05r abis edge dimension ing dn7032309

Abis EDGE Dimensioning

DN7032309Issue 3-0 en draft

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2 (25) # Nokia Corporation DN7032309Issue 3-0 en draft


Contents

Contents 3

Summary of changes 5

1 Abis EDGE dimensioning 71.1 Definition of channels in EDGE transmission 71.2 Nokia Dynamic Abis 9

2 Planning process 13

3 Key strategies for EDGE dimensioning 15

4 Dimensioning process 174.1 Dimensioning of network elements and interfaces 174.2 Abis EDGE dimensioning process 214.3 Inputs for Abis EDGE dimensioning 234.4 Abis EDGE dimensioning calculations 234.5 Outputs of Abis EDGE dimensioning 244.6 Practical advice on detailed planning 24

5 Abis traffic monitoring principles 25



Contents

Summary of changes

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

Changes made between issues 3-0 and 2-0

The document has been restructured for better usability and the focus is more onthe actual dimensioning process. The following changes have been made:

. Chapter EDGE dimensioning has been renamed as Planning process. Thedimensioning strategy information has been moved to chapter Keystrategies for EDGE dimensioning and an overview of the dimensioningsteps has been moved to chapter Dimensioning of network elements andinterface and the content has been updated.

. Information not directly related to dimensioning has been removed fromchapter Abis EDGE dimensioning.

. Definitions of territories has been moved to BTS EDGE dimensioning.

. All steps in the dimensioning process are now under the main chapterDimensioning process.

. The Abis dimensioning process has been simplified. The new process isdetailed in chapters Abis EDGE dimensioning process, Inputs for AbisEDGE dimensioning, Abis EDGE dimensioning calculations, and Outputsfor Abis EDGE dimensioning.

. Chapter Practical advice for detailed planning has been added.

. Chapter Examples of Abis EDGE dimensioning has been removed. Adimensioning example is now included in the BSC EDGE Dimensioningdocument, in chapter Example of BSS connectivity dimensioning.

. Chapter Traffic monitoring principles has been moved to the EDGE andGPRS Key Performance Indicators document.

. Information on Enhanced Quality of Service (EQoS) has been removedbecause it is not supported in BSS12. EQoS will be available in BSS13.



Summary of changes

Changes made between issues 2-0 and 1-0

Information on that the outputs of Abis dimensioning are used as inputs for BSCdimensioning has been added to Abis EDGE dimensioning and Outputs of AbisEDGE dimensioning.

Figures have been updated.

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

The radio timeslot terminology has been unified.



1 Abis EDGE dimensioning

These guidelines provide information on dimensioning the Abis interface forEDGE into an existing GSM network. The focus is on calculating the neededtransmission capacity in the Abis interface for the successful operation of theEDGE network.

The dimensioning principles in EDGE networks differ quite dramatically fromthe transmission dimensioning in GSM/GPRS networks. This is due to theintroduction of dynamic Abis, which makes it possible to transport higher datarate radio channels over the Abis interface more efficiently than static channelallocation in GSM/GPRS networks. In GSM/GPRS networks, each timeslot inthe radio interface has a corresponding timeslot in Abis where traffic (voice/data)is carried. Because higher data rates are supported in EDGE networks than inGPRS networks, more capacity in Abis is needed in EDGE networks. This ishandled by the EGPRS dynamic Abis pool (EDAP), which implements supportfor variable data rates.

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

The EDGE dimensioning guidelines in the BSS system documentation set coverBTS, Abis, BSC, Gb, and SGSN dimensioning and some parts of pre-planning.An example of BSS connectivity dimensioning is included in the BSC EDGEDimensioning document.

1.1 Definition of channels in EDGE transmission

In an EDGE transport network, the following channels must be carried via theavailable Abis links:



Abis EDGE dimensioning

. transceiver (TRX) traffic channels (TCHs)

TRX traffic channels carry user traffic (voice/data calls). Each TRX cancontain a different amount of these traffic carriers, but the maximumnumber of channels per TRX available for user traffic is eight (unless halfrate is used). The actual number of these channels depends on the TRXTCH configuration. The number of the channels carrying user traffic canbe less than eight if stand-alone dedicated control channels (SDCCH) orbroadcast control channels (BCCH) are allocated to the TRX.

From the transport point of view, the allocation/usage of the TRX channelsdoes not change, regardless of whether the channels are used for thededicated channels (SDCCH or BCCH) or for TCHs carrying user traffic.From the transport point of view, there are always eight channels availableper TRX. Each of these channels reserves 16 kbit/s bandwidth. This isfixed and remains the same regardless of the carried traffic type (voice/data).

These channels are so called fixed allocation channels in Abis and theamount of the channels does not change. One TRX has eight channels; twoTRXs have 16, and so on.

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

LAPD channels (TRXSIG, OMUSIG) are used for signalling or managingthe traffic between the BSC and BTS. There is one TRXSIG LAPDchannel for each TRX. The capacity of the channel can vary. For example,the use of half rate affects the required capacity of the TRXSIG LAPDchannels.

