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Flow ControlFeature Parameter Description

Copyright Huawei Technolog ies Co., Ltd. 2010. All righ ts reserved.

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

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The purchased products, services and features are stipulated by the commercial contract made between

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information, and recommendations in this document are provided AS IS without warranties, guarantees or

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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, andrecommendations in this document do not constitute the warranty of any kind, express or implied.

Huawei Proprietary and Confidential

Copyright Huawei Technologies Co., Ltd


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iii

Contents

1 Introduction ................................................................................................................................1-1

1.1 Scope ............................................................................................................................................1-1

1.2 Intended Audience ........................................................................................................................ 1-1

1.3 Change History.............................................................................................................................. 1-1

2 Overview .....................................................................................................................................2-1

3 Inner RNC Board Flow Control .............................................................................................3-1

3.1 Overview .......................................................................................................................................3-1

3.2 Flow Control Items for Boards.......................................................................................................3-1

3.3 Detection of CPU Congestion ....................................................................................................... 3-3

3.4 Detection of Message Block Congestion ...................................................................................... 3-3

3.5 Flow Control Algorithms ................................................................................................................ 3-4

3.5.1 Switch Algorithm................................................................................................................... 3-4

3.5.2 Linear Algorithm.................................................................................................................... 3-4

3.5.3 Hierarchical Algorithm........................................................................................................... 3-5

4 Flow Control over Interfaces .................................................................................................4-1

4.1 Flow Control over the Iu Interface................................................................................................. 4-1

4.1.1 Overview............................................................................................................................... 4-1

4.1.2 Flow Control Based on Iu Signaling Links............................................................................ 4-1

4.1.3 Flow Control Based on the Peer SCCP Subsystem ............................................................ 4-1

4.1.4 Flow Control Based on RANAP Overload ............................................................................ 4-1

4.1.5 Flow Control Based on SCCP CC/CR.................................................................................. 4-2

4.2 Flow Control over the Iub Interface............................................................................................... 4-2

4.3 Flow Control over the Uu Interface ............................................................................................... 4-2

4.3.1 Overview............................................................................................................................... 4-2

4.3.2 CAPS Control ....................................................................................................................... 4-2

4.3.3 RRC Shaping and Queuing.................................................................................................. 4-4

4.4 Paging Control............................................................................................................................... 4-5

5 Load Sharing in RNC...............................................................................................................5-1

5.1 Basic Concept ............................................................................................................................... 5-1

5.2 Load Sharing on the Control Plane............................................................................................... 5-1

5.3 Load Sharing on the User Plane................................................................................................... 5-2

6 Parameters .................................................................................................................................6-1

7 Counters ......................................................................................................................................7-1

8 Glossary ......................................................................................................................................8-1

9 Reference Documents .............................................................................................................9-1


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1 Introduction

1.1 Scope

This document describes the feature WRFD-040100 Flow Control.

Flow control is a set of mechanisms applied to the RNC to prevent the system from becomingoverloaded by regulating the input transmission rate.

1.2 Intended Audience

This document is intended for:

Personnel who are familiar with WCDMA basics

Personnel who need to understand flow control

Personnel who work with Huawei products

1.3 Change History

This section provides information on the changes in different document versions.

There are two types of changes, which are defined as follows:

Feature change: refers to the change in the flow control feature.

Editorial change: refers to the change in wording or the addition of the information that was notdescribed in the earlier version.

Document Issues

The document issues are as follows:

03 (2010-10-15)

02 (2010-06-20)

01 (2010-03-30)

Draft (2009-12-05)

03 (2010-10-15)

This is the third commercial release of RAN12.0.

Compared with the 02 (2010-06-20), this issue optimizes the description.

02 (2010-06-20)This is the second commercial release of RAN12.0.

The CAPS control and RRC shaping and queuing functions are introduced in this issue of RAN12.0.Descriptions of these features are added to section 4.3.2 "CAPS Control" and 4.3.3 "RRC Shaping andQueuing."

01 (2010-03-30)

This is the first commercial release of RAN12.0.

Compared with the draft (2009-12-05), this issue optimizes the description.


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This is the draft of the document for RAN12.0.

Compared with issue 02 (2009-06-30) of RAN11.0, this issue optimizes the description


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2 Overview

Flow control is a mechanism for the RNC to prevent network and system overload. It aims to minimizethe risk of network and system overload through detection and prevention measures. When the system

is overloaded, the RNC prevents services from accessing the network and terminates low-priorityservices so that the system load restores within the shortest time. This ensures system stability androbustness. Moreover, resources are preferentially allocated to high-priority services so that high-priorityservices can access the network.

