(e)gprs radio networks - dimensioning guideline

1/31 Document TypeAuthorUnit/Dept.

Document TitleDate, VersionFor internal use

(E)GPRS Radio Networks – Dimensioning Guidelines for exNokia BSS releases (PCU1 and PCU2) v2.2

Owner: GERAN Program - Ville SalomaaScope: EDGE Radio Networks - Planning TheoryOriginator: CSIStatus: Version 2.14Document ID:Location:

Change History

Issue Date Handled by CommentsVer. 1.0 24.10.2005 Pal SzabadszallasiVer. 2.0 18.12.2006 Pal SzabadszallasiVer. 2.12 07.12.2007 Paul Felices S12 update and re-writeVer. 2.13 21.12.2007 Raimo Ahosola Planning aspects for Abis,

PCU and Gb added.Ver. 2.14 4.2.2008 Raimo Ahosola Planning aspects for Abis,

PCU and Gb converted to dimensioning aspects.

Approved byVille Salomaa GERAN Program



1. Introduction...........................................................................................41.1 (E)GPRS BSS Dimensioning..............................................................................................41.2 Dimensioning Inputs............................................................................................................51.2.1 Voice Traffic......................................................................................................................51.2.2 Data Traffic.......................................................................................................................51.2.3 Other Inputs......................................................................................................................6

2. Capacity Dimensioning.........................................................................82.1 Radio Interface....................................................................................................................82.1.1 Erlang B............................................................................................................................92.1.2 Erlang B Approximation....................................................................................................92.2 Number of radio timeslots required...................................................................................102.3 Data Quality of Service......................................................................................................112.4 Setting the default and dedicated data territories..............................................................112.5 Dimensioning example......................................................................................................122.5.1 Inputs..............................................................................................................................122.5.2 Process..........................................................................................................................132.5.3 Quick check method.......................................................................................................15

3. Abis interface......................................................................................153.1 Abis dimensioning.............................................................................................................153.2 Dimensioning example......................................................................................................17

4. PCU.....................................................................................................194.1 PCU dimensioning............................................................................................................204.2 Dimensioning example......................................................................................................21

5. Gb Link Dimensioning.........................................................................225.1 Gb Link Dimensioning – BSS point of view.......................................................................225.2 Gb Link Dimensioning Example – BSS view.....................................................................235.3 Gb Link Dimensioning – SGSN point of view....................................................................235.3.1 PAPU capacity................................................................................................................245.4 Gb Link Dimensioning Example – SGSN view..................................................................25

6. Implementation....................................................................................266.1 Dimensioning.....................................................................................................................266.2 Network Audit....................................................................................................................266.3 Planning............................................................................................................................266.4 Pre-activation....................................................................................................................266.5 Activation...........................................................................................................................276.6 Monitoring..........................................................................................................................27

7. References..........................................................................................28



8. Appendixes.........................................................................................29



1. IntroductionThe purpose of the (E)GPRS Radio Networks – Dimensioning Guidelines is to describe the (E)GPRS Radio Network dimensioning activities and requirements for BSS releases with PCU1 and PCU2. This completes the Dimensioning Quick Guide having background information required to understand the theory behind the used dimensioning method.

This document is part of the (E)GPRS Radio Networks planning document set, which is organized as follows:

(E)GPRS Radio Networks – Dimensioning Quick Guide

(E)GPRS Radio Networks – Dimensioning Guidelines

(E)GPRS Radio Networks – Planning Guidelines

(E)GPRS Radio Networks – Planning Theory

(E)GPRS Radio Networks – Optimization Guidelines

1.1 (E)GPRS BSS Dimensioning Correct dimensioning is strongly linked to good (E)GPRS performance. The high bit-rates possible at the radio interface require sufficient capacity to be available further up the network. The nature of user multiplexing at the radio interface also requires sufficient radio resource so that users obtain the best possible throughputs.

As (E)GPRS is a packet-based technology designed to share resources with existing CS voice services, data dimensioning must take into account the existing voice traffic, and grade of service required for that voice traffic.

This document will outline a basic dimensioning method for (E)GPRS, whether or not data is already implemented in the network.

The main inputs are:

Expected voice traffic

Voice Grade of Service

Data traffic expected

Average throughput per timeslot

Data Quality of Service if required

The dimensioning process will be as follows:

Calculate the number of radio timeslots required for both voice and data per cell



Calculate the number of TRXs required per cell

Dimension the EDAP per site

Calculate the number of PCUs required per BSC

Set the Gb link capacity per PCU

1.2 Dimensioning InputsThe inputs for the dimensioning process are normally provided by the operator, although these can be obtained by Nokia Siemens Networks if agreed in advance with the operator. This section defines the inputs required and how they can be derived. Actual collection of the data is not covered as this will vary from client to client. Dimensioning is always performed for some point in the future so that the network can be ready in time, so some forecasting may be required.

It is recommended that network data collected for dimensioning is collected during the cell voice weekday busy hour for 10 working days and averaged over those days. If no data network data is available, default or forecast values can be used.

1.2.1 Voice Traffic

As both voice and data share the same radio resources, we need to include voice traffic in our dimensioning. We require three items of voice data:

Voice traffic growthThe growth in voice traffic during the weekday voice busy hour over the last three or six months. This growth trend can be calculated either on a per cell basis or as an average over a particular area.

Expected voice trafficThe average expected voice traffic per cell in Erlangs during the weekday voice busy hour. The data collected from the network is combined with the voice traffic growth trend to obtain the expected voice traffic at the point in the future for which the dimensioning is being performed.

