Packet Scheduler Optimisation

Activation and Monitoring of PS features

CHANGE HISTORY

Version Date Edited by Comments0.9 10.7.2007 Kirsi Teravainen First version for review0.91 27.8.2007 Kirsi Teravainen Ready for SIG review

Editor: Kirsi TeräväinenDate: July 2007Version:Approved by:

Table of Contents

1 Introduction of Packet Scheduler.................................................................41.1 Packet Scheduler parameters....................................................................................................8

2 Setting Initial and Minimum Bitrates............................................................92.1 Parameters...............................................................................................................................10

3 Dynamic Link Optimization for NRT traffic Coverage.................................113.1 Feature Activation and Parameters..........................................................................................143.2 Impact to the other PS features................................................................................................153.3 Monitoring and Counters..........................................................................................................15

4 Enhanced Priority Based Scheduling and NRT Overload Control.............164.1 Feature Activation and Parameters..........................................................................................204.2 Impact to the other PS features................................................................................................224.3 Monitoring and Counters..........................................................................................................224.4 KPI survey for Enhanced PBS and Overload Control..............................................................23

5 Flexible Upgrade........................................................................................275.1 Feature Activation and Parameters..........................................................................................295.2 Impact to the other PS features................................................................................................305.3 Monitoring and Counters..........................................................................................................30

6 Throughput Based Optimization................................................................316.1 Feature Activation and Parameters..........................................................................................346.2 Impact to the other PS features................................................................................................356.3 Monitoring and Counters..........................................................................................................366.4 KPI survey for throughput based optimisation and flexible upgrade........................................37

References.....................................................................................................43

1 Introduction of Packet SchedulerPacket Scheduler consists of multiple different functions which can be categorized based on the scope of the function. UE specific part of the Packet Scheduler is monitoring and measuring

utilization of one NRT DCH RAB while cell specific part contains functions working based on cell level measurements and conditions. Table below presents Nokia packet scheduler main features per release.

RAN release

Feature Function Affected resourcesRadio BTS AAL2

RAN1.5 Admission control RT over NRT pre-emption

X X X

RAN1.5 Packet scheduler Tunable inactivity timer X X X

Radio interface overload triggered downgrade

X -(RAS05)

-(RAS05)

Dynamic link optimisation

X X -(RAN 04

CD2)Packet scheduler retry with lower bit rate in congestion (ED2 CD05)

X X X

RAS05 Enhanced priority based scheduling and overload control for NRT traffic

New user triggered RB downgrade

X X X

Radio interface overload triggered downgrade

X X X

RT over NRT pre-emption

X X X

RAS05 Throughput based optimisation of the PS algorithm

Throughput based RB release

X X X

RAS05.1 Throughput based RB downgrade

X X X

RAS04CD Flexible upgrade of NRT DCH Data Rate

Light weight flexible upgrade

X X X

RAS05.1 Flexible upgrade X X X

Table 1 Nokia Packet Scheduler main features

NOTE!! PSIT – Packet Scheduler Interruption timer is a removal item of RAS06, and is not considered in this document

The NRT DCH RAB can be downgraded or released due the multiple causes.

1. Dynamic Link optimization for NRT traffic coverage (DyLO) – the existing NRT DCH can be downgraded in the downlink transmission power exceed a predefined threshold

2. Enhanced Overload Control (RAS05 Optional feature) -In an overload situation PS start modification or reconfiguration of existing NRT DCHs radio bearers to be able to decrease loading.

3. Priority Based Scheduling (RAS05 Optional feature) - Existing NRT allocations can be downgraded or released if there are other users requesting initial capacity in the congested situation

4. Throughput Based Optimization (RAS51 Optional feature) - Throughput based optimization of the PS algorithm adapts the DCH resource reservation to meet the actual utilization (or used bit rate) of the DCH.

