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Page 1: 59844688 Abis Dimensioning

Abis EDGE Dimensioning

DN7032309Issue 4-0 en25/03/2008

# Nokia Siemens Networks 1 (31)

BSC3153Nokia GSM/EDGE BSS, Rel. BSS13, BSC andTCSM, Rel. S13, Product Documentation, v.1

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The information in this document is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This documentation is intended for theuse of Nokia Siemens Networks customers only for the purposes of the agreement under whichthe document is submitted, and no part of it may be used, reproduced, modified or transmitted inany form or means without the prior written permission of Nokia Siemens Networks. Thedocumentation has been prepared to be used by professional and properly trained personnel,and the customer assumes full responsibility when using it. Nokia Siemens Networks welcomescustomer comments as part of the process of continuous development and improvement of thedocumentation.

The information or statements given in this documentation concerning the suitability, capacity, orperformance of the mentioned hardware or software products are given “as is” and all liabilityarising in connection with such hardware or software products shall be defined conclusively andfinally in a separate agreement between Nokia Siemens Networks and the customer. However,Nokia Siemens Networks has made all reasonable efforts to ensure that the instructionscontained in the document are adequate and free of material errors and omissions. NokiaSiemens Networks will, if deemed necessary by Nokia Siemens Networks, explain issues whichmay not be covered by the document.

Nokia Siemens Networks will correct errors in this documentation as soon as possible. IN NOEVENT WILL NOKIA SIEMENS NETWORKS BE LIABLE FOR ERRORS IN THISDOCUMENTATION OR FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO SPECIAL,DIRECT, INDIRECT, INCIDENTAL OR CONSEQUENTIAL OR ANY LOSSES, SUCH AS BUTNOT LIMITED TO LOSS OF PROFIT, REVENUE, BUSINESS INTERRUPTION, BUSINESSOPPORTUNITY OR DATA, THAT MAYARISE FROM THE USE OF THIS DOCUMENT OR THEINFORMATION IN IT.

This documentation and the product it describes are considered protected by copyrights andother intellectual property rights according to the applicable laws.

The wave logo is a trademark of Nokia Siemens Networks Oy. Nokia is a registered trademark ofNokia Corporation. Siemens is a registered trademark of Siemens AG.

Other product names mentioned in this document may be trademarks of their respective owners,and they are mentioned for identification purposes only.

Copyright © Nokia Siemens Networks 2008. All rights reserved.

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Contents

Contents 3

List of tables 4

List of figures 5

Summary of changes 7

1 Abis EDGE dimensioning 91.1 Definition of channels in EDGE transmission 91.2 Nokia Dynamic Abis 11

2 Planning process 15

3 Key strategies for EDGE dimensioning 17

4 Dimensioning process 214.1 Dimensioning of network elements and interfaces 214.2 Abis EDGE dimensioning process 254.3 Inputs for Abis EDGE dimensioning 274.4 Abis EDGE dimensioning calculations 284.5 Outputs of Abis EDGE dimensioning 294.6 Practical advice on detailed planning 29

5 Abis traffic monitoring principles 31

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Contents

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List of tables

Table 1. BTS multiplexing factor 28

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List of figures

Figure 1. Allocation of Abis TSLs using different MCSs 12

Figure 2. Available data capacity 18

Figure 3. Required data capacity 19

Figure 4. Available data capacity process 21

Figure 5. Required data capacity process 23

Figure 6. Abis dimensioning process 27

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List of figures

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Summary of changes

Changes between document issues are cumulative. Therefore, the latestdocument issue contains all changes made to previous issues.

Changes made between issues 4-0 and 3-0

Updated the TRX dependency information.

Values of the bit rates for coding schemes were updated.

Changes made between issues 3-0 and 2-0

The document has been restructured for better usability and the focus ismore on the actual dimensioning process. The following changes havebeen made:

. Chapter EDGE dimensioning has been renamed as Planningprocess. The dimensioning strategy information has been moved tochapter Key strategies for EDGE dimensioning and an overview ofthe dimensioning steps has been moved to chapter Dimensioning ofnetwork elements and interface and the content has been updated.

. Information not directly related to dimensioning has been removedfrom chapter Abis EDGE dimensioning.

. Definitions of territories has been moved to BTS EDGEdimensioning.

. All steps in the dimensioning process are now under the mainchapter Dimensioning process.

. The Abis dimensioning process has been simplified. The newprocess is detailed in chapters Abis EDGE dimensioning process,Inputs for Abis EDGE dimensioning, Abis EDGE dimensioningcalculations, and Outputs for Abis EDGE dimensioning.

. Chapter Practical advice for detailed planning has been added.

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Summary of changes

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. Chapter Examples of Abis EDGE dimensioning has been removed.A dimensioning example is now included in the BSC EDGEDimensioning document, in chapter Example of BSS connectivitydimensioning.

. Chapter Traffic monitoring principles has been moved to the EDGEand GPRS Key Performance Indicators document.

. Information on Enhanced Quality of Service (EQoS) has beenremoved because it is not supported in BSS12.

Changes made between issues 2-0 and 1-0

Information on that the outputs of Abis dimensioning are used as inputs forBSC dimensioning has been added to Abis EDGE dimensioning andOutputs of Abis EDGE dimensioning.

Figures have been updated.

The calculations and examples in Abis EDGE dimensioning calculationsand Examples of Abis EDGE dimensioning have been modified.

The radio timeslot terminology has been unified.

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1 Abis EDGE dimensioning

These guidelines provide information on dimensioning the Abis interfacefor EDGE into an existing GSM network. The focus is on calculating theneeded transmission capacity in the Abis interface for the successfuloperation of the EDGE network.

The dimensioning principles in EDGE networks differ quite dramaticallyfrom the transmission dimensioning in GSM/GPRS networks. This is dueto the introduction of dynamic Abis, which makes it possible to transporthigher data rate radio channels over the Abis interface more efficientlythan static channel allocation in GSM/GPRS networks. In GSM/GPRSnetworks, each timeslot in the radio interface has a corresponding timeslotin Abis where traffic (voice/data) is carried. Because higher data rates aresupported in EDGE networks than in GPRS networks, more capacity inAbis is needed in EDGE networks. This is handled by the EGPRS dynamicAbis pool (EDAP), which implements support for variable data rates.

Abis dimensioning results in a specific output that is used as input in thenext dimensioning phase, BSC EDGE dimensioning.

The EDGE dimensioning guidelines in the BSS system documentation setcover BTS, Abis, BSC, Gb, and SGSN dimensioning and some parts ofpre-planning. An example of BSS connectivity dimensioning is included inthe BSC EDGE Dimensioning document.

1.1 Definition of channels in EDGE transmission

In an EDGE transport network, the following channels must be carried viathe available Abis links:

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. transceiver (TRX) traffic channels (TCHs)

TRX traffic channels carry user traffic (voice/data calls). Each TRXcan contain a different amount of these traffic carriers, but themaximum number of channels per TRX available for user traffic iseight (unless half rate is used). The actual number of these channelsdepends on the TRX TCH configuration. The number of thechannels carrying user traffic can be less than eight if stand-alonededicated control channels (SDCCH) or broadcast control channels(BCCH) are allocated to the TRX.

The required Abis capacity for the given TRX is based on thechannel allocation of the TRX. For each TCH on the TRX a 16k TCHchannel is needed on Abis. In case a RTSL carries only signalling(BCCH, SDCCH) there is no need to reserve TCH on Abis for thatparticular RTSL. The signalling traffic of a TRX is carried by the TRXsignalling link of the given TRX. Abis capacity is allocated for eachTRX signalling link.

If there is any feature activated which might change the role of aTRX dynamically it shall be taken into account when planning theAbis channel allocation.

These channels are so called fixed allocation channels in Abis andthe number of the channels does not change dynamically. Thenumber of the fixed channels may change when the TRX channelconfiguration is changed.

. link access procedure on the D-channels (LAPD)

LAPD channels (TRXSIG, OMUSIG) are used for signalling ormanaging the traffic between the BSC and BTS. There is oneTRXSIG LAPD channel for each TRX. The capacity of the channelmay vary. For example, the use of half rate affects the requiredcapacity of the TRXSIG LAPD channels.