Figure 2-1 shows the information exchange between RNC boards. Through information exchangebetween inner RNC boards and between RNC interface boards and NodeB/MSC, flow control isimplemented on inner RNC boards, Iub interface, and Iu interface and load balance is achieved betweenmultiple SPU boards.

Figure 2-1 Information exchange between RNC boards

Table 2-1describes the trigger condition, method, and flow control items on each RNC board.

Table 2-1 Flow control on each RNC board

Board/Subsystem Trigger Condition for FlowControl

Flow ControlMethod

Flow Control Item

All RNC boards CPU congestion and messageblock congestion

Inner RNCboard flowcontrol

Log

Performance monitoring

Print

Debug

MPU High CPU usage, messageblock usage, and Call AttemptsPer Second (CAPS)

Load sharing Load sharing on the control

plane

Load sharing on the user plane


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Flow controlover the Iuinterface

Flow control based on Iusignaling links

Flow control based on the peer

SCCP subsystem Flow control based on RANAP

overload

Flow control based on SCCPCC/CR

Flow controlover the Iubinterface

Flow control on signaling links overthe Iub interface

SPU Congestion on the control planeover the Iu, Iub, or Uu interface

Flow controlover the Uuinterface

CAPS control

RRC shaping and queuing

Paging control

Interface board,including UOI,FG2, and GOUboards

Congestion on the user planeover the Iu, Iub, or Uu interface

Flow control onthe user planeover the Iu, Iub,or Uu interface

This document focuses on flowcontrol on the control plane. Fordetails on flow control on the userplane, see the TransmissionResource Management FeatureParameter Description.

Each SPUa board has four subsystems and each SPUb board has eight subsystems. By default,subsystem 0 of the main control SPUa or SPUb board in a subrack is the main control SignalingProcess Unit (SPU) subsystem, called the Main Processing Unit (MPU). The MPU maintains controlplane and user plane resources in the subrack and performs Digital Signal Processor (DSP) statusmanagement.

Except the MPU, all subsystems in an SPU board are responsible for signaling processing. In thisdocument, the term SPU refers to an SPU subsystem on an SPU board.

Figure 2-2shows the sequence of flow control items in the RNC.


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Figure 2-2 Sequence of flow control items in the RNC

1. The RNC performs CAPS control on RRC connection requests. This avoids the impact of a largeamount of signaling from a single NodeB or a cell on the capability of the NodeB, cell, and RNC.

2. The MPU performs load sharing on RRC connection requests between the SPU subsystems.

3. After load sharing is complete, the RRC connection request is sent to an SPU subsystem. Then, theSPU subsystem queues the RRC connection requests that cannot be processed in time. When CPUusage is low, the SPU subsystem processes the queued RRC connection requests. This is theprocess of RRC shaping and queuing.

4. The RNC performs flow control within RNC boards after an RRC connection is established to reducethe load caused by tracing, print, log, and paging.

5. The RNC performs congestion-based flow control over the Iu or Iub interface.


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3 Inner RNC Board Flow Control

3.1 Overview

The RNC board software monitors system resources in real time, including CPU usage and messageblock usage.

The CPU processes all data in the system, and therefore any function consumes CPU resources.

Message blocks are the primary resources for inner RNC communication.

The RNC decides whether to perform flow control, depending on system resource usage.

When resource usage is high, the RNC may not have enough resources to process services. In thiscase, flow control disables some functions to ensure that basic functions are available.

When resource usage drops below the threshold, the functions disabled by flow control can berestored.

Figure 3-1shows the model of the flow control system for RNC boards.

Figure 3-1 Model of flow control system for RNC boards

3.2 Flow Control Items for Boards

The RNC board software monitors system resources in real time and determines whether to start flow control

according to the system resource load, such as CPU usage and message block usage.

Table 3-1 lists the flow control items of each RNC board. The first column in Table 3-1 lists the boardtypes displayed on the LMT.


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Table 3-1 Flow control items for RNC boards

Board Type Flow Control Item

SCU Printing

Debugging Performance monitoring

Logging

SPU Printing

Debugging

Performance monitoring

Resource auditing

Paging

Handover

Iur uplink transfer Iur downlink transfer

CBS

Log

Cell URA update

AC

Iu

Iur-g

NOTE:

The MPU of an SPU board processes only four flow control items: printing,debugging, performance monitoring, and logging.

DPU Printing

Debugging

Logging

AEU/PEU/AOU/UOI/FG2/GOU/POU Printing

Debugging

Logging

GCU/GCG Printing

Debugging Logging

Flow control items for the RNC boards are set through the SET FCSW command. Whether flow controlis performed for the flow control items can be set through the SET FCSW command.


