Addition of suggested neighbours by WNCS/GPEH (Including deletion of unused neighbours if required) if deemed valid 3. Analysis of existing neighbours on cell 4. Analysis of coverage area of cell (Problem Cell and Proposed Neighbour) and Target Cells using the Planning Tool, existing drive tests or by performing new drive tests 5. Perform Downtilts and other physical optimization as required After these steps are performed, monitoring should continue on a cluster of cells around the affected cell to determine the performance improvement.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Drops Due to RL Addition Failures (Valid Neighbours) When a large number of Radio Link Addition failures are detected on a cell/RBS, this may highlight a problem with the transport network (T1’s, IMA Groups) or Hardware issues. This metric is developed from two of the available metrics in the Retainability Report: 

Voice Drops due to Missing Neighbor



Voice Drops due to inability to add Neigh to AS

RL Addition Failure Drops = Inability to Add to AS – Missing Neighbour Drops The following steps are a suggestion for troubleshooting: 1. Check for alarms on the site for Hardware Issues 2. Check the T1 Errors on the site 3. Check the Cell Availability (Auto Downtime) on the cells. This may cause these issues if the PICH radiates while the cell is locked down 4. Determine if the issue affects only one cell or a RBS or a cluster of Sites This issue should be dealt with in the normal T-Mobile process for T1’s and hardware issues. After these steps are performed, monitoring should continue on a cluster of cells around the affected cell to determine the performance improvement.

Drops Due to UL Sync UL Synchronization drops are difficult drops to define the exact reason for the drop. The algorithms that cause the counter to be incremented are: 1. Supervision of radio link synchronization status 2. Supervision of RLC protocol (Layer 2 failures) 3. Supervision of connections on common channels This can be a symptom of lack out of UL or DL coverage or high UL Interference. The following steps are a suggestion for troubleshooting: 1. Using Drive Tests (Existing or New)and W-MRR, investigate the UE Tx Power for high values 2. Check the parameters for the Max UE Tx Power and maxSir values 3. Analysis of coverage area of cell (Problem Cell and Proposed Neighbour) and Target Cells using the Planning Tool, existing drive tests or by performing new drive tests 4. Use of GPEH event (INTERNAL_MEASUREMENT_HANDLING_ EVALUATION) to determine the number of Event 6a occurrences to determine UE Reports on Max Tx Power or number of Event 2d occurrences to determine reported EcNo in a cell

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

After these steps are performed, monitoring should continue on a cluster of cells around the affected cell to determine the performance improvement.

Drops Due to IRAT This cause is determined by calculation using a number of counters from the Mobility report. Issues with IRAT Drops may show an issue with the defined neighbours for the cell. These include: 

Incorrect Prioritization



Neighbour List too long (Too long in compressed mode searching for neighbours)

The following steps are a suggestion for troubleshooting: 1. Neighbour List cleaning/deletion based on Relation Usage counters to reduce the search time/time in compressed mode 2. Coverage area verification for IRAT Neighbours 3. Re-prioritization of Neighbour Relations based on usage After these steps are performed, monitoring should continue on a cluster of cells around the affected cell to determine the performance improvement.

Drops Due to Congestion This cause is related to a lack of Hardware or Software licenses on the RBS Base Band or to interference. It uses Power and UL RTWP measurements to resolve the overload in the Uplink and Downlink. The following steps are a suggestion for troubleshooting: 1. Check the downswitch counters for congestion reasons – determine whether the issue is in the UL or DL 2. Investigate the RRC Accessibility Failures due to Lack of DL Power and Lack of Channelization Codes 3. Perform analysis of the coverage area and reduce overshooting 4. Verify the CE Usage and HW Allocation and dimensioning with the BSS Team

Miscellaneous Drops These drops are the remaining drops that cannot be accounted for in the drop reasons outlined above. There are a number of reasons for these and the drops with defined reasons above should be actioned first. Some of the causes for the drops include: 1. Transport Issues (T1’s etc) 2. Hardware Issues 3. RF Issues outside of the previously mentioned counters 4. UE Issues

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Some of the corrections for the previous issues will aid the remedy of these Miscellaneous/Other drops. For further investigation of the drop causes, GPEH, CTR and the Tektronix K-18 tools should be used to determine the reason behind the drop.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

CS Voice RRC Retainability The metric for CS Voice RRC Retainability is only made up of 2 counters. This metrics can be run on an RNC/Market level or on a cell level. The counters are below:

Counter

Description

Condition

MO Class

pmTotNoRrcConnectReqCsS ucc

Total number of Successful Conversation al Call (originating and terminating) and Emergency Call RRC Connection attempt. Number of abnormal disconnect of a speech call for the Best Cell in the Active Set..

