Abis_Dimensioning

BSC3153 Nokia GSM/EDGE BSS, Rel. BSS13, BSC and TCSM, Rel. S13, Product Documentation, v.1

Abis EDGE Dimensioning

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# Nokia Siemens Networks

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The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This documentation is intended for the use of Nokia Siemens Networks customers only for the purposes of the agreement under which the document is submitted, and no part of it may be used, reproduced, modified or transmitted in any form or means without the prior written permission of Nokia Siemens Networks. The documentation has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia Siemens Networks welcomes customer comments as part of the process of continuous development and improvement of the documentation. The information or statements given in this documentation concerning the suitability, capacity, or performance of the mentioned hardware or software products are given as is and all liability arising in connection with such hardware or software products shall be defined conclusively and finally in a separate agreement between Nokia Siemens Networks and the customer. However, Nokia Siemens Networks has made all reasonable efforts to ensure that the instructions contained in the document are adequate and free of material errors and omissions. Nokia Siemens Networks will, if deemed necessary by Nokia Siemens Networks, explain issues which may not be covered by the document. “

”

Nokia Siemens Networks will correct errors in this documentation as soon as possible. IN NO EVENT WILL NOKIA SIEMENS NETWORKS BE LIABLE FOR ERRORS IN THIS DOCUMENTATION OR FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO SPECIAL, DIRECT, INDIRECT, INCIDENTAL OR CONSEQUENTIAL OR ANY LOSSES, SUCH AS BUT NOT LIMITED TO LOSS OF PROFIT, REVENUE, BUSINESS INTERRUPTION, BUSINESS OPPORTUNITY OPPORTUNITY OR DATA, DATA, THAT THAT MAY ARISE FROM THE USE OF THIS DOCUMENT OR THE INFORMATION IN IT. This documentation and the product it describes are considered protected by copyrights and other intellectual property rights according to the applicable laws. The wave logo is a trademark of Nokia Siemens Networks Oy. Nokia is a registered trademark of Nokia 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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The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This documentation is intended for the use of Nokia Siemens Networks customers only for the purposes of the agreement under which the document is submitted, and no part of it may be used, reproduced, modified or transmitted in any form or means without the prior written permission of Nokia Siemens Networks. The documentation has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia Siemens Networks welcomes customer comments as part of the process of continuous development and improvement of the documentation. The information or statements given in this documentation concerning the suitability, capacity, or performance of the mentioned hardware or software products are given as is and all liability arising in connection with such hardware or software products shall be defined conclusively and finally in a separate agreement between Nokia Siemens Networks and the customer. However, Nokia Siemens Networks has made all reasonable efforts to ensure that the instructions contained in the document are adequate and free of material errors and omissions. Nokia Siemens Networks will, if deemed necessary by Nokia Siemens Networks, explain issues which may not be covered by the document. “

”

Nokia Siemens Networks will correct errors in this documentation as soon as possible. IN NO EVENT WILL NOKIA SIEMENS NETWORKS BE LIABLE FOR ERRORS IN THIS DOCUMENTATION OR FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO SPECIAL, DIRECT, INDIRECT, INCIDENTAL OR CONSEQUENTIAL OR ANY LOSSES, SUCH AS BUT NOT LIMITED TO LOSS OF PROFIT, REVENUE, BUSINESS INTERRUPTION, BUSINESS OPPORTUNITY OPPORTUNITY OR DATA, DATA, THAT THAT MAY ARISE FROM THE USE OF THIS DOCUMENT OR THE INFORMATION IN IT. This documentation and the product it describes are considered protected by copyrights and other intellectual property rights according to the applicable laws. The wave logo is a trademark of Nokia Siemens Networks Oy. Nokia is a registered trademark of Nokia 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 Cont Conten ents ts 3 List List of tabl tables es 4 List List of figu figure res s