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3.3 Detection of CPU Congestion

The system periodically checks CPU usage every second. When CPU usage reaches a user-specifiedthreshold and the flow control switch is on, flow control is performed. Each flow control item forCPU-usage-based flow control has two thresholds: control threshold and restore threshold.

To minimize the impact of instant fluctuations in CPU usage on the flow control decision, the averagevalue of CPU usage measured during the previous seconds is used. The data in the previous secondsforms a filter window, as shown in Figure 3-2.

Figure 3-2 Filter window

When the average CPU usage in the filter window reaches or exceeds the corresponding controlthreshold, flow control is started.

When the average CPU usage is lower than the corresponding restore threshold, flow control isterminated.

To control the traffic flow when CPU usage becomes high within a short period, the system provides afast judgment window. That is, the system compares the average CPU usage measured in the precedingshort period with the critical threshold. If all the CPU usage values in the fast judgment window reach orexceed the critical threshold, flow control for all the flow control items is started.

The critical threshold takes precedence over the thresholds of other flow control items. The decisions ofother flow control thresholds are effective only when CPU usage is lower than the critical threshold.

You can run the SET FCCPUTHDcommand to set the thresholds for CPU usage.

3.4 Detection of Message Block Congestion

A decision on message block usage is made by the system after the system allocates messages tentimes. When message block usage reaches a specified threshold and the flow control switch is on, flowcontrol is started. Each flow control item for message block flow control has two thresholds: controlthreshold and restore threshold.

To minimize the impact of instant fluctuations in message block usage, the system provides a filter

window. That is, the system compares the average message block usage measured in the precedingperiod with the control threshold.

When the average message block usage in the filter window reaches or exceeds the correspondingcontrol threshold, flow control is started.

When the average message block usage is lower than the restore threshold, flow control is terminated.

The critical threshold takes precedence over the thresholds of other flow control items. The decisions ofother flow control thresholds are effective only when message block usage is lower than the criticalthreshold. The critical threshold decision does not use the filter mechanism. That is, the size of the filterwindow is 1.

You can run the SET FCMSGQTHDcommand to set the thresholds for message block usage.


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3.5 Flow Control Algori thms

The RNC uses three types of flow control algorithms: the switch algorithm, linear algorithm, andhierarchical algorithm. Different algorithms are used for different services. These algorithms, however,cannot be set on the LMT.

3.5.1 Switch Algorithm

The principles of the switch algorithm are as follows:

When resource usage, such as CPU usage or message block usage, exceeds the control threshold ofa flow control item, flow control is performed.

When resource usage is lower than the restore threshold, flow control is not performed.

Figure 3-3 Switch algorithm

3.5.2 Linear Algorithm

The principles of the linear algorithm are as follows:

When resource usage is higher than the control threshold of a flow control item, flow control isperformed.

When resource usage is lower than the restore threshold of a flow control item, flow control is notperformed.

When resource usage is between the restore threshold and the control threshold of a flow control item,the flow control level changes linearly with the resource usage.


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Figure 3-4 Linear algorithm

The flow control level of the linear algorithm, that is, the probability (P) of performing flow control, iscalculated as follows:

P = (resource usage restore threshold) x 100%/(control threshold restore threshold)

3.5.3 Hierarchical Algori thm

The principles of the hierarchical algorithm are as follows:

When resource usage is higher than the control threshold of a flow control item, flow control isperformed.

When resource usage is lower than the restore threshold of a flow control item, flow control is notperformed.

When resource usage is between the restore threshold and the control threshold of a flow control item,the flow control level changes hierarchically with the resource usage.

Figure 3-5 Hierarchical algorithm

The flow control level of the hierarchical algorithm is calculated as follows:

Flow control level = [(resource usage restore threshold) x total number of flow control grades for theflow control item/(control threshold restore threshold)]


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The [ ] symbol indicates an integer value.

The total flow control grades for each flow control item are specified in the system software and cannot be set on the LMT.They vary according to the flow control items.


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4 Flow Control over Interfaces

4.1 Flow Control over the Iu Interface

4.1.1 Overview

When a signaling link on the Iu interface, the peer SCCP subsystem or CN is congested, or the rate ofSCCP Connection Confirm messages/Connection Request messages (CC/CR) is low, the RNC rejectsservices selectively based on the congestion level. Emergency calls are not rejected.