. channels in the EGPRS dynamic Abis pool, used to carry EGPRSdata dynamically

EDAP channels belong to the EGPRS dynamic Abis pool that isused for EGPRS data traffic. The dynamic Abis pool is used byEDGE traffic (MCS2-MCS9) or by GPRS with CS2 - CS4 (CS-2 onlyif an EDGE TRX is used). Voice and high speed circuit switched data(HSCSD) traffic use the statically allocated TRX traffic channels.

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The amount of these channels depends on the data traffic(especially EGPRS). The amount of the channels may vary. Themaximum number of EDAP channels in a single EDAP is 48 (12DS0 or 64 kbit/s channel). Multiple pools can be created within onePCM circuit, within the limits of the physical capacity of the PCM.

. other channels (for example, E911 in the ANSI environment, Q1management channel, and synchronisation control bits)

Other channels that must be carried via Abis must be taken intoaccount when dimensioning Abis. The other channels can include amanagement channel for additional transmission equipment.

All channels mentioned above are transported in the timeslots of thePCM frame. One 64 kbit/s timeslot can be divided into four 16 kbit/stimeslots. These 16 kbit/s timeslots are referred to as sub-timeslots.The timeslots in the radio interface are referred to as radio timeslots.The throughput of a radio timeslot depends on the used codingscheme.

1.2 Nokia Dynamic Abis

The Abis interface is static in GSM and GPRS with coding schemes 1 and2. This means that the TRX TCH allocation onto the PCM timeslot doesnot change, regardless of whether there is traffic. Because of moreefficient modulation and the use of higher coding schemes, EDGEnetworks are capable of delivering higher data rates than GPRS. For thisreason, the concept of dynamic Abis has been introduced in Nokia EDGEnetworks. In EDGE, some traffic timeslots are statically allocated as inGSM/GPRS, while other timeslots are allocated dynamically whenneeded. This enables a more efficient way of allocating Abis resources. Italso makes it possible to share available resources from the EDAP duringpeak traffic.

Dynamic Abis is mandatory for EDGE and CS-3/CS-4.

For more information on Dynamic Abis, see chapter Dynamic Abis in (E)GPRS System Feature Description.

Allocation of Abis timeslots

In Dynamic Abis, each timeslot in the radio interface has onecorresponding fixed sub-timeslot in the Abis PCM frame. These staticallyallocated channels are called master channels. When the data rates gobeyond 16 kbit/s (when the coding scheme is in the range from MCS2 toMCS9 and CS-3 and CS-4), extra traffic channels are required to handle

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the traffic, and these are allocated from the EDAP. The extra channels arecalled slave channels. This also applies to GPRS CS-2, if the GPRStemporary block flow (TBF) is set via a TRX that is connected to an EDAP.This is caused by the BTS-BSC inband signalling on the Abis interface.The inband signalling increases and the size of the radio link control (RLC)block increases from 268 bits to 368 bits (268 bps / 20 ms = 13.4 kbit/s,368 bps / 20 ms > 16 kbit /s ).

Figure Allocation of Abis TSLs using different MCSs depicts the data ratesof different coding schemes and the required amount of 16 kbit/s timeslotsfrom the EDAP.

Figure 1. Allocation of Abis TSLs using different MCSs

Dynamic Abis capabilities

The following lists the capabilities of the Abis interface implementation:

. The maximum size of the dynamic Abis pool is 12 timeslots.

. The master 16 kbit/s timeslots in the fixed part and the timeslots forthe EDAP must be located in the same PCM frame.

If partial E1/T1 switching is used, the PCM timeslots that aresupposed to be on the same E1/T1 frame must always be switchedto the same path.

. All timeslots that belong to an EDAP should be contiguous.