Voice Grade of Service (GoS)The GoS required by the operator for their voice offering. Normally this value is 2% for Air interface.

1.2.2 Data Traffic

If the network already has data activated, then we can use the real traffic figures with a suitable growth trend applied. If there is no data then the operator will have to provide the expected number of subscribers and their traffic profile. We require the following items of information:

Data traffic expectedThe amount of data traffic expected is very dependent on the data services offered, expected take-up rate and number of subscribers. The data traffic forecast can be given per cell or defined for an area. If given by area, the cell



traffic can be obtained either by simply dividing by the number of cells or by using a radio planning tool to spread the traffic according to morphology.

Average throughput per timeslotGiven enough capacity, the average throughput per timeslot is dependent on the average C/I distribution across the cell. If this is not known a value of 35 kbps for EGPRS is recommended. For GPRS the average throughput is 11 kbps if only CS1/CS2 is implemented or 15 kbps if CS1 to CS4 is implemented.

Data Quality of Service (QoS)Data QoS can be offered if the operator requires. QoS can take two forms in dimensioning: a simple minimum load requirement per cell or a guaranteed throughput per user. This second method is more involved as a process and can lead to much larger TRX requirements.

1.2.3 Other Inputs

These inputs are required for the dimensioning process but are not related to traffic figures only to configurations.

All operators have a traffic timeslot to TRX mapping. This mapping takes into account the number of signaling channels that are required and provides a quick way of knowing how many TRXs are required to support a given number of traffic timeslots. An example mapping that is commonly used is shown in Table 0-1.

Table 0-1: Traffic timeslot - TRX mapping in a cell

Number of TRXs

Number of TCHs Number of signaling channels

1 6/7 1/2

2 14 2

3 22 2

4 29 3

5 37 3

6 44 4

7 52 4

8 59 5

The number of free timeslots for CS voice traffic is given in Table 0-2 assuming default settings for the BSC parameters Free TSL for CS downgrade (95%) and Free TSL for CS upgrade (4s). The maximum of each setting is used.



Table 0-2: Number of free timeslots for CSW traffic

Number of TRXs

Free TSL for CS downgrade

Free TSL for CS upgrade

Free Timeslots

1 1 1 1

2 1 2 2

3 1 2 2

4 1 3 3

5 2 4 4

There is a difference in PCU capacity depending on the type of PCU card and BSS software version in use. Table 0-3 shows the current element limits.

Table 0-3 PCU types and capacity limits

PCU Type

BSC Types Network Elements BSS10.5 BSS11.5BSS10.5

ED BSS122)

BSS11 BSS133)

PCU BSCE2), BSC22), BSCi, BSC2i

BTS 64 64SEG 64 64TRX 128 128Radio TSLs 256 128Abis 16 kbps channels 256 256Gb 64 kbps channels1) 32 32

PCU-S BSCE2), BSC22), BSCi, BSC2i

BTS 64 64SEG 64 64TRX 128 128Radio TSLs 256 128Abis 16 kbps channels 256 256Gb 64 kbps channels1) 32 32

PCU-T BSCE2), BSC22), BSCi, BSC2i

BTS 64 64SEG 64 64TRX 128 128Radio TSLs 256 256Abis 16 kbps channels

256 256



Gb 64 kbps channels1) 32 32

PCU2-U BSCE2), BSC22), BSCi, BSC2i

BTS N/A 128SEG N/A 64TRX N/A 256Radio TSLs N/A 256Abis 16 kbps channels N/A 256Gb 64 kbps channels1) N/A 32

PCU-B BSC3i BTS 2 x 64 2 x 64SEG 2 x 64 2 x 64TRX 2 x 128 2 x 128Radio TSLs 2 x 256 2 x 256Abis 16 kbps channels 2 x 256 2 x 256Gb 64 kbps channels1) 2 X 32 2 x 32

PCU2-D BSC3i BTS N/A 2 x 128SEG N/A 2 X 64TRX N/A 2 x 256Radio TSLs N/A 2 x 256Abis 16 kbps channels N/A 2 x 256Gb 64 kbps channels1) N/A 2 x 32

note 1) E1/T1 frame limits the Frame Relay bearer to 31 or 24 PCM timeslots

note 2)BSCE and BSC2 not supported by BSS12 onwards

note 3) prelimninary figures for BSS13

2. Capacity DimensioningThis section describes the dimensioning process. An example is given for each sub-section that will be carried through all the dimensioning stages.

2.1 Radio InterfaceThe radio interface dimensioning must provide the minimum capacity possible for the traffic expected whilst maintaining the required Quality of Service. No half rate is assumed in these examples: that is, one TCH represents one timeslot and vice versa. However the HR Erlang-B table is added in chapter 8.1



2.1.1 Erlang B

Capacity for voice traffic is given by the Erlang B traffic formula. This formula provides the probability of a call being rejected because all channels are busy. It provides a relationship between offered traffic, Grade of Service (GoS) and the number of traffic channels. The traffic model is based on a series of assumptions:

The arrival of calls follows a Poisson distribution

Call arrivals are independent

Holding times are exponentially distributed

This model has been extensively used and is considered reliable.

An Erlang is defined as a channel, in this case a TCH, in use for one hour. Offered traffic is given in Erlangs and the Erlang B formula will give the number of TCHs required to meet the required GoS. For example, a cell is offered 4 Erlangs of traffic. If the operator requires a 2% GoS, the number of TCHs required will be 9.