IUFCSW indicates the switch for Iu signaling flow control. IUCTHDindicates the maximum traffic ratio forrestriction in the case of congestion on the Iu interface

4.1.2 Flow Control Based on Iu Signaling Links

The RNC checks the load of Iu signaling links and takes relevant measures. If the load is heavy, the

RNC rejects access selectively. As the load increases, the RNC rejects the access of low-priorityservices and then rejects the access of high-priority services. In this way, the flow control mechanismensures that the admitted services are effectively processed and that services beyond the load capacityof the RNC are temporarily barred from the network to avoid continuous system overload.

The Iu SCCP determines the congestion level based on the congestion status reported from the lowerlayer.

4.1.3 Flow Control Based on the Peer SCCP Subsystem

If the peer SCCP subsystem is congested, the peer equipment sends the RNC an SCCPSubsystem-Congested (SCCP-SSC) message which indicates the congestion level of the peerequipment.

When an RRC connection is set up, the RNC determines whether to start flow control according to thecongestion level and the service type of the RRC connection. If the flow control conditions are met, thisRRC connection setup request is rejected. There are three types of RRC connection services: shortmessage, call, and location registration. The RNC rejects service setup requests upon congestion in thefollowing order: short message service > call service > location registration service. All three types ofservices use the linear algorithm for flow control.

4.1.4 Flow Control Based on RANAP Overload

The RNC rates traffic volume over the Iu interface in 21 levels ranging from 0 to 20. Level 20 is thelowest traffic level. When the traffic volume level is N, the RNC discards Initial Direct Transfer messagesover the Iu interface at a 1-N/20 probability.

When a CN node is overloaded, the RNC receives the OVERLOAD message from the CN. The RNCthen reduces the traffic volume on the CN node. With Iu Flex applied, the RNC needs to select a CNnode that is not in the overloaded state when the RNC does not receive the NRI parameter from IDNNS.

The CN short-time flow control timer IgorTmr and the CN long-time flow control timer IntrTmrareconfigured on the RNC side for flow control. Note that IntrTmrmust be greater than IgorTmr. You canrun the SET UIUTIMERANDNUMcommand to set IgorTmrandIntrTmr.

The procedure is as follows:

Step 1 The overloaded CN node sends the OVERLOAD message to the RNC to initiate a flow controlprocedure.


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S

S

S

S

tep 2 On the RNC side, if the timer specified by IgorTmris not running and an OVERLOAD messageor the "Signaling Point Congested" information is received, the traffic volume is reduced by onestep. It is also possible, optionally, to indicate the number of steps to reduce the traffic within theNumber of Steps IE. At the same time, timers IgorTmrand IntrTmrmust be started.

tep 3 During the period specified by IgorTmr, all received OVERLOAD messages or "Signaling PointCongested" information is ignored.

tep 4 This step-by-step reduction of the traffic volume is continued until the maximum reduction isobtained at the last step.

tep 5 If the timer specified by IntrTmrexpires, the traffic volume is increased by one step and the timerspecified by IntrTmris restarted unless the number of steps by which the traffic volume isreduced returns to zero.

4.1.5 Flow Control Based on SCCP CC/CR

The RNC checks whether the Iu interface is congested according to the rate of SCCP CC/CR. If the

number of CR messages is greater than 50 and the rate of SCCP CC/CR is less than 80% within the last30 seconds, the Iu interface is considered congested. In this case, the RNC performs linear flow controlover the Iu interface. The RNC rates the congestion in eight levels. If the Iu interface is congested in thelast 30 seconds, the RNC raises the congestion level by 1. Otherwise, the RNC lowers the congestionlevel by 1.

4.2 Flow Control over the Iub Interface

The RNC checks the load of Iub signaling links. When the load is heavy, the RNC rejects the RRCconnection requests of services, except of emergency call services and attach and detach services. TheIub signaling flow control helps to relieve the congestion caused by the increase of the Network ControlProtocol (NCP) link load and enables the NCP link to recover more rapidly.

This document focuses on flow control on the control plane. For details on flow control on the user plane,see the Transmission Resource Management Feature Parameter Description.

4.3 Flow Control over the Uu Interface

4.3.1 Overview

RRC congestion strongly affects network performance. Congestion occurs when a large number of UEsrequest calling services at the same time, such as in festivals and major sport events.

When RRC congestion occurs, the number of Call Attempt Per Second (CAPS) becomes large. These

call attempts may exhaust network resources and result in very low throughput due to RAB setup failure.

When traffic volume is extremely large, the RNC will perform CAPS control at cell level or NodeB leveland perform RRC shaping at system (SPU) level to balance the traffic of calling services.

4.3.2 CAPS Control

The CAPS control function can be enabled at the cell level or NodeB level. The CallShockCtrlSwitchparameter specifies whether the function is enabled.

Procedure for CAPS Control

The following figure shows the procedure for CAPS control.


