gprs netperfqual

8/11/2019 GPRS NetPerfQual

http://slidepdf.com/reader/full/gprs-netperfqual 1/12

Ed 02 Released

MND FFUV4XE2.DOC v 3 3DC 21144 0033 TQZZA 1/12

A l l r i g h t s r e s e r v e

d .

P a s s i n g o n a n

d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0

0 4 ( 9 0 0 7 ) A 4

FUNCTIONAL FEATURE DESCRIPTION

GPRS Network Performances and Quality in Release B7

This document covers the following features:

30 18 30 Fast Broadcasting of GPRS System Information30 20 12 Fast Paging on Master Channel30 20 30 Non-DRX Mode After Packet Data Transfer30 20 32 Delayed Downlink TBF Release



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

Contents

1. REFERENCES.................................................................................................................................3

2. INTRODUCTION .............................................................................................................................4

3. ABSTRACT...................................................................................................................................... 5

4. FAST BROADCASTING OF GPRS SYSTEM INFORMATION.......................................................6

5. FAST PAGING AND NON-DRX MODE...........................................................................................7

5.1 The DRX compromise ...........................................................................................................7

5.2 Fast Paging on Master Channel ............................................................................................8

5.3 Non-DRX Mode after Packet Data Transfer .......................................................................... 8

6. DELAYED DOWNLINK TBF RELEASE ........................................................................................10

6.1 Delayed downlink TBF release concept .............................................................................. 10

6.2 Delayed downlink TBF release states diagram ................................................................... 11



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

1. REFERENCES

GSM 05.02 Multiplexing and multiple access on the radio path

ABBREVIATIONS

BCCH Broadcast Control ChannelBSS Base Station SubsystemCS Circuit-SwitchedDL DownlinkDRX Discontinuous ReceptionGPRS General Packet Radio ServiceGSM Global System for Mobile communicationsHTTP HypeText Transfer ProtocolIMSI International Mobile Subscriber IdentityLLC Logical Link controlMS Mobile StationOMC-R Operation and Maintenance Centre : Radio partLLC Logical Link controlPDU Protocol Data UnitRLC Radio Link ControlSGSN Serving GPRS Support Node3GPP Third Generation Partnership ProjectTBF Temporary Block Flow (see also glossary)Um Air interfaceWAP Wireless Application Protocol

GLOSSARY

READY When GPRS activity is taking place e.g. during data transfer or shortly aftercompletion of data transfer. This state is entered upon initiation of uplinkdata transfer or upon response to GPRS paging. A READY timer (typically a

few tens of seconds) set at the MS and SGSN sides supervises this state.STANDBY When the mobile is attached to GPRS service but no data transfer has

started or no transfer has occurred for a while (determined by the READYtimer), the mobile is in the STANDBY state.

TBF A Temporary Block Flow is a temporary, unidirectional physical connectionacross the Um interface, between one mobile and the BSS. The TBF isestablished when data units are to be transmitted across the Um interfaceand is released as soon as the transmission is completed.



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

2. INTRODUCTION

This document describes several improvements to GPRS introduced in the BSS release B7.

The present functional feature description is a complement to the description of the followingfeatures provided in the document “GSM 900/GSM 1800 BSS Feature Description”:

• 30 18 30 Fast Broadcasting of GPRS System Information

• 30 20 12 Fast Paging on Master Channel

• 30 20 30 Non-DRX Mode After Packet Data Transfer

• 30 20 32 Delayed Downlink TBF Release (release B7.2)

This document is organised as follows:

• Chapter 3 gives a short introduction on these features and the key benefits they bring,

• Chapter 4 describes the "Fast Broadcasting of GPRS System Information" feature,

• Chapter 5 proposes a reminder on DRX techniques, then describes the "Fast Paging onMaster Channel" and "Non-DRX Mode after Packet Data Transfer" features.

• Chapter 6 describes the "Delayed Downlink TBF Release" feature introduced in release B7.2.



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

3. ABSTRACT

The BSS software release B6.2 focussed on introducing all features necessary for the successfullaunch of a GPRS service in the networks. The B7 software release introduces a number of

improvements in the perspective of GPRS growth, in terms of data rates and traffic capacity. In thiscontext, a number of improvements to GPRS network performances and quality are introduced in B7as further described in this document.

The present document highlights the benefits from the following features:

Release B7.1 features:

• Fast Broadcasting of GPRS System Information (30 18 30) speeds up the GPRS cell re-selection, thus improving the data speed perceived by moving users.