5

Summa Summary ry of chan change ges s

7

1 1.1 1.1 1.2

Abis EDGE dimensioning 9 Defi Defini niti tion on of chan channe nels ls in EDGE EDGE tran transm smis issi sion on Nokia Dynamic Abis 11

2

Planning process

3

Key strategies for EDGE dimensioning

4 4.1 4.1 4.2 4.3 4.4 4.4 4.5 4.6 4.6

Dimensioning process 21 Dime Dimens nsio ioni ning ng of netw networ ork k elem elemen ents ts and and inte interf rfac aces es Abis Abis EDG EDGE dimension ioning process 25 Inp Inputs for for Abis EDGE dimensioning 27 Abis Abis EDGE EDGE dime dimens nsio ioni ning ng calcu alcula lati tion ons s 28 Outpu tputs of Abis EDG EDGE dimensioning 29 Prac Practi tica call advi advice ce on deta detail iled ed plan planni ning ng 29

5

Abis traffic monitoring principles

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17 21

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List of tables Table 1.

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BTS multiplexing factor 28


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List of figures

List of figures Figure 1.

Allocation of Abis TSLs using different MCSs

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

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Figure 6.

Abis dimensioning process

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Summary of changes

Summary of changes

Changes between document issues are cumulative. Therefore, the latest document 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 is more on the actual dimensioning process. The following changes have been made: .

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Chapter EDGE dimensioning has been renamed as Planning process . The dimensioning strategy information has been moved to chapter Key strategies for EDGE dimensioning and an overview of the dimensioning steps has been moved to chapter Dimensioning of network elements and interface and the content has been updated. Information not directly related to dimensioning has been removed from chapter Abis EDGE dimensioning . Definitions of territories has been moved to BTS EDGE dimensioning . All steps in the dimensioning process are now under the main chapter Dimensioning process . The Abis dimensioning process has been simplified. The new process is detailed in chapters Abis EDGE dimensioning process , Inputs for Abis EDGE dimensioning , Abis EDGE dimensioning calculations , and Outputs for Abis EDGE dimensioning . Chapter Practical advice for detailed planning has been added.


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.

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Chapter Examples of Abis EDGE dimensioning has been removed. A dimensioning example is now included in the BSC EDGE Dimensioning document, in chapter Example of BSS connectivity dimensioning . Chapter Traffic monitoring principles has been moved to the EDGE and GPRS Key Performance Indicators document. Information on Enhanced Quality of Service (EQoS) has been removed 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 for BSC dimensioning has been added to Abis EDGE dimensioning and Outputs of Abis EDGE dimensioning . Figures have been updated. The calculations and examples in Abis EDGE dimensioning calculations and Examples of Abis EDGE dimensioning have been modified. The radio timeslot terminology has been unified.

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Abis EDGE dimensioning

1

Abis EDGE dimensioning These guidelines provide information on dimensioning the Abis interface for EDGE into an existing GSM network. The focus is on calculating the needed transmission capacity in the Abis interface for the successful operation of the EDGE network. The dimensioning principles in EDGE networks differ quite dramatically from the transmission dimensioning in GSM/GPRS networks. This is due to the introduction of dynamic Abis, which makes it possible to transport higher data rate radio channels over the Abis interface more efficiently than static channel allocation in GSM/GPRS networks. In GSM/GPRS networks, each timeslot in the radio interface has a corresponding timeslot in Abis where traffic (voice/data) is carried. Because higher data rates are supported in EDGE networks than in GPRS networks, more capacity in Abis is needed in EDGE networks. This is handled by the EGPRS dynamic Abis pool (EDAP), which implements support for variable data rates. Abis dimensioning results in a specific output that is used as input in the next dimensioning phase, BSC EDGE dimensioning . The EDGE dimensioning guidelines in the BSS system documentation set cover BTS, Abis, BSC, Gb, and SGSN dimensioning and some parts of pre-planning. An example of BSS connectivity dimensioning is included in the BSC EDGE Dimensioning document.

1.1

Definition of channels in EDGE transmission In an EDGE transport network, the following channels must be carried via the available Abis links:

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.

transceiver (TRX) traffic channels (TCHs) TRX traffic channels carry user traffic (voice/data calls). Each TRX can contain a different amount of these traffic carriers, but the maximum number of channels per TRX available for user traffic is eight (unless half rate is used). The actual number of these channels depends on the TRX TCH configuration. The number of the channels carrying user traffic can be less than eight if stand-alone dedicated control channels (SDCCH) or broadcast control channels (BCCH) are allocated to the TRX. The required Abis capacity for the given TRX is based on the channel allocation of the TRX. For each TCH on the TRX a 16k TCH channel is needed on Abis. In case a RTSL carries only signalling (BCCH, SDCCH) there is no need to reserve TCH on Abis for that particular RTSL. The signalling traffic of a TRX is carried by the TRX signalling link of the given TRX. Abis capacity is allocated for each TRX signalling link. If there is any feature activated which might change the role of a TRX dynamically it shall be taken into account when planning the Abis channel allocation. These channels are so called fixed allocation channels in Abis and the number of the channels does not change dynamically. The number of the fixed channels may change when the TRX channel configuration is changed.

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link access procedure on the D-channels (LAPD) LAPD channels (TRXSIG, OMUSIG) are used for signalling or managing the traffic between the BSC and BTS. There is one TRXSIG LAPD channel for each TRX. The capacity of the channel may vary. For example, the use of half rate affects the required capacity of the TRXSIG LAPD channels.

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channels in the EGPRS dynamic Abis pool, used to carry EGPRS data dynamically EDAP channels belong to the EGPRS dynamic Abis pool that is used for EGPRS data traffic. The dynamic Abis pool is used by EDGE traffic (MCS2-MCS9) or by GPRS with CS2 - CS4 (CS-2 only if 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. The maximum number of EDAP channels in a single EDAP is 48 (12 DS0 or 64 kbit/s channel). Multiple pools can be created within one PCM circuit, within the limits of the physical capacity of the PCM. .

other channels (for example, E911 in the ANSI environment, Q1 management channel, and synchronisation control bits) Other channels that must be carried via Abis must be taken into account when dimensioning Abis. The other channels can include a management channel for additional transmission equipment. All channels mentioned above are transported in the timeslots of the PCM frame. One 64 kbit/s timeslot can be divided into four 16 kbit/s timeslots. 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 coding scheme.

1.2

Nokia Dynamic Abis The Abis interface is static in GSM and GPRS with coding schemes 1 and 2. This means that the TRX TCH allocation onto the PCM timeslot does not change, regardless of whether there is traffic. Because of more efficient modulation and the use of higher coding schemes, EDGE networks are capable of delivering higher data rates than GPRS. For this reason, the concept of dynamic Abis has been introduced in Nokia EDGE networks. In EDGE, some traffic timeslots are statically allocated as in GSM/GPRS, while other timeslots are allocated dynamically when needed. This enables a more efficient way of allocating Abis resources. It also makes it possible to share available resources from the EDAP during peak 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 one corresponding fixed sub-timeslot in the Abis PCM frame. These statically allocated channels are called master channels. When the data rates go beyond 16 kbit/s (when the coding scheme is in the range from MCS2 to MCS9 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 are called slave channels. This also applies to GPRS CS-2, if the GPRS temporary 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 rates of different coding schemes and the required amount of 16 kbit/s timeslots from the EDAP. Coding scheme

GMSK

GMSK

8-PSK

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

Bit rate (bps)

GPRS

9050 13400 15600 21400

EDGE

8,800 11,200 14,800 17,600 22,400 29,600 44,800 54,400 59,200

Figure 1.

Abis PCM allocation (fixed + pool)

Slave groups

Allocation of Abis TSLs using different MCSs

Dynamic Abis capabilities The following lists the capabilities of the Abis interface implementation: .

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The maximum size of the dynamic Abis pool is 12 timeslots. The master 16 kbit/s timeslots in the fixed part and the timeslots for the EDAP must be located in the same PCM frame. If partial E1/T1 switching is used, the PCM timeslots that are supposed to be on the same E1/T1 frame must always be switched to the same path.

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All timeslots that belong to an EDAP should be contiguous.


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One EDAP cannot be shared between several base control function (BCF) cabinets. Sharing an EDAP between several cabinets may damage the TRX or the transmission unit (DTRU) hardware. The EDAP can be shared between the TRXs in the same BCF; it cannot be shared by the TRXs in different BCFs. As soon as a new BCF is added, a new pool is needed to take care of the packetswitched data handled by the BCF.

For more information on the connectivity restrictions of the PCU, see the BSC EDGE Dimensioning document. There are also different BTS hardware restrictions for implementing the Abis interface. For more information on these restrictions, see the applicable BTS documentation. Related topics

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BTS EDGE Dimensioning

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BSC EDGE Dimensioning

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Gb EDGE Dimensioning


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Planning process

2

Planning process Dimensioning is the part of network planning that produces a master plan indicating the selected network architecture and the number of network nodes and communication links required during the roll-out of the network. The following phases are included in the network planning process: .

dimensioning

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pre-planning

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detailed planning

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implementation

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optimisation

Network dimensioning is done by creating a traffic model of the network and selecting the equipment to support it. Dimensioning takes into account the available equipment specifications, business plans, site availability and type, quality of service (QoS) requirements, and charging cases. The EDGE dimensioning guidelines in the BSS system documentation set cover BTS, Abis, BSC, Gb, and SGSN dimensioning and some parts of pre-planning. These guidelines focus on dimensioning. Network optimisation is not included in the guidelines. The dimensioning guidelines consist of both hardware dimensioning and software dimensioning. Hardware dimensioning defines how many traffic type 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 with traffic dependent units. You can modify the existing configuration once the

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amount of needed traffic dependent hardware and the associated software settings have been defined. If necessary, you can place an order for additional products and licences, based on the agreed standard configurations. Nokia Siemens Networks has a wide range of services and training available to support all phases of system planning, deployment, and optimisation. Contact your local Nokia Siemens Networks representative for 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

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required data capacity

The dimensioning strategy must be selected before the BTS dimensioning begins. Available data capacity Available data capacity strategy is used when you want to introduce EDGE to an existing network. Dimensioning determines how much traffic is available through the current system. The dimensioning input is a predefined system configuration. The dimensioning output is the available traffic volume with a defined performance level. Alternatively, you can calculate available capacities for different alternative configurations.

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All current resources in a cell Input information: Current network configuration

Average voice traffic resource usage

Current equipment’s EDGE capability

Average available resources

Current network’s voice performance Current network’s radio conditions (C/N, C/I)

Average voice traffic resource usage

Figure 2.

EDGE data

Planned EDGE data resources are used for voice traffic when needed

Available data capacity

Required data capacity Required data capacity strategy is used when you want to design a network that supports the defined amount of traffic and targeted performance level. The dimensioning inputs are traffic volume, type, and performance requirements. The dimensioning output is the needed amount of traffic dependent hardware and the associated software configurations.

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All current resources in a cell Average voice traffic resource usage Average available resources

Input information:

Current network configuration Current equipment’s EDGE capability Current network’s voice performance Current network’s radio conditions (C/N, C/I)

Required EDGE Capacity

Required EDGE capacity Required EDGE performance Shared

Dedicated

EDGE data Average voice traffic resource usage

Figure 3.

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Planned EDGE data resources may be fully or are at least partially dedicated to data traffic. Dedicated resources are not used for voice traffic.

Required data capacity


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Dimensioning process

4


4.1

Dimensioning of network elements and interfaces The dimensioning of GSM EDGE network elements and interfaces is proposed to be done as described in this section. Depending on the dimensioning strategy, you can use either the available capacity strategy or the required capacity strategy. At first, the input for BTS dimensioning has to be agreed. Once this has been done, the output of each element or interface serves as the input for the next phase. Available data capacity strategy The dimensioning process of the available data strategy is illustrated in figure Available data capacity process .