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

EDAP channels belong to the EGPRS dynamic Abis pool that is used forEGPRS 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 TRXis used). Voice and high speed circuit switched data (HSCSD) traffic usethe statically allocated TRX traffic channels.

The amount of these channels depends on the data traffic (especiallyEGPRS). The amount of the channels may vary. The maximum number ofEDAP 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 ofthe 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 into accountwhen dimensioning Abis. The other channels can include a managementchannel for additional transmission equipment.

All channels mentioned above are transported in the timeslots of the PCMframe. 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 inthe radio interface are referred to as radio timeslots. The throughput of aradio 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. Thismeans that the TRX TCH allocation onto the PCM timeslot does not change,regardless of whether there is traffic. Because of more efficient modulation andthe use of higher coding schemes, EDGE networks are capable of deliveringhigher data rates than GPRS. For this reason, the concept of dynamic Abis hasbeen introduced in Nokia EDGE networks. In EDGE, some traffic timeslots arestatically allocated as in GSM/GPRS, while other timeslots are allocateddynamically when needed. This enables a more efficient way of allocating Abisresources. It also makes it possible to share available resources from the EDAPduring 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)GPRSSystem Feature Description.

Allocation of Abis timeslots

In Dynamic Abis, each timeslot in the radio interface has one corresponding fixedsub-timeslot in the Abis PCM frame. These statically allocated channels arecalled master channels. When the data rates go beyond 16 kbit/s (when the codingscheme is in the range from MCS2 to MCS9 and CS-3 and CS-4), extra trafficchannels are required to handle the traffic, and these are allocated from the EDAP.The extra channels are called slave channels. This also applies to GPRS CS-2, ifthe GPRS temporary block flow (TBF) is set via a TRX that is connected to anEDAP. 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) blockincreases 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 ofdifferent coding schemes and the required amount of 16 kbit/s timeslots from theEDAP.




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 for theEDAP must be located in the same PCM frame.

If partial E1/T1 switching is used, the PCM timeslots that are supposed tobe on the same E1/T1 frame must always be switched to the same path.

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

. One EDAP cannot be shared between several base control function (BCF)cabinets. Sharing an EDAP between several cabinets may damage the TRXor the transmission unit (DTRU) hardware.

. The EDAP can be shared between the TRXs in the same BCF; it cannot beshared by the TRXs in different BCFs. As soon as a new BCF is added, anew pool is needed to take care of the packet-switched data handled by theBCF.

. The theoretical maximum number of TRXs attached to one dynamic Abispool is 20. However, since the TRXs using EDAP resources must beallocated to the same Abis ET_PCM line with the EDAP, the maximumTRX count for the EDAP is less than 20.

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

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

8,00012,00014,40020,000

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



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

There are also different BTS hardware restrictions for implementing the Abisinterface. For more information on these restrictions, see the applicable BTSdocumentation.

Related topics

. BTS EDGE Dimensioning

. BSC EDGE Dimensioning

. Gb EDGE Dimensioning

. SGSN EDGE Dimensioning




2 Planning process

Dimensioning is the part of network planning that produces a master planindicating the selected network architecture and the number of network nodes andcommunication 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

. modernisation

Network dimensioning is done by creating a traffic model of the network andselecting the equipment to support it. Dimensioning takes into account theavailable 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 coverBTS, Abis, BSC, Gb, and SGSN dimensioning and some parts of pre-planning.

These guidelines focus on dimensioning. Network optimisation is not included inthe guidelines.

The dimensioning guidelines consist of both hardware dimensioning andsoftware dimensioning. Hardware dimensioning defines how many traffic typeand traffic volume dependent hardware units are needed in the BTS, BSC, andSGSN to support the targeted traffic and service performance. Softwaredimensioning defines the key system settings associated with traffic dependentunits. You can modify the existing configuration once the amount of neededtraffic dependent hardware and the associated software settings have beendefined. If necessary, you can place an order for additional products and licences,based on the agreed standard configurations.



Planning process

Nokia has a wide range of services and training available to support all phases ofsystem planning, deployment, and optimisation. Contact your local Nokiarepresentative for details.



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 dimensioning begins.

Available data capacity

Available data capacity strategy is used when you want to introduce EDGE to anexisting network. Dimensioning determines how much traffic is available throughthe current system. The dimensioning input is a pre-defined system configuration.The dimensioning output is the available traffic volume with a definedperformance level. Alternatively, you can calculate available capacities fordifferent alternative configurations.

Figure 2. Available data capacity

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


EDGE data



Key strategies for EDGE dimensioning

Required data capacity

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

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 availableresources


EDGE data

Shared Dedicated

Required EDGE Capacity



4 Dimensioning process

4.1 Dimensioning of network elements and interfaces

The dimensioning of GSM EDGE network elements and interfaces is proposed tobe done as described in this section. Depending on the dimensioning strategy, youcan use either the available capacity strategy or the required capacity strategy. Atfirst, 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 figureAvailable 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



Dimensioning process

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/timeslot (TSL).. Calculate the available capacity/number of TSLs based on the

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

The dimensioning process results in throughput/TSL, territory size/BTS,guaranteed/not guaranteed throughput, TSL configuration of TRXs,amount 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, thenumber 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.. Calculate the amount of payload.. Verify the number of network service elements (NSEs) and BCSUs.. Estimate the need for redundant links.. Evaluate the results.