However, we only actually need 4 TCHs to carry 4 Erlangs. The other 5 TCHs are there to provide the required GoS in case more than 4 calls should arrive at the same time.

As a packet-based service, data can use any spare capacity not used by voice. When a timeslot can be used by both voice and data, voice takes priority thus both GoS and the instant connection that voice users expect can be provided. As a background service, data can use the resources when these are not in use by voice services.

Our 9 TCHs will only carry 4 Erlangs of voice so the remaining capacity can be used by data. This gives us 5 Erlangs of data, also known as data Erlangs. Voice GoS is not affected as voice takes priority.

A data Erlang is defined as a channel (timeslot) used for data for one hour. It can be derived by dividing the hourly payload through the cell by the average throughput per timeslot as shown in Equation 0-1.

Equation 0-1: Data Erlang definition

As long as the offered data traffic is below the extra TCHs provided by the Erlang B formula for voice GoS, we can use this method to calculate the number of radio resources required.

The problem arises when the amount of data traffic is larger than this. We need another method to calculate the number of TCHs required. There is a also a counter based KPI (Actual UL/DL data throughput / nr of blocks) which copuld be used as well if the equation provides aproblem



2.1.2 Erlang B Approximation

In order to approximate the Erlang B function we must provide enough TCHs to carry both the voice and data traffic and guarantee the voice GoS.

The BSS will always keep some TCHs free so that a voice call can be served immediately. The number of free TCHs depends on the number of TRXs installed. As the traffic increases, more TRXs will be needed but also, as the traffic increase the greater the probability that more calls will arrive at the same time so more TCHs must be kept free.

In our example we had 4 Erlangs of voice traffic. Now we will add 2 Erlangs of data traffic. We will need to provide at least 6 TCHs just to carry the traffic which will require 1 TRX (Table 0-1). With default parameters, the number of free timeslots for 1 TRX is 1 (Table 0-2). So the total number of TCHs required will be 7.

The free timeslot calculation is circular, so by required 7 TCHs we need 2 TRXs which requires 2 free timeslots, not 1. So the final number of TCHs required is 8 timeslots.

However we have a problem as the Erlang B function tells us we need 9 timeslots to carry 4 Erlangs of voice at 2% GoS. Our approximation tells us we only need 8 timeslots. This method is not adequate if the data traffic is low relative to the voice traffic.

If we increase the amount of data traffic to 7 Erlangs, we would need 13 timeslots: 4 for voice traffic, 7 for data traffic and 2 free timeslots. Now we have sufficient timeslots to meet the voice GoS as Erlang B only requires 9.

2.2 Number of radio timeslots requiredEach method has a failing but by combining them we can eliminate these failings.

The Erlang B function is sufficient for small amounts of data traffic relative to voice traffic. The approximation method works for large amounts of data traffic relative to voice traffic. By choosing the function that gives us the largest number of timeslots we will always have enough capacity to carry both the voice and data traffic and guarantee a voice GoS.

This formula is given in Equation 0-2.

Equation 0-2: Number of timeslots required - combined method

Some of the data traffic will be carried by the dedicated data timeslots but the rest of the traffic will have to share resources with the voice traffic. The minimum number of timeslots required is what is needed to carry the voice traffic at a particular GoS and this is given by Erlang B. If the data traffic is sufficiently large then more timeslots will be needed and the maximum condition chooses the method that returns the largest number of timeslots.



Note that the free timeslots requirement always has to be met by the BSS as this prevents voice blocking. If necessary, the data territory will be downgraded in order to meet this free TCH requirement. It is this behavior that allows us to approximate to Erlang B and maintain voice GoS: a new call is allocated to a free timeslot and, if necessary, the data territory is downgraded to provide another free timeslot.

Once the number of timeslots required has been calculated, Table 0-1 can be used to obtain the number of TRXs.

2.3 Data Quality of ServiceData QoS can take two forms. In the simple form the operator simply requires the cell to support a certain data load. Data load is measured in kbps/cell. The only way to guarantee a minimum load is to dedicate timeslots for data.

The number of timeslots required is given by the minimum load expected divided by the average throughput per timeslot as shown in Equation 0-3.

Equation 0-3: Dedicated data timeslots required

The second method of data QoS involves guaranteeing a certain data load per user. This method is much more involved and can rapidly lead to large numbers of TRXs with a low utilization. This method is not described here but an explanation can be found in Appendix B.2 of [4].

2.4 Setting the default and dedicated data territoriesThe default territory size recommendation is at least 4 timeslots for serving 4 TSL DL capable terminals without a territory upgrade. The majority of modern phones are multi-slot class 10 devices that support 4 downlink timeslots. With sufficient HMC penetration, there may be a case of a default size of 5 timeslots.

If the data load on a site is going to be high then a larger default data territory can be defined. Although at the radio level voice can still use these resources so there is not much impact, the larger default territory will ensure than sufficient resources are provided at the Abis and PCU levels.

Normally enough default timeslots should be provided to support the data traffic in Erlangs or the device multislot class, whichever is larger. This is shown in Equation 0-4.

Equation 0-4: Setting the default territory

A minimum of one dedicated timeslot is recommended as the dedicated territory size unless Equation 0-3 gives a higher number. If no dedicated timeslots are provided then there is no guarantee of data service.



The default territory affects the number of PCUs required for a network. However, dedicated timeslots do not impact PCU capacity as the dedicated timeslots are considered part of the default territory.

