Umts access kpi troubleshooting guide rrc

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UMTS Access KPI
Troubleshooting Guide
Author/ Email: v.niketh@huawei.com
Version: V1.0(718812)

HUAWEI TECHNOLOGIES CO., LTD. Page 2Huawei proprietary. No spread without permission.
Author / ID v.niketh@huawei.com
Co-author / ID
Approver / ID Sandeep.wadhwa@huaewi.com
Description
UMTS Access KPI troubleshooting Guide

 Access Signaling flow
 Huawei Access KPI and Performance stats formula
 RRC Access failure Root causes
 RRC Access Failure classification based on Performance counters
 RRC Access Failure troubleshooting for Resource congestion
 RRC Access Failure troubleshooting for RF problem
 RRC Access Failure due to Equipment Alarm
Contents

Call Setup(Access) Signaling Flow

Call Setup Signaling setup Procedure
Call Setup setup procedure in UMTS can be classified into
below Phases, (we will see an example for MOC AMR Access
Procedure)
 RRC Connection setup
 Signaling connection setup(to exchange NAS Information)
 Authentication and security mode Control
 Radio Bearer and call Setup procedure

RRC Connection setup Phase

Signaling Establish Procedure
The Signaling connection setup procedure is performed to exchange the
NAS(Non Access Stratum) information between the CN and UE. The UE sends
Direct transfer message to initiate signaling connection setup procedure

1.The authentication and security mode control procedure is performed for
the UE and the network to implement Bi –directional authentication and to
negotiate and configure the integrity protection and Ciphering algorithm.
2.This procedure ensures integrity and correctness of signaling .
Authentication and Security Mode Control

Radio bearer and call setup Procedure

Radio Access Success Rate (Cell)
 A full call setup procedure contains the RRC connection, RAB setup, and Direct
Transfer. Generally only the RRC connection and the RAB setup can be observed from
RAN.
 Access setup success rate KPI can classified based on bearer Qos Services or as a w
ole.we can see a simple Access KPI for CS and PS Services here
 CS Radio Access success Rate (AMR ,Video)
 PS Radio Access Success Rate
 Radio access Setup Success Rate =( RAB Assignment Success/RAB
assignment request) * (RRC Connection setup Success/RRC connect setup
request) ×100%
CS Radio Access Success Rate Formula
CS Radio Access Success Ratio (Cell) =CS RRC Setup Success Ratio(Cell)*CS RAB Setup
Success Ratio(Cell)*100%
=[(RRC.SuccConnEstab.OrgConvCall+RRC.SuccConnEstab.TmConvCall+RRC.SuccConnEstabE
EmgCall)/(RRC.AttConnEstab.OrgConvCall+RRC.AttConnEstab.TmConvCall+
RRC.AttConnEstab.EmgCall)]*[VS.RAB.SuccEstabCS.Conv+VS.RAB.SuccEstabCS.Str)/(VS.RAB
.AttEstabCS.Conv+VS.RAB.AttEstabCS.Str)]*100%

Contd…
PS Radio Access Success Ratio (Cell)
PS Radio Access Success Ratio (Cell) =PS RRC Setup Success Ratio(Cell)*PS RAB Setup
Success Ratio(Cell)*100%
=([(RRC.SuccConnEstab.OrgBkgCall+RRC.SuccConnEstab.OrgItrCall+RRC.SuccConnEstab.Tm
BkgCall+RRC.SuccConnEstab.TmItrCall)/(RRC.AttConnEstab.OrgBkgCall+RRC.AttConnEs
tab.OrgInterCall+RRC.AttConnEstab.TmBkgCall+RRC.AttConnEstab.TmInterCall)]*
[(VS.RAB.SuccEstabPS.Conv+VS.RAB.SuccEstabPS.Str+VS.RAB.SuccEstabPS.Int+VS.RAB
.SuccEstabPS.Bkg)/(VS.RAB.AttEstabPS.Conv+VS.RAB.AttEstabPS.Str+VS.RAB.AttEstab
PS.Int+VS.RAB.AttEstabPS.Bkg)]*100%

Radio access setup success rate
 Counter:
 RRC_REQ：
 Measurement point: when RNC receives and valid RRC CONNECTION
REQUEST message
 RAB_SETUP_SUCC:
 Measurement point ：the RABs successfully setup in the message RANAP
RAB ASSIGNMENT RESPONSE for the “X”service

RRC access KPI Troubleshooting
This guide is intended to cover the Huawei RRC signaling related measurement
counters ,related KPI, failure points ,root cause analysis and solution to
improve it .

RRC connection setup measurement
Points

RRC connection setup measurement
per cell overview
 When an UE needs to access the network, setting up the RRC connection is
the first step. From the cell where the UE is located, the UE sends a RRC
CONNECTION REQUEST message to request network access.
 After receiving the RRC CONNECTION REQUEST message, the RNC initiates
the admission procedure and allocates relevant resources to the UE.
Following successful allocation of resources, the RNC sends a RRC
CONNECTION SETUP message to the UE and waits for a RRC CONNECTION
SETUP COMPLETE message, a response message from the UE. When the
RNC receives a RRC CONNECTION SETUP COMPLETE message, the
procedure for RRC connection setup is finished

Contd….

RRC connection setup counter and
sub-counter relation

Contd….

Access Failure Root causes
 We will see the Major access failure root causes as in below table

RRC Connection Failure measurement

RRC Connection Reject measurement points

RRC connection reject measurement points(Please refer the Flow
for measurement points)

RRC connection rejection counters

Counters and Sub counters relation

RRC Access Failure analysis Flow

Admission procedure

Resource congestion counters(counter name self explanatory for
specific resource congestion measurement)

Resource Congestion
 Resource congestion is classified into
 CE congestion
 Power congestion(DL and UL)
 Code congestion
 Iub

CE Congestion optimization
1. Check for CE utilization and suggest baseband board upgrade for CE
utilization >70%
2. For short term optimization can follow the below procedure ,which can
impact to user experience
Solution1
 Enable LDR
Solution2
 Modify initial bit rate of DCH/HSUPA DCCC rate threshold /Low activity bit
rate from 64Kbps to 32Kbps
Solution2
 Modify DCH/HSUPA inter and BKG service GBR from 64Kbps to 32Kbps

CE Congestion optimization Contd….
Solution 4
 Modify DCH/HSUPA DCCC 4A threshold ,and limit user rate upgrade
Solution 5
 Enable PS BE HSDPA/HSUPA state transition
Solution 6
 Enable the TTI dynamic adjustment algorithm for admission CE based
HSUPA services

Admission control for power

Contd….

power Congestion
From RAN 12 version, New counters are added to find the congestion cause is
UL for DL.
How to optimize UL power congestion?
Use UL CAC algorithm II – based on ENU(Equivalent number of users)- most
widely used CAC algorithm
Solution 1
 Modify UL CAC from 80 to 120-200(be careful to check increase in RTWP
and CDR and DL power congestion)
Solution 2
 Enable UL LDR
Solution 3
 Increase UL CAC threshold 5% from current setting

Contd….
Solution 4
 Modify initial bit rate of DCH/HSUPA DCCC rate threshold /Low activity bit
rate from 64Kbps to 32Kbps
Solution 5
 Modify UL DCH/HSUPA inter and BKG service GBR from 64Kbps to 32Kbps
Solution 6
 Modify UL DCH/HSUPA DCCC 4A threshold ,and limit user rate upgrade
 Solution 7
 Optimize/Reduce SHO ratio by physical or change 1A ,1B relative event
threshold and trigger timer

DL power Congestion Optimization
Solution 1
 Modify DL CAC from 80 to 120-200(be careful to check increase in RTWP
and CDR and DL power congestion)
Solution 2
 Enable DL LDR
Solution 3
 Increase DL CAC threshold 5% from current setting
Solution 4
 Limit the Max power of Radio bearer (for example PS 384K Max DL power
is 4 dB relative to Pilot power , reduce it to 2dB)

Contd….
Solution 4
 Modify initial bit rate of DL DCH DCCC rate threshold /Low activity bit rate
from 64Kbps to 32Kbps
Solution 5
 Modify DL DCH inter and BKG service GBR from 64Kbps to 32Kbps
Solution 6
 Modify DL DCH DCCC 4A threshold ,and limit user rate upgrade
Solution 7
 Optimize/Reduce SHO ratio by physical or change 1A ,1B relative event
threshold and trigger timer

Code Congestion Solution
Solution 1
 Reduce HS-PDSCH code number (if manual allocation) or HS-PDSCH min
code number (Automatic allocation)
Solution 2
 Reduce HS-SCCH code number (for example from 4 to 2)
Solution 3
 Enable Code LDR
Solution 4
 Enable Node B dynamic code allocation(if not activated)

Contd….
Solution 5
 Modify initial bit rate of DL DCH DCCC rate threshold /Low activity bit rate
from 64Kbps to 32Kbps
Solution 6
 Modify DL DCH inter and BKG service GBR from 64Kbps to 32Kbps
Solution 7
 Modify UL DCH/HSUPA DCCC 4A threshold ,and limit user rate upgrade