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Table 4-1 Procedure for CAPS control

Decision on Entering the RRC Congestion StateThe decision on entering the RRC congestion state is made periodically at the cell level and NodeB levelseparately, as described in the following table. The period is specified by the CallShockJudgePeriodparameter.

Table 4-2 Conditions for entering the RRC congestion state

Level When the following conditions are met, the cell and NodeB enter the RRC congestion state.

Cell The number of RRC connection requests in the cell during the specified period exceeds thethreshold specified by CellTotalRrcNumThd .

NodeB The number of RRC connection requests in the NodeB during the specified period exceeds

the threshold specified by NBTotalRrcNumThd or the NodeB Control Port (NCP) iscongested.

CAPS Control Actions When the Cell or NodeB Is in the RRC Congestion State

CAPS control is performed at cell or NodeB level when the cell or NodeB is in the RRC congestion state.

Level The following flow control actions are taken at the cell or NodeB level when the cell or NodeBis in the RRC congestion state.


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Cell Set up an RRC connection for the UE to register on a FACH instead of a DCH.

Increase the RRC connection retry timer (RrcConnRejWaitTmr)to15 seconds.

Reject the RRC connection request for PS services.

Limit the maximum number of admitted RRC connection requests for AMR per second tothe threshold specified by CellAmrRrcNum.

Limit the maximum number of admitted RRC connection requests per second for registerand inter-RAT cell reselection to the threshold specified by CellHighPriRrcNum.

NodeB Set up an RRC connection for the UE to register on a FACH instead of a DCH.

Prolong the RRC connection retry timer (RrcConnRejWaitTmr)to 15 seconds.

Reject the RRC connection request for PS services.

Limit the maximum number of admitted RRC connection requests for AMR per second tothe threshold specified by NBAmrRrcNum.

Limit the maximum number of admitted RRC connection requests per second for register

and inter-RAT cell reselection to the threshold specified by NBHighPriRrcNum.

To set up an RRC connection for the UE to register on a FACH instead of a DCH, turn on the switchspecified by RegByFachSwitch.

CAPS control is performed on RRC requests with high priority and for PS services.

CAPS Control is not performed on emergency calls, terminated calls, detach requests, and low-priorityRRC requests.

4.3.3 RRC Shaping and Queuing

The RRC shaping function can be enabled at the system level. The RsvdPara1parameter is used todetermine whether to enable RRC shaping and queuing. You can set this parameter to RSVDBIT14totrigger RRC Shaping and Queuing function.

The process of RRC shaping and queuing is as follows:

Shaping:

The SPU admits RRC connection requests according to the capability of the SPU. The requests thatcannot be handled by the SPU are forwarded to other SPUs for load sharing.

Queuing:

Entering queues

After load sharing between boards and subracks is complete, if the RRC connection requests cannotbe allocated resources, the RRC connection requests are queued. If the queues are full, the requestsare discarded.

Discarding after expiry

The SPU periodically inspects the queues. If the duration of waiting for an RRC connection request islonger than the duration specified by T300, the request is discarded.

Coming out of queue

The SPU periodically inspects the queues and allocates the remaining resources to the RRCconnection requests in the queues. RRC connection requests for emergency calls and terminatedconversational calls are handled prior to other RRC connection requests.


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The maximum number of RRC Connection Reject messages due to SPU flow control is limited to thethreshold specified by SysRrcRejNum. Superfluous messages are discarded.

4.3.4 Paging Control

With the development of PS services, there are more and more PS paging messages. PS pagingmessages may exhaust the paging resources and result in low throughput of CS services. Flow controlfor paging can help improve the probability of CS paging.

Cells support transmitting paging messages for a maximum of eight UEs according to the 3GPP protocol.When the number of UEs exceeds eight, the RNC prioritizes the paging messages in the followingsequence:

1. Paging messages for PTT services.

2. Paging messages for terminated conversational calls

3. Paging messages for non-terminated conversational calls

4. Paging messages for retransmitted terminated conversational calls

5. Paging messages for retransmitted non-terminated conversational calls

You can enable the paging control function by running the SET UDPUCFGDATA: RsvdPara10 = 1command.


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5 Load Sharing in RNC

Load sharing on the control plane and user plane can be implemented based on resource sharing.

5.1 Basic ConceptHost SPU: In the RNC, the SPU that controls a NodeB is the host SPU of the NodeB.

Host subrack: The subrack that is connected to a NodeB over the Iub interface is the host subrack ofthe NodeB.

5.2 Load Sharing on the Control Plane

SPU Processing or Forwarding Services

When an SPU receives a service request, the SPU determines whether to process the service requestdirectly or to forward it to the MPU according to the current SPU state. The SPU state is determined by

the current SPU load (CPU usage) and Call Attempts per Second (CAPS).