Setting these parameters is not straightforward. Please see [3] for further information.

2.5 Dimensioning exampleThe aim of this example is to dimension a BSC for EGPRS and thus illustrate the process being described in this document. This example will be carried through the document.

2.5.1 Inputs

The following inputs are used in the calculation example:

One BSC with 40 BCFs, all with 3 BTSs

Site configurations (Figure 0-1)

Sub-urban sites – 25 BCFs – colored light blue

Urban sites – 15 BCFs – colored deep blue

Figure 0-1 Site configuration and amount

Voice traffic:

A sub-urban site on average has traffic of 8 Erl per BTS

An urban site on average has traffic of 15 Erl per BTS

Voice grade of service: 2%



Data traffic:

2 TRXs per cell to be enabled for data

Average throughput per timeslot = 35 kbps

Minimum cell data load – 50 kbps

Average data throughput per BTS

Urban sites - 275 kbps

Sub-urban sites – 100 kbps

Please note that these inputs have been chosen to best illustrate the dimensioning process. The Urban site data load is very, very high and sites like this will be rare in current networks.

2.5.2 Process

As we need to provide a minimum data capacity per cell, we first calculate the number of dedicated timeslots required using Equation 0-3.

Number of dedicated timeslots required = roundup(50 kbps/35 kbps) = 2

If no minimum load had been specified, one timeslot should be dedicated for data.

We need to convert the forecast data traffic into data Erlangs. As an Erlang is a measure of utilization, the conversion is done by dividing the load through the cell by the throughput per timeslot. This will give the number of timeslots that will have to be fully occupied to transfer the data load: the same definition as Erlangs.

So,

Urban site data Erlangs = 275 kbps/35 kbps = 7.9 Erl

Sub-urban site data Erlangs = 100 kbps/35 kbps = 2.9 Erl

We can now use Equation 0-2 to calculate the required number of timeslots. We will need to make a guess at the number of free timeslots required for the first iteration. The easiest way to do this is to add the voice and data Erlangs and dedicated timeslots and use the TRX mapping Table 0-1 to get the number of TRXs and then use the free timeslot Table 0-2 to obtain the number of free timeslots to be used.

For an urban site,

= 15 Erl (voice) + 7.9 Erl (data) + 2 (dedicated) = 24.9

Which is 25 timeslots giving us 4 TRXs. The number of free timeslots is 3.

For a sub-urban site,



= 8 Erl (voice) + 2.9 Erl (data) + 2 (dedicated) = 12.9

Which is 13 timeslots giving us 2 TRXs. The number of free timeslots is 2.

With this last calculation we can see that adding the number of free timeslots already causes us to increase the number of TRXs. This is why we must re-calculate the number of free timeslots after the first iteration.

So, using Equation 0-2 to calculate the number of free timeslots:

For an urban site,

= max(23, 15 + 3 + 7.9 -2) + 2

= 24 + 2

= 26 timeslots

Here the approximation to Erlang B returns a larger number of timeslots. We require 4 TRXs and so the number of free timeslots remains at 3. No more iterations are required.

For a sub-urban site,

= max(14, 8 + 2 + 2.86 -2) + 2

= 14 + 2

= 16 timeslots

In this example the Erlang B term returns a larger number of timeslots. We require 3 TRXs to support this and so we need to re-calculate the number of free timeslots as we originally assumed 2 TRXs. However, on using Table 0-2 we still only need 2 free timeslots for 3 TRXs so no more iterations are required.

In summary,

An urban site needs 4 TRXs per cell and 8 timeslots for default data territory

A sub-urban site needs 3 TRXs per cell and 4 timeslots for default data territory

Both configurations will have 2 timeslots for the dedicated data territory but we set the default territory as per Equation 0-4.

2.5.3 Quick check method

There may be cases when a network needs to be quickly evaluated to see if data performance will be adequate once data is activated. In these cases there may not be enough time to correctly dimension the radio network. A formula can be derived from Equation 0-2 that will return the number of timeslots available to carry data traffic during the voice busy hour.



If the number of timeslots is more than four, to account for class 10 devices, then data performance will be adequate. This is given in Equation 0-5.

Equation 0-5: Average available data timeslots at voice busy hour

Where the busy hour voice traffic is given in Erlangs and number of free timeslots can be derived from Table 0-2.

3. Abis interfaceThe Abis is the connection between the BTS and the BSC. All data that is carried on the air interface must have capacity provided for on the Abis.

If GPRS with CS1 and CS2 only is being activated then no further dimensioning is required for the Abis. The radio timeslot will already have been assigned a 16 kbps channel on the Abis. As the data-rate of CS2 is 12 kbps, this Abis channel is sufficient capacity.

However, if all GPRS coding schemes up to CS4 or EGPRS is being activated then extra capacity will have to be provided to carry the extra data. In the Nokia BSS this is achieved by defining a shared resource known as an EGPRS Dynamic Abis Pool (EDAP). All TRXs that are attached to the EDAP share its resources and it is common to define just one EDAP per site. If the site consists of several BTS cabinets, e.g. 6+6+6 implemented by using two UltraSite EDGE BTS cabinets, each cabinet needs pool of its own as TRXs from different cabinets are not able to share the same pool.

Inadequate EDAP capacity will lead to a reduction in throughput per timeslot with a corresponding impact on subscribers’ experience.

