aqm

AQM Feature Parameter Description

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 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 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.

Issue 02 (2009-09-30) Huawei Proprietary and Confidential

Copyright Huawei Technologies Co., Ltd.

i

BSS AQM Contents

Issue 02 (2009-09-30) Huawei Proprietary and Confidential Copyright Huawei Technologies Co.,

Ltd.

iii

Contents 1 Introduction to This Document .............................................................................................1-1

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

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

3 Technical Description ..............................................................................................................3-1

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

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

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

7 Glossary ......................................................................................................................................7-1

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

BSS AQM 1 Introduction to This Document


Ltd.

1-1

1 Introduction to This Document 1.1 Scope This document describes active queue management (AQM) algorithm description in the AQM feature.

1.2 Intended Audience It is assumed that users of this document are familiar with GPRS basics and have a working knowledge of GPRS telecommunication.

This document is intended for:

z Personnel working on Huawei GPRS products or systems z System operators who need a general understanding of this feature

1.3 Change History The change history provides information on the changes in different document versions.

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

z Feature change Feature change refers to the change in the AQM feature of a specific product version.

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

Document Version The document issues are as follows:

z 02 (2009-09-30) z 01 (2009-06-30)

02 (2009-09-30) This is the second commercial release of GBSS9.0.

Compared with 01 (2009-06-30) of GBSS9.0, issue 02 (2009-09-30) of GBSS9.0 incorporates the changes described in the following table.

Change Type Change Description Parameter Change

Feature change None. None.

Editorial change The template of the document is optimized. None.

01 (2009-06-30) This is the first commercial release of GBSS9.0.

Compared with 02 (2009-04-30) of GBSS8.1, issue 01 (2009-06-30) of GBSS9.0 has no change.

BSS AQM 2 Overview


Ltd.

2-1

2 Overview Active queue management (AQM) is an algorithm used to maintain the buffer queue length within an appropriate range by discarding data packets in the buffer queue actively. It increases data throughput and reduces service delay at the price of buffer utilization.

AQM applies to scenarios in which bandwidth is limited and congestion is likely to occur. AQM not only ensures high link utilization but also reduces the delay of services that require low transfer delay. It also enhances fair utilization of bandwidth among services and increases data throughput.

Compared with the wired link bandwidth, the wireless link bandwidth is small. Therefore, the wireless link bandwidth is a bottleneck for end-to-end data transfer. AQM can relieve network congestion due to excessive TCP data streams. When network congestion occurs, AQM discards data packets actively according to the packet discarding policy. After detecting packet loss, the TCP receiver informs the TCP transmitter of the packet loss by using the retransmission acknowledgement mechanism. Then, the TCP transmitter decreases the size of the transmit window according to the congestion control mechanism, thus reducing the transmission rate and relieving network congestion.

At present, most data services use the transmission control protocol (TCP) protocol. The TCP protocol, however, has its limitations. When multiple TCP connections are set up at the same time in the communications system, one TCP connection may occupy a high bandwidth, and thus the transfer delay is long for other connections. For example, a user clicks a button on an hyper text transfer protocol (HTTP) web page when file transfer protocol (FTP) downloading is ongoing. In such a case, a long time elapses before the corresponding web page is displayed because the link resource is occupied by the FTP service. If AQM is used, it discards packets of services with excessive traffic flow actively and ensures high link utilization. This decreases the data transmission rate and thus reduces the delay of services that require low transfer delay. This also enhances fair utilization of bandwidth among services.

AQM is applicable to interactive services, background services, and best effort (BE)services (namely, services without QoS requirements). It is not applicable to conversational services or streaming services.

BSS AQM 3 Technical Description


Ltd.

3-1

3 Technical Description Parameters Before AQM takes effect, you must configure related parameters. That is, you must set AQM Switch to Open to enable AQM. In addition, you must set the following parameters related to AQM according to a specific application scenario:

z AQM Congestion Threshold This parameter specifies the lower threshold at which the buffer queue is congested. If the buffer queue length exceeds this threshold, packets are discarded actively.

z AQM Maximum Threshold This parameter specifies the upper threshold at which the buffer queue is congested. If the buffer queue length exceeds this threshold, a packet is discarded each time a packet arrives at the queue.

z AQM Target Threshold This parameter specifies the target threshold at which the buffer queue is congested. This parameter is used to adjust the interval at which packets are discarded.

z Aqm Ninit This parameter specifies the initial value of the interval (indicated by N) at which a packet in the buffer queue is discarded. The value of N indicates the frequency at which packets are discarded. If the value of N is large, the frequency of discarding packets is low and thus a fewer number of packets are discarded over a certain period of time.

z AQM Packet Discard Interval Lower Threshold This parameter specifies the lower threshold of the interval (indicated by N) at which a packet in the buffer queue is discarded.

z AQM Packet Discard Interval Upper Threshold This parameter specifies the upper threshold of the interval (indicated by N) at which a packet in the buffer queue is discarded.

z Aqm M This parameter specifies the frequency (indicated by M) of updating the value of N, that is, how many packets are transmitted before the value of N is updated.

AQM Policy for Discarding Packets AQM is implemented in the BSC. For interactive services, background services, or BE services, AQM manages the buffer queue of downlink LLC PDUs of each MS.

The key to the AQM algorithm is the packet discarding policy, which varies according to the AQM algorithm. The packet discarding policy of Huawei AQM algorithm is as follows:

z If the length of the buffer queue is smaller than AQM Congestion Threshold, no packet is discarded. z If the length of the buffer queue is greater than AQM Congestion Threshold and smaller than AQM

Maximum Threshold, a packet is discarded each time N packets arrive at the queue. z If the length of the buffer queue is greater than AQM Maximum Threshold, a packet is discarded

each time a packet arrives at the queue. The two methods of discarding packets are tail drop and head drop. The AQM algorithm uses the head drop method.

