GPRS Optimization Handbook

7/23/2019 GPRS Optimization Handbook

1/135

SIEMENS Shanghai Mobile Communications, Ltd. 1/135 2005-09-12MN SE NPGPRS Network Optimization Handbook

GPRS Network Optimization

Optimization Handbook

(Preliminary)

For internal use only

Issued by: Siemens Shanghai Mobile Communications, Ltd.

Network Performance Headquarter

777 ChuanQiao Road, 201206, Shanghai, China


2/135


History of Document:

Version: Date: Changes:

1.0 2005.09.12 First release


3/135


Table of Contents

1 INTRODUCTION ................................................................................................................................ 5

1.1 NETWORK OPTIMIZATION CONCEPTS ............................................................................................... 51.2 NETWORK OPTIMIZATION PROCESS ................................................................................................. 61.3 AIM OF THIS HANDBOOK.................................................................................................................. 7

2 GPRS BASIC ........................................................................................................................................ 8

2.1 GENERAL INTRODUCTION................................................................................................................ 82.2 GPRSNETWORK SYSTEM ARCHITECTURE ...................................................................................... 82.3 GPRS PROTOCOLS......................................................................................................................... 112.4 GPRS PROCEDURES BASIC ............................................................................................................ 14

2.4.1 Mobility Management States ............ ........... ........... .......... ........... ........... .......... ........... ......... 142.4.2 Packet Data Protocol states ................................................................................................. 152.4.3 GPRS attach ......................................................................................................................... 162.4.4 Routing area update ............. ........... ........... .......... ........... ........... .......... ........... ........... .......... 172.4.5 Cell update............................................................................................................................ 182.4.6 PDP context activation......................................................................................................... 19

2.5 GPRS RADIO NETWORK................................................................................................................ 202.5.1 GPRS Um interface .............................................................................................................. 202.5.2 GPRS radio network features in BR7 ................................................................................... 22

2.6 GB INTERFACE............................................................................................................................... 242.6.1 Gb physical connection......................................................................................................... 25

2.7 GPRS CORE NETWORK.................................................................................................................. 262.7.1 SGSN architecture................................................................................................................ 262.7.2 GGSN architecture ............................................................................................................... 292.7.3 GSN Hardware components capacity assumptions ........... ........... ........... ........... ........... ....... 32

3 GPRS PARAMETERS IN BSC DATABASE.................................................................................. 33

3.1 SBSDATABASE STRUCTURE WITH GPRS RELATED OBJECTS ........................................................ 333.2 INTRODUCTION OF GPRS RADIO PARAMETERS ............................................................................. 34

3.2.1 GPRS channel configuration parameters .......... ........... .......... ........... ........... .......... ........... ... 343.2.2 Coding scheme and Link Adaptation parameter .................................................................. 353.2.3 GPRS feature parameter....................................................................................................... 363.2.4 RLC/MAC parameter.............. ........... .......... ........... .......... ........... .......... ........... .......... .......... 383.2.5 Other parameters.................................................................................................................. 393.2.6 Recommended GPRS radio parameter settings from TAC3 ........... ........... .......... ........... ...... 40

4 INTRODUCTION OF GPRS RADIO PERFORMANCE MEASUREMENTS........................... 40

4.1 GENERAL CONCEPTS...................................................................................................................... 404.2 STRUCTURE OF SCANNERS ............................................................................................................ 424.3 SBS OPTIMIZATION WORK FLOW OF PERFORMANCE MEASUREMENT............................................. 444.4 MAIN GPRS RADIO NETWORK PERFORMANCE KPIS (BASED ON BR7) ......................................... 45

5 INTRODUCTION OF GPRS CORE PERFORMANCE MEASUREMENTS ............................ 46

5.1 GENERAL CONCEPTS...................................................................................................................... 465.2 PERFORMANCE DATA HANDLING ................................................................................................... 485.3 DATA REQUIRED FOR CORE MEASUREMENT EVALUATION (BASED ON PO2.1)............................... 49

5.3.1 SGSN evaluation................................................................................................................... 495.3.2 GGSN evaluation.................................................................................................................. 515.3.3 Set up the PDC ..................................................................................................................... 51

5.4 GPRS CORE NETWORKKPIS ......................................................................................................... 52

6 INTRODUCTION OF COMMON GPRS NETWORK OPTIMIZATION TOOLS ................... 54


4/135


7 MAIN GPRS OPTIMIZATION SKILLS ........................................................................................ 55

7.1 END-TO-END GPRS PERFORMANCE TESTS .................................................................................... 557.1.1 General introduction ............................................................................................................ 557.1.2 GPRS end-to-end test tools................................................................................................... 567.1.3 Preparations before test ....................................................................................................... 577.1.4 Using TEMS investigation.................................................................................................... 59

7.1.5 Test items.............................................................................................................................. 657.2 GPRS RADIO MEASUREMENT ANALYSIS WITH BATRANA2004 ...................................................... 72

7.2.1 Introduction .......... ........... .......... ........... ........... .......... ........... ........... .......... ........... ........... ..... 727.2.2 Using MySQL ....................................................................................................................... 727.2.3 Getting Data from project .................................................................................................... 757.2.4 MySQL connection and configuration .......... ........... ........... .......... ........... ........... .......... ........ 777.2.5 Project Operation................................................................................................................. 787.2.6 Import Data .......... ........... ........... .......... ........... ........... .......... ........... ........... .......... ........... ..... 797.2.7 Network Performance Analysis ............. ........... ........... ........... ........... .......... ........... ........... ... 81

7.3 GPRS CORE MEASUREMENT ANALYSIS WITHNETAN2000 ............................................................ 847.3.1 Introduction to NETAN2000........... ........... .......... ........... ........... ........... ........... .......... ........... 847.3.2 NETAN Basics .......... ........... ........... .......... ........... ........... .......... ........... ........... .......... .......... .. 857.3.3 NETAN2000 Result Files ........... .......... ........... .......... ........... .......... ........... ........... .......... ....... 87

7.3.4 Evaluations of SSNC/GPRS ........... .......... ........... ........... .......... ........... ........... .......... ........... .. 917.3.5 Long Term Statistics .......... .......... ........... ........... .......... ........... ........... .......... ........... ........... . 1047.4 GPRSSIGNALING ANALYSIS (CALL ANALYZER,K1205)............................................................ 105

7.4.1 Introduction .......... ........... .......... ........... ........... .......... ........... ........... .......... ........... ........... ... 1057.4.2 K1205 introduction............................................................................................................. 1057.4.3 Call Analyzer introduction ................................................................................................. 121

8 GPRS OPTIMIZATION CASE STUDIES.................................................................................... 126

8.1 GPRS RADIO OPTIMIZATION CASES ............................................................................................. 1268.1.1 Increase throughput by improving C/I........ ........... ........... ........... .......... ........... ........... ....... 1268.1.2 Activating GPRS forced intra cell handover ........ ........... ........... ........... .......... ........... ........ 1278.1.3 Peak throughput management ............................................................................................ 1278.1.4 Reduce delay on Gb interface........... ........... ........... ........... .......... ........... ........... ........... ...... 1288.1.5 Cell reselection parameter: CELLRESH............................................................................ 1298.1.6 Reconfigure number of Abis subslots under FAAS ........... ........... ........... ........... .......... ....... 129

8.2 GPRS CORE OPTIMIZATION CASES............................................................................................... 1308.2.1 GMM/SM procedure analysis by call analyzer .................................................................. 1308.2.2 Investigation on data transfer pause ........... ........... ........... ........... ........... .......... ........... ...... 1318.2.3 WAP performance analysis................................................................................................. 1328.2.4 Mis-Configuration of VLAN ......... ........... .......... ........... ........... .......... ........... ........... .......... . 1348.2.5 Detect radio problems from core network side...... ........... ........... .......... ........... ........... ....... 135


5/135


1 Introduction

1.1 Network optimization concepts

Network optimization is a value-added service product which can be provided to amobile network operator. A service package may comprise many customer-orientedcontents such as: comprehensive audit of the running network quality, in-depthanalysis of network problems, solutions to improve network performance, networkmonitoring, cutover support, etc.

The network performance is usually quantified by several number of keyperformance indicators (KPIs) defined in a network optimization contract. These KPIswill be evaluated before and after the provision of network optimization service inorder to quantify the result of contract execution.

General contents and evolvement of network optimization service is shown in the

following chart:

As a first step we ensure the basic coverage and capacity for basic services such as:voice call, SMS, etc. by necessary expansions.

Secondly, the quality of existing coverage and capacity will be optimized in order toensure subscriber satisfaction and keep the operator competitive in the market.