3.1 Abis dimensioningDimensioning the EDAP involves evaluating three conditions. The EDAP is dimensioned in 64 kbps Abis timeslots as this is the minimum granularity. This is also the amount of extra capacity a radio timeslot supporting MCS9 requires.

The EDAP must be large enough to support the number of devices at maximum bit-rate that the operator wishes to support. This is linked to the multislot capability of the mobile. If EGPRS is activated the maximum bit-rate is MCS9 (59.2 kbps) and each radio timeslot will need a full 64 kbps EDAP timeslot. So if the operator wishes to support one multislot class 10 device, four 64 kbps EDAP timeslots will be needed. If two class 10 devices need to be supported, then eight 64 kbps EDAP timeslots will be needed.

Therefore the first estimate of EDAP size is given in Equation 0-6 and is 4 Abis timeslots for a class 10 device.

Equation 0-6: Minimum EDAP size from condition 1



The EDAP must also be sufficiently large to provide every radio timeslot in use in the largest default territory with a full 64 kbps Abis timeslot and thus the ability to support MCS9. This is the second condition and is given in Equation 0-7.


If the BTSs attached to the EDAP have different default territory size we can take the average default territory size and correct this with a factor k, given in Table 0-4. This is the third condition and is given in Equation 0-8.


The theoretical maximum value for the reasonable k-factor is a number of BTSs (cells) sharing the EDAP (i.e. 3 for case of TRXs from three cell are sharing the same EDAP). The likelihood to have high traffic on all cells at the same is not typically high and thus the practical k-value is smaller. The k-values are given in Table 0-4 BTS multiplexing factor.

The theoretical smallest value for k is one. This assumes that the there is no traffic in the other cells when the fist cell has nominal traffic. This could be applied in areas where the traffic is low. To make it easier to consider other than recommended k-values some impact calculations is done. Table 2-8 show how the number of cells per PCU and per PAPU is affected by various EDAP and CDEF selections.

If the operator has only defined 1 timeslot as then territory the device multislot capability could be used as well to get indication for the minimum EDAP size.

Table 0-4 BTS multiplexing factor

Number of BTSs sharing EDAP K

1 1.0

2 1.3

3 1.5

The minimum EDAP will be given by the largest value returned by the three conditions described above as shown in Equation 0-9.

Equation 0-9: Minimum EDAP size

This equation is calculated for every site.



3.2 Dimensioning exampleFrom the radio dimensioning we have:

An urban site needs 4 TRXs per cell and 8 timeslots for default data territory

A sub-urban site needs 3 TRXs per cell and 4 timeslots for default data territory

At least one preferable two GPRS TRXs per cell is required. Both configurations will have 2 timeslots for the dedicated data territory but we set the default territory as per Equation 0-4.

We can now calculate the minimum EDAP size according to the equations in the previous section. All BCFs have three BTSs each and the default data device is class 10.

For the Urban site:

Minimum EDAP size 1 = 4 Abis timeslots


Minimum EDAP size 3 = 1.5 * average(8, 8, 8) = 1.5 * 8 = 12 Abis timeslots

Minimum EDAP size = max(4, 8, 12) = 12 Abis timeslots

For the Sub-urban site:



Minimum EDAP size 3 = 1.5 * average(4, 4, 4) = 1.5 * 4 = 6 Abis timeslots

Minimum EDAP size = max(4, 4, 6) = 6 Abis timeslots

In terms of total Abis capacity we must add the EDAP to the Abis resources required by the TRXs. Taking the following assumptions:

Each TRX requires 2 Abis timeslots (64 kbps each)

Each TRXSIG is 32 kbps (half an Abis timeslot)

Each OMUSIG is 32 kbps

So,

For the Urban site:

Total number of TRXs = 12 = 24 Abis timeslots (6 GPRS TRXs)

TRXSIG capacity = 12 * 0.5 = 6 Abis timeslots



OMUSIG capacity = 0.5 Abis timeslots

EDAP capacity = 12 Abis Timeslots

Total = 42.5 Abis timeslots

This will require 2 E1 or T1 PCMs. The actual mapping will depend on the PCM configuration used. This may also involve the EDAP split into two T1 lines. If the EDAP and the TRXs associated to it and their signaling links does not fit to the same T1 or E1 frame a new iteration is required. In this example in ANSI environment all the EGPRS resources do not fit to a single T1. One option is to map two cells under one and the third cell to an another T1 frame. One EDAP is created for two cells and the third will have an EDAP of its own. The number of EDAPs will increase and it will have an impact to PCU dimensioning as well. The iteration involves the following equations: Equation 0-6, Equation 0-7, Equation 0-8 and Equation 0-9

For the Sub-urban site:

Total number of TRXs = 9 = 18 Abis timeslots

TRXSIG capacity = 9 * 0.5 = 4.5 Abis timeslots

OMUSIG capacity = 0.5 Abis timeslots

EDAP capacity = 6 Abis Timeslots

Total = 29 Abis timeslots

This will require either 1 E1 or 2 T1 PCMs. The actual mapping will depend on the PCM configuration used.

To fulfill the given rule for BTS configurations requiring more than one E1 or T1 PCM line the TRXs shall be grouped into two groups: EGPRS-TRXs and non-EGPRS-TRXs. The TCH and the TRX signaling link of the non-EGPRS TRX are mapped on the second E1/T1 line.

The Figure 0-2 and Figure 0-3 shows the number of EGPRS TRXs as a function of the EDAP size that can be fitted to single E1 and T1 line.



