1

(E)GPRS Network Dimensioning

2

At the end of the module the participant will be able to:

•Describe the procedures of dimensioning of a (E)GPRS network

Objectives

3

Network Element and Configuration Audit - Summary

•BSC •GGSN

•IP/MPLS/IPoATM•-

•Applicatio•n Servers

•(co•-•located

•2G•SGSN

•BTS

•HLR/•AC/•EIR

•TCSM

•TC

•MSC/VLR

•Abis •Gb•BSC •BSC

•GGSN•GGSN

•-•backbone

•Application •Servers

•2G•SGSN•2G

•SGSN•BTS

•HLR/•AC/•EIR

•HLR/•AC/•EIR

•TCSM

•TC

•MSC/VLR

•Gn•Gi

•Gs

•

•RF interface

• Capacity on time slots

• Traffic volume

•MS/Client parameters

• GPRS/EDGE capability and release

•Multislot support

•Abis interface

• Abis size / dimensioning

• # of E1/T1s

• GPRS/EDGE traffic

•Gb interface

• Bearer size

• IP v.s. FR

• Dimensioning

•BTS

• GPRS territory

• BTS HW considerations (TRX & other cards)

• BTS SW

•BSS

• PCU variant & dimensioning

• PCU strategy in mixed configuration

• BSS SW and features

•SGSN

• Unit capacity (PAPU etc.)

• BSS Gb Flow control

•RF

•Server

• load

• settings (Linux/Win)

•HLR

• QoS profile

• GPRS settings

4

• The aim behind the preparation of deployment plan is to– adapt the existing network configuration for (E)GPRS– maximize the TSL data rate (RLC/MAC) and multislot usage – minimize the impact of PSW services on CSW services (and vice

versa)– take all the hardware and software considerations into account– keep investment controlled

• The analysis of the different options can give exact picture about the network based on:– Hardware types, software releases– Features, parameters – Current network structure and functionality– Coverage, quality and capacity characteristics of BSS

Deployment Planning

5

Capacity Planning – Inputs

• The following information should be available to define the available/required capacity:• BSC

• BSC variant

• PCU variant

• Restrictions (Abis, pools, DSPs)

• BTS

• Segment

• TRX

• SW version

• PCU pooling

• BTS

• TRXs

• Time slots (Territory)

• Voice traffic load

• TRX configuration

• Signaling channels

• Free timeslots (Guard TSL)

• GPRS Territory (DED/DEF/ADD.)

• Deployment

• Coverage

• Interference

• Throughput/TSL

• GPRS/EDGE

• Data volume

• Traffic mix – Voice/Data

• Abis

• Available time slots

• Abis sharing probability

• TRX/PCM

• PCM usage

• TRX signaling

• Link management

• E1/T1 links

6

Air Interface Capacity Calculations

• The dimensioning of the radio network can be based on two different approaches:

– Available capacity:• Calculation determines how (E)GPRS resