RACH Storm Filtration(GBSS14.0_01)

RACH Storm Filtration GBSS14.0

Feature Parameter Description

Issue

01

Date

2012-04-28

HUAWEI TECHNOLOGIES CO., LTD.

Copyright © Huawei Technologies Co., Ltd. 2012. All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means without prior written consent of Huawei Technologies Co., Ltd.

Trademarks and Permissions and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd. All other trademarks and trade names mentioned in this document are the property of their respective holders.

Notice The purchased products, services and features are stipulated by the contract made between Huawei and the customer. All or part of the products, services and features described in this document may not be within the purchase scope or the usage scope. Unless otherwise specified in the contract, all statements, information, and recommendations in this document are provided "AS IS" without warranties, guarantees or representations of any kind, either express or implied. The information in this document is subject to change without notice. Every effort has been made in the preparation of this document to ensure accuracy of the contents, but all statements, information, and recommendations in this document do not constitute the warranty of any kind, express or implied.

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Website:

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Email:

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GSM BSS RACH Storm Filtration

Contents

Contents 1 About This Document .................................................................................................................. 1-1 1.1 Scope ...................................................................................................................................... 1-1 1.2 Intended Audience ................................................................................................................... 1-1 1.3 Change History ........................................................................................................................ 1-1 1.4 Document Issues ..................................................................................................................... 1-1

2 Overview ........................................................................................................................................... 2-1 3 Technical Description .................................................................................................................. 3-1 3.1 Working Principles ................................................................................................................... 3-1 3.2 Feature Implementation............................................................................................................ 3-1

4 Related Features ............................................................................................................................ 4-1 5 Impact on the Network ................................................................................................................. 5-1 5.1 Impact on System Capacity ...................................................................................................... 5-1 5.2 Impact on Network Performance .............................................................................................. 5-1

6 Engineering Guidelines ............................................................................................................... 6-1 6.1 When to Use RACH Storm Filtration ......................................................................................... 6-1 6.2 Information to Be Collected ...................................................................................................... 6-1 6.3 Network Planning ..................................................................................................................... 6-1 6.4 Deploying RACH Storm Filtration.............................................................................................. 6-1 6.5 Performance Optimization ........................................................................................................ 6-1 6.6 Troubleshooting ....................................................................................................................... 6-2

7 Parameters ....................................................................................................................................... 7-1 8 Counters ........................................................................................................................................... 8-1 9 Glossary ............................................................................................................................................ 9-1 10 Reference Documents .............................................................................................................10-1

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GSM BSS RACH Storm Filtration

1 About This Document

1 About This Document 1.1 Scope This document describes the GBFD-511505 RACH Storm Filtration feature, including its technical description, related features, network impact, and engineering guidelines.

1.2 Intended Audience This document is intended for: 

Personnel who need to understand the RACH Storm Filtration feature



Personnel who work with Huawei GSM products

1.3 Change History This section provides information about the changes in different document versions. There are two types of changes, which are defined as follows: 

Feature change: refers to a change in the RACH Storm Filtration feature of a specific product version.



Editorial change: refers to a change in wording or the addition of information that was not described in the earlier version.

1.4 Document Issues The document issue is as follows: 

01 (2012-04-28)

01 (2012-04-28) This is the first release of GBSS14.0. This is a new document.

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2 Overview

2 Overview When initiating a call, an MS sends a random access request message to the BTS on the random access channel (RACH) to request a channel. The random access request message contains the following information: 

Channel setup cause: paging response, emergency call, mobile-originated call, short message service (SMS), location update, or other causes



Random access reference value: five bits randomly selected by the MS

If an MS sends excessive random access request messages to the BTS, an RACH storm may occur, which deteriorates counters. The possible causes for an RACH storm are as follows: 

MS exceptions



A large number of abrupt location update requests



A large number of abrupt random access requests due to malicious manual operations



A large number of abrupt paging requests

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3 Technical Description

3 Technical Description 3.1 Working Principles The RACH Storm Filtration feature effectively restrains the RACH storm. Figure 3-1 shows its working principles. Figure 3-1 Working principles for the RACH Storm Filtration feature

If N consecutive random access request messages with the same random access reference value meet the specified time and timing advance (TA) filter conditions, the BTS filters out these messages to restrain the RACH storm.

3.2 Feature Implementation After this feature is enabled, the BTS discards random access request messages that meet the filter conditions. The parameters for implementing this feature are categorized into the following types:

Function Parameters 

RACHFLTSWITCH: specifies whether to enable the RACH Storm Filtration feature.



RACHFLTTYPE: specifies whether to filter out the random access request messages whose channel setup cause is emergency call.

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3 Technical Description

Filter Condition Parameters After this feature is enabled, the BTS filters out random access request messages that meet the filter conditions specified by the following parameters: 



RACHFLTFREQ: specifies the frequency filter condition, which is the maximum number of consecutive random access request messages with the same random access reference value. The recommended value is 4. If the number of random access request messages with the same random access reference value is greater than the value of this parameter, the frequency filter condition is met. RACHFLTTATHD: specifies the TA filter condition, which is the minimum TA difference between two consecutive random access request messages with the same random access reference value. The recommended value is 4. If the actual TA difference is less than or equal to the value of this parameter, the TA filter condition is met.