Max number of TRXs as a funtion of the EDAP size (E1)

0

2

4

6

8

10

12

14

3 4 5 6 7 8 9 10 11 12

TSL

#T

RX

#EGPRS TRX (E116 Sig)

#EGPRS TRX (E1 32 Sig)

#EGPRS TRX (E1 64 Sig)

Figure 0-2 Maximum number of EGPRS TRXs on the E1 line as a function of the EDAP size

Max number of TRXs as a funtion of the EDAP size (T1)

0123456789

10

3 4 5 6 7 8 9 10 11 12

TSL

#T

RX

#EGPRS TRX (T116 Sig)

#EGPRS TRX (T1 32 Sig)

#EGPRS TRX (T1 64 Sig)

Figure 0-3 Maximum number of EGPRS TRXs on the T1 line as a function of the EDAP size

.

4. PCUIn this sub-section we calculate the number of logical PCUs that are required in the BSC. The actual data traffic is not considered as the PCU supports radio and Abis timeslots and these are considered to have already been correctly dimensioned previously in this process.



The actual allocation of EDAPs to PCUs may result in a more efficient dimensioning result but this is part of PCU planning service and would take a lot longer.

4.1 PCU dimensioningPCU dimensioning involves evaluating the connectivity limits per BSC and then calculating how many logical PCUs are needed to support this.

The element limits per PCU type are listed in Table 0-3. It is possible to have a mix of PCU types in a network so it may be necessary to perform this dimensioning for each PCU type implemented.

There is a maximum Gb throughput of 2 Mbps per PCU. In practice, it is very rare to have a Gb of this size so this element has been removed from consideration in the dimensioning process. However it may be necessary to consider this if the Gb dimensioning step returns a Gb of maximum size.

The PCU utilization used for dimensioning is normally 70% when considering the radio and Abis timeslots. This gives a utilization range of 60% to 80% in individual PCU for the known capacity requirements allowing the rest of the capacity to be used for territory upgrades

The number of EDAPs, Segments, BTSs and TRXs can reach the maximum values defined in Table 0-3 as these elements will not change quantity dynamically

Equation 0-10 is used to calculate the required number of logical PCUs per BSC

Equation 0-10 Required number of logical PCUs

Where,

“Radio timeslots” is the total number of radio timeslots in default PS territories,

“Abis channels” is the total number of Abis channels connected to PCUs. This consists of the TCHs, one 16 kbps Abis channel for each default PS territory radio timeslot, and EDAP channels; four Abis channels per each 64 kbps EDAP timeslot.

“EDAPs” is the total number of EGPRS Abis Pools. (The maximum number of EDAPs that can be allocated to both PCU1 and PCU2 is 16.)

“BTSs” is the total number of BTSs under a SEGment having GENA=Y plus the number of non-segmented BTSs having GENA=Y.

“SEGs” is the total number of SEGments having GENA=Y

“TRXs” is the total number of data TRXs (GTRX=Y)



4.2 Dimensioning exampleTo calculate the required number of PCUs we need to evaluate each term within Equation 0-10:

Number of EDAPs = one per site = 40 EDAPs

Number of BTSs = 40 * 3 = 120 BTSs

Segment concept is not in use so the number of segments is the same as BTSs

Number of TRXs = 120 * 2 (as only 2 TRXs per cell are enabled for data) = 240 TRXs

Number of (default) radio timeslots = 25 * 12 + 15 * 24 = 660 radio timeslots

Number of Abis channels = 25 * (12 TCHs for radio timeslots + 6 * 4 Abis channels for EDAP) + 15 * (24 TCHs for radio timeslots + 12 * 4 Abis channels for EDAP) = 1980 channels

We will take the element limits for a PCU-T or PCU-B from Table 0-3 as these are the PCU types currently being supplied.

So,

PCUs required = roundup(max( 3.7, 11.0, 2.5, 1.9, 1.9, 1.9)

The minimum number of logical PCUs required is 11.

The actual hardware to be installed depends on the number of BCSUs. The full BSC2i configuration has 8+1 BCSUs. Each of these needs to have an identical configuration, so in this case two PCU cards are needed in each BCSU, total 18 PCU plug-in units, as each plug-in unit can support only one logical PCU. For the BSC 3i 660, there will be 6+1 BSCUs but each plug-in unit can support 2 logical PCUs, so only 6+1 PCU cards are needed. In BSC3i 1000/2000 there could be 10+1 BCSUs each having 2 PCU1 or up to 5 PCU2 plug in units. One possible solution could be BSC3i 1000/2000 with 2+1 BCSUs each serving up to 200 TRX. Each BCSU is equipped with 3 PCU2 variants total 12 usable logical PCUs.

5. Gb Link DimensioningEach PCU has at least one Gb link towards the SGSN. In case of redundant Gb two independent links are needed.

The outcome of the Gb link dimensioning process is the average size of the Gb link to carry the data traffic forecast. This part of the process affects SGSN dimensioning and should be conducted together with PS Core planning.



The Gb should be capable of supporting the instantaneous data traffic being carried by all cells connected to a particular PCU. If there is insufficient capacity the effective user rate at the radio cell will be reduced.

5.1 Gb Link Dimensioning – BSS point of viewThe aim in the Gb dimensioning is to ensure that the Gb link is large enough to handle the short term peak traffic of any single EDAP. In addition to this the target is to estimate that the Gb link is large enough to support simultaneous traffic of several EDAPs. This is highly dependent on the traffic distribution. Equation 0-11 is used to calculate the average Gb link size (= Frame Relay Bearer Channel capacity).