• Fast Paging on Master Channel (30 20 12) allows speeding up the paging and initiation ofdownlink packet transfers, thus improving the data speed as seen from the end-users.

• Non-DRX Mode after Packet Data Transfer (30 20 30) speeds up the initiation of downlinkpacket transfers thus improving the data speed perceived by the end-user.

Release B7.2 feature:

• Delayed Downlink TBF Release (30 20 32) maintains artificially an on-going Downlink TBF,thus increasing the data thoughput offered to the end-user when bursty applications such asWAP or HTTP are used.



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

4. FAST BROADCASTING OF GPRS SYSTEM INFORMATION

Under certain conditions, this feature speeds up the GPRS cell re-selections, by the use of anextended BCCH channel. This improves both the mobile controlled, and network controlled cell re-selections.

The networks using GSM 1800 frequencies may need to broadcast large volume of systeminformation on the BCCH. Because of this, both the System Information Type 2bis and 2termessages may have to be broadcast over the BCCH.

One consequence for GPRS is that the repetition rate of the System Information Type 13 messagewill get slower.

Because the GPRS mobiles have to decode this System Information Type 13 message from theneighbour cell, before performing GPRS cell re-selection, it is highly desirable to ensure a quickacquisition of this message by the GPRS mobiles.

To achieve this, the System Information Type 13 message can be broadcast on the extended BCCHrather than on the normal BCCH. When large volume of system information has to be broadcast overthe normal BCCH, the extended BCCH guarantees that the System Information Type 13 message isscheduled more often. The mean time for the mobile to acquire this message is then reduced to c.a.0.9 s, from 1.9 s otherwise.

Shorter data transfer interruptions due to cell re-selections is expected from this feature. This willimprove the network performance perceived by the end-user.

When the extended BCCH is configured in the cell, this feature can be enabled from OMC-R throughthe EN_SI13_EXT flag. When this feature is disabled, the System Information Type 13 is broadcastover the normal BCCH.



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

5. FAST PAGING AND NON-DRX MODE

This chapter describes two improvements introduced in B7 in order to speed up data transfers. First,a short overview on Discontinuous Reception (DRX) aspects is proposed in section 5.1, in order to

understand the benefits from these two features.

5.1 The DRX compromise

What is DRX?

Discontinuous Reception (DRX) is a set of techniques used in cellular systems to increase thebattery autonomy of the mobile stations.

What is it used for, in the GPRS system?

DRX is used for paging the GPRS mobiles in STANDBY state (see glossary).

Another application is the establishment of the GPRS radio communication pipe between the mobileand the base station (TBF, see glossary) for sending or receiving data. Indeed, the paging channel isalso used to assign downlink radio resource to GPRS mobiles in READY state.

How does it work?

The paging channel is divided into paging sub-groups. Each mobile station pertains to a given sub-

group in the serving cell. A paging message towards a given MS can only be sent by the BSS in aradio occurrence corresponding to the MS sub-group. Thus, battery savings are obtained, becausethe MS needs not monitoring all occurrences of the paging channel and can therefore go idlebetween occurrences of its own paging sub-group.

Note: The paging sub-group of a particular MS is derived from its International Mobile SubscriberIdentity (IMSI) and from the configuration of the paging channel in the current cell.

However, DRX causes longer paging cycle and delays the establishment of the radio data pipe,which result in transmission delays that may be in the order of hundreds of milliseconds, or evenseconds. These delays depend on the cell configuration parameters. This is described in details inthe GSM 05.02 standard.

Note: The total number of paging sub-groups in the cell depends on the configuration of the pagingchannel, and determines the paging cycle.



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

The non-DRX period applied by the mobile and BSS depends on the following two parameters:

• The NON_DRX_TIMER parameter negotiated between the mobile and SGSN during theGPRS attachment procedure. This parameter is stored by the SGSN and then passed to the

BSS with each paging request and each downlink packet, on a per MS basis.

• The DRX_TIMER_MAX parameter set at OMC-R by the operator, on a per BSS basis. Thisvalue is broadcast in the cell as GPRS system information. Possible values are 0, 1, 2 and 4 s.

The mobile and BSS apply the minimum value of both parameters: min (NON_DRX_TIMER,DRX_TIMER_MAX).

The expected savings on TBF establishment time are in the order of a few hundreds of milliseconds.This is not negligible because, TBF establishment time have to be kept as short as possible

compared to data transmission time. In particular for e.g. WAP based applications consisting ofmany short TBF



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

6. DELAYED DOWNLINK TBF RELEASE

In addition to the benefits brought by the "Non-DRX mode after packet data transfer" feature alreadysupported in release B6.2, the Alcatel BSS release B7.2 introduces the recently 3GPP standardisedfeature "Delayed downlink TBF release ”.