5. Maximum bit rate limitation – Another RAB is setup for the same UERAS05.1 supports the following multi-services: • Maximum 3 NRT (interactive/Background) PS RABs, • AMR + maximum 3 NRT (interactive/background) PS RABs, • CS-T + maximum 3 NRT (interactive/background) PS RABs, • 1 RT PS (streaming) RAB + maximum 3 NRT (interactive/background) PS RABs.

6. Inactivity of the radio bearer

The DCH downgrade procedure is performed in CELL_DCH state and it can be performed by• Reconfiguration of radio bearer (also transmission, WBTS and RNC resources)• Limitation of the maximum transport format combinations (temporary)

The NRT DCH RAB can be upgraded due to

1. High amount of data in buffer – Capacity Request/Bit Rate upgrade2. High Utilization/throughput (RAS51 Optional feature) – Flexible upgrade of the NRT

DCH data rate

The dedicated channel upgrade procedure is performed in CELL_DCH state and it requires the reconfiguration of radio link, transmission and RNC internal resources

UE specific part of the packet scheduler is monitoring utilization of one NRT DCH RAB. Example below shows packet scheduler actions during PS call when cell is unloaded, and throughput based optimisation and flexible upgrade is activated.

AC - AC makes admission decision and allocates a 0 bit rate to the NRT radio bearerPS1 - “Bit rate allocation”, after receiving a capacity request PS allocates initial bit ratePS2 - “Flexible upgrade”, after receiving a capacity request PS allocates maximum (high) bit ratePS3 - “Throughput-based optimisation“, PS performs radio bearer reconfiguration to lower bit ratePS4 - “Flexible upgrade”, PS performs radio bearer reconfiguration to higher bit ratePS5 - “RRC state transition”, PS initiates state transition to CELL_FACH due to inactivity

Figure 1 Packet Scheduler actions during call – Unloaded cell

Load control provides periodical load information on cell basis to the cell-specific packet scheduler. This information includes BTS measurements and estimates made by load control. Example below shows packet scheduler actions during SP call when cell is loaded. Enhanced Priority Based scheduling and overload control is activated.

AC - AC makes admission decision and allocates a 0 bit rate to the NRT radio bearerPS1 - “Priority based scheduling”, after receiving a capacity request PS allocates initial bit rate after downgrading an existing bearer (load margin)PS2 - “Flexible upgrade”, after receiving a capacity request PS allocates higher bit rate (normal load)PS3 - “Enhanced Overload control“, PS performs RB reconfiguration to until min. bit rate (overload)PS4 - “Flexible upgrade”, PS performs radio bearer reconfiguration to higher bit rate (normal load)PS5 - “RRC state transition”, PS initiates state transition to CELL_FACH due to inactivity

Figure 2 Packet Scheduler actions during call- Loaded Cell

HSDPA UL NRT DCH return channel can be also downgraded or released.

Enhanced Overload control and Priority based scheduling threat HSDPA UL return channel as a normal DCH and can cause downgrade or release of it, if activated.

• If Flexible upgrade and Throughput based optimization features are activated in the Network – It is possible to activate them to HSDPA Associated UL Channel also by Enabling Parameter DynUsageHSDPAReturnChannel (Dynamic usage of UL NRT DCH HSDPA return Channel)

• This parameter is used to switch "On" and "Off" the Flexible Upgrade of NRT Data Rate and Throughput Based Optimisation of the PS Algorithm feature used for UL NRT DCH HSDPA return channel.

• If Throughput based optimisation is activated to UL return channel, it can be downgraded due the low utilization until minimum bit rate

1.1 Packet Scheduler parametersPacket Scheduler contains 168 parameters (RAS51). Some parameters are related to optional PS features and are not in use if the feature is not activated (e.g. Throughput based optimisation contains 42 parameters, which are not in use when feature is inactive). For most of the parameters, default value is used, but for some parameters other than default value is recommended or used. Activation of feature can also replace parameter with other, e.g. Activation of Flexible upgrade replace traffic volume measurements parameters TrafVolThresholdULHigh and TrafVolThresholdDLHigh with the parameters TrafVolThresholdULHighBitRate and TrafVolThresholdDLHighBitRate.