Equation 0-11 Minimum Gb size – first evaluation

The k-factor is based on the estimate of the short term traffic distribution. If no specific information about the distribution is available it is recommended to use the default values. Table 0-5 gives the k values.

The theoretical minimum k-value (1.25) is assuming that the short term traffic is totally unequal, meaning that when one EDAP is full of traffic the others within the same PCU have no traffic.

The theoretical maximum k-value is the number of EDAPs allocated into one PCU. This assumes that all the EDAPs are heavily loaded at the same short term period and the Gb link is supposed to carry such traffic without additional delays.

In reality some delay is allowed during heavy simultaneous short term traffic bursts and thus it is assumed that k-values greater than 2 are rear.

If no estimate is available for short term traffic distribution the default value shall be used. To show more cost effective results unequal distribution may be considered.



Table 0-5: Example of k-factor for Gb link

k-factor

Short term traffic distribution

Unequal (low likelihood of heavy simultaneous short

term traffic)

Default Equal (high likelihood of heavy simultaneous short

term traffic)

30% 50% 70%

1.4 2 3

During the planning phase when individual EDAPs are associated to PCUs more accurate values for individual Gb links are calculated taking into account the usage of individual E1/T1 links.

To make it easier to consider other than recommended k-values some impact calculations is done. Table 2-8 show how the number of cells per PCU and per PAPU is affected by various Gb, EDAP and CDEF selections.

5.2 Gb Link Dimensioning Example – BSS viewThe used input for Gb link dimensioning are:

15 Urban sites having EDAP size 12 TSL

25 Sub-urban sites having EDAP size 6 TSL

Average EDAP size = (15*12 TSL + 25*6 TSL)/40 = 8.25 TSL

The average Gb size according Equation 0-11 is 2 * 8.25 TSL = 16 TSL

Practical Gb-size would be 15 and 16 TSL to fully occupy an E1 line.

5.3 Gb Link Dimensioning – SGSN point of view

The SGSN connectivity is one aspect that needs to be considered when defining the Frame Relay Bearer Channel capacity (Gb- link size). To efficiently utilize the



internal PCM lines and external E1/T1 lines the calculated Gb link sizes are adjusted to closest practical value taking the PAPU connectivity in to account.

Table 0-6: Number of Frame Relay bearer per PAPU as a function of the bearer size

Nokia SGSN <SG6 HW SG 6 HWtotal bearer TSL PQU-Amax # PCM per PAPU

PAPU6 * 32 TSL

PAPU16 * 32 TSL

bearer size

#bearer channels per

E1

#bearer channels

per T1total # bearer ch per PAPU

total # bearer ch per PAPU

4 7 6 48 1285 6 4 36 966 5 4 30 807 4 3 24 648 3 3 24 649 3 2 18 48

10 3 2 18 4811 2 2 12 3212 2 2 12 3213 2 1 12 3214 2 1 12 3215 2 1 12 3216 1 1 12 32… 1 1 6 1624 1 1 6 1625 1 0 6 16… 1 0 6 1631 1 0 6 16

5.3.1 PAPU capacity

This document gives only the principle of SGSN capacity. The actual capacity figures may vary depending on the SW and HW release. Consult the relevant SGSN product documentation for relevant figures. In addition to the connectivity in case of Frame Reay based Gb link, there are three independent limiting factors which are considered: subscriber capacity (attached subscribers), throughput and the total number of PDP contexts.

Table 0-7: SGSN Configurations and Capacities [6]



1. The maximum throughput is 500 Mbps in 2G only mode (for Gb over FR or Gb over IP) and 1 Gbps in 3G only mode.

2. Data Throughput per PAPU: ~30 Mbps (2G only, for Gb over FR or Gb over IP) or ~60 Mbps (3G only)

5.4 Gb Link Dimensioning Example – SGSN viewThe total traffic in this 40 site area expressed as throughput is 25*100 kbps + 15*275 kbps < 10 Mbps i.e. clearly within a capacity of a single PAPU. If due to the connectivity limit, more than one PAPU is be required the Gb link sizes needs to be reconsidered. If the sizes can not be decreased, either more PAPUs are needed for these cells or IP based Gb should be considered.

In this example there was 11 PCUs.

It was calculated that the average Gb link is 15 or 16 TSL.

Applying Table 0-6 it can be verified that single PAPU supports up to 12 Frame Relay Bearer Channels of size 15 t o16 TSL. This is just one more that is required for 11 PCUs.

The SGSN consideration did not change the Gb calculation in this example.



6. ImplementationThe process of implementing EGPRS is logical and not that complex but for best results it is advisable to follow all the steps. This section gives a brief description of the implementation process.

6.1 DimensioningThe first step is to dimension the network to support the traffic that is expected. This can be done by following the instructions and method in this document. The dimensioning can be performed at the same time as the network audit as both are inputs into the rest of the implementation process.

6.2 Network AuditOnce we know what we need in order to support data services, we can audit the network to find out what is currently in place and thus know what needs to be done. Some of the items that will have to be checked include, but is not limited to:

Software versions at the BTS, FXC and BSC

BTS, PCU and BSC types

Number of TRXs and PCUs

Number of PCMs, Abis mapping and Gb size

Once all this information has been collected, we can compare with what is needed to identify the list of pre-activation items that need to be completed.

