aqm feature parameter description(eran2.0_01)

eRAN

AQM Feature Parameter Description

Issue 01

Date 2010-07-30

Huawei Proprietary and Confidential Copyright Huawei Technologies Co., Ltd.

Copyright Huawei Technologies Co., Ltd. 2010. 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 the property 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.

Huawei Technologies Co., Ltd.

Address: Huawei Industrial Base Bantian, Longgang Shenzhen 518129 People's Republic of China

Website: http://www.huawei.com

Email: [email protected]


eRAN AQM 1 Introduction

Issue 01 (2010-07-30) Huawei Proprietary and Confidential Copyright Huawei Technologies Co., Ltd.

1-1

Contents

1 Introduction.................................................................................................................................1-1 1.1 Scope.............................................................................................................................................................1-1 1.2 Intended Audience.........................................................................................................................................1-1 1.3 Change History..............................................................................................................................................1-1

2 Overview of AQM .....................................................................................................................2-1

3 Technical Description ...............................................................................................................3-1 3.1 Queue Management ......................................................................................................................................3-1 3.2 Packet Discarding..........................................................................................................................................3-2 3.3 Cooperation with TPE...................................................................................................................................3-2

4 Engineering Guidelines............................................................................................................4-1

5 Parameters ...................................................................................................................................5-1

6 Counters .......................................................................................................................................6-1

7 Glossary .......................................................................................................................................7-1 7.1 Terms.............................................................................................................................................................7-1 7.2 Acronyms and Abbreviations ........................................................................................................................7-1

8 Reference Documents ...............................................................................................................8-1

eRAN AQM 1 Introduction


1-1

1 Introduction 1.1 Scope

the Active Queue Management (AQM) feature in terms of key g guidelines.

1.2 Intend This document is intended for:

z Personnel who need to understand AQM o work with Huawei products

1.3 Changeis

Ther ined as follows:

Feature change: refers to the change in the AQM feature of a specific product version. Editorial change: refers to the change in wording or the addition of the information that

Document Issue The document issue is as follows:

01 (2010-07-30)

01 (2010-07-30) Compared with draft (2010-05-20) of eRAN2.0, issue 01 (2010-07-30) of eRAN2.0 i hang ribed in the following table.

This document describes techniques and engineerin

ed Audience

z Personnel wh

History Th section provides information on the changes in different document versions.

e are two types of changes, which are def

z z

was not described in the earlier version.

zz Draft (2010-05-20)

ncorporates the c es desc

1 Introduction eRANAQM


Change Type Change Description Parameter Change

Feature change None. None.

Editorial change een sections and features is added.

None. The mapping betw

Draft (2010-05This is the draft.

-20)

eRAN AQM 2 Overview of AQM


2-1

2 Overview of AQM A radio link has a lower bandwidth than a wired link. In addition, the bandwidth occupied bya radio link fluctuates. Therefore, a large amount of buffer data may congest on the air interface during downlink data transmission.

At present, most data services use the Transmission Control Protocol (TCP). The TCP, however, has its limitations. When multiple TCP connections are simultaneously set up on one radio bearer, the TCP connections with large data volume occupy a high bandwidth, and thus the TCP connecti

ons with small data volume encounter long transmission delay. In addition, many packets may arrive at a buffer queue over a short period because of the burst

lume, while ay, the buffer queue can be kept at a proper length.

s the transmission delay of the services (for example, b

band

z on

z s a relatively short queue so that the data throughput and transmission delay can anced

z

characteristic of data services. Therefore, if a large amount of buffer data persists when the queue is filled or nearly filled, data overflow and TCP service disruption may occur becauseof data congestion.

AQM is introduced to actively discard packets for the services with large data vomaintaining a high link usage. In this wThis relieves queue congestion, reducewe browsing) that have a high requirement for interaction, enhances the fairness of

width allocation among data streams, and thus improves user experience.

AQM has the following advantages:

Detects possible congestion in the buffer queue at the earliest and minimizes congestiby discarding packets Maintainbe balAvoids global synchronization caused by the simultaneous overflow of multiple data streams

Multiple TCP senders sharply decrease the send window upon detection of lost packets. Then, the parrival rate declines quickly. In this way, the network is not congested. The TCP senders, however,

acket start

on-GBR (GBR is short for guaranteed bit rate) services.

This document describes optional features LOFD-001027 Active Queue Management (AQM) and TDLOFD-001027 Active Queue Management (AQM). AQM is controlled by the AqmAlgoSwitch parameter.

to increase the transmission rate after detecting that the network is not congested, which results in network congestion again. This problem occurs repeatedly, which is called global synchronization.

Huawei AQM is applicable to n

eRAN AQM 3 Technical Description


3-1

3 Technical Description LTE AQM is implemented through queue management and packet discarding. When AQM detects that the length of a queue buffered at the Packet Data Convergence Protocol (PDCP) layer exceeds a specified threshold, it discards some TCP packets to avoid possible congestion.

he delay of interactive services and improves the fairness among

3.1 Queueue exceeds a specified threshold. The

working area of AQM is divided into normal area, congestion avoidance area, and congestion um and maximum congestion thresholds. Figure 3-1 shows

Max represents the maximum packet discarding rate of a

In this way, AQM reduces tdata streams.

Management AQM discards some packets when the length of the que

control area based on the minimthe AQM working area, where non-GBR service in the congestion avoidance area.

Figure 3-1 AQM working area

3 Technical Description eRANAQM

3-2 Huawei Proprietary and Confidential Copyright Huawei Technologies Co., Ltd.