In Table 2, results from customer network survey are listed and parameters that typically can have other than default value are presented. Survey results are from RAN04 & RAN05 networks.

Object Parameter Default% at

default

Deployed values - Range Comment

WBTS PSAveragingWindowSize 2 3%Only one operator is using the default.

97% of operators are using 5.

WBTS LoadControlPeriodPS 1200 ms 7%400, 500,

1000, 1200 ms

Most operators are using 400 ms (86%).

RNC ActivationTimeOffset 300ms 10%300, 400, 500, 600, 700, 800

ms

Recommendation is 700ms. No clear differentiation according to SRB

bitrate. 52% of networks are using 700ms.

WCEL MinAllowedBitRateDL 32 kbps 14% 32 - 128Most operators are using 64kbps.

Default value has been changed to 8kbps in RAS05.1*

WCEL MinAllowedBitRateUL 32 kbps 14% 32, 64 kbpsMost operators are using 64kbps.

Default value has been changed to 8kbps in RAS05.1*

RNC InactivityTimerDLDCH64 3 s 24% 3 - 10 sRNC InactivityTimerDLDCH128 2 s 31% 2 - 20 sRNC InactivityTimerULDCH64 3 s 34% 1 - 20 sRNC InactivityTimerDLDCH384 2 s 38% 1 - 10 sRNC InactivityTimerULDCH128 2 s 41% 1 - 20 sRNC InactivityTimerULDCH384 2 s 45% 1 - 20 s

WCEL OCdlNrtDCHgrantedMinAllocT60 (not active)

47% 0, 10, 15, 60sEnhanced Overload Control is not

active in almost half of the networks

RNC TrafVolThresholdDLHigh 1024 bytes 69%1024, 3072, 4096 bytes

Most operators are using 1024bytes

Table 2 PS Parameters survey results

* Prior to RAS51, Initial and minimum allowed bit rate is set with the parameter MinAllowedBitRateUL/DL. From RAS51 onwards there is own parameters for minimum and initial bit rate. These customer parameters sets were collected by the 3G SIG during 2007 and can be further studied in Error: Reference source not found. It can be useful to propose a PS parameter optimization based on these results as the survey shows that some settings have been done for historical rather than technical reasons (ie MinAllowedBitRateDL/ MinAllowedBitRateUL).

2 Setting Initial and Minimum BitratesIn RAS05 Initial and minimum allowed bit rate is set with WCEL parameters MinAllowedBitRateUL and MinAllowedBitRateDL. From RAS51 onwards, there are own parameters for Initial and Minimum bit rates. Initial bit rate is set with WCEL parameters InitialBitRateUL and InitialBitRateDL. Minimum bit rate is set with parameters MinAllowedBitRateUL and MinAllowedBitRateDL. Minimum Allowed bit rate parameter defines the minimum allowed bit rate that PS can downgrade a NRT DCH bearer bit rate in congestion situations.

Setting high bit rates already from the initial Radio Bearer allocation gives not only higher peak bit rate but also lower RTT and faster TCP slow start. However, setting a high initial bit rate can be problematic from the service accessibility point of view since if there is not enough Air interface, BTS HW (CE) or Iub capacity, the RAN will reject the capacity allocation.

This may be avoided with the use of Enhanced Priority Based Scheduling feature which allow the downgrade or release of existing NRT allocation if there is another user requesting initial capacity in the congested situation. Priority Based Scheduling introduces service differentiation based on traffic class and handling priority. Benefits can be achieved only with correct parameter settings (PBSPolicy “any”), otherwise it would be possible that capacity request is rejected due the priority settings.

RN2.2 supports the following UL NRT DCH bit rates: 8, 16, 32, 64, 128, 2