CS-1CS-2CS-3CS-4

MCS-1MCS-2MCS-3MCS-4MCS-5MCS-6MCS-7MCS-8MCS-9

9050134001560021400

8,80011,20014,80017,60022,40029,60044,80054,40059,200

GPRS

EDGE

Coding scheme Bit rate (bps) Abis PCM allocation (fixed + pool)

Slavegroups

GMSK

GMSK

8-PSK

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. One EDAP cannot be shared between several base control function(BCF) cabinets. Sharing an EDAP between several cabinets maydamage the TRX or the transmission unit (DTRU) hardware.

. The EDAP can be shared between the TRXs in the same BCF; itcannot be shared by the TRXs in different BCFs. As soon as a newBCF is added, a new pool is needed to take care of the packet-switched data handled by the BCF.

For more information on the connectivity restrictions of the PCU, see theBSC EDGE Dimensioning document.

There are also different BTS hardware restrictions for implementing theAbis interface. For more information on these restrictions, see theapplicable BTS documentation.

Related topics

. BTS EDGE Dimensioning

. BSC EDGE Dimensioning

. Gb EDGE Dimensioning

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2 Planning process

Dimensioning is the part of network planning that produces a master planindicating the selected network architecture and the number of networknodes and communication links required during the roll-out of the network.

The following phases are included in the network planning process:

. dimensioning

. pre-planning

. detailed planning

. implementation

. optimisation

Network dimensioning is done by creating a traffic model of the networkand selecting the equipment to support it. Dimensioning takes into accountthe available equipment specifications, business plans, site availability andtype, quality of service (QoS) requirements, and charging cases.

The EDGE dimensioning guidelines in the BSS system documentation setcover BTS, Abis, BSC, Gb, and SGSN dimensioning and some parts ofpre-planning.

These guidelines focus on dimensioning. Network optimisation is notincluded in the guidelines.

The dimensioning guidelines consist of both hardware dimensioning andsoftware dimensioning. Hardware dimensioning defines how many traffictype and traffic volume dependent hardware units are needed in the BTS,BSC, and SGSN to support the targeted traffic and service performance.Software dimensioning defines the key system settings associated withtraffic dependent units. You can modify the existing configuration once the

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amount of needed traffic dependent hardware and the associated softwaresettings have been defined. If necessary, you can place an order foradditional products and licences, based on the agreed standardconfigurations.

Nokia Siemens Networks has a wide range of services and trainingavailable to support all phases of system planning, deployment, andoptimisation. Contact your local Nokia Siemens Networks representativefor details.

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3 Key strategies for EDGE dimensioning

The dimensioning of a network can be based on two different approaches:

. available data capacity

. required data capacity

The dimensioning strategy must be selected before the BTS dimensioningbegins.

Available data capacity

Available data capacity strategy is used when you want to introduce EDGEto an existing network. Dimensioning determines how much traffic isavailable through the current system. The dimensioning input is a pre-defined system configuration. The dimensioning output is the availabletraffic volume with a defined performance level. Alternatively, you cancalculate available capacities for different alternative configurations.

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Figure 2. Available data capacity

Required data capacity

Required data capacity strategy is used when you want to design anetwork that supports the defined amount of traffic and targetedperformance level. The dimensioning inputs are traffic volume, type, andperformance requirements. The dimensioning output is the neededamount of traffic dependent hardware and the associated softwareconfigurations.

All current resources in a cell

Average voice trafficresource usage

Averageavailableresources

Input information:

Current network configuration

Current equipment’sEDGE capability

Current network’s voiceperformance

Current network’s radioconditions (C/N, C/I)

Planned EDGE data resourcesare used for voice trafficwhen needed

Average voice trafficresource usage

EDGE data

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Figure 3. Required data capacity

Input information:

Current network configuration

Current equipment’sEDGE capability

Current network’s voiceperformance

Current network’s radioconditions (C/N, C/I)

Required EDGE capacity

Required EDGE performance

Planned EDGE dataresources may be fully orare at least partiallydedicated to data traffic.Dedicated resources are notused for voice traffic.