The dimensioning process results in the number of timeslots, number ofpayloads, number of network service virtual connections (NS-VCs), andnumber of frame relay timeslots/data transfer capacity.

6. SGSN dimensioning. Use the output of BTS and Gb dimensioning as the input.. Define the maximum number of 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 previouslycalculated generated traffic and the expected subscribers served inthe area.

. Check all other restrictions, especially the expected mobility profilesof 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 figureRequired 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




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/TSL.. Calculate the required number of TSLs.. Verify the dimensioning outcome.

The dimensioning process results in throughput/TSL, territory size/BTS,guaranteed/not guaranteed throughput, TSL configuration of TRXs,amount of TRX/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 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, thenumber 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.. Calculate the amount of payload.. Calculate the required number of NSEs and BCSUs.. Estimate the need for redundant links.. Evaluate the results.

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



6. SGSN dimensioning. Use the output of BTS and Gb dimensioning as the input.. Define the required number of 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 inthe area.

. Check all other restrictions, especially the expected mobility profilesof 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 isunnecessarily wasted. Respectively, if the input values are too low, Abiscapacity may become the bottleneck of the BSS throughput when EDGEtraffic is high.

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

Choose the minimum EDAP size from the multislot classes needed to besupported 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 factorcan be taken into account when calculating the sufficient EDAP size formultiple BTSs.

3. 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 EDAPsize based on the PCU connectivity (when upgrading an existing EGPRSBTS). Resize the EDAP, if needed, according to the principles described inthe BSC EDGE Dimensioning document.

After the dimensioning and implementation of the EDAP in the Abis interface, itis important to monitor and evaluate the performance of the Abis interface byusing certain traffic counters and key performance indicators (KPIs). With trafficmonitoring, it is possible to verify the dimensioning traffic assumptions and to




initiate re-dimensioning process according to traffic needs. For more informationon the principles of traffic monitoring, see chapter Traffic monitoring principlesin the EDGE and GPRS Key Performance Indicators document and chapter Abistraffic monitoring in this document.

The Abis dimensioning process is illustrated in a flowchart format in Figure Abisdimensioning process.

Figure 6. Abis dimensioning process

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



4.3 Inputs for Abis EDGE dimensioning

The following are the inputs for Abis EDGE dimensioning:

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

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

As choosing the highest multislot class may lead to overdimensioning of theEDAP, you may want to choose a value closer to the average multislot class inuse in the network.

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

4.4 Abis EDGE dimensioning calculations

Choose the minimum EGPRS dynamic Abis pool (EDAP) size from the multislotclasses needed to be supported or from the maximum default territory size of asingle BTS, whichever requires a higher number of TSLs. You can use thefollowing 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 betaken into account if the EDAP peak load is estimated to exceed one BTS. TheBTS multiplexing factor (k) is chosen according to the number of attached BTSs,for example according to table BTS multiplexing factor.

Table 1. BTS multiplexing factor

Number of BTSs k

1 1.0

2 1.3

3 1.5

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 yourneeds.

4.5 Outputs of Abis EDGE dimensioning

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

4.6 Practical advice on detailed planning

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

. All the traffic channels (TCHs) of each transceiver (TRX) and theirsignalling 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 begrouped 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 toanother E1 frame. All cells are served by one EDAP.

This option saves the packet control unit (PCU) resources andreduces the need for total Abis capacity because the maximumtrunking gain of the EDAP is achieved. Careful consideration in themaintenance and upgrades of the configuration is needed to maintainthe functional split.

. Grouping by cell so that, for example, two cells are allocated to oneE1 and the third one to a second E1. EDAPs are created for bothgroups.

This approach is straightforward to maintain and upgrade. Smallertrunking gain of the EDAPs requires more total Abis capacity. Inaddition, the higher number of EDAPs uses more PCU resources.

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

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



5 Abis traffic monitoring principles

The sufficiency of the downlink EGPRS dynamic Abis pool (EDAP) resources isthe most important performance indicator to be followed in Abis trafficmonitoring. Typically, downlink EDAP congestion starts before uplink EDAPcongestion. If there is downlink congestion, it is important to monitor uplinkcongestion too. For information on key performance indicators (KPIs), see theEDGE and GPRS Key Performance Indicators document.

Counters 076000-076008 can be used to understand Abis traffic in more detail.For more information, see Dynamic Abis Measurement in BSC/TCSMdocumentation.

To provide excellent end user throughput performance, it is important to ensurethat dynamic Abis does not limit system throughput unnecessarily. If there is Abiscongestion, the packet control unit (PCU) asks the mobile station to use lowermodulation and coding scheme (MCS) classes to be able to get the data throughAbis interface.



Abis traffic monitoring principles

05r abis edge dimension ing dn7032309

Documents

prior written permission

expected mobility profiles

packet control unit

base control function

key performance indicators

total abis capacity

generated user traffic

bts multiplexing factor