The counter is increased when an RRC Connection Setup Complete message is received following an attempt to setup an originating or terminating conversational call.

UtranCell

The counter is only increased for the speech RAB, that is the conversational/speech 12.2 Kbps RAB". The counter is only increased when the RRC Connection is released with the RRC Connection Release command with "release cause" = anything but ’normal event ’ or ’user inactivity’ or ’Directed Signalling Connection Reestablishment’. In case of multi-RAB or multi signaling connection, the RRC Connection will remain after that the signaling connection or RAB to one CN have been released and therefore the counter is not be increased. The counter is only increased the first time the RRC Connection Release is sent to the UE. (The RNC may transmit several RRC messages to increase the probability of proper reception of the message by the UE).

UtranCell

pmNoSpeechDchDiscAbnor m

VoiceRRCDr opRate(%)  100 * [

pmNoSpeechDchDiscAbnorm ] pmTotNoRrc ConnectReqCsSucc

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

These metrics can be investigated in the same way as the RAB Drops.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

PS Interactive RAB Retainability The KPI for PS Interactive is the PS Interactive RAB Drop Rate %. These metrics can be run on an RNC/Market level or on a cell level. This includes the HSDPA RAB’s as well as PS R99 RAB’s. The main report for identifying and troubleshooting retainability issues in T-PIM is the Retainability Report. This contains the Drop Rate and Drop Count. This is made up of the following counters: Counter

Description

Condition

MO Class

pmNoNormalRabReleasePac ket

Number of successful normal RAB releases (PS Data) for the best cell in the active set. When releasing a HS RAB, this counter is stepped for the Serving HSDCH cell

UtranCell

pmNoSystemRabReleasePac ket

Number of successful system RAB releases (PS Data) for the best cell in the active set. When releasing a HS RAB, this counter is stepped for the Serving HSDCH cell

This counter is only increased due to a RANAP Iu Release Command or RAB Assignment Request message with “release cause” = ’Normal Release’, ’Successful Relocation’, ’Resource Optimisation Relocation’, ’User Inactivity’ or ’release-due-to-UE-generatedsignalling-connection-release’. It is for the Best Cell in the Active Set and when releasing a HS RAB, this counter is stepped for the Serving HS-DCH cell. This counter is only increased due to a RANAPIu Release Command or RAB Assignment Request message with “release cause” = anything except ’Normal Release’, ’Successful Relocation’, ’Resource Optimisation Relocation’, ’User Inactivity’ or ’release-due-to-UE-generatedsignalling-connection-release’. This counter is incremented for the best cell in the Active Set in the SRNC and when releasing a HS RAB, this counter is stepped for the Serving HS-DCH cell

UtranCell

The KPI is defined in T-PIM shows the percentage of system/abnormal RAB releases over the total number of RABs. It is defined as follows:

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

PSInterRABDropRate (%)  100 * [

pmNoSystemRabReleasePacket ] pmNoSystemRabReleasePacket  pmNoNormalRabReleasePacket

There are no IRAT Drop Counters for PS Interactive so a useful metric is the PS Interactive IRAT Failure Rate (%). PSInterRAB _ IRAT _ Failure (%)  100 * [1 

pmNoOutIratCcSuccess ] pmNoOutIratCcAtt

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

The raw counter descriptions for these are below. Counter

Description

Condition

MO Class

pmNoOutIratCcReturnOldCh

Total number of the PS Inter-RATCC attempts for UE on DCH where the UE returns to old channel. The counter is stepped for the best cell in the active set, but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is not stepped. Total number of the PS Inter-RATCC attempts on DCH. The counter is stepped for the best cell in the active set, but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is not stepped.