The SPU can be in one of the three states shown in Figure 5-1.

Figure 5-1 Load states on the control plane

Table 5-1 SPU states and actions

State Definit ion Action

State I The SPU has a light load. State I requires that:

The message-block load is lower than the message-block overloadthreshold.

The SPU processes allreceived servicerequests and acceptsthe service requestsforwarded by the MPU.

The CPU load is lower than the value of CtrlPlnSharingOutThd,and the CAPS is lower than the value of MaxCAPSLowLoad .Alternatively, the CPU load is lower than the CPU overloadthreshold, and the CAPS is lower than the value ofSharingOutCAPSMidLoad.


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State Definit ion Action

State II The SPU has a heavy load. State II requires that:

The message block load is lower than the message block overload

threshold.

The SPU forwards allreceived servicerequests to the MPUand accepts the servicerequests forwarded bythe MPU. The SPUshares the load withother SPUs.

The CPU load is between the CPU overload threshold and thevalue of CtrlPlnSharingOutThd, and the CAPS is between thevalue of SharingOutCAPSMidLoadand the value ofMaxCAPSMidLoad.

State III The SPU is overloaded. In state III, the SPUforwards all receivedservice requests to theMPU, and the MPUdoes not forward anyservice request to the

SPU.

You can run the SET UCTRLPLNSHAREPARA commandto set the load sharing function amongsubracks.

MPU Distribut ing Services

When a service request arrives, the host SPU processes the service request if the SPU is in state I, orthe host SPU forwards the service request to the MPU for further distribution if the SPU is in state II or III.In the case of state II or III, the MPU selects a proper SPU in either the host subrack or a differentsubrack to process the service request.

If the control plane load of the host subrack minus the value of CtrlPlnSharingOutOffsetis higherthan the control plane load of any other subracks, the MPU in the host subrack forwards the servicerequest to the MPU with the minimum control plane load in other subracks. The target MPU thenforwards the service request to the SPU with the minimum load in the target subrack.

Otherwise, the MPU selects an SPU from its host subrack. If the load of the host SPU is equal to orhigher than the CPU overload threshold, or if the load of the host SPU minus the value ofCtrlPlnSharingOutOffsetis higher than the load of any other SPUs in the host subrack, the MPUforwards the service request to the SPU with the minimum load in the host subrack.

If no SPU can handle the service request, the service request is rejected.

You can run the SET SHARETHDcommand to set the CPU overload threshold and the message block

overload threshold.

5.3 Load Sharing on the User Plane

The MPU in a subrack manages and allocates the user plane resources in the subrack. When thesubrack load is heavy, the MPU forwards the resource requests to other subracks.

The MPU maintains the user plane resources in the subrack and performs DSP status management. Inaddition, the MPU in the subrack exchanges user plane load information with other MPUs.

Figure 5-2shows how the MPUs manage and allocate user plane resources.


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Figure 5-2 User plane resource sharing

The user plane load is calculated according to the sum of the GBRs of all the services in the DPU or theCPU usage. If the GBR is set to 0, the GBR is changed to 32 kbit/s by this function.

When a service request arrives and the service needs user-plane resources, the SPU requests the MPUin the host subrack for the resources. The MPU proceeds as follows:

If the user plane CPU usage of the host subrack is lower than the threshold specified byUserPlnCpuSharingOutThd and the user plane GBR load of the host subrack is lower than thethreshold specified by UserPlnSharingOutThd, the MPU allocates the user plane resources of theDSP with the minimum load in the host subrack to the service.

If the user plane CPU usage of the host subrack is higher than the threshold specified byUserPlnCpuSharingOutThd, orthe user plane GBR load of the host subrack is higher than thethreshold specified by UserPlnSharingOutThd, the MPU selects the subrack with the minimum loadin the RNC and forwards the user plane resource request to the MPU in the target subrack. The targetMPU then allocates the resources of the DSP with the minimum load in the target subrack to theservice.

When the GBR load of the DPU is overloaded and the CPU usage is overloaded (larger than thethreshold specified by DSPRestrainCpuThd), the service request is rejected. Otherwise, the serviceis admitted.

You can run the SET UUSERPLNSHAREPARA command to set the function of load sharing on the userplane.


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6-1

6 Parameters

Table 6-1 Parameter description

Parameter ID NE MML Command DescriptionRsvdPara10 BSC6900 SET

UDPUCFGDATA(Optional)

Meaning: This parameter is saved for the comingusage.