6.3 PlanningThe planning and design activities can be conducted in parallel with the pre-activation work. The planning activities include:

Setting the (E)GPRS parameters

Allocating the BTSs to each PCU

Setting new HR load thresholds or timeslot definitions if necessary

Deciding on the activation plan

Designing and setting up a test plan for post-activation

6.4 Pre-activationBefore activation, the network must be prepared as EGPRS activation is a remote activity. Examples of pre-activation activity are:

BTS swap for EGPRS capable BTSs (e.g. Nokia IntraTalk to UltraSite EDGE BTS)



TRX swap for EGPRS capable TRXs or installation of extra TRXs

Software upgrades for FXC, BTS or BSC

Installation of extra PCU cards

Ordering and installation of extra PCM capacity for either Abis or Gb

Necessary cross-connections for any Abis re-mapping

Any PS Core network upgrades as required.

BTS/BSC re-parenting

6.5 ActivationThe activation itself is relatively straightforward:

1. The appropriate license files are enabled

2. Abis re-mapping, if necessary

3. The EDAPs are created on the PCMs and attached to the correct PCU

4. The EGPRS parameters are set on network elements

5. Some basic field testing is performed to confirm activation

Any work related to changing the Abis or Gb timeslot mapping needs to be synchronized so that the changes are activated at the same time frame at both ends to minimize the site or service outage.

Some operators conduct some fairly detailed field testing on a small sub-set of sites to fully confirm that the expected performance is being achieved, but this does not have to be done on the activation night in question. The priority then is to ensure the network is up and functioning correctly.

6.6 MonitoringOnce EGPRS has been activated, data services have to be added to the normal network monitoring process. Data KPIs will have to be agreed with the operator, either using existing NSN formulas or designing new ones. Most standard KPIs have already been defined according to the counters available.

In order to calculate these KPIs and to provide general information on the performance of the data network certain measurements need to be activated in the BSC. The measurement period and granularity will depend on the network but in general all measurements should be activated over 24 hours and with a granularity of not more than 60 mins.

The following data measurements, in addition to the CS measurements, are recommended for all EGPRS networks:



Packet Control Unit

Coding Scheme

Dynamic Abis

RLC Blocks per TRX

Quality of Service

Frame relay

The following measurements are recommended if certain features, like NCCR or EQoS are enabled:

PBCCH

GPRS Cell re-selection

GPRS RX Level and Quality

Enhanced Quality of Service

Gb over IP

7. References[1] (E)GPRS Radio Networks – Planning Theory v2.0

[2] EDGE Transmission Network Planning Guidelines for internal use

[3] (E)GPRS Radio Networks – (E)GPRS Parameters v2.0

[4] GSM, GPRS and EGPRS Performance, 2nd Edition, John Wiley and Sons, Ltd, 2003

[5] BSC Site IP Connectivity Guidelines (BSC NED)

[6] SGSN Product Description (SGSN NED)

[7] GERAN Radio/Official guidance material: https://sharenet-ims.inside.nokiasiemensnetworks.com/Open/357688489

[8] GSM Access/Official guidance material: https://sharenet-ims.inside.nokiasiemensnetworks.com/Open/358201397



8. AppendixesTable 2-8 . Example PCU configuration for three sector sites and the reference figures for cells per PCU and cell per PAPU if all the cells were similar. The throughput figures are for PCU1 only. In PCU2 the figure is 100% for all given configurations.

n+n+n with single EDAP

low low low mix Medium Medium Medium Medium Mix

INPUTS A B A B A B C A C

CDEF 2 1 2 1 4 4 2 4 2

EDAP size 4 4 4 4 6 6 6 6 6

OUTPUTs # of EDAPs 8 12 5 5 4 6 7 4 2

# of cells 24 36 15 15 12 18 21 12 6PCUPCM Abis ch U 176 228 110 95 144 216 210 144 60PCUPCM Abis ch U% 69% 89% 80% 56% 84% 82% 80%

Dynamicsfree PCUPCM Abis ch 80 28 51 112 40 46 52 average free ch per cell 3.3 0.8 1.7 9.3 2.2 2.2 2.9

Throughput

% of cells supporting 4 RTSL with MCS-9 (RLC/MAC 236.8 kbps) 100% 50% 100% 78% 100% 100% 100%% of cells supporting at least 2 RTSL with MCS-9 plus 2 RTSL with MCS-7 (RLC/MAC 208 kbps) 100% 100% 100% 100% 78% 100% 100% 100%% of cells supporting at least 4 RTSL with MCS-7 (RLC/MAC 179.2 kbps) 100% 100% 100% 100% 100% 100% 100% 100%Average number of simultaneous 4 RTSL MCS-9 users limited by EDAP size 1 1.5 1.5 1.5

Gbminimum Gb link size (single link) 5 5 5 7 7 7 7 recommended Gb link size (single link) 5 5 5 8 8 8 8



recommended Gb link size (two links), each 5 5 5 6 6 6 6

PAPU prior SG6 HW

number of Gb links (PCUs) under a PAPU (single link) 36 36 36 24 24 24 24 number of cells per PAPU (single link) 864 1296 540 288 432 504 288

PAPU with SG6 HW

number of Gb links (PCUs) under a PAPU (single link) 96 96 96 64 64 64 64 number of cells per PAPU (single link) 2304 3456 1440 768 1152 1344 768



8.1 HR Erlang-B table

(e)gprs radio networks - dimensioning guideline

Documents

data dimensioning

dimensioning aspects

dimensioning example215

dimensioning example174

dimensioning inputs51

dimensioning example122

dimensioning process

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