1.

Estimate the average available data capacity and throughput. 2. Use existing TRX hardware capacity. 3.-6. Dimension the rest of the elements according to the available capacity estimate done in step 1. 3

1

4

5

6

2

TSL

TRX

Cell

PCU

BTS

Figure 4.

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Abis

BSC

Basic unit

Gb

2G SGSN

Available data capacity process


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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.

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Calculate the existing traffic load.

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Review the hardware/software capability.

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Define the BTS/transceiver (TRX) configuration.

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2.

Simulate the coverage and interference performance (carrierto-noise ratio (C/N), carrier-to-interference ratio (C/I)).

BTS dimensioning .

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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 of TRXs, numbers of TRXs per cell, and the simulation results. 3.

Abis dimensioning .

Use the output of BTS dimensioning as the input.

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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.

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Verify the amount of packet control units (PCUs).

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Verify the number of BSC signalling units (BCSU) and Exchange Terminals (ETs).

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Verify the Gb requirements for BSC dimensioning.

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Define the BSC configuration.

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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 Gb interfaces. 5.

Gb dimensioning .

Use the output of BTS and BSC dimensioning as the input.

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Calculate the amount of payload.

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Verify the number of network service elements (NSEs) and BCSUs.

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Estimate the need for redundant links.

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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 transfer capacity. 6.

SGSN dimensioning .

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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 the routing area (RA) served by the SGSN. Calculate the amount of total data payload (generated user traffic) during a busy hour. Verify the needed basic units/SGSN according to the previously calculated generated traffic and the expected subscribers served in the area. Check all other restrictions, especially the expected mobility profiles of the users versus the dynamic capacity of the SGSN.

The dimensioning process results in the number of packet processing units (PAPUs) and signalling and mobility management units (SMMUs). Required data capacity strategy The dimensioning process of the required data strategy is illustrated in figure Required data capacity process .

1.

Calculate the required TSL count based on required da ta capacity 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. 3

1

4

5

6

2

TSL TRX

Cell

BTS

Figure 5.

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Basic unit

PCU

Abis

BSC

Gb

2G SGSN

Required data capacity process


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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.

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Determine the targeted traffic capacity.

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Estimate the traffic mix.

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Review the hardware/software capability.

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Define the BTS/TRX configuration.

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2.

Simulate the coverage and interference performance (C/N, C/ I).

BTS dimensioning .

Calculate the required throughput.

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Estimate throughput/RTSL.

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Calculate the required number of RTSLs.

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Verify the dimensioning outcome.

The dimensioning process results in throughput/RTSL, territory size/ BTS, guaranteed/not guaranteed throughput, TSL configuration of TRXs, number of TRXs/cell, and the simulation results. 3.

Abis dimensioning .

Use the output of BTS dimensioning as the input.

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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.

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Calculate the needed amount of PCUs.

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Calculate the number of BCSUs and ETs.

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Calculate the Gb requirements for BSC dimensioning.

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Define the BSC configuration.

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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 Gb interfaces. 5.

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Gb dimensioning .

Use the output of BTS and BSC dimensioning as the input.

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Calculate the amount of payload.

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Calculate the required number of NSEs and BCSUs.

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Estimate the need for redundant links.

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Evaluate the results.


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The dimensioning process results in the number of timeslots, the number payloads, the number of NS-VCs, and the number of frame relay timeslots/data transfer capacity. 6.

SGSN dimensioning .

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.

.

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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 expected subscribers served in the area. Check all other restrictions, especially the expected mobility profiles of the users versus the dynamic capacity of the SGSN.

The dimensioning process results in the number of PAPUs and SMMUs.

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 is unnecessarily wasted. Respectively, if the input values are too low, Abis capacity may become the bottleneck of the BSS throughput when EDGE traffic is high.

2.