Inter-RATCC from UTRAN to GPRS, UE on DCH. The counter is increased when the Cell Change Order From UTRAN Failure (RRC) message is received from the UE

GsmRelati on

Inter-RATCC from UTRAN to GPRS, UE on DCH. The Handover evaluation function triggers this function to indicate that we need to make handover to a GSM cell. (A Measurement Report message (RRC) for event 3a has been received from the UE). The counter is increased when the Cell Change Order From UTRAN (RRC) message has been sent to the UE. Inter-RAT CC from UTRAN to GPRS, UE on DCH. The Handover Evaluation function triggers this function to indicated that we need to make a handover to a GSM cell (A

GsmRelati on

pmNoOutIratCcAtt

pmNoOutIratCcSuccess

Number of successful PS Inter RAT cell change attempts for UE on dedicated channel. The counter is triggered by CN Iu Release Command following the sending of the CELL CHANGE

GsmRelati on

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Counter

Description

Condition

ORDER FROM UTRAN message. The counter is stepped for the best cell in the active set, but only if that cell has a cell relation towards the target cell. If the best cell in the active set has no cell relation towards the target cell, the counter is not stepped

Measurement Report message (RRC) for event 3a has been received from the UE). The Cell Change Order from UTRAN (RRC) message is sent to the UE and the counter is increased when a Iu Release Command is received from the PS CN, with cause ‘Normal release’ or ‘Successful Relocation’.

MO Class

The IRAT Drop Rate can be estimated from the following formula: PSInterRAB _ IRATDrop (%)  100 *

pmNoOutIratCcAtt - pmNoOutIratCcSuccess - pmNoOutIratCcReturnOldCh ] pmNoOutIratCcAtt

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Iur Drops As in the CS Voice example, where more than one RNC is used, drops may occur over the Iur Boundary. These can be seen in the retainability Iur report and can be broken down by Iur Link MO. This metric uses the same counter names as the Drop Rate metric but on an Iur MO.

As can be seen from the graph above, the Iur Drop Rate is higher than the overall RNC Drop Rate and the number of samples is much lower. This mirrors the experience on CS Voice. These plots should be used as an indication of issues that should be investigated further on a Cell/RBS basis. Detailed troubleshooting will be included in the Cell Analysis section.

Cell/RBS Analysis The Drop Rate and Count metrics can be used on a Cell level also. The Worst Offenders in an RNC/Market/Region level should be ranked by the following metrics: 

PS Interactive Drop Rate



PS Interactive Count (Contribution to Total RNC/Market/Region)

These PS Interactive drops do not have broken down drop reasons similar to the Voice examples. There are a number of possible reasons for these drops and they should be investigated like the miscellaneous drops in CS Voice. 1. Transport Issues (T1’s etc) 2. Hardware Issues 3. RF Issues outside of the previously mentioned counters 4. UE Issues

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Some of the corrections for the Voice drop issues will aid the remedy of these PS Interactive drops. For further investigation of the drop causes, GPEH, CTR and the Tektronix K-18 tools should be used to determine the reason behind the drop.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

1.2. PS Interactive RRC Retainability The metric for PS Interactive RRC Retainability is only made up of 3 counters. This metrics can be run on an RNC/Market level or on a cell level. The counters are below:

Counter

Description

Condition

MO Class

pmNoPacketDchDiscAbnorm

Number of abnormal disconnects of a packet call over DCH and E-DCH for the Best cell in the Active set

UtranCell

pmNoCellFachDisconnectAb norm

Number of abnormal disconnectio ns from common channels (that is, CELL_FACH state).

The counter is only increased when the RRC Connection is released with the RRC Connection Release command with "release cause" = anything but ’normal event ’ or ’user inactivity’ or ’Directed Signalling Connection Re-establishment’. In case of multi-RAB or multi signaling connection, the RRC Connection remains after that the signaling connection/RAB to one CN have been released and therefore the counter shall not be increased. The counter is only increased the first time the RRC Connection Release is sent to the UE. (The RNC may transmit several RRC messages to increase the probability of proper reception of the message by the UE). This counter is only increased when the packet FACH RRC Connection is released with an RRC Connection Release message with “release cause” = anything except ’normal event ’ or ’user inactivity’ or ’Directed Signalling Connection Re-establishment’. The counter is only increased the first time the RRC Connection Release is sent to the UE. (The RNC may

UtranCell

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

Counter

pmTotNoRrcConnectReqPsS ucc

PSInterRRCDropRate (%)  100 * [

Description

Total number of Successful ’Originating Interactive Call’, ’Terminating Interactive Call’, ’Originating Background Call’, ’Terminating Background Call’, or ’Originating Subscribed Traffic Call’ RRC connection setups.

Condition transmit several RRC messages to increase the probability of proper reception of the message by the UE). The counter is increased when an RRC Connection Setup Complete message is received following an attempt to setup Originating Interactive Call’, ’Terminating Interactive Call’, ’Originating Background Call’, ’Terminating Background Call’ or ’Originating Subscribed Traffic Call’.