Thirdly, in order to maximize the operators revenue, the network has to be moreprofitable and efficient. Special optimization tasks will carried out such as signalingload optimization (hence network can serve more subscriber with availableequipments), TRX re-allocation (hence investment on expansion is delayed), cell loadbalancing (traffic is shared among the available cells) , dual-band optimization(hence network capacity is fully utilized), etc.

As a last step, new services (e.g. packet services) will be optimized in order to allowthe operator to operate them at high quality level (i.e. subscriber satisfaction) andshare network resources properly between basic services and new services (i.e.operator benefit), so that return of investment from new services is also high.

In general, the network optimization service chain is provided in order to guaranteean mobile network operators long-term success in the competitive market.

Coverage and capacity forbasic services

Network Quality

Efficiency &Profitability

Opt. ofnew services E

volvement


6/135


1.2 Network optimization process

An overview flow of the network optimization process is presented in the chart below:

No

No

Yes

Audit Report

ProblemSolved?

TargetsReached?

ContractAcquisition

ProjectPreparation

ProjectKickoff

Audit

Analysis

Solution

Implementation

Verification

Monitoring

New problemFound?

ChangeRequest

StageReport

TimeReached?

FinalReport

Customerapproval

Yes

Yes

No

YesNo


7/135


1.3 Aim of this handbook

The aim of this handbook is to provide information of basic 2.5G GPRS networkoptimization skills and related background knowledge of packet switched data

services. Both GPRS radio and core network will be concerned. A few case studieswill be provided in chapter 8 in this handbook to give the reader a little feeling onwhat GPRS optimization can do and how they are implemented in the field.

The target readers of this handbook are beginners who intend to learn basic skills ofGPRS network optimization or field engineers who would like to use this handbook asan easy reference for daily tasks.


8/135


2 GPRS basic

2.1 General introduction

The original GSM network is only able to provide circuit-switched data service withlimited data rate of 9.6kbps. With more and more mobile data service requirementsfrom the mobile subscribers, the GSM phase2+ standard had introduced enhancedmobile data communication technologies into GSM network to meet the demand. Asone of the new technologies of GSM phasae2+, GPRS(General Packet Radio Service)was designed to provide the packet-switched high speed data service based on thetraditional GSM network.

The main features why GPRS can provide higher speed mobile data service are thenew coding schemes and channel bundling of GPRS radio network. Channel bundlingmeans that one GPRS subscriber can use more than one radio timeslotsimultaneously for the same data session while the traditional GSM data service can

use only one radio timeslot. As for the new coding schemes, GPRS provides 4 codingschemes: CS1, CS2, CS3, CS4. The higher coding scheme, the higher data rate isexpected over air interface.

On the other hand, one GPRS radio timeslot can be shared not only by multiple GPRSsubscribers at the same time, but also shared dynamically by GPRS data service andGSM voice service at different time. All these features improve the radio channelresource efficiency, which is the traditional bottleneck, of the mobile network andfinally benefit the mobile operator by higher network resource efficiency and beingmore attractive to mobile data users.

Since the GPRS offers a new packet data service and brings much complexity intothe mobile network, more GPRS network details will be introduced in the next foursmall chapters: network architecture, protocols, procedures and radio networkspecific information. Please be noted that the information given in this handbook isquite brief, for more detailed and complete technical information, please refer toplenty of other Siemens official documentations. In the last chapter, a fewrecommended documents and links will be provided.

2.2 GPRS Network system architecture

GPRS network consists of radio and core network: GPRS network shares the common

radio network with GSM network but has its own new GPRS core network.The network architecture of GPRS network is shown in the chart below: (The redcolor marks the GPRS network elements and the yellow color marks the GSMnetwork elements; The two vertical dashed lines separate the radio network, corenetwork and external network)


9/135


In the radio network part, GPRS doesnt need new network node while PCUs (PacketControl Unit) shall be added as part of the BSC no matter the PCU modules areintegrated into BSC racks or installed in an extra new PCU rack (Siemens solution isto integrate PCU module into BSC rack). The basic function of PCU is to take care ofGPRS radio channel scheduling/multiplexing, data packet segmentation/assemblingand the routing of data packets to GPRS core.

In addition to the new PCU module, new BSS software is also necessary in both BSCand BTS to accomplish the GPRS functionalities. In Siemens solution, SBS BR55 isthe first BSS software release starting to support GPRS. The GPRS functionality unitin BTS is normally named as CCU(Channel Codec Unit) and please note that CCUstands for only software enhancement in BTS without addition of any new hardwaremodules.

In the core network part, GPRS introduces two new major nodes: SGSN(ServingGPRS Support Node) and GGSN(Gateway GPRS Support Node). SGSN handlesmainly the mobility of the subscribers and radio related protocol toward the mobilestation. GGSN interworks with the external packet data network. Besides the SGSNand GGSN, the GPRS core network consists of some other network elements, whichare also important and necessary to accomplish other GPRS control functionalities,such as DNS server, Border Gateway, etc.

GPRS core nodes have to be connected to the radio network and other GSM networknodes in order to convey the user data and control message across the wholenetwork, accordingly a lot of new interfaces have been introduced by GPRS as shownin the chart below:


10/135


The major GPRS interfaces are following: Gb interface: between SGSN and BSC Gn interface: between SGSN and GGSN Gs interface: between SGSN and MSC Gi interface: between GGSN and external data network Gr interface: between SGSN and HLR Gd interface: between SGSN and SMS-G-MSC Gp interface: between GGSN and Border Gateway

Even though all above interfaces are defined in the GPRS standard, not all of them

are mandatory to be implemented in live GPRS networks. Take the Gs interface forexample: although Gs interface can improve the GPRS network performance bysupporting the combined GPRS-GSM procedures and reducing the overall networksignaling load, it is not really implemented yet in most of the GPRS networks.On the other hand, we shall note that some interfaces carry only signaling (forexample Gs), while the others carry both signaling and user data (for example Gb).

GPRS user subscription data is stored in HLR. This is the reason why Gr interface ismandatory so that SGSN can communicate with the HLR to ask for user subscriptiondata. Consequently the HLR has to be upgraded to be higher than Siemens SR8.0 inorder to support GPRS functionality.

Finally the mobile phone shall be GPRS capable. According to standard, there arethree different classes of MS regarding to their GPRS capability:

Class A: MS supports simultaneous and independent handling of GPRS and GSMservices (operation & signaling).Class A MS consists of two independent Tx & Rx.

Class B: MS supports GPRS and GSM services, but cannot handle themsimultaneously (signalling for both, GPRS & GSM). GPRS traffic will be suspended incase of pending or established CS connection.


11/135


Class C: Alternate use of GSM or GPRS services. Class C MS are either GSM or GPRSMS at one time.

Moreover, GPRS capable MS can be divided into different multislot classes accordingto its capability of supporting radio timeslots. The multislot class information is listedin the table below.

Multislot class Maximum number of slots Minimum number of slots

Rx Tx Sum Tta Ttb

1 1 1 2 3 2

2 2 1 3 3 2

3 2 2 3 3 2

4 3 1 4 3 1

5 2 2 4 3 1

6 3 2 4 3 1

7 3 3 4 3 1

8 4 1 5 3 1

9 3 2 5 3 1

10 4 2 5 3 111 4 3 5 3 1

12 4 4 5 2 1

For instance, Ericsson mobile phone R520 used widely in GPRS field test is amultislot class 4 and class B GPRS mobile phone, which means that it can support upto 3 downlink radio timeslots at the same time.

2.3 GPRS protocols

A lot of new protocols are introduced into the GPRS network on all interfaces, mostof them are designed to fit the character of packet data transferring. One of themajor highlights of GPRS network is that it uses IP protocol both internally andexternally so that GPRS network could have direct connection to external datanetworks.

