Data Forwarding at Intra-LTE Handover.pdf

Data Forwarding at Intra-LTE Handover

USER DESCRIPTION

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Copyright

Ericsson AB 2012. All rights reserved. No part of this document may bereproduced in any form without the written permission of the copyright owner.

Disclaimer

The contents of this document are subject to revision without notice due tocontinued progress in methodology, design and manufacturing. Ericsson shallhave no liability for any error or damage of any kind resulting from the useof this document.

Trademark List

All trademarks mentioned herein are the property of their respective owners.These are shown in the document Trademark Information.

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Contents

Contents

1 Introduction 1

1.1 Basic Characteristics 1

1.2 Benefits 2

1.3 Additional Information 2

2 Feature Operation 3

2.1 Network Requirements 3

2.2 Feature Operation Sequence Diagram 3

2.3 Process Steps 4

3 Parameters 5

3.1 Introduced Parameters 5

3.2 Affected Parameters 5

4 Network Impact 7

4.1 Capacity 7

4.2 Handover 7

5 Associated Features and Affected Functions 9

5.1 Prerequisite Features 9

5.2 Affected Features 9

5.3 Related Features 9

5.4 Affected System Functions 9

6 Performance 11

6.1 KPIs 11

6.2 Counters 11

6.3 Events 11

7 O&M Information 13

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Introduction

1 Introduction

This document describes the Data Forwarding at Intra-LTE Handover featureand its main benefits and impacts in the LTE RAN.

The information in this document reflects the feature at the time of its release.

The feature overview section provides basic information about the feature'sidentity, benefits, and dependencies. More detail is given in the followingsections.

This section describes the main benefits and impacts of the Data Forwarding atIntra-LTE Handover feature in the LTE RAN.

The purpose of Data Forwarding at Intra-LTE Handover feature is to ensure thatno downlink data packets are lost when performing an X2 Intra-LTE handoveror intra-eNodeB handover. This is achieved by allocating forwarding user planetunnels between the source and target RBS during the handover process. Datacontinuously flows from the Serving Gateway (SGW) to the User Equipment(UE) through source and target RBS until the handover is complete. As a result,Transmission Control Protocol (TCP) throughput degradation is minimized.

Data forwarding at Intra-RBS handover is also supported. This is achieved byinternal functions, so no external signaling is needed.

Data forwarding does not apply to S1 handover. In that case, data forwarding isnot possible and leads to throughput degradation.

With this feature a connected user can handover from one cell to another withminimal disruption to data throughput. If the feature is not activated, the packetssent from the SGW are lost and must be retransmitted. This causes a delay inthe session, leading to throughput reduction and can have a major effect onreal time applications, such as voice.

1.1 Basic Characteristics

This section describes the basic characteristics of the feature.

Feature identity:FAJ 221 0966, Data Forwarding at Intra-LTE Handover

Replaces: N/A

Dependencies

This feature requires the following RAN features to be active:

Intra-LTE Handover

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This feature affects no other features.

1.2 Benefits

This section describes the benefits of this feature.

The major benefit of this feature is to reduce packet losses during handover.With TCP mechanisms, such as slow start, this has a dramatic affect on theuser throughput and also cell capacity.

1.3 Additional Information

More information about this feature and related topics can be found in thefollowing documentation:

Intra-LTE Handover

Managed Object Model

3GPP TS 29.281, 36.300, 36.331, 36.401, 36.413, 36.423

The 3GPP documentation is available at www.3gpp.org.

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Feature Operation

2 Feature Operation

This section describes the Data Forwarding at Intra-LTE Handover feature inmore detail including network configuration requirements and operation flows.

2.1 Network Requirements

This section describes the network configuration requirements, which concernnetwork architecture and licenses.

The following must be fulfilled at feature activation:

Activation of the Intra-LTE Handover feature

Activation of the Data Forwarding at Intra-LTE Handover feature

2.2 Feature Operation Sequence Diagram

The objective of data forwarding is to guarantee that packet loss is reducedduring an X2 handover and intra-eNodeB handover, except in the transportnetwork. The packets forwarded are those stored in the source RBS buffer priorto the handover execution, as well as the incoming packets from the SGW,which are directed to the target RBS. Forwarding occurs only with Packet DataConvergence Protocol (PDCP) Service Data Units (SDUs) in the downlink.

During the phases of intra-LTE handover, the phases listed in Table 1 are doneif the Data Forwarding at Intra-LTE Handover feature is active.

Table 1 Phases of Data Forwarding at Intra-LTE Handover

Phase Description

Handover Is Prepared The source RBS attempts to allocate forwardingtransport bearers toward the target RBS. If thisis successful, a forwarding user plane tunnel isestablished for each E-RAB(1) between the sourceand target RBS.

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Phase Description

Handover IsPerformed

When the HANDOVER COMMAND and securityparameters (ueSecurityReconfigInd) arereceived in the target RBS, all buffered and incomingdata is forwarded from the source to target RBS.To minimize out-of-order packet delivery, forwardeddata is first delivered to the target RBS and then S1user plane data follows.

Handover Completes For X2 Handover, the target RBS sends a PATHSWITCH message to the MME. The MME thensends a USER PLANE UPDATE REQUESTmessage to the SGW, which switches theuser-plane path from source to target RBS. Thesource RBS continues to forward packets whilepackets are being received from the SGW and thesource RBS buffer contains data. When the ENDMARKER packet is received in the target RBS or thetHODataFwdReOrdering timer expires, the targetRBS discards any further forwarding data packets.Forwarding tunnels are then released.

For intra-eNodeB handover, the MME is notinvolved. The source RBS continues to forwardpackets while packets are being received from theSGW and the source RBS buffer contains data.When the tHODataFwdReOrdering timer expires,the target RBS discards any further forwarding datapackets. Forwarding tunnels are then released.

(1) E-UTRAN Radio Access Bearer

Each RBS has a source and target data buffer of equal size. The source databuffer holds data packets when handover fails and the UE returns to the sourceRBS. The target data buffer holds data packets when they cannot be forwardedonto the UE because of handover interruption.

2.3 Process Steps

This section describes the main process steps for the feature flow. Except thelicensing for this feature, the new MOM parameter dataFwdPerQciEnabledis introduced by this feature. If the Data Forwarding at Intra-LTE Handoverfeature is activated and dataFwdPerQciEnabled is set to true, the dataforwarding will be done.

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Parameters

3 Parameters

This section describes the parameters introduced by the Data Forwarding atIntra-LTE Handover feature and parameters affected by activating the feature.

3.1 Introduced Parameters

Table 2 describes the parameters introduced by the feature.

Table 2 Introduced Parameters

Parameter Description

featureStateIntraLTEHODataFwd Activates or deactivates the licensed feature

tHODataFwdReordering Timer that supervises the downlink data forwarding in thetarget cell during X2 handover

It starts from the reception of the first S1 user plane datapacket. At expiration, the downlink forwarding tunnels arereleased.

dataFwdPerQciEnabled Enables forwarding of data for this QCI

The parameter is only valid if the IntraLTEHODataFwdlicence is installed and active.

3.2 Affected Parameters

The implementation of this feature affects no parameters.

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Network Impact

4 Network Impact

This section describes how the Data Forwarding at Intra-LTE Handover featureimpacts the network functions and capabilities.

4.1 Capacity

This section provides information on the impact of the feature on networkcapacity.

The Data forwarding at Intra-LTE Handover feature can be used to ensurethat user data rates remain high following a handover. Without it, user datais lost and TCP slow-start mechanisms reduce the throughput. This affectshigh-rate users particularly and also users on the cell border experiencing ahigh number of handovers.

4.2 Handover

This section provides information about handover.

The feature ensures that data rates remain high and the data will not be lost.

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Associated Features and Affected Functions

5 Associated Features and AffectedFunctions

This section describes how Data Forwarding at Intra-LTE Handover affectsother features and functions.

5.1 Prerequisite Features

Table 3 lists prerequisite features to the Data Forwarding at Intra-LTE Handoverfeature, that is, they must be active prior to introducing the Data Forwarding atIntra-LTE Handover feature.

Table 3 Prerequisite Features

Feature Description

Intra-LTE Handover The Intra-LTE Handover feature is needed to allow X2 andIntra-eNodeB handover to perform the Data Forwarding atIntra-LTE Handover feature.(1)

(1) Only X2 and Intra-eNodeB packet forwarding are currently supported.

5.2 Affected Features

This feature affects no other feature.

5.3 Related Features

This feature is not related to any other feature.

5.4 Affected System Functions

This feature affects no system functions.

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Performance

6 Performance

This section describes performance indicators, counters, and events associatedwith the Data Forwarding at Intra-LTE Handover feature.

6.1 KPIs

This feature has no associated Key Performance Indicators (KPIs).

6.2 Counters

Table 4 lists the counters associated with the Data Forwarding at Intra-LTEHandover feature.

Table 4 Counters

Counter Description

pmPdcpPktDiscDlHo Total number of packets (PDCP SDUs) lost due to handover inthe downlink direction

Continuous measurement will be performed for the UEaggregated to cell level.

pmPdcpPktFwdDl Total number of DRB packets (PDCP SDUs) forwarded to targetcell at handover for downlink sessions.

Packet forwarding is started when source cell transmitRRCConnectionReconfiguration and is stopped when sourcereceives the end marker or when the source receives UE ContextRelease from target.

More information about counters can be found in Managed Object Model RBS.

6.3 Events

Table 5 lists the events associated with the Data Forwarding at Intra-LTEHandover feature.

Table 5 Events

Event Event Parameter Description

INTERNAL_PER_UE_TRAFFIC_REP

The following event parametersrelated to this feature are includedin this event:

EVENT_PARAM_PER_UE_PACKET_LOST_HO_DL

EVENT_PARAM_PER_UE_PACKET_FWD_DL

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More information about events can be found in PM Event List.

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O&M Information

7 O&M Information

This section provides Operation and Maintenance (O&M) information for theData Forwarding at Intra-LTE Handover feature.

A license activates the Data Forwarding at Intra-LTE Handover feature. Fulldetails of the license activation process can be found in License Management.

Other associated features are the Intra-LTE Handover feature. Intra-LTEHandover and the Managed Object Model RBS provide full details of theconfiguration and activation of Data Forwarding at Intra-LTE Handover feature.

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toc1 Introduction1.1 Basic CharacteristicsDependencies1.2 Benefits1.3 Additional Information2 Feature Operation2.1 Network Requirements2.2 Feature Operation Sequence Diagram2.3 Process Steps3 Parameters3.1 Introduced Parameters3.2 Affected Parameters4 Network Impact4.1 Capacity4.2 Handover5 Associated Features and Affected Functions5.1 Prerequisite Features5.2 Affected Features5.3 Related Features5.4 Affected System Functions6 Performance6.1 KPIs6.2 Counters6.3 Events7 O&M Information

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Data Forwarding at Intra-LTE Handover.pdf