Issue 01 (2010-07-30)

AQM ximum cong lds. AQM then performs different operations in different conditions:

z

eue length.

ets is

When the rate on the air interface is very high, AQM does not discard packets. If AQM discards packets in this situation, packets of low-rate services will have little chance to be

P connections can reach the original rates rapidly after packet

3.2 Packet

To ensure normal data transmission, AQM does not discard special packets such as TCP ACK packets, IPSec packets, and SYN packets. To ensure normal web browsing and improve user

ard the packets from special ports such as TCP ports 80 and

3.3 Cooper that reduces the transmission rates of TCP

of a TCP connection. For details about TPE, see the TPE Feature Parameter Description.

Cooperation between AQM and TPE is enabled by selecting the AqmTpeUnitSwitch check box under the AqmAlgoSwitch parameter.

calculates the average queue length and compares it with the minimum and maestion thresho

z Average queue length Minimum congestion threshold In the normal area, AQM does not discard any packet because the queue is not congested. Minimum congestion threshold < Average queue length < Maximum congestion threshold In the congestion avoidance area, AQM discards some packets because the queue is congested to some extent. The probability of discarding packets increases linearly with the data amount and average qu

z Average queue length Maximum congestion threshold In the congestion control area, AQM discards every newly arriving packet because the queue is severely congested.

AQM adjusts the congestion thresholds based on the rate of the data stream reported by theRadio Link Control (RLC) layer. For example, if the rate of the data stream is low, AQM sthe congestion thresholds to small values because the probability of congestion is high in thcase.

transmitted although TCdiscarding.

Discarding AQM can discard packets in the way of head drop or tail drop. In the way of head drop, the packet at the beginning of the queue is discarded first. In the way of tail drop, the newly arriving packet is discarded first. The head drop algorithm affects the PDCP header compression algorithm. Therefore, Huawei eRAN2.0 AQM uses the tail drop algorithm.

experience, AQM does not disc8080.

ation with TPE TCP Performance Enhancer (TPE) is a technologyconnections when AQM decides to discard packets. TPE avoids data retransmissions due to packet discarding and thus improves transmission performance. The decrease in the TCP window size may cause an unexpected failure

eRAN AQM 4 HEngineering GuidelinesH


4-1

4 Engineering Guidelines When multiple types of service are carried on one radio bearer, it is recommended that the AqmAlgoSwitch check box under the AqmAlgoSwitch parameter be selected. The purpoare to ensure the transmission bandwidth and

ses delay of the data streams with small data

When both the AQM and TPE features are enabled, TPE data transmission rate limitation rather than AQM packet discarding can be used if the AqmTpeUnitSwitch check box under the AqmAlgoSwitch parameter is selected. This relieves congestion of the buffer queue.

volume and to enhance the fairness of bandwidth allocation among data streams. After the AqmAlgoSwitch check box under the AqmAlgoSwitch parameter is selected, the packet discarding mechanism is started upon congestion of the buffer queue. This decreases the transmission delay of interactive services.

eRAN AQM 5 Parameters


5-1

5 Parameters This chapter describes all the parameters presented in this document.

, see Table 5-1. For the default value, value ranges, and MML commands of each parameter, see T

T r

For the description of each parameterable 5-2.

able 5-1 Paramete description (1)

MO Description Parameter ID

CellAlgoSwitch AqmAlgoSwitch e AQM

PE/AQM joint algorithm is enabled. In this case, flow control is performed on TCP services on the basis of cell resource usage, to improve fairness between streams in terms of bandwidth usage. When this switch is set to OFF, the TPE/AQM joint algorithm is disabled.

AqmAlgoSwitch: Indicates the switch that is used to enable and disable the AQM algorithm. When this switch is set to ON, thfunction is enabled. In this case, service-based flow control is performed on the basis of cell resource usage, to improve fairness between streams in terms of bandwidth usage. When this switch is set to OFF, the AQM function is disabled. AqmTpeUnitSwitch: Indicates the switch that is used to enable and disable the TPE/AQM joint algorithm. When this switch is set to ON, the T

Tab Paramle 5-2 eter description (2)

MO Parameter ID

Default Value

GUI Value Range Actual Value Range Unit MML Command

CellAlgoSwitch

AqmAlgoSwitch

Off, AqmTpeUnitSwitch:Off

AqmAlgoSwitch, AqmTpeUnitSwitch

AqmAlgoSwitch, AqmTpeUnitSwitch

None MOD CELLALGOSWITCH

AqmAlgoSwitch:

eRAN AQM 6 Counters


6-1

6 Counters For details about the counters related to AQM, see the eNodeB Performance Counter Reference.

eRAN AQM 7 Glossary


7-1

7 Glossary 7.1 Terms

7.2 Acronyms and Abbreviations

col

TCP Transmission Control Protocol

TPE TCP Performance Enhancer

None.

AQM Active Queue Management

IPSec IP Security

PDCP Packet Data Convergence Proto

RLC Radio Link Control

eRAN AQM 8 Reference Documents


8-1

8 Reference Documents This chapter lists the reference documents related to AQM.

[1] eNodeB Performance Counter Reference [2] eNodeB MO Reference

1 Introduction 1.1 Scope 1.2 Intended Audience 1.3 Change History

2 Overview of AQM 3 Technical Description 3.1 Queue Management 3.2 Packet Discarding 3.3 Cooperation with TPE

4 Engineering Guidelines 5 Parameters 6 Counters 7 Glossary 7.1 Terms 7.2 Acronyms and Abbreviations

8 Reference Documents