MO Class

UtranCell

pmNoPacketDchDiscAbnorm  pmNoCellFachDisconnectAbnorm ] pmTotNo RrcConnectReqPsSucc

These metrics can be investigated in the same way as the PS Interactive RAB Drops.

HSDPA Data RAB Retainability The KPI for HSDPA is HSDPA RAB Drop Rate %. These metrics can be run on an RNC/Market level or on a cell level. This is made up of the following counters: Counter

Description

Condition

MO Class

pmNoSystemRbReleaseHs

Number of successful system releases of packet RABs mapped on HS-DSCH in the Serving HS-DSCH cell Number of successful normal

The counter is stepped for the Serving HS-DSCH cell at RAB/RB combination transition from PS Interactive 64/HS (or 384/HS or EUL/HS) - HS-DSCH to SRB-DCH or to Idle mode due to the same reasons as for stepping the existing counter pmNoSystemRabReleasePacket The counter is stepped for the Serving HS-DSCH cell at RAB/RB combination transition

UtranCell

pmNoNormalRbReleaseH

UtranCell

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

releases of packet RABs mapped on HS-DSCH in the Serving HS-DSCH cell.

from PS Interactive 64/HS (or 384/HS or EUL/HS) - HS-DSCH to SRB-DCH or to Idle mode due to the same reasons as for stepping the existing counter pmNoNormalRabReleasePacket

The KPI is defined in T-PIM shows the percentage of system/abnormal RAB releases over the total number of RABs. It is defined as follows: HSDPA _ RABDropRat e(%)  100 * [

pmNoSystemRbReleaseH ] pmNoSystemRbReleaseH  pmNoNormalRbReleaseH

HSDPA MB Per Drop Another metric, aside from the Drop Rate and Count, which can be monitored, is the MB Per Drop (MBPD). This gives a measure of the Customer Experience on the network. This is given by: MB Per Drop = MB Downloaded / Total Number of HSDPA Dropped Calls

Cell/RBS Analysis The Drop Rate and Count metrics can be used on a Cell level also. The Worst Offenders in an RNC/Market/Region level should be ranked by the following metrics: 

HSDPA Drop Rate



HSDPA Count (Contribution to Total RNC/Market/Region)

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

These HSDPA drops do not have broken down drop reasons. There are a number of possible reasons for these drops and they should be investigated like the miscellaneous drops in CS Voice. 1. Transport Issues (T1’s etc) 2. Hardware Issues 3. RF Issues outside of the previously mentioned counters 4. UE Issues Some of the corrections for the Voice drop issues will aid the remedy of these HSDPA Drops. For further investigation of the drop causes, GPEH, CTR and the Tektronix K-18 tools should be used to determine the reason behind the drop.

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

2.Configuration Management Configuration Management tools and methods should also be used in improving retainability. Some of these items have been discussed already but these include: –

Neighbour List Optimization •

•

Counts (3G-3G and 3G-2G) –

Removals

–

Additions

Selection Priority (3G-3G and 3G-2G) –

–

Counter Based Changes to Priority levels

Antenna Changes •

Tilts

•

Azimuths

UMTS RAN Performance Trouble Shooting Guidelines – Ericsson UMTS Retainability

3.Troubleshooting Tools The following tools can be used for troubleshooting: 

W-NCS  The WCDMA Neighbouring Cell Support (W-NCS) is an Ericsson OSS Tool which provides suggestions on missing neighbour additions and neighbour removals  More detail on this tool can be found in ALEX



GPEH  The General Performance Event Handling (GPEH) tool is a feature in the Ericsson OSS that provides capability similar to a protocol analyzer. This also has visibility of internal RNC events such as Missing neighbour etc  This can be run on an RNC level  More detail on this tool can be found in ALEX



CTR/Uech  The Call Trace (CTR) tool is a feature in the Ericsson OSS that provides capability similar to the GPEH Tool  This can be run on a Cell level for specific cell troubleshooting. These files can be read in Actix  More detail on this tool can be found in ALEX



UETR  The User Equipment Trace (UETR) tool is a feature in the Ericsson OSS that provides capability similar to the GPEH Tool  This is run on a particular IMSI for specific issue troubleshooting, typically a test SIM attempting to recreate problem conditions. These files can be read in Actix  More detail on this tool can be found in ALEX