All current resources in a cell

Average voice trafficresource usage

Average availableresources

Average voice trafficresource usage

EDGE data

Shared Dedicated

Required EDGE Capacity

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4 Dimensioning process

4.1 Dimensioning of network elements and interfaces

The dimensioning of GSM EDGE network elements and interfaces isproposed to be done as described in this section. Depending on thedimensioning strategy, you can use either the available capacity strategyor the required capacity strategy. At first, the input for BTS dimensioninghas to be agreed. Once this has been done, the output of each element orinterface serves as the input for the next phase.

Available data capacity strategy

The dimensioning process of the available data strategy is illustrated infigure Available data capacity process.

Figure 4. Available data capacity process

1. Estimate the average available data capacity andthroughput.

2. Use existing TRX hardware capacity.3.-6. Dimension the rest of the elements according to the

available capacity estimate done in step 1.

TSL

TRX

Cell

BTS

PCU

BSC

Basic unit

2G SGSNGbAbis

1

2

3 4 5 6

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The available data capacity strategy consists of the following steps:

1. Definition of the input information. Select the data deployment strategy.. Calculate the existing traffic load.. Review the hardware/software capability.. Define the BTS/transceiver (TRX) configuration.. Simulate the coverage and interference performance (carrier-

to-noise ratio (C/N), carrier-to-interference ratio (C/I)).

2. BTS dimensioning. Estimate throughput/ radio timeslot (RTSL).. Calculate the available capacity/number of RTSLs based on

the circuit-switched (CS) traffic needs.. Verify the dimensioning outcome.

The dimensioning process results in throughput/RTSL, territory size/BTS, guaranteed/not guaranteed throughput, RTSL configuration ofTRXs, numbers of TRXs per cell, and the simulation results.

3. Abis dimensioning. Use the output of BTS dimensioning as the input.. Define the EGPRS dynamic Abis pool (EDAP) size.

The dimensioning process results in the size of each EDAP.

4. BSC dimensioning. Use the output of BTS and Abis dimensioning as the input.. Verify the amount of packet control units (PCUs).. Verify the number of BSC signalling units (BCSU) and

Exchange Terminals (ETs).. Verify the Gb requirements for BSC dimensioning.. Define the BSC configuration.. Perform a use check.

The dimensioning process results in the number and type of BSCs,the number and type of PCUs, and the number and size of Gbinterfaces.

5. Gb dimensioning. Use the output of BTS and BSC dimensioning as the input.. Calculate the amount of payload.. Verify the number of network service elements (NSEs) and

BCSUs.. Estimate the need for redundant links.. Evaluate the results.

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The dimensioning process results in the number of timeslots,number of payloads, number of network service virtual connections(NS-VCs), and number of frame relay timeslots/data transfercapacity.

6. SGSN dimensioning. Use the output of BTS and Gb dimensioning as the input.. Define the maximum number of attached subscribers and

packet data protocol (PDP) contexts to be expected in therouting area (RA) served by the SGSN.

. Calculate the amount of total data payload (generated usertraffic) during a busy hour.

. Verify the needed basic units/SGSN according to thepreviously calculated generated traffic and the expectedsubscribers served in the area.

. Check all other restrictions, especially the expected mobilityprofiles of the users versus the dynamic capacity of the SGSN.

The dimensioning process results in the number of packetprocessing units (PAPUs) and signalling and mobility managementunits (SMMUs).

Required data capacity strategy

The dimensioning process of the required data strategy is illustrated infigure Required data capacity process.

Figure 5. Required data capacity process

1. Calculate the required TSL count based on required datacapacity and throughput.

2. Calculate the required amount of TRX hardware.3.-6. Dimension the rest of the elements according to the

required capacity calculation done in step 1.

TSL

TRX

Cell

BTS

PCU

BSC

Basic unit

2G SGSNGbAbis

1

2

3 4 5 6

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The required data capacity strategy consists of the following steps:

1. Definition of the input information. Select the data deployment strategy.. Determine the targeted traffic capacity.. Estimate the traffic mix.. Review the hardware/software capability.. Define the BTS/TRX configuration.. Simulate the coverage and interference performance (C/N, C/

I).

2. BTS dimensioning. Calculate the required throughput.. Estimate throughput/RTSL.. Calculate the required number of RTSLs.. Verify the dimensioning outcome.