RACHFLTTMINTVAL: specifies the time filter condition, which is the minimum interval between two consecutive random access request messages with the same random access reference value. If the actual interval is less than or equal to the value of this parameter, the time filter condition is met. If this parameter is set to a large value, two consecutive random access request messages with the same random access reference value are likely to meet the time filter condition. The recommended value is 1 and the unit is 100 ms. Within the specified interval, different MSs are highly likely to use the same random access reference value because only five bits are used for MSs to select a random access reference value. As a result, some random access request messages are filtered out by mistake after this feature is enabled.

Figure 3-2 shows the procedure for implementing the RACH Storm Filtration feature

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3 Technical Description

Figure 3-2 Procedure for implementing the RACH Storm Filtration feature



AB, which stands for access burst, indicates a random access request message.



After this feature is enabled, the BTS discards random access request messages with the same random access reference value without reporting any information to the BSC. After filtering out the messages for 5 minutes, the BTS decides on filter conditions again.

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4 Related Features

4 Related Features None

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5 Impact on the Network

5 Impact on the Network 5.1 Impact on System Capacity If the interval specified by RACHFLTTMINTVAL exceeds 3000 ms, the traffic volume may decrease. The larger the value of this parameter, the more significantly the traffic volume may decrease.

5.2 Impact on Network Performance If this feature is enabled with RACHFLTFREQ set to 4 and RACHFLTTATHD set to 4, the RACH storm can be restrained, increasing the immediate assignment success rate.

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6 Engineering Guidelines

6 Engineering Guidelines 6.1 When to Use RACH Storm Filtration It is recommended that the RACH Storm Filtration feature be enabled in cells that occasionally meet the following conditions in a week: 

The traffic volume remains unchanged.



The immediate assignment success rate decreases.



The SDCCH congestion rate increases.



The KPIs, including TCH traffic volume, assignment success rate, and call drop rate, remain unchanged.

6.2 Information to Be Collected Before deploying this feature, collect the following historical information about cells: 

Traffic volume



Immediate assignment success rate



SDCCH congestion rate

6.3 Network Planning N/A

6.4 Deploying RACH Storm Filtration For details about how to activate, verify, and deactivate this feature, see Configuring RACH Storm Filtration.

6.5 Performance Optimization Monitoring After the RACH Storm Filtration feature is enabled, monitor the counters listed in Table 6-1. Table 6-1 Counters to be monitored Measureme nt Unit

Counter Name

Description

KPI Measureme nt per Cell(CALL.K PICalc.CELL )

CELL.KPI.TCH.TRAF.ERL.TRAF

K3014: Traffic Volume on TCH

CELL.KPI.TCHH.TRAF.ERL

K3034: TCHH Traffic Volume

Immediate Assignment Measureme nt per Cell(CALL.I

CELL.ESTB.IND.SUCC.RATE.IMM. ASS

RA303I: Success Rate of Call Setup (Immediate Assignment)

CELL.IMM.ASS.CMD.TCHF

A3017: Immediate Assignment Commands (TCHF)

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mmAss.CEL L)

6 Engineering Guidelines

CELL.IMM.ASS.CMD.TCHH

A3018: Immediate Assignment Commands (TCHH)

CELL.IMM.ASS.CMD.SD

A3010: Immediate Assignment Commands (SDCCH)

Parameter Optimization Optimize the parameters related to this feature based on the monitored counters. 

If the value of the RA303I counter increases and the values of the K3014 and K3034 counters remain unchanged, parameter optimization is not required.



If the value of the RA303I counter increases and the values of the K3014, K3034, A3017, A3018, and A3010 counters decrease, set RACHFLTTMINTVAL to a smaller value and set RACHFLTFREQ to a larger value.

6.6 Troubleshooting N/A

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7 Parameters

7 Parameters Table 7-1 Parameter description Parameter ID

NE

MML Command Description

RACHFLTFREQ

BSC6900

SET GCELLSOFT

Meaning: Minimum number of consecutive random access requests with the same random access cause. If the number of consecutive random access requests with the same random access cause is greater than the value of this parameter, the BTS filters out the random access requests. GUI Value Range: 1~20 Actual Value Range: 1~20 Default Value: 4 Unit: None

RACHFLTSWITCH

BSC6900

SET GCELLSOFT

Meaning: Whether to enable the RACH storm filtration algorithm. GUI Value Range: NO(No), YES(Yes) Actual Value Range: NO, YES Default Value: NO(No) Unit: None

RACHFLTTATHD

BSC6900

SET GCELLSOFT

Meaning: TA difference between two consecutive random access requests with the same random access value. If the TA difference is less than or equal to the value of this parameter, the TA filter condition is met. GUI Value Range: 0~63 Actual Value Range: 0~63 Default Value: 4 Unit: None

RACHFLTTMINTVAL BSC6900

SET GCELLSOFT

Meaning: Interval between two consecutive random access requests with the same random access value. If the interval is less than or equal to the value of this parameter, the time filter condition is met. GUI Value Range: 1~3000 Actual Value Range: 100~300000 Default Value: 1 Unit: 100ms

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7 Parameters

Parameter ID

NE

MML Command Description

RACHFLTTYPE

BSC6900

SET GCELLSOFT

Meaning: Random access type used for the RACH storm filtration algorithm. GUI Value Range: EMERGENCY_CALL_ALLOWED(Emergency Call Allowed) Actual Value Range: EMERGENCY_CALL_ALLOWED Default Value: EMERGENCY_CALL_ALLOWED-0 Unit: None

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8 Counters

8 Counters There are no specific counters associated with this feature.

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9 Glossary

9 Glossary For the acronyms, abbreviations, terms, and definitions, see the Glossary.

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10 Reference Documents

10 Reference Documents None

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