The protocol layers of the GPRS network have two types: one for transmission plane(for user data) and one for control plane (for signaling). The protocol layer oftransmission plane is shown in chart below:


12/135


13/135


S G S N

G M M / S MGP RS MobilityManagement

andSession

Management

FRF r ame R e l ay

L 1 b i sP h y s i c a l

L a y e r

B S S G PB SS

G P R SP r o t o c o l

L L CL o g i c a l L i n k

C o n t r o l

M S

G M M / S MGP RS MobilityManagement

andSession

Management

R L CR a d i o L i n k

C o n t r o l

M A CM e d i u m A c c e s s

C o n t r o l

G S M R F

IP / X.25

L L CL o g i c a l L i n k

C o n t r o l

U m G b

GPR S a t tach / de tach

secur ity routing area update, locationupdate

PDP contex t ac tiva tion ,modificat ion & deactivation

logical connection acknowledge/ unacknowledged peer -to -p ee r oper at io n

c iphering SAPs to h igher l ayer (SND CP,

G M M , S M S )

M A C

G S M

R F

R L C

F R

L 1bis

B S S

G P

R e l a y

Signall ing P lanes between SG SN and M S

The control plane protocols used in Gn and Gi interfaces are similar to the one usedon transmission plane of these two interfaces. Comparatively the control planeprotocol of Gc,Gr,Gf,Gd and Gs interface are different and they are close to thestandard CCS7 signaling protocol, as shown in charts below:

L 1

S C C PS ignalling C onne-ction C ontrol P art

T C A PTrans actionC apabilities

Application P art

M A PM o b i l e

A p p l ic a t io n

Pa r t

M T P L 2

M T P L 3

L 1

S C C P

T C A P

M A PM o b i l e

A p p l ic a t io n

Pa r t

M T P L 2

M T P L 3

L 1

S C C P

M T P L 2

M T P L 3

L 1

S C C P

M T P L 2

M T P L 3

B S S A P +B S S A P +

B S S

A p p l ic a t io n

Pa r t +

S G S N H L R , E I R ,S M S - G M S CGr, f ,d

S G S N M S C /V L RG sH L RG cG G S N

G P R S -specif ic

M A Pextension

Subse t o f B S S A Pfunction-alities

G PR S S ignalling P lanes


14/135


2.4 GPRS procedures basic

They layer3 protocols in the GPRS signaling plane contains two parts: GMM (GPRSMobility Management) and SM (Session Management).The mobility management functions are used to keep track of the current location of

an MS within the PLMN. The MM functions are located in MS and SGSN.The session management functions are used for activation, modification anddeactivation of PDP (packet data protocol) contexts, i.e. of packet routing andtransfer capability. The SM functions are located in MS, SGSN and GGSN.

2.4.1 Mobility Management States

In IDLE state, the MS is not attached (i.e. detached) to the PLMN. There is no validlocation or routing information for the MS available in SGSN or GGSN. Only GPRSsubscription information in the HLR is available. User data transfer and paging of theGPRS MS are not possible.In READY state, the SGSN knows as well the cell selected by the MS within the RAI.If the MS enters a new radio cell, it updates the SGSN by signaling. Therefore pagingis not necessary, if the SGSN wants to transmit packet data downlink. The MS maysend and receive PDP PDUs (protocol data unit) in this state. However, the readystate does not imply any established physical connection between MS and SGSN.In STANDBY state, the MS is attached to the PLMN. The SGSN knows the routingarea identity (RAI) of the roaming MS, but not the specific cell within that RAI. TheMS as well as the SGSN may initiate data transfer at that state by PDP contextactivation (MS) or paging (SGSN). As a consequence, the MS and the SGSN willchange to ready state.

IDLE READY STANDBY

MM State Model of MS

STANDBY timerexpired

PDU transmission

GP RS Attach

READY timerexpired,

Force to STANDBY,abnormal RLC condition

GPRS Detach

IDLE READY STANDBY

MM State Model of SGSN

STANDBY timer expired,Cancel Location

PDU transmission

GP RS Attach

READY timer

expired,Force to STANDBY,

abnormal RLC condition

Cancel Location,GPRS Detach

Mobility Managem ent State Transitions

The MM procedures are: GPRS Attach, GPRS Detach, Routing Area Update,Authentication, Identity Check, GPRS Paging.


15/135


2.4.2 Packet Data Protocol states

In INACTIVE state PDP context is not activated. There is no related routing contextin the MS and SGSN/GGSN. The transition to the ACTIVE state is performed by theactivation of a PDP context. The mobility management states STANDBY or READY atMS and SGSN are a precondition for PDP context activation. Otherwise transmission

of PDUs from MS side will be rejected.In ACTIVE state the MS and SGSN/GGSN hold a routing context, i.e. a PDP contextis activated. PDU transfer is possible. The mobility management states STANDBY orREADY at MS and SGSN are a precondition for the state ACTIVE. With PDP contextdeactivation, the state of a PDP context changes to INACTIVE. In case of change tomobility management state idle (GPRS Detach or STANDBY timer expiry), allactivated PDP contexts change to INACTIVE.

The SM procedures are: PDP Context Activation, PDP Context Modification, PDPContext Deactivation.

Functional PDP State Model

INACTIVE

no routing andmapping of PDPPDUs possible

no data transmission

ACTIVE

routing andmapping ofPDP PDUs possible

location updatetakes place

Activate PDP Context

Deactivate PDP Context

MM state change to IDLE

The GMM/SM procedures are crucial to GPRS network performance. For example, if aGPRS end-user wants to have fast GPRS network access and data transfer, fast andsuccessful GPRS attach and PDP context activation are always the prerequisite beforeany user data packet is transmitted or received. Therefore, performance of GMM/SMprocedures shall be under careful monitoring and they are normally regarded to asmajor GPRS Key Performance Indicators.

Some of the important GMM/SM procedures are illustrated in the followings sub-chapters.


16/135


2.4.3 GPRS attach

The GPRS attach procedure is used to establish a GMM context in the MS and theSGSN. After a successful GPRS attach, the GPRS mobile subscriber data are stored inthe SLR (SGSN location register).After switching on, the MS initiates the attach procedure by the transmission of an

Attach Request and the following procedures are shown in chart below:


17/135


2.4.4 Routing area update

Routing Area (RA) is defined as a group of cells which is the minimum range of GPRSpacket paging. When the mobile phone moves from one RA to another RA, a RoutingArea Update (RAU) will be initiated by the MS. One routing area is always a subset of

one location area. By initial planning, the size routing areas are set same to the sizeof location areas.

In the GMM STANDBY mode, Periodic RAUs will be initiated by MS under control ofthe periodic RAU timer. Normal RAUs (when MS moves into a new RA), compriseintra-SGSN RAU and inter-SGSN RAU. The message flow of an intra-SGSN RAU isshown in chart below:

R o u t i n g A r e a U p d a t e R e q u e s t

(old R A I, Update T ype)

S e c u r i t y F u n c t i o n s

R o u t i n g A r e a U p d a t e A c c e p t

(P-T M S I, P -TM S I R eallocation)

R o u t i n g A r e a U p d a te C o m p l et e

(P-TMSI)

BS S

S G S NM S

R o u t i n g A r e a U p d a t e R e q u e s t

(old R A I, Update T ype)

S e c u r i t y F u n c t i o n s

R o u t i n g A r e a U p d a t e A c c e p t

(P-T M S I, P -TM S I R eallocation)

R o u t i n g A r e a U p d a te C o m p l et e

(P-TMSI)

BS SBS S

S G S NM S


18/135


2.4.5 Cell update

In GPRS network, cell reselection instead of handover will be carried out when theMS moves from one cell to another cell. If the MS is in MM idle or standby state, theGPRS cell reselection is just the same as the non-GPRS mobile cell reselection. Whilein GMM READY state, the GPRS core network shall always be aware of the MS

location on cell level and consequently, the cell update procedure will be initiated byMS which will generate some extra signaling on Gb interface as shown in chart below:

The detailed description for the above messages are:

(1) A cell update takes place when the MS enters a new cell inside the current RAand the MS is in READY state. The MS performs the cell update procedure by sendingan uplink LLC frame of any type containing the MS's identity to the SGSN. Towardsthe SGSN, the BSS adds the BVCI and Cell Global Identity including RAC and LAC.(2) When the SGSN detects the cell change, it send a FLUSH-LL PDU to the old BVCto initiate the following procedure:

- at a cell change within one NSEI (e.g. one PCU represents one NSEI) andwithin one routing area, LLC-PDU(s) for a given TLLI stored at an "old" BVCI(corresponding to the old cell) are either deleted or transferred to a "new"

BVCI (corresponding to the new cell) with which the TLLI is currentlyassociated.

(3) In response to a FLUSH-LL PDU the BSS shall send a FLUSH-LL-ACK PDU to theSGSN containing:

- the TLLI received in the FLUSH-LL PDU and- an indication of whether the LLC-PDU(s) were "transferred" or "deleted". Incase the SDUs were "transferred" the BVCI (new) IE shall be included.

(4) Data transfer is continued in the new cell.


19/135


2.4.6 PDP context activation

The PDP context contains necessary information for GPRS data service like PDPaddress, QoS parameter and so on, accordingly the PDP context has to be set up inboth MS and network via PDP context activation procedure before data packet can betransferred.