The dimensioning process results in throughput/RTSL, territory size/BTS, guaranteed/not guaranteed throughput, TSL configuration ofTRXs, number of TRXs/cell, and the simulation results.

3. Abis dimensioning. Use the output of BTS dimensioning as the input.. Define the EDAP size.

The dimensioning process results in the size of each EDAP.

4. BSC dimensioning. Use the output of BTS and Abis dimensioning as the input.. Calculate the needed amount of PCUs.. Calculate the number of BCSUs and ETs.. Calculate the Gb requirements for BSC dimensioning.. Define the BSC configuration.. Perform a use check.

The dimensioning process results in the number and type of BSCs,the number and type of PCUs, and the number and size of Gbinterfaces.

5. Gb dimensioning. Use the output of BTS and BSC dimensioning as the input.. Calculate the amount of payload.. Calculate the required number of NSEs and BCSUs.. Estimate the need for redundant links.. Evaluate the results.

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The dimensioning process results in the number of timeslots, thenumber payloads, the number of NS-VCs, and the number of framerelay timeslots/data transfer capacity.

6. SGSN dimensioning. Use the output of BTS and Gb dimensioning as the input.. Define the required number of attached subscribers and PDP

contexts to be expected in the RA served by the SGSN.. Calculate the amount of total data payload (generated user

traffic) during a busy hour.. Calculate the needed basic units/SGSN according to the

previously calculated generated traffic and the expectedsubscribers served in the area.

. Check all other restrictions, especially the expected mobilityprofiles of the users versus the dynamic capacity of the SGSN.

The dimensioning process results in the number of PAPUs andSMMUs.

4.2 Abis EDGE dimensioning process

Abis dimensioning can be divided into the following steps:

1. Gather the necessary inputs.

Note that if the input values are exaggerated, Abis capacity isunnecessarily wasted. Respectively, if the input values are too low,Abis capacity may become the bottleneck of the BSS throughputwhen EDGE traffic is high.

2. Define the EGPRS dynamic Abis pool (EDAP) size based on thegiven inputs.

Choose the minimum EDAP size from the multislot classes neededto be supported or from the maximum default territory size of a singleBTS. Choose the option that requires a higher number of TSLs.

If the EDAP has more than one BTS attached, the BTS multiplexingfactor can be taken into account when calculating the sufficientEDAP size for multiple BTSs.

3. In detailed planning, check that the defined EDAPs fit into theexisting E1/T1 links. Also check whether it would be beneficial toadjust the EDAP size based on the PCU connectivity (whenupgrading an existing EGPRS BTS). Resize the EDAP, if needed,according to the principles described in the BSC EDGEDimensioning document.

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After the dimensioning and implementation of the EDAP in the Abisinterface, it is important to monitor and evaluate the performance of theAbis interface by using certain traffic counters and key performanceindicators (KPIs). With traffic monitoring, it is possible to verify thedimensioning traffic assumptions and to initiate re-dimensioning processaccording to traffic needs. For more information on the principles of trafficmonitoring, see chapter Traffic monitoring principles in the EDGE andGPRS Key Performance Indicators document and chapter Abis trafficmonitoring in this document.

The Abis dimensioning process is illustrated in a flowchart format in FigureAbis dimensioning process.

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Figure 6. Abis dimensioning process

4.3 Inputs for Abis EDGE dimensioning

The following are the inputs for Abis EDGE dimensioning:

Inputs for EDAPdimensioning

1. Site configurations2. Territory sizes3. MS multislot classes

STEP1

STEP2

Inputs for detailedplanning

1. Existing Abis configuration2. Possibility to add E1/T1 links

Capacity limitations of the BSC1. PCU capacity

Adjust the EDAPsize according toBTS multiplexing

STEP3

Resizing may havean impact on throughput

Doesthe EDAP

fit into the existingE1/T1 links?

Calculate theminimum EDAPsize

Enlarge the EDAPsize (if needed)

Abis dimensioning planis ready for implementation

Yes

NoIs it

possible toadd a newE1/T1 link?