The aim of this feature is to cope with bursty data applications (such as WAP, HTTP), which maylead to multiple subsequent time-consuming TBF establishments.

The benefits of the delayed downlink TBF release feature are the following:

- After the end of a transfer, it allows the network to initiate sending of more data to the MSwithout performing a downlink TBF establishment;

- It allows a zero delay start of data transfer to the MS on the downlink (even if a continuousallocation is not given to the MS), resulting in zero establishment delay downlink operation;

- In turn, the data throughput offered to the mobile station end users is improved for burstyapplications.

6.1 Delayed downlink TBF release concept

The “Delayed Downlink TBF release ” concept consists in maintaining an artificial data transfer, evenwhen there are no more useful data to be transmitted to the MS.

For this purpose, a dummy downlink data block is defined, backward compatible with Release 97mobiles. This dummy downlink RLC (Radio Link Control) data block is formed by inserting an LLC(Logical Link Control) Dummy UI Command into a downlink RLC data block. The LLC Dummy UICommand is an invalid LLC PDU which is discarded by the LLC entity in the MS. After the end of theuseful data transfer, the BSS regularly sends such dummy downlink data blocks to the MS, in orderto delay the permanent release of the TBF. Those blocks contain polling requests to allow the MSrequesting an uplink TBF establishment.

During the period of the delayed TBF release, any useful data arriving for this MS can be transmittedimmediately over the radio on the downlink.

At the end of the Delayed TBF release period, if no useful data has been received, the BSS initiatesthe release of the TBF.



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

6.2 Delayed downlink TBF release states diagram

The following diagram presents the different states of the TBF: establishing, active, delayed,releasing, released.

The “Delayed Downlink TBF release ” feature is supported in both RLC acknowledged andunacknowledged mode.The following differences between the two RLC modes can be highlighted:

- In RLC acknowledged mode, retransmissions of useful and dummy RLC data blocks arepossible before all RLC blocks are acknowledged by the MS.

- In RLC unacknowledged mode, there is no retransmission of useful or dummy RLC datablocks. At normal TBF release procedure, the last MS acknowledgement consists in aPacket Control Acknowledgement message.

Idle

LLC PDUs receivedfrom SGSN

DL TBFestablishment procedure on(P)CCCH

TBF establishmentsuccessful

TBF in active state

Useful RLC block

Delayed DL TBF releaseactivated:

Last DL RLC PDU (FBI=0) +Dummy UI Command AND all usefulRLC blocks acknowledged

TBF in delayedrelease state

Dummy UICommand (FBI=0,S/P=1)

New useful DL RLCblock (FBI=0)

TBF releasing

Delayed DL TBFrelease not activated:

Last useful DL RLCblock (FBI=1)

Last Dummy UICommand (FBI=1,S/P=1)

Last MSacknowledgement

TBF releasedT3193, T3192activated

T3192 expiry

Fast DL TBF re-establishmentprocedure on

PACCH

LLC PDUs receivedfrom SGSN

Successful

failure failure

Figure 1 – Scenarios of TBF establishment and release in B7.2

At the end of the useful data transfer, if the “Delayed downlink TBF release ” feature is enabled, thelast useful RLC data block is completed by a dummy LLC PDU in order to maintain the TBF alive,and the FBI (Final Bit Indicator) bit is not set. At this time, a polling period timer(T_DELAYED_DL_TBF_POL) is started.



Ed 02 Released



d .


d c o p y

i n g o

f t h i s

d o c u m e n

t , u s e a n

d c o m m u n

i c a t i o n o f

i t s c o n

t e n

t s

n o

t p e r m

i t t e d w

i t h o u

t w r i t t e n a u

t h o r i z a

t i o n .

1 A A 0 0 0 1 4 0 0 0 4 ( 9 0 0 7 ) A 4

At polling period timer expiry, a new RLC PDU containing an LLC Dummy UI command is sent to theMS and polling period timer is restarted. Polling period timer should satisfy synchronisationrequirements, and allow the MS to request UL TBF establishment often enough. The overall periodof delayed TBF release is controlled by two timers (T_DELAYED_DL_TBF_REL_RADIO +T_NETWORK_RESPONSE_TIME).Upon this summed-up period expiry, the last dummy RLC PDUis sent and the BSS set the FBI bit toinitiate the release of the TBF. If new useful LLC PDUs arereceived before this period expiry, the transfer resumes immediately.

End of Document

gprs netperfqual

Documents