ZTE UMTS CPU Overload Control Feature Guide

CPU Overload Control WCDMA RAN

Feature Guide

CPU Overload Control Feature Guide

ZTE Confidential Proprietary © 2011 ZTE Corporation. All rights reserved. 1


Version Date Author Reviewer Remarks

V5.0 2010-10-15 Zhao Zesheng Cai Lan

© 2011 ZTE Corporation. All rights reserved.

ZTE CONFIDENTIAL: This document contains proprietary information of ZTE and is not to be disclosed or used without the prior written permission of ZTE. Due to update and improvement of ZTE products and technologies, information of the document is subjected to change without notice.



TABLE OF CONTENTS

1 Functional Attribute ........................................................................................ 3

2 Introduction .................................................................................................... 3 2.1 Function Introduction ........................................................................................ 3 2.1.1 CPU Overload Control Function ....................................................................... 3

3 Technical Description .................................................................................... 4 3.1 Overload Control Function ................................................................................ 4 3.1.1 CPU Load Statistics .......................................................................................... 4 3.1.2 Congestion Control and Restoration ................................................................. 4 3.1.3 CPU Overload Control for New Call Attempts ................................................... 5 3.1.4 CPU Overload Control for Existing Calls ........................................................... 6

4 Parameters and Configuration ...................................................................... 6 4.1 Parameter List .................................................................................................. 6

5 Counter and Alarm ......................................................................................... 6 5.1 Counter List ...................................................................................................... 6 5.2 Alarm List ......................................................................................................... 6

6 Glossary .......................................................................................................... 7



1 Functional Attribute

System version: [RNC V3.09, Node B V4.09, OMMR V3.09, OMMB V4.09]

Attribute: [Optional]

Involved NEs:

UE Node B RNC MSCS MGW SGSN GGSN HLR

- - √ - - - - -

Note:

*-: Not involved.

*√: Involved.

Dependency: [None]

Mutual exclusion: [None]

Remarks: [None]

2 Introduction

2.1 Function Introduction

RNC CPU Overload Control based on the statistics value of RNC processors, perform

Admission Control of service in accordance with pre-configured CPU load threshold, and

keep the processor load in the normal range.

This document describes the CPU load control technology in the UMTS RNC. It is written

mainly for operators and engineers who want to understand the detail functionality of the

RNC CPU load control.

2.1.1 CPU Overload Control Function

The CPU overload control is implemented on the RCP board (RNC Control-plane

Processor). The RNC monitors the CPU load of the RCP based on the statistics and

determines whether the CPU load exceeds pre-configured CPU load threshold. The RNC

defines several radio processes. Before implementing the process, the RNC calls the

interface supplied by the system load control mechanism to determine whether the called

can be implemented. If the CPU admission result is “Reject”， the process will not be

implemented. If the CPU admission result is “Allowed”, the process will be implemented.

This action stabilizes the CPU load.



3 Technical Description

3.1 Overload Control Function

3.1.1 CPU Load Statistics

CPU load statistics refers to the CPU utilization rate within a period, that is, the

proportion of the effective calculation time implemented by the CPU in the total run time.

Perform the following steps to get the CPU utilization rate:

Design a reference code. When the system starts, execute the reference code many

times. Then, obtain the execution time of the reference code and calculate the average

run time (t) of the reference code.

Create an idle task with the lowest priority in the system. Execute the reference code

circularly in the idle task and count the execution times. Assume that the reference code

is executed n times at the interval of T s within the specified time, calculate the CPU

utilization rate (CPURate) in the following formula:

CPURate = (100 - (100 * n * t / T)) %

Calculate the CPU utilization rate every two seconds in the task and output the CPU

utilization rate for application query.

3.1.2 Congestion Control and Restoration

The process of congestion control and restoration is as follows:

The system queries the CPU utilization rate periodically (every second). When the CPU

utilization rate exceeds 80%, the system state is identified as congested. The system

then sets the service admission proportion (R) to 0.1 and then starts restricting service

admission according to the proportion R.

If the CPU utilization rate is still higher than 80% in the next continuous ten seconds from

the beginning of congestion, the system sets R to 0.01. If the CPU utilization rate is still

higher than 80% in the next continuous twenty seconds from the beginning of congestion,

the system sets R to zero.

If the system detects that the CPU utilization rate is lowered to 75% in one query (RNC

query the CPU load each second), the system sets R to 1 and then cancels the

restriction on service admission. The CPU is returned from congested to normal.

The admission process of service operations is as follows:

When receiving a service process request, the system firstly query the current service

admission proportion (R) by calling the load control interface. If R is less than 1, the

system generates a random number between 0 and 100 and divides the random number

by 100 to get the parameter r.



If r is greater than R, the system rejects to execute the service process. If r is less than

or equal to R, the system implements the service process.

3.1.3 CPU Overload Control for New Call Attempts

For new call attempt, a RRC Connection Request message will be received, before

implementing RRC connection process, the system needs to call the load control

interface to determine whether the process can be implemented. Perform the following

steps to determine whether RRC connection process can be implemented:

When the RNC receives a RRC Connection Request, the system will invoke CPU

Load Control defined in Section 3.1.2 to determine whether the connection is

allowed.

If CPU Load Control returns reject, the RRC connection will be rejected, the RNC

generates a RRC Connection Reject message and sends it to the UE, and then

quits from handling.

If CPU Load Control returns allowed, the RRC connection will be allowed, the

system proceeds with the subsequent handling.

UE RNC

RRC Connection Request

CPU Load Control defined by Section 3.1.2

RRC Connection Reject

RRC Connection Setup

CPU Load Control return Reject

CPU Load Control return Allowed

Figure3-1: RRC connection process in CPU congestion



3.1.4 CPU Overload Control for Existing Calls

Some procedures including DRBC, channel switching and handover will be executed for

existing calls, and these procedures will also be determined by CPU Overload Control.

Refer the following statement for details.

When a measurement report message from UE is received, CPU Overload

Control function is invoked at first, if the function return reject, this measurement

report will be discarded (e.g. act as the message is not received).

When DRBC is triggered, CPU Overload Control function will be invoked before

execution, if the function return reject, this execution will be discarded.

When handover including soft Handover, intra-frequency hard handover, inter-

frequency hard handover and Inter-RAT handover is triggered, CPU Overload

Control function will be invoked before execution, if the function return reject, this

execution will be discarded.

When channel switching is triggered, CPU Overload Control function will be

invoked before execution, if the function return reject, this execution will be

discarded.

4 Parameters and Configuration

4.1 Parameter List

There is no relevant parameter configuration

5 Counter and Alarm

5.1 Counter List

Counter No. Description

C311340000 Peak load of CPU usage of the main processor

C311340001 Mean ratio of the CPU usage

C311340002 Duration of the main processor keeping in busy state

5.2 Alarm List Alarm Code 198002560

Description The usage of CPU is over the threshold



Severity Major

Cause

1. Excessive data traffic at higher layer.

2. System is performing data synchronization or saving.

3. CPU alarm threshold setting is under configured

6 Glossary

CN Core Network

DRBC Dynamic Radio Bearer Control

MSC Mobile services Switching Centre

OMC Operation & Maintenance Center

RCP RNC Control plan Processor

RNC Radio Network Controller

ROMP RNC Operation & Maintenance Processor

SGSN Serving GPRS Support Node

UMTS Universal Mobile Terrestrial System

WCDMA Wideband Code Division Multiple Access

ZTE UMTS CPU Overload Control Feature Guide

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