GUI Value Range: 0~4294967295Actual Value Range: 0~4294967295Unit: NoneDefault Value: 0

IIUCTHD BSC6900 SETFCSW(Optional)

Meaning: Maximum traffic rate for restriction in thecase of congestion on the IU interface. This parameteris valid only when "Board Class" is "XPU".


IUFCSW BSC6900 SETFCSW(Optional)

Meaning: Whether to control signaling traffic on the IUinterface

GUI Value Range: ON, OFFActual Value Range: ON, OFFUnit: NoneDefault Value: ON

UserPlnSharingOutThd

BSC6900 SETUUSERPLNSHAREPARA(Optional)

Meaning: The parameter is added to trigger the loadsharing when the GBR usage of the subrack exceedsthis threshold, thus achieving load balance betweensubracks.


T300 BSC6900 SETUIDLEMODETIME

R(Optional)

Meaning: T300 is started when UE sends the RRCCONNECTION REQUEST message. It is stopped

when UE receives the RRC CONNECTION SETUPmessage. RRC CONNECTION REQUEST will beresent upon the expiry of the timer if V300 is lower thanor equal to N300, else enter idle mode.

GUI Value Range: D100, D200, D400, D600, D800,D1000, D1200, D1400, D1600, D1800, D2000, D3000,D4000, D6000, D8000Actual Value Range: 100, 200, 400, 600, 800, 1000,1200, 1400, 1600, 1800, 2000, 3000, 4000, 6000, 8000Unit: msDefault Value: D2000


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UserPlnCpuSharingOutThd


Meaning: The parameter is added to trigger the loadsharing when the DSP CPU usage exceeds thisthreshold, thus achieving load balance betweensubracks.

GUI Value Range: 0~100Actual Value Range: {0~100}Unit: %Default Value: 50

DSPRestrainCpuThd


Meaning: The parameter is added to stop CPUS fromassigning users to a DSP whose CPU usage hasexceeded this threshold.

GUI Value Range: 0~100Actual Value Range: 0~100Unit: %

Default Value: 75

CtrlPlnSharingOutOffset

BSC6900 SETUCTRLPLNSHAREPARA(Optional)

Meaning: The sharing offset should be added to thetarget subrack or subsystem. This parameter is usedfor preferable selection of the homing subrack andhoming subsystem during call forwarding.

GUI Value Range: 1~10Actual Value Range: 0.01~0.1, step:0.01Unit: %Default Value: 5

UserPlnSharin

gOutThd

BSC6900 SET

UUSERPLNSHAREPARA(Optional)

Meaning: Percentage of User Plane Sharing Out

threshold.The range of this threshold is changed from{50~100} to {0~100} to facilitate load balancingbetween subracks. Because when this threshold islower than 50, load sharing is easier to be triggeredbetween subracks.GUI Value Range: 0~100Actual Value Range: 0~100Unit: NoneDefault Value: 90

UserPlnSharingOutOffset

BSC6900 SETUUSERPLNSHARE

PARA(Optional)

Meaning: Percentage of User Plane Sharing OutOffset.



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CtrlPlnSharingOutThd


Meaning: Forwarding threshold of control plane loadsharing. When the CPU usage is between the sharingthreshold and overload threshold, and call number ineach second reaches "Sharing out capability middle

load", new arrival call attempts will be shared out toother SPU.

GUI Value Range: 0~100Actual Value Range: 0~1, step:0.01Unit: %Default Value: 50

SharingOutCAPSMidLoad


Meaning: Numbers of incoming calls to be sharedwhen the load exceeds the forwarding threshold. Whenthe CPU usage is between the sharing out thresholdand overload threshold, and number of incoming callsin each second reaches the threshold, new arrival call

attempts will be shared out to other SPU.


MaxCAPSMidLoad


Meaning: Maximum numbers of incoming calls in onesecond when the load exceeds the forwardingthreshold. When the CPU usage is between thesharing out threshold and overload threshold, and callnumber in one second reaches the threshold, newarrival call attempts will be shared out to other SPUand none will be shared in this SPU.


MaxCAPSLowLoad


Meaning: Maximum numbers of incoming calls in onesecond when the load is lower than the forwardingthreshold. When the CPU usage is lower than thesharing out threshold and overload threshold, and callnumbers in each second reach the threshold, new

arrival call attempts will be shared out to other SPUand none will be shared in this SPU.



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CallShockCtrlSwitch

BSC6900 SETUCALLSHOCKCTRL(Optional)

Meaning: Indicating whether to control call shockcontrol.