PDP context activation can be initiated by either GGSN or MS depending on whetherthe first data packet transfer request comes from in downlink or uplink direction. TheMS initiated PDP context activation process is shown in chart below:

Create PDP Context Request

(PDP Type, PDP Address, TID, ...)

Activate PDP Co ntex t Accep t

(PDP Type, PDP Address, TI, ...)

Acti vate PDP Co ntex t Reques t

(NSAP I, TI, PDP Type, ... )

Security Functions

BSS

SGSN GGSN

MS

Create PDP Context Respon se

(TID, PDP Address, ... )

Create PDP Context Request

(PDP Type, PDP Address, TID, ...)

Activate PDP Co ntex t Accep t

(PDP Type, PDP Address, TI, ...)

Acti vate PDP Co ntex t Reques t

(NSAP I, TI, PDP Type, ... )

Security Functions

BSSBSS

SGSN GGSN

MS

Create PDP Context Respon se

(TID, PDP Address, ... )


20/135


2.5 GPRS radio network

With the introduction of GPRS into the GSM network, the radio network hasintroduced a lot of new terms, features and procedures even though there is not

much hardware changes in the radio network. These new functionalities arecompletely different from the traditional ones of circuit switched services becausethey are adapted to be suitable to the packet data service characteristics.In order to understand better the GPRS data service and GPRS network, it is quiteimportant and useful to get more knowledge of the GPRS radio network. Moreover,the GPRS radio network optimization is a dispensable part of the overall GPRSnetwork optimization.

2.5.1 GPRS Um interface

In the GPRS radio network, the involved interfaces and protocols are shown in chartbelow:

L L C

R L C

M A C

G S M R F G S M R F

R L C

M A C

U m

M S B S C

G S M R F L 1 b i s

A b i s

B T S E

L L C

t ra n s m i s s io n

t o S G S N

The main functions of the protocol layers are:

GSM RF: The GSM RF is the physical radio channel used to transfer packetdata.

MAC: The Medium Access Controlprovides the access to the physical radioresources. It is responsible for the physical allocation of a packetdata channels (PDTCH).

RLC: The Radio Link Control layer provides a reliable link over the air

interface that fits the block structure of the physical channel.Therefore it segments and re-assembles the LLC frames.Additionally, it performs a sub-multiplexing to support more thanone MS by one physical channel and the channel combining toprovide up to eight physical channels to one MS.

LLC: The Logical Link Controllayer provides a logical connection betweenMS and SGSN even if no physical connection is established and thelogical connection is identified by TLLI(Temporary Logical Link


21/135


Identity). The physical connection is set up by RLC/MAC layer whenthere is data to transmit.

The MAC provides the establishment of a Temporary Block Flow (TBF), which is aphysical connection between one specific MS and the network to support theunidirectional transfer of LLC Packet Data Units on packet data physical channels.

TBF is an allocated radio resource on one or more PDCHs and comprises a number ofRLC/MAC blocks carrying one or more LLC PDUs. A TBF to/from the MS is maintainedonly for the duration of the data transfer. When the data transfer is finished, the TBFshall be released and the radio resource shall be reserved for further allocation.

Each TBF is assigned a Temporary Flow Identity (TFI) by the network. The TFI isassigned in a resource assignment message and will be stored in the first octet of theRLC/ MAC blocks. The importance of the TFI can be understood when considering themultiplexing of more MSs on the same PDCH.

On uplink direction, GPRS radio network uses USF(Uplink State Flag) to controlthe multiplexing of different MS on uplink PDCH to prevent collision on uplink channel:Uplink state flag (USF) sent from the Packet Control Unit (PCU) is included in the

header of each RLC/MAC block on a downlink PDCH. The MS monitors the USFs onthe allocated PDCHs and transmits Radio Blocks on those, which currently bear theUSF value reserved for the usage of the MS.

The RLC/MAC has two working mode: Acknowledged mode and Unacknowledgedmode. The transfer of RLC data blocks in the RLC acknowledged mode usesretransmissions of RLC data blocks. The transmitting side numbers the RLC datablocks via the block sequence number (BSN). The BSN is used for retransmission andfor reassembly. The receiving side sends PACKET Ack./ Nack messages in order torequest retransmission of RLC data blocks.

As shown by the name GSM RF, the physical layer of GPRS radio network is the

same with the physical layer of GSM network on Um interface. But the channelcoding of GPRS Um interface is totally different from the channel coding of voicetraffic: 4 types of coding schemes (CS1,CS2,CS3,CS4) are used by GPRS radionetwork. The coding technical details of these 4 coding schemes are listed in tablebelow:

Scheme Code

rate

Radio

block

Coded

bits

Punctur

ed bits

Data

ratekb/s

Redun

dancy

CS-1 1/2 181 456 0 9.05 high

CS-2 2/3 268 588 132 13,4 middle

CS-3 3/4 312 676 220 15,6 low

CS-4 1 428 456 - 21,4 no

It can be seen that the higher coding scheme can provide higher data rate, whereasthe drawback is clear too: higher coding schemes (e.g. CS4) are more vulnerable topacket loss on the Um interface due to poor radio link quality because it has lessprotection and redundancy.


22/135


In other words, the GPRS data service can benefit from higher coding schemes onlywhen the radio link quality (e.g. higher radio C/I ) is good enough. If the radiocondition becomes worse (for instance lower radio C/I), the higher coding schemewill have high BLER(Block Erase Rate) and retransmission always take place inacknowledged mode. Consequently, the data rate of higher coding scheme might beeven lower than the one of lower coding schemes.

2.5.2 GPRS radio network features in BR7

Siemens BSS network starts to support GPRS service from SBS BR5.5, but the GPRSnetwork of BR5.5 works with quite limited GPRS functions. For example, in BR5.5GPRS radio network supports only coding scheme CS1 and CS2.With the introduction new SBS release, GPRS functions have been enhanced andGPRS performance has been improved as well. In the following contents, some newGPRS radio features brought by BR7 will be introduced briefly.

Support of CS3/CS4 and EDGE

The reason why CS3/CS4 is not supported in previous release is that: CS3 and CS4needs more than 16kbps transport capacity on the Abis interface while the previousrelease network can provide only 16 kbps Abis transport channel. Consequently, CS3and CS4 implementation is only possible when new transport mechanism on Abisinterface is realized.EDGE (Enhanced Data Rates for the GSM Evolution) brings higher data rates (up to60kbps) by introducing 8PSK modulation to the GSM RF. Apparently the traditionalAbis 16Kbps bottleneck must be broken in order to support EDGE.

Thanks to the new Abis channel control feature FAAS , Siemens GPRS radionetwork is able to support GPRS coding scheme CS3, CS4 and EDGE starting from

BR7.

FAAS

The Flexible Abis Allocation Strategy (FAAS) is introduced to allocate the Abisresources in a more flexible way. Without FAAS, one radio timeslot is staticallyassociated to one 16Kbps Abis subslot (terrestrial traffic channel). The Abis subslotsare configured by O&M procedures and stored into BSC database. While for voice andGPRS coding scheme CS1 and CS2 each time slot on the air interface is assigned afixed 16 kb/s Time Slot on the Abis interface. With the introduction of coding schemeCS3 and CS4 (and EDGE coding schemes), characterized by data rates with morethan 16 kb/s on the air interface, may require up to 5x16 kbit/s Abis capacity inorder to transport an RLC/MAC radio block via the Abis interface. In this case a static

Abis allocation would be highly inefficient.

Hence Flexible Abis Allocation Strategy is introduced to allocate the appropriatenumber (one or more than one) of Abis 16kbps timeslots according to the servicerequirement. As soon as the radio timeslot is released the allocated Abis resourcesare set free again to Abis resource pool. In order to allocate more than one Abistimeslots for one radio timeslot, a new format of PCU frames, concatenated PCUframe, is introduced.


23/135


The number of used concatenated PCU frames depends on the coding scheme usedfor radio block transmission: for GPRS when using the coding scheme CS1, a singlePCU frame is needed, while the other coding schemes (CS2, CS3, CS4) require twoconcatenated PCU frames.

In general the FAAS feature can improve the Abis resource efficiency by applying

Abis channel dynamic allocation and reuse with the concept of abis pool. Accordinglythe network operator can save costs for abis transmission especially when the higherGPRS coding scheme or EGPRS coding scheme is applied.