Based on the relations among the length of the buffer queue, AQM Congestion Threshold, and AQM Target Threshold, the AQM algorithm adjusts the interval at which packets are discarded. The AQM algorithm changes the value of N based on the value of M. The algorithm of adjusting the value of N dynamically is as follows:

3 Technical Description BSS

AQM

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

Ltd.

Issue 02 (2009-09-30)

z If the length of the buffer queue is greater than AQM Target Threshold and smaller than AQM Maximum Threshold, the value of N is decreased by one each time M packets arrive at the queue. Thus, the number of packets that are discarded over a certain period of time increases. When the value of N reaches AQM Packet Discard Interval Lower Threshold, it no longer decreases.

z If the length of the buffer queue is greater than AQM Congestion Threshold and smaller than AQM Target Threshold, the value of N is increased by one each time M packets arrive at the queue. Thus, the number of packets that are discarded over a certain period of time decreases. When the value of N reaches AQM Packet Discard Interval Upper Threshold, it no longer increases.

Technologies Related to AQM z Methods of discarding packets

AQM supports two methods: head drop and tail drop. In the head drop method, packets at the head of the buffer are discarded when necessary. In the tail drop method, new packets are discarded when necessary. The response speed in the head drop method is faster than that in the tail drop method. In addition, in the head drop method, packets are not continuously discarded. Thus, Huawei AQM algorithm uses the head drop method.

z Service types supported by AQM AQM is applicable to interactive services, background services, and BE services. It is not applicable to conversational services or streaming services.

z Upper-layer protocols supported by AQM The logical link control (LLC) layer provides services for the upper-layer sub-network dependent convergence (SNDC), GPRS mobility management (GMM), short message service (SMS), and tunnelling of messages (TOM) protocols. AQM manages only the LLC PDU queues providing services for the SNDC protocol.

BSS AQM 4 Engineering Guidelines


Ltd.

4-1

4 Engineering Guidelines AQM is associated with flow control on the Gb interface. AQM and flow control on the Gb interface can coexist but have an impact on each other. The impact between these two features depends on the configuration policy of the operator. If AQM-related thresholds are low, flow control on the Gb interface may be unable to take effect to a certain extent. If the operator considers that flow control on the Gb interface has a higher priority than AQM, AQM-related thresholds can be set to higher values. In this way, AQM takes effect only when severe network congestion occurs.

BSS AQM 5 Parameters


Ltd.

5-1

5 Parameters The following describes the parameters related to AQM.

For the meaning of each parameter, see Table 5-1. For the default value, value range, and related MML commands of each parameter, see Table 5-2.

Table 5-1 Parameter description (1)

Parameter Description

AQM Switch AQM switch.

AQM Congestion Threshold

Congestion threshold of the TBF buffer queue. If the congestion level in the TBF buffer queue exceeds this threshold, whether the packets are discarded actively is determined according to the packet discarding policy.

AQM Maximum Threshold

Upper length threshold of the TBF buffer queue. If the length of the TBF buffer queue exceeds this threshold, whether the packets are discarded is determined according to the packet discarding policy.

AQM Target Threshold Target threshold of the TBF buffer queue.

AQM Packet Discard Interval Lower Threshold

Lower threshold of the interval for discarding the packets in the TBF buffer queue, that is, the minimum value of N (packet drop interval).

AQM Packet Discard Interval Upper Threshold

Upper threshold of the interval for discarding the packets in the TBF buffer queue, that is, the maximum value of N (packet drop interval).

Table 5-2 Parameter description (2)

Parameter Default Value GUI Value Range

Actual Value Range

Unit MML Command Impact

AQM Switch CLOSE

CLOSE(Close), OPEN(Open)

CLOSE, OPEN None

SET BSCPSSOFTPARA(Optional) BSC

AQM Congestion Threshold 256 1~65535

1~64, step:1024 bit


AQM Maximum Threshold 1024 1~65535

1~64, step:1024 bit


5 Parameters BSS

AQM

5-2 Huawei Proprietary and Confidential Copyright Huawei Technologies Co.,

Ltd.

Issue 02 (2009-09-30)

Actual Default GUI Value MML Parameter Value Range Value Unit Impact CommandRange

AQM Target Threshold 384 1~65535

1~64, step:1024 bit


AQM Packet Discard Interval Lower Threshold 10 1~65535 1~65535 packet


AQM Packet Discard Interval Upper Threshold 20 1~65535 1~65535 packet


BSS AQM 6 Counters


Ltd.

6-1

6 Counters None.

BSS AQM 7 Glossary


Ltd.

7-1

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

BSS AQM 8 Reference Documents


Ltd.

8-1

8 Reference Documents z 3GPP TS 44.060 "Radio Link Control/Medium Access Control (RLC/MAC) protocol" z 3GPP TS 23.107 "Quality of Service (QoS) concept and architecture" z 3GPP TS 48.018 "BSS GPRS Protocol (BSSGP)" z BSC6900 Feature List z BSC6900 Optional Feature Description z BSC6900 GSM Parameter Reference z BSC6900 GSM MML Command Reference

1 Introduction to This Document 1.1 Scope 1.2 Intended Audience 1.3 Change History 2 Overview 3 Technical Description 4 Engineering Guidelines 5 Parameters 6 Counters 7 Glossary 8 Reference Documents