Define the EGPRS dynamic Abis pool (EDAP) size based on the given inputs. Choose the minimum EDAP size from the multislot classes needed to be supported or from the maximum default territory size of a single BTS. Choose the option that requires a higher number of TSLs. If the EDAP has more than one BTS attached, the BTS multiplexing factor can be taken into account when calculating the sufficient EDAP size for multiple BTSs.

3.

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


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After the dimensioning and implementation of the EDAP in the Abis interface, it is important to monitor and evaluate the performance of the Abis interface by using certain traffic counters and key performance indicators (KPIs). With traffic monitoring, it is possible to verify the dimensioning traffic assumptions and to initiate re-dimensioning process according to traffic needs. For more information on the principles of traffic monitoring, see chapter Traffic monitoring principles in the EDGE and GPRS Key Performance Indicators document and chapter Abis traffic monitoring in this document. The Abis dimensioning process is illustrated in a flowchart format in Figure Abis dimensioning process .

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Inputs for EDAP dimensioning

STEP1

Inputs for detailed planning

Collect the inputs

1. Existing Abis configuration 2. Possibility to add E1/T1 links

1. Site configurations 2. Territory sizes 3. MS multislot classes

STEP2

Calculate the minimum EDAP size

Adjust the EDAP size according to BTS multiplexing

Capacity limitations of the BSC 1. PCU capacity

STEP3 Does the EDAP fit into the existing E1/T1 links?

Is it possible to add a new E1/T1 link?

No

Yes

No

Yes

Enlarge the EDAP size (if needed)

Reduce the EDAP size

Resizing may have an impact on throughput

Any benefit to resize the EDAP based on PCU?

Yes

Resize the EDAP

No

Abis dimensioning plan is ready for implementation

Figure 6.

4.3

Abis dimensioning process

Inputs for Abis EDGE dimensioning The following are the inputs for Abis EDGE dimensioning:

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

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

.

As choosing the highest multislot class may lead to overdimensioning of the EDAP, you may want to choose a value closer to the average multislot class in use in the network. Note that choosing the average multislot class in use means that users with higher than average multislot class MSs never achieve the maximum throughput. Define the default territory size according to the principles described in the BTS EDGE Dimensioning document.

4.4

Abis EDGE dimensioning calculations Choose the minimum EGPRS dynamic Abis pool (EDAP) size from the multislot classes needed to be supported or from the maximum default territory 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 factor can be taken into account if the EDAP peak load is estimated to exceed one BTS. The BTS multiplexing factor (k) is chosen according to the number of attached BTSs and can be estimated, for example, with the following formula: k = 2/(1+1/x) where x = the amount of BTSs in one EDAP (see table BTS multiplexing factor for an example).

Table 1.

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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 to your needs.

4.5

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

4.6

Practical advice on detailed planning After the dimensioning of the Abis interface, the following need to be taken into consideration in the detailed planning phase: .

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All the traffic channels (TCHs) of each transceiver (TRX) and their signalling links which are associated to the EGPRS dynamic Abis pool (EDAP) must be on the same E1/T1. There are two options for the Abis timeslot (TSL) allocation: TRXs can 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 are mapped to another E1 frame. All cells are served by one EDAP. This option saves the packet control unit (PCU) resources and reduces the need for total Abis capacity because the maximum trunking gain of the EDAP is achieved. Careful consideration in the maintenance and upgrades of the configuration is needed to maintain the functional split.

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Grouping by cell so that, for example, two cells are allocated to one E1 and the third one to a second E1. EDAPs are created for both groups. This approach is straightforward to maintain and upgrade. Smaller trunking gain of the EDAPs requires more total Abis capacity. In addition, the higher number of EDAPs uses more PCU resources.

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The use of several pools should be avoided, that is, one EDAP per base control function (BCF) is recommended. Only TRXs from one BCF can be connected to the same EDAP.


DN7032309 Issue 4-0 en 25/03/2008

Abis_Dimensioning

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