Iub Congestion Optimization
1. If the RNC allocates the maximum bandwidth to the subscriber when a
service is established, a large proportion of the Iub transmission bandwidth
is unused. For example, downloading a 50 KB page takes only about one
second, but reading this page needs dozens of seconds.
2. Thus, over 90% of the Iub transmission bandwidth is not used.
3. To save the Iub transmission bandwidth we can reduce activity factor to
admit more users and better utilize bandwidth
Solution 1
 Modify PS R99/HSDPA/HSUPA interactive and Background activity factor
from 100% to 70%-30%
Solution 2
 Modify R99/HSDPA/HSUPA interactive and Background GBR from 64Kbps
to 32Kbps

RF problem Analysis
 The RRC.FailConnEstab.NoReply is a cell-level index which indicates the RF
related problem for Access failure
 The major causes of the problem include the following two types:
 The UE fails to receive the RRC CONNECTION SETUP message from RNC.
The cause of the problem is irrational configuration of coverage, cell
selection and cell reselection parameters.
 After the UE send the RRC CONNECTION SETUP COMPLETE message, but
the RNC does not receive it. Maybe the initial transmit power of uplink DCH
is over low.

VS.RRC.FailConnEstab.NoReply
The measurement is triggered at point A as shown in the figure, if the RNC fails to receive a
RRC CONNECT SETUP COMPLETE message from the UE before the timer expires after the
RNC sends the RRC CONNECT SETUP message to the UE. In this case, this counter is
measured in the cell where the UE is located

Analysis Procedure
 After the RNC Receives the RRC Setup Request Message from UE, It Sends
the RRC Connection Setup Message Which Is Not Received by UE
 The causes of this problem include:
 Weak coverage
 Improper parameters of cell selection and reselection
 Check the CPICH Ec/Io. If it is lower than –12 dB (the default value is
configured based on Ec/Io as –12 dB) and
 If there is no more qualified cell listed in the monitor set, the problem is
about coverage.
 If there is more qualified cell listed in the monitor set, the problem is about
cell reselection.

Solutions are as below:
When the coverage is weak:
 If conditions permit, solve coverage problems by enhancing coverage, such
as adding sites to cover blind areas and adjusting engineering parameters.
If you cannot enhance the coverage, you can increase FACH power. Adjust
FACH power according to the coverage conditions of PCPICH Ec/Io.
 Check for Weak coverage due to overshooting by analyzing the TP and if
more samples are pegged in high TP distance ,try adding down tilt
Cell selection and reselection:
 Adjusting cell selection and reselection parameters accelerates cell selection
and reselection and helps solve RRC connection setup failure problems
caused by improper parameters of cell selection and reselection.
High RTWP
 If RTWP is high ,check the reason for high RTWP(high traffic, internal
,external interference) and solve it to improve the RRC access success rate

Contd….
 The RRC CONNECTION SETUP message is carried by FACH. After the
UTRAN side receives the PRACH preamble, the UE sends the RRC
CONNECTION REQUEST message on RACH based on current preamble
power. The preamble transmit power keeps increasing until response is
received (restricted by maximum retransmission times of preamble).
Therefore, in poor coverage areas, unbalanced coverage by RACH and
FACH is probable. Consequently the UTRAN side can receive the RRC
CONNECTION REQUEST message while the UE fails to receive the RRC
CONNECTION SETUP message.
 Check for FACH channel signaling congestion add an SCCPCH to reduce
FACH congestion
 In case of imbalance in DL coverage where UE not able to receive RRC
connection setup message ,increase FACH channel power

VS.RRC.Rej.RL.Fail
 If ATM transmission mode is adopted check the bit error rate of E1.
 If framing error rate is higher than 0.1% then bit error rate of E1 is high---
check for transmission fault and clear it
 If IP mode of transmission is adopted, check packet loss rate of IP.If packet
loss rate is greater than 1% check for fault in IP transmission and clear it
 Check for Node B DSP .Baseband board signaling load and if it greater than
70% ,suggest for base band board and BBU expansion
 Check for any event, promotion which causes signaling storm lead to radio
link failure
 Check the mean SPU load SPU to which the worse cell is located and it
should not exceed 60% then suggest for SPU expansion
 If any of the above cannot lead to solution submit GCRMS ticket to TAC
and R&D team

VS.RRC.Rej.TNL.Fail
 Check for AAL2path or IPPATH configuration is correct (path id ,path
type,Qos settings,VCI/VPI should be correct and match the peer end)
 Check the path of Adj node are available
 Check for packet or Bit error in IP /ATM transmission(refer RL fail
procedure)

Alarms impact to Access KPI
The below alarms can impact to Accesss KPI,but not limited to it alone .
Added to it transmission related alarm and losses from measurement stats to
be checked for analysis

Thank you
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Umts access kpi troubleshooting guide rrc

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