GUI Value Range: SYS_LEVEL(SYS_LEVEL),

NODEB_LEVEL(NODEB_LEVEL),CELL_LEVEL(CELL_LEVEL)Actual Value Range: SYS_LEVEL, NODEB_LEVEL,CELL_LEVELUnit: NoneDefault Value: None

RegByFachSwitch


Meaning: Indicates whether register beared by fachunder call shock control. This function only appliesunder NodeB level or cell level call shock control.

GUI Value Range: OFF, ONActual Value Range: OFF, ON

Unit: NoneDefault Value: ON

CallShockJudgePeriod


Meaning: Indicating the period of call shock controludging.

GUI Value Range: 1~5Actual Value Range: 1~5Unit: sDefault Value: 3

SysRrcRejNum BSC6900 SETUCALLSHOCKCTR

L(Optional)

Meaning: When call shock control starts, it is the maxnumber of RRC_REJ message.


NBTotalRrcNumThd


Meaning: When the RRC REQ total number of oneNodeB reach this threshold the RRC flow control will betriggered.

GUI Value Range: 1~200Actual Value Range: 1~200

Unit: NoneDefault Value: 60

NBAmrRrcNum BSC6900 SETUCALLSHOCKCTRL(Optional)

Meaning: When call shock control starts, theAMR_RRC number can be accessed per second forNodeB.



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NBHighPriRrcNum


Meaning: When call shock control starts, the registerand 3G->2G reselect number can be accessed persecond for NodeB.


CellTotalRrcNumThd


Meaning: When the RRC REQ total number of one cellreach this threshold the RRC flow control will betriggered.


CellAmrRrcNum


Meaning: When call shock control starts, theAMR_RRC number can be accessed per second forcell.


CellHighPriRrcNum


Meaning: When call shock control starts, the registerand 3G->2G reselect number can be accessed persecond for cell.



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RsvdPara1 BSC6900 SETUCACALGOSWITCH(Optional)

Meaning: Reserved Parameter1.

GUI Value Range: RSVDBIT1(Reserved Switch 1),RSVDBIT2(Reserved Switch 2), RSVDBIT3(Reserved

Switch 3), RSVDBIT4(Reserved Switch 4),RSVDBIT5(Reserved Switch 5), RSVDBIT6(ReservedSwitch 6), RSVDBIT7(Reserved Switch 7),RSVDBIT8(Reserved Switch 8), RSVDBIT9(ReservedSwitch 9), RSVDBIT10(Reserved Switch 10),RSVDBIT11(Reserved Switch 11),RSVDBIT12(Reserved Switch 12),RSVDBIT13(Reserved Switch 13),RSVDBIT14(Reserved Switch 14),RSVDBIT15(Reserved Switch 15),RSVDBIT16(Reserved Switch 16)Actual Value Range: RSVDBIT1, RSVDBIT2,RSVDBIT3, RSVDBIT4, RSVDBIT5, RSVDBIT6,RSVDBIT7, RSVDBIT8, RSVDBIT9, RSVDBIT10,RSVDBIT11, RSVDBIT12, RSVDBIT13, RSVDBIT14,RSVDBIT15, RSVDBIT16Unit: NoneDefault Value: None

RsvdPara1 BSC6900 SETURRCTRLSWITCH(Optional)

Meaning: Reserved parameter 1.GUI Value Range: RSVDBIT1_BIT1,NAS_QOS_MOD_SWITCH, RSVDBIT1_BIT3,RSVDBIT1_BIT4, RSVDBIT1_BIT5, RSVDBIT1_BIT6,RSVDBIT1_BIT7, RSVDBIT1_BIT8, RSVDBIT1_BIT9,RSVDBIT1_BIT10, RSVDBIT1_BIT11,

RSVDBIT1_BIT12, RSVDBIT1_BIT13,RSVDBIT1_BIT14, RSVDBIT1_BIT15,RSVDBIT1_BIT16, SYSHO_CSIN_PERMIT_SWITCH,RSVDBIT1_BIT18, RSVDBIT1_BIT19,RSVDBIT1_BIT20, RSVDBIT1_BIT21,RSVDBIT1_BIT22, RSVDBIT1_BIT23,RSVDBIT1_BIT24, RSVDBIT1_BIT25,RSVDBIT1_BIT26, RSVDBIT1_BIT27,RSVDBIT1_BIT28, RSVDBIT1_BIT29,RSVDBIT1_BIT30, RSVDBIT1_BIT31,RSVDBIT1_BIT32Actual Value Range: This parameter is set to 0 or 1according to the related domains.Unit: NoneDefault Value: None


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7-1

7 Counters

For details, see the BSC6900 UMTS Performance Counter Reference.


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8-1

8 Glossary

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


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9 Reference Documents

None.