Link Adaptation

The Link Adaptation algorithm is performed dynamically in order to select the codingscheme that best suits a certain radio condition of the air interface. The switchingpoints are determined via appropriate BLER measurements. The principles and theadvantage for switching to a more robust coding scheme will be illustrated in thefollowing example for the switch between GPRS CS-1 and CS-2.The figure shows, that an optimal data throughput can be achieved, if the system

switches on the switching point =. Let us assume that currently the system workswith CS-1. In case of improved radio conditions there is a switch to CS-2. In theother versus, if system works with CS-2, in case of worse radio conditions thesystem switches back to CS-1. Theoretically a switch (up or downgrade) exactly at= would give the best overall performance. However in reality this could result in aunstable systems behavior and so a hysteresis can be configured for the switchingpoints.

As C/I values are difficult to estimate in a real network, the Link Adaptation

algorithm is based on BLER measurements. Once the connection is established theblock error rate (BLER) is continuously updated by checking if RLC blocks have beentransmitted faultlessly. The ratio of repeated blocks versus the number oftransmitted blocks in total is calculated.The goal of Link Adaptation is throughput maximization: The data transmission isstarted with an initial coding scheme set by the O&M. In case of bad conditions(noise, fading, interference) a more robust coding scheme is chosen soon. Ifconditions improve later on an upgrade of coding scheme (following therecommendations) is performed.


24/135


2.6 Gb interface

The Gb interface connects the BSC to the SGSN, transferring signaling informationand user data. Several BSCs may be interfaced to one SGSN on the Gb interface.

The main characteristics of the Gb interface are:

a) resources are given to a user upon activity (when data is sent or received) andthey are reallocated immediately thereafter; this is in contrast to the A interface,where a single user has the only use of a dedicated physical resource throughout thelifetime of a call, irrespective of activity;b) GPRS/EGPRS signalling and user data are sent in the same physical channel. Nodedicated physical resources are required to be allocated for signalling purposes (likee.g. the A interface where SS7 links are used to transmit signalling between the BSCand the MSC).The protocol stack of the Gb interface is shown in chart below:

LLC Relay

MAC

RLC

New TRAUframe L1

NS

BSSGP

L1

NSL2

L1

GTP

SNDCP

LLC

BSSGP

BSC/PCU SGSNGb

The various layers of Gb interface realize the following functions:

NetworkService The Network Service (NS) performs transport of NS Service Data Units

(SDU) between the SGSN and BSS. The Gb interface is based onFR(Frame Relay) as specified in GSM 08.16. FR supports high rate datatransmission with low delay. Frames of different sizes may betransmitted. FR performs congestion control and error detection,however error correction is not supported.

BSSGP Primary functions of the Base Station Subsystem GPRS protocol(BSSGP) are providing connection-less link between the SGSN and BSS

(layer 2 level), providing tools for bi-directional control of the data flowand handling paging requests from the SGSN to the BSS.

LLC The Logical Link Control layer (LLC) provides logical links between anMS and a corresponding SGSN. The transport of both data andsignalling is supported.

SNDCP SubNetwork Dependent Convergence Protocol (SNDCP) supports adirect peer to peer (i.e. point-to-point) communication between an MS


25/135


and a SGSN. User data is transported from a network layer protocol,e.g. IP or X.25.

2.6.1 Gb physical connection

In principle four types of configurations are possible in connecting the GPRS entitieson the Gb interface:

1. a direct line (e.g. PCM30) between the two entities (static and permanentphysical point to point connections);

2. an intermediate frame relay network;3. Nailed Up Connection (NUC) through the MSC via a frame relay network;4. NUC through MSC, without using an intermediate frame relay network.

In the early phase of GPRS network implementation, NUC connection had beenadapted by operators because NUC is cost effective by taking advantage of existingtransmission resource. The negative impact of the NUC is its limited bandwidth andlong delay. For commercial use of GPRS the direct connection is recommended whichcan provide larger bandwidth and improve GPRS network performance to someextent.


26/135


2.7 GPRS core network

General architecture of GPRS core network will be introduced in this chapter.

2.7.1 SGSN architecture

In general, the SGSN architecture must be able to provide single as well as combinedSGSN entities both in combination with the Circuit Switched System. The followingentities are required for PO2.0/2.1:

2G-SGSN entity only 3G-SGSN entity only combined 2G/3G-SGSN entity

All these entities are derived from a common architecture with a minimum set ofdifferent configurations. However in chapter only the general architecture of 2G-SGSN will be introduced.

The 2G SGSN is the Serving GPRS Support Node in GPRS and handles beside othersthe mobility of the subscribers and radio related protocol toward the mobile station.The system functions of the 2G SGSN are structured in functional areas as shownbelow.

Figure 1 2G-SGSN System Functions / Functional Areas

The functional area Packet Handling contains the functions:Packet Routing and Transfer

Sub-network Dependent Convergence (SNDCP) Logical Link Control (LLC) including ciphering Flow Control Overload Control GPRS Tunnelling Protocol (GTP) Buffer Management on MP Message Handler MP-SP Protocol (MSP) Yet Another Tunnel Protocol (YATP)

2G-SGSN

Packet Handling

Mobility

Management

Session

Management

Interception

Handling

Configuration

Management

SMS HandlingProtocol

&

Interfaces

Performance

Management

Fault & Maintenance

Management

Acc oun tin gResource

Management

Handover Control CAMEL

Handling


27/135


The functional area Mobility Management contains the functions: Mobility Management (including security functions and paging) SGSN Location Register (SLR) GTP-MAP conversion

The functional area Session Management contains the functions: PDP Context Handling

Subscription Check Network Facility Check Context Table

The functional area Resource Management contains the functions: management of internal resources for admission control management of packet flow contexts

The functional area SMS Handling contains the functions: SMS handling in SGSN

The functional area Handover Control contains the functions: SGSN change handling

The functional area Accounting contains the functions: Accounting Management Charging Collection Record formatting for accounting and interception Support of a centralised as well as distributed charging gateway

The functional area CAMEL Handling contains the functions: PrePaid Service VPN Service for SMS and Change of APN

The functional area Interception contains the functions: Interception Management Interception Data Base (IDB) Delivery of interception related data and interception products

The functional area Configuration Management contains the functions: Configuration Management Security Management

The functional area Performance Management contains the functions: Performance Management

The functional area Fault & Maintenance Management contains the functions: Interface to System Maintenance Interface to other maintenance areas, e.g. Trunk/Line Maintenance and SS7

Maintenance Central GPRS maintenance functions, e.g. audit framework, alarming

framework error handlingThe functional area Protocols and Interfaces contains the functions:

Gb Interface including BSSGP Gr Interface including MAP Gn Interface including IP and related protocols Gd Interface including MAP

Gs Interface CAP Interface SS7, SCCP, TCAP, including MAP service provider

The following figure shows the general architecture of the 2G-SGSN. it is derivedfrom the general node GSN.


28/135


Figure 2 General 2G-SGSN Architecture(unused parts of the SGSN architecture shadowed)

First it consists of the SSNC common part which covers the basic functions like SS7handling (MTP, SCCP) and accounting management (charging collection) and may beshared with the circuit switched part. Second there is the SGSN specific core part ofthe SSNC hosting the functions packet routing, session management, mobility

management, resource management, interception handling and CAMEL support forPrePaid services. Last but not least the inter-connection toward the external worldwith respect to the traffic channel is represented by two XP140 each serving the twointerfaces Gb and Gn. The XP140 covers also the interface specific protocol handling(BSSGP and GTP). Whereas Figure 2 shows the general architecture of the SGSN,Figure 3 depicts the architectural approach with respect to the Gb side of the SGSN.

The main constraint, which influences the architecture, is the distribution ofsubscribers to MP:PD/SH as well as the flow control function on the Gb interface. Tosolve this issue the approach of the cluster solution is used where one or moreMP:PD/SH serves a certain area which covers one or more routing areas entirely. If asubscriber enters the SGSN area his/her context will be assigned to one of theMP:PD/SH serving the originating routing area. As long as the subscriber roams

inside the area which is served by the current cluster the context will be hold on theselected MP:PD/SH which was selected first. Otherwise, if the subscriber leaves thisarea but still roams within the SGSN area his/her context will be migrated to anMP:PD/SH of the cluster which serves the new area. Because each MP:PD/SH of onecluster must operate all cells of the served area it must be able to handle the flowcontrol inside the cluster in a co-ordinated way between all MP:PD/SH of the cluster.It is assumed that a cluster size of three MP:PD/SH will be the upper limit due to co-ordination effort. In PO2.0/2.1 a cluster size of one is used because the expected

sSGSN

Xp140XP140

LIC:*SP:GTPSP:GTP LIC:*

MP:PD/SHMP:PD/SH

SP:BSSGPSP:BSSGPLIC:FRLIC:FR/*

SSNC

Gn interfaceGb interface

MP:MMMP:MM MP:RANAPMP:RANAP

Iu interfaceGr/Gd/Gs/Ge interface

MP:OAM

O&M interface (Q3, SNMP)Interception interface

MP:ACCMP:ACC

MP:SM LIC:E1(SS7) MP:SLTLIC:ATM

(SS7 + Traffic)LIC:ATM

(SS7 + Traffic)MP:SLTLIC:E1

(SS7)

Legend

light blue

light red

light yellowSSNC parts

XP140 parts

atomic functionrunning on a specifichardware platform

dottedborder

continuousborder

packet oriented systemspecific software parts

software parts which may be sharedby the ciruit switched system

traffic path

signalling path

MP:ACCIO(OAM dependent)

YATP YATP

MSP MSP

Ga/charginginterface

MCP


29/135


traffic of one routing area is lower than the performance (throughput) of oneMP:PD/SH.

Figure 3 SGSN Cluster Solution

2.7.2 GGSN architecture

The Gateway GPRS Support Node is the node which interworks with the external IPnetwork. The GGSN is structured in functional areas as shown below.

Figure 4 GGSN System Functions / Functional Areas

The functional area Packet Handling contains the functions: Packet Routing and Transfer Overload Control GPRS Tunnelling Protocol (GTP)

MP:PD/SH MP:PD/SH MP:PD/SH

MP:MM

area 1 area 2 area n

GGSN

Packet Handling

Session

Management

Configuration

Management

Protocol

&

Interfaces

Performance

Management

Fault & Maintenance

Management

Accoun ting

Resource

Management


30/135


Message Handler MP-SP Protocol (MSP) Yet Another Tunnel Protocol (YATP)

The functional area Session Management contains the functions: PDP Context Handling Network Facility Check

Context TableThe functional area Resource Management contains the functions:

mapping of QoS parameters management of internal resources like processor performance

The functional area Accounting contains the functions: Accounting Management Charging Collection Record formatting for accounting Support of a centralised and distributed charging gateway

The functional area Configuration Management contains the functions: Configuration Management Security Management Software Management

The functional area Performance Management contains the functions: Performance Management

The functional area Fault & Maintenance Management contains the functions: Interface to System Maintenance Interface to other maintenance areas Central GPRS maintenance functions, including error handling

The functional area Protocols and Interfaces contains the functions: Gi Interface including IP and related protocols Gn Interface including IP and related protocols Ga Interface including IP and related protocols

Figure 5 below shows the general architecture of the GGSN.

First it consists of the XP140 part which covers the functions like sessionmanagement, remote access server functions, accounting management (chargingcollection) and the interfaces to the GPRS backbone network as well as the externalIP network. Second there is an OEM part which covers the Accounting File Server(AFS).The GGSN provides interworking with external IP networks. It may serve one ormore ISPs or corporate IP networks with possible overlapping IP address spaces.One SP:ISP is able to serve different external IP networks and one external IPnetwork may be served by one or more SP:ISPs.


31/135


Figure 5 GGSN Architecture

Since GR3.1c, a new IP router based GGSN solution (CPG-3200, CPG-3300) isintroduced with Cisco router.

Fig. Core PO release structure

Detailed information about Cisco GGSN will be provided in later versions of thishandbook.

sGGSN

36140XP140

LIC:*SP:GTPSP:ISP LIC:*LIC:FRLIC:*

OEM

Gi interfaceGn/Ga interface

O&M interface (SNMP)

Legend

light blue

light red

light yellowOEM parts

XP140 parts

atomic functionrunning on a specifichardware platform

traffic path

signalling path

charginginterface

MCP

SP:GTPSP:GTPYATP

AFSAFS

MSP

MSP


32/135


2.7.3 GSN Hardware components capacity assumptions

For the GSN hardware configurations the following assumptions are done: the ASNcompact (5Gbit/s) is available including a new shelf the MPU-D is available for PO2.0, while the MPU-E is available for PO2.1 MP-OAMD (MP:ACCIO) can be used for charging data storage and IO

processing from PO2.1 on 2 port STM1 LIC available for XP140

The following performance figures are used as base for the hardware configuration.Note, that throughput values are given for an average value of 300 byte packet sizeaccording to the PO traffic model (Sysload 1), while larger values given in bracketsindicate throughput at 600 byte average packet size (Sysload 2).

Component Performance PO2.0 Performance PO2.1

with MPU-D with MPU-E

MP:MM (including CAP) 150.000 subscriber 230.000 subscriber

MP:PD/SH for UMTS 100.000 subscriber110.000 sessions

100.000 subscriber80.000 sessions

MP:PD/SH for GPRS about 3 Mbit/s (6 Mbit/s)

50.000 subscriber55.000 contexts

about 6 Mbit/s (12 Mbit/s)50.000 subscriber55.000 contexts*

MP:RANAP 150.000 subscriber1.600 MSU/sec

300.000 subscriber3.200 MSU/sec

MP:SLT 250.000 subscriber 250.000 subscriber

SP:BSSGP 22 Mbit/s (45 Mbit/s) 22 Mbit/s (45 Mbit/s)

SP:GTP(2G-SGSN & GGSN)

100.000 subscriber30 Mbit/s (60 Mbit/s)


SP:GTP(3G-SGSN)

100.000 subscriber18,5 Mbit/s (37 Mbit/s)


* 39.000 contexts with IP header compression


33/135


3 GPRS parameters in BSC database

In addition to new added GPRS related hardware modules, BSC database has to beupdated with new GPRS related objects in order to enable GPRS function in the

network.In BSC database, the new GPRS objects are PCU, PTPPKF, FRL and so on. Underthese objects, there are many new GPRS control parameters.Some old database objects, such as TRX has to include new parameters with theintroduction of GPRS functionality.

3.1 SBS Database structure with GPRS related objects

Based on Siemens SBS BR7, all the GPRS new and related database objects areshown below in an object-tree structure:


34/135


3.2 Introduction of GPRS radio parameters

In this chapter, main GPRS radio parameters concerned by optimization will beexplained briefly based on their functional groups.Please be noted that the existence and definition SBS database parameters are

closely related with the SBS software release versions, i.e. their existence andmeaning may vary in different releases. The introduction in this chapter will base onBR7. For complete information about SBS database parameters, please refer toofficial BSC Database Parameter Description.

3.2.1 GPRS channel configuration parameters

For packet switched service, four basic Packet Data Logical Channels have beenintroduced:

Packet Broadcast Control Channel (PBCCH) Packet Common Control Channel (PCCCH) Packet Data Traffic Channel (PDTCH) Packet dedicated control channels (PTCCH and PACCH)

Accordingly the GPRS channel configuration can be divided into two parts: controlchannel and traffic channel (PDTCH).In the early phase of GPRS deployment, there is normally no dedicated GPRS controlchannel PBCCH and PCCCH, which means that the GPRS control message (likesystem information) has to be sent within the old GSM control channel (like BCCH).The first reason of no PBCCH/PCCCH is to save radio resource consumed by GPRSwhen GPRS traffic was still too low in early phase; The second reason is that the oldGPRS mobile phones mostly dont support PBCCH and they cant work properly in

case of PBCCH existence.Following table lists the main parameters for GPRS control channel configurations.

Object/Package

DB Name Range Meaning

CHANNEL GDCH 1 ... 3GPRSPBCCH,GPRSPCCCH,Null

Is used to control if the channel isconfigured to carry dedicated controlinformation for GPRS

PTPPKF BSPBBLK 0 .. 3 Indicates the number of blocksallocated to the PBCCH in the multi-frame


35/135


Basically the GPRS traffic channel (PDTCH) configuration in radio cells shall base onthe data traffic volume and circuit-switched traffic load; Furthermore the PDTCH isdivided into reserved GPRS channel or dynamic GPRS channel.Reserved GPRS channel means that the channel is reserved for PS traffic only so thatnew CS channel request will be rejected if all the channel except reserved PDTCH areoccupied. The reserved PDTCH is used to guarantee the radio channel availability for

GPRS data service.Comparatively the dynamic PDTCH can be assigned on demand for either by PS orCS traffic. If the PS call ends in dynamic PDTCH, this PDTCH shall be released soonand be ready to be used for either PS or CS.Moreover, in BR7 GPRS channel allocation is based on Automatic Horizontal/VerticalAllocation and its controlling parameters shall be well considered during GPRSchannel configuration.

Following table lists main parameters of GPRS traffic channel configuration:

Object/

Package


TRX GSUP 0..1False/True

This attribute indicates if the GPRSservice is supported or not.

PCU TEMPCH

Timer EmptyChannel

1..254 sec.

Default: 90sec.

Specifies the time for releasing PDTCH ifno activities are done. This timer shouldprevent a faster PDTCH channelallocation/ release that can increase TDPCload

PTPPKF GPDPDTCHA 0...100;Default = 30

It indicates the percentage of availablechannels dynamically dedicated by thesystem to GPRS traffic.

PTPPKF GMANPRES 0 190

Default = 0

Maximum Number of Packet channel

reservedPTPPKF GASTRTH-

HV0...100;Default = 10

Defines the percentage of idle channel inthe cell in order to trigger the switchbetween horizontal and vertical allocation.

PTPPKF GASTRTH-VH

0...100;Default = 20

Defines the percentage of idle channel inthe cell in order to trigger the switchbetween vertical and horizontal allocation.

PTPPKF GASTRTH-EU

0...100;Default = 20

Threshold Idle Channel EU - indicates thethreshold over which the upgrading ofradio resources is enabled..

3.2.2 Coding scheme and Link Adaptation parameter

The induction of CS3 and CS4 in BR7 makes it possible to reach much higher datarate over air interface than before. On the other hand, CS3 and CS4 require muchbetter radio link quality (radio C/I) than before. As the result, in order to optimizethe coding scheme utilization and finally get real higher data rate for GPRS, the


36/135


parameter of controlling coding schemes and link adaptation must be carefullyoptimized based on the radio quality of the target live networks.The coding scheme and link adaptation parameters are listed in table below:

Object/

Package


PTPPKF INICSCH CS-1, CS-2, CS-3,CS-4Default = CS-2

Indicates the coding scheme to beused when the packet transferstarts

BSC CSCH3CSCH4SUP FALSE, TRUE It enables/disables the CS3/CS4support at BSC level

PTPPKF CSCH3CSCH4SUP FALSE, TRUE It enables/disables the CS3/CS4support at cell level

PTPPKF ELKADPT FALSE, TRUE Enables or disables Link Adaptationalgorithm.

PTPPKF INIBLER PER10, PER20,

PER30, PER40,PER50, PER60,PER70, PER80,PER90

Defines the initial BLER estimation

in a cell to be used in ResourceManagement to calculate the initialnumber of radio resources to beassigned to packet services whenno 'historical' information aboutBLER is available.

PTPPKF BLERAVEDL UNIT025,UNIT050,UNIT100,UNIT150,UNIT200,UNIT250,

UNIT300,UNIT350,UNIT400(unit= radioblocks)

Specifies the filtering period forBLER calculation in downlink(expressed in number of radioblock, one radio block = 20ms)

3.2.3 GPRS feature parameter

In order to take full advantage of the new features and finally keep the GPRS

network in optimum status, all feature related parameter must be set properly,otherwise the feature implementation might not naturally and surely lead to thenetwork performance improvement.

Besides the Automatic Horizontal/Vertical Allocation and Link Adaptation featuresthat have been mentioned already, there are still many more GPRS features in SBS:

FAAS (Flexible Abis Allocation Strategy) NCCR (Network Controlled Cell Reselection) Downlink TBF Delay Release


37/135


Forced Intracell Handover GPRS Resource Management

Part of the GPRS feature related parameters used in optimization are listed in tablebelow:

Object/Package


BSCB ENFOIAHO TRUE, FALSE

Default = FALSE

The parameter enables Forced IntracellHandovers which are used to moveCircuit Switched Calls to other freetimeslots in the same cell in order to getadjacent timeslots for GPRS.

PCU TIMEDTBFREL 0..49 (100msecstepsize)Default: 15

Time delay TBF release. This attribute isused to delay the release of a DLTemporary Block Flow (TBF).

BSCB CPOLICY Default =NO_PREFERENCE

Specifies the BSC channel allocationpolicy when different services arerequired.

BSCB DGRSTRGY Default =NO_DOWNGRADE

Defines the downgrade strategy forHSCSD and GPRS calls used during theresource reallocation procedure for TCHrequests for single-channel circuitswitched calls.

BTSM GASTRABISTH Default:thresholdIdleAbisHV = 10

thresholdIdleAbisVH = 20thresholdIdleAbisSU = 0thresholdIdleAbisRU = 10

Control the switch from/tovertical/horizontal allocation strategyand the stop/restore of Abis upgrading

due to Abis scarcity.It is composed of four fields.

BSCB UPGRFREQ Default:Uplink = SEC1Downlink = SEC1

Controls the time to pass between twoconsecutive radio resource upgradeattempts for packet services separatelyfor the uplink and the downlink in stepsof 1 second.

BSCB NCRESELFLAG ENABLE, DISABLEDefault =DISABLE

Determines whether GPRS networkcontrolled cell reselection is enabled ordisabled.


38/135


PTPPKF CRESELTRHSOUT

50 100(unit= %)Default = 85

Cell RESELection ThReSHold OUTput -defines the % of 'occupation' threshold:when the number of active GPRS mobileis over this value, the networkcontrolled cell reselection procedure canorder gprs mobiles to reselect another

cell until the number of GPRS activemobile is again under the threshold.

3.2.4 RLC/MAC parameter

In the RLC/MAC layer, there are some timers and parameter to control the TBFrelated procedures. In some cases, these timers and parameter might be tuned tooptimize the TBF procedure on RLC/MAC layer.

Part of the timer and parameters are listed in table below:

Object/Package


PCU T3191

On network side

1 to 30 sec.

Default: 5sec.

This timer defines the waiting timefor reuse of the TFI and USF afterhaving sent the last RLC block

PCU T3193 1 to 42

Default = 4

This timer defines the waiting timefor reuse of TFI after reception of thefinal Packet Downlink Ack./Nack.from the MS.

PCU N3105

Counter onNetwork side

1..255

Default: 10

This parameter implements the

threshold for not received RLC/MACcontrol message from the MS aftersending a RRBP field on downlink. Ifthis threshold is reached, thecommunication with the associatedMS is broken

PTPPKF BSCDVMA 1..15

Default: 15

This parameter represents the valueof timer T3198, at MS side,expressed in number of RLC blocks

PCU N3103

Counter onNetwork side

1..255

Default: 10

This parameter implements the

threshold for not received PACKETCONTROL ACK as answer of thePACKET UPLINK ACK/NACK. In casethis threshold is reached, thecommunication with the associatedMS is broken.


39/135


PTPPKF PKTNDEC 0..7

Default:2

This parameter defines the number ofdecrement for counter N3102performed if the T3182 expireswithout reception packet UplinkACK/NACK. It is used for RLC layer atMS side.

PTPPKF PKTNINC 0..7

Default:2

This parameter defines the number ofincrement for counter N3102performed after receiving packet ULACK/NACK. It is used for RLC layer atMS side.

3.2.5 Other parameters

Besides the parameters mentioned in above chapters, there are still many moreparameters directly or indirectly related to GPRS radio performance. Especially some

parameters are also involved in GSM voice network optimization because the GPRSdata and GSM voice traffic in fact share the same radio network.In order to give brief hints on these parameters, some introduction are given belowfor reference:

Cell reselectionGPRS MS uses cell reselection procedure other than handover procedure when itmoves around in the radio network. Without NCCR and PBCCH, the GPRS cellreselection is similar with the normal cell reselection procedure (C1,C2 algorithm) asvoice MS in the GSM network. The only difference is that theCellReselectionHysterisis needs to taken into account in CellUpdate of GPRS while inGSM voice MS it works only in the location update procedure.In case of PBCCH presence in GPRS network, there will be much more GPRS

dedicated control information broadcasted in PBCCH and the new GPRS cellreselection algorithms CS31 and C32 might be applied by lots of other newparameters.

Radio coverage tuningRadio coverage is the fundamental basis for everything of the GSM network,accordingly the radio coverage enhancement or tuning is very important to radionetwork performance. As for GPRS, the aim of radio coverage optimization is toprovide sufficient signal level for GPRS MS and furthermore manage the radiocoverage in an optimum way to avoid chaotic radio signal overlapping, which willcause unnecessary ping pong cell reselection.The radio coverage tuning is mainly related to the base station power parameters,cell access parameter and other antenna physical parameters.

Radio network qualityRadio network quality is always one of the main targets of network optimizationbecause radio network quality is important to both voice quality and GPRS datathroughput. On the other hand, radio quality optimization is certainly a complicatedand systematic work, which might involve a lot of efforts, e.g. internal and externalinterference reduction, radio coverage control, hardware malfunction removal.


40/135


Consequently the radio quality optimization is always part of the GPRS optimizationwork and the traditional optimization methodology for GSM voice optimization shallbe carried out.

3.2.6 Recommended GPRS radio parameter settings from TAC3

For each SBS release, TAC3 issues Recommendations for GPRS/EDGE relatedParameter settings in BRxx. Updates can be found on IMS folder: GERAN dataservice.The complete path on IMS:Enterprise | ICM | ICM N | Products & Solutions | Technical Support | Mobile RadioNetwork | GERAN | GERAN_Feature and product description | Data services

Here we will attach the document for recommendations for BR7.0:

GPRS_Par amet er _Set t i ngs_f or_BR7. 0.

4 Introduction of GPRS radio performance measurements

4.1 General concepts

Performance measurements are essential for the surveillance of a mobile network.They provide information about:

The availability of network resources Traffic behavior and load Quality of Service

These information can be used to identify failures and problem zones within thenetwork which are not detected by fault management. This helps also to optimizeand extend the existing network.

Each measurement taken alone only gives elementary information. However,combined with other measurements and together with additional information (e.g.alarms or configuration data), they provide valuable overall information about whatis going on in the network.

The Siemens Base Station (SBS) provides a set of performance measurements fornetwork surveillance. These measurements are partly compliant to GSM 12.04,

partly Siemens proprietary. The measurements can be grouped into severalcategories as follows:


41/135


Fig. Categories of SBS Performance Measurements

As part of the SBS performance measurements campaign, the introduction of GPRShas brought new GPRS performance measurements counters. Since BR7.0 thenumber of GPRS related counters has been greatly enlarged which gives the GPRSradio optimizers much more possibilities to quantify the GPRS radio networkperformance.


42/135


4.2 Structure of Scanners

The processes which accumulate data and assemble it for collection and inspectionare called measurement jobs or shortly, scanners. Each scanner will collect dataat a particular frequency known as the granularity of the measurement.

The scanners have following structure:

Every measurement job (scanner) consists of one or more measurement types. The measurement type(s) contained in a scanner may apply to one or more

network resources of the same type, e.g. a measurement job may be related toone or several BTSs.

A measurement type has a fixed number of counters, there are precisely definedtrigger events for a counter.

Following picture gives the structure of scanners:

Fig. Scanner structure

According to their nature, different measurement types can be subdivided intodifferent administration groups or we can say, object classes. The administrationgroups of BR7.0 is given below in the table below:

Object Class

Counter

Measurement type

...Counter

Counter

Measurement type

...

Counter

...

Counter

Measurement type

...

Counter

Counter

Measurement type

...Counter

...

...

Object Class


43/135


Tab. Overview of administration groups of BR7.0

GPRS related performance measurements counters in BR7.0 are categorized intofollowing groups: packet channel configuration, packet flow establishment, active

packet flow, packet flow release, Gb interface and cell reselection. Moreover theprocessor measurements provide the PCU load statistics.

Fig. GPRS related performance measurements


44/135


4.3 SBS optimization work flow of performance measurement

The following flow chart gives a general work flow of SBS performance measurementwhich is commonly followed by SBS optimization engineers.

To complete procedure 1 to 5, we need to operate the BSC via Radio Commander,there are two basic approaches for operating Radio Commander:

- Working under RC GUI- Executing CLI scripts

Radio commander GUI offers user-friendly graphical approach for OAM operations,which is suitable for simple and less numbered tasks. CLI (Command Line Interface)offers Unix based interface for executing so called CLI commands, which is suitablefor advanced and large numbered tasks, such as a batch task.

Create scanner

Exportingmeasurementdata into ASCIIfile

Modifyscanner ifnecessary

Import ASCII

measurementfiles and BSC

databases into

BATRANA2004

Analyze SBSperformance

withBATRANA2004

1

2

4

6

7

Upload BSC databaseand convert it toASCII file by DBAEM.

5

Uploadingmeasurementdata (Automaticor Manual)

3


45/135


For detailed information about step 1 to 5, please refer to BSC or RC operationmanual, step 6 and 7 will be explained in chapter 7.2: GPRS radio measurementanalysis with Batrana2004.

4.4 Main GPRS radio network performance KPIs (Based on BR7)

In BR7 there are much more GPRS performance counters available and thereforeGPRS KPIs can be more abundant than earlier releases. For simplicity andcompleteness, here we will simply insert > issued by Network Engineering.Please refer to chapter 14 for GPRS related KPIs.

KPIs_SBS_BR_7.p

It shall be aware that all available counters can be used in flexible ways to build upoperator or project specific KPIs in order to best match customers requirements andconcerns on network quality.

Other Reference Documents:

For detailed information about SBS counters and message flows, please refer tofollowing documents:

- PM:SBS Counter (A30308-X3247-L40-2-7618)- PM:SBS Message Flow, A30808-X3247-L41-2-7618


46/135


5 Introduction of GPRS core performance measurements

5.1 General concepts

Within the GPRS core network a main processor (MP) platform and a serverprocessor (SP) platform are distinguished. The MP platform provides for the corefunctions such as accounting, SS7, mobility management, session management,resource management and mobile related packet handling. It is managed by meansof the Q3 interface. The SP platform mainly controls the interconnection towards theexternal interfaces with respect to the traffic channel, and the required protocols forthese interfaces. It is managed by means of SNMP.

Performance management handles the count of events, administration ofmeasurement parameters and storage and transfer of measurement data. It is usedto monitor the load of the system, to detect problems with regard to erroneous orinadequate dimensioned system components or for statistical reasons.

MP platform:

On the MP platform we have the STATS functionality as a generic solution to theproblem of implementing performance management counters.

Every 15 minutes (the granularity period) the SGSN collects performance data fromits counters with respect to:

The system load The processor load The protocol load

Managed object classes and their attributes are used on the object-oriented interface(Q3) between the SGSN and the switch commander (SC) in the operations system(OS).

Before measurement data from the counters can be collected, the measurement jobsthat generate the required data must be activated in the SGSN. In object-orientedterms, this corresponds to the instantiation of managed objects that model themeasurement process.

As long as the measurement job is active, the measurement results are generatedevery 15 minutes. The results of each period are recorded in a report notificationthat is forwarded to a measurement log file in the SGSN. These measurementreports can then be transferred to the switch commander.

Packet-switched performance measurements are grouped in object classes. Theobject classes are called currentDatas from the STATS point of view. The followingfigure gives the structure of PM object classes implemented on the MP platform:


47/135


SP platform:

On the SP platform the STATS concept is not supported. All counters are defined inmanagement information bases (MIBs), and are handled in a de-central way by eachapplication. Every 15 minutes the switch commander reads all these variables usingSNMP. The main functions of performance measurement: administration, collectionand storage are carried out by the switch commander, which offers a graphical userinterface (GUI) that allows access to the combined CMIP/SNMP interface.

In general, the picture below shows the exact processors from which different typesof measurements are generated.


48/135


Note:MPU load types for PO: SM, SLT: SS7 HANDLING PD/SH: PACKET DISPATCHING AND SESSION HANDLING RANAP: RADIO ACCESS NETWORK APPLICATION PART MM/CAP: MOBILITY MANAGEMENT AND CAMEL

ACC: ACCOUNTING OAM, OAMD: O&M FUNCTIONS (ACCOUNTING IN OAMD)

MP:OAM is also known as MP:SA

5.2 Performance data handling

In the figure below, it can be seen that measurements are started from SwitchCommander and collected later via different interface protocols by the SC with PDC(Performance Data Collector) application.

The PDC is responsible for Fetching measurement data from the defined NE Editing the collected data (e.g. insert counter names) Form a unique output design for all types of measurement

The measurement files are now ready on the SC to be copied for post-processing.Transfer the files to your PC via LAN, USB hard disk, etc. You can easily check the

correct format of the file after transferring to your PC, the file must be readable in anormal text editor and must not contain any unreadable characters.

Example of a SSNC/SGSN raw file format:

HEADER;vcpuCurrentdata;26;EWSDV13; ;0;SCANNER;;0;vcpu00mpTotalAverageLoad;vcpu00mpTotalMaximumLoad;vcpu01SystemIntegrityAverageLoad;vcpu01SystemIntegrityMaximumLoad;vcpu02sltPrhAverageLoad;vcpu02sltPrhMaximumLoad;vcpu03oamAverageLoad;vcpu03oamMaximumLoad;vcpu04ca


49/135


llpAverageLoad;vcpu04callpMaximumLoad;vcpu05SystemUpgradeAverageLoad;vcpu05SystemUpgradeMaximumLoad;vcpu