Yes

No

Reduce theEDAP size

Resize the EDAP

Anybenefit to

resize the EDAPbased onPCU?

Yes

No

Collect the inputs

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. the highest (or average) multislot class of the mobile stations (MSs)needed to be supported in the network

. the maximum default territory size of the BTSs attached to theEGPRS dynamic Abis pool (EDAP)

As choosing the highest multislot class may lead to overdimensioning ofthe EDAP, you may want to choose a value closer to the average multislotclass in use in the network. Note that choosing the average multislot classin use means that users with higher than average multislot class MSsnever achieve the maximum throughput.

Define the default territory size according to the principles described in theBTS EDGE Dimensioning document.

4.4 Abis EDGE dimensioning calculations

Choose the minimum EGPRS dynamic Abis pool (EDAP) size from themultislot classes needed to be supported or from the maximum defaultterritory size of a single BTS, whichever requires a higher number of TSLs.You can use the following calculation formula:

min_EDAP_size = max(MS_multislot_capability,max_default_territory_size_of_one_BTS)

If the EDAP has more than one BTS attached, the BTS multiplexing factorcan be taken into account if the EDAP peak load is estimated to exceedone BTS. The BTS multiplexing factor (k) is chosen according to thenumber of attached BTSs and can be estimated, for example, with thefollowing formula:

k = 2/(1+1/x)

where x = the amount of BTSs in one EDAP (see table BTS multiplexingfactor for an example).

Table 1. BTS multiplexing factor

Number of BTSs k

1 1.0

2 1.3

3 1.5

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The EDAP can be dimensioned using the following formula:

EDAP_size = k x min_EDAP_size

You can adjust the EDAP size in the detailed planning phase according toyour needs.

4.5 Outputs of Abis EDGE dimensioning

The result of the Abis EDGE dimensioning process is the size of eachEGPRS dynamic Abis pool (EDAP). The output is used as input in the nextdimensioning phase, BSC EDGE dimensioning.

4.6 Practical advice on detailed planning

After the dimensioning of the Abis interface, the following need to be takeninto consideration in the detailed planning phase:

. All the traffic channels (TCHs) of each transceiver (TRX) and theirsignalling links which are associated to the EGPRS dynamic Abispool (EDAP) must be on the same E1/T1.

. There are two options for the Abis timeslot (TSL) allocation: TRXscan be grouped either by function or by cell.. Grouping by function so that all EDGE TRXs and EDAPs are

allocated to one E1, while the non-EDGE resources aremapped to another E1 frame. All cells are served by oneEDAP.

This option saves the packet control unit (PCU) resources andreduces the need for total Abis capacity because themaximum trunking gain of the EDAP is achieved. Carefulconsideration in the maintenance and upgrades of theconfiguration is needed to maintain the functional split.

. Grouping by cell so that, for example, two cells are allocated toone E1 and the third one to a second E1. EDAPs are createdfor both groups.

This approach is straightforward to maintain and upgrade.Smaller trunking gain of the EDAPs requires more total Abiscapacity. In addition, the higher number of EDAPs uses morePCU resources.

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. The use of several pools should be avoided, that is, one EDAP perbase control function (BCF) is recommended.

. Only TRXs from one BCF can be connected to the same EDAP.

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5 Abis traffic monitoring principles

The sufficiency of the downlink EGPRS dynamic Abis pool (EDAP)resources is the most important performance indicator to be followed inAbis traffic monitoring. Typically, downlink EDAP congestion starts beforeuplink EDAP congestion. If there is downlink congestion, it is important tomonitor uplink congestion too. For information on key performanceindicators (KPIs), see the EDGE and GPRS Key Performance Indicatorsdocument.

Counters 076000-076008 can be used to understand Abis traffic in moredetail. For more information, see Dynamic Abis Measurement in NokiaBSC/TCSM Product Documentation.

To provide excellent end user throughput performance, it is important toensure that dynamic Abis does not limit system throughput unnecessarily.If there is Abis congestion, the packet control unit (PCU) asks the mobilestation to use lower modulation and coding scheme (MCS) classes to beable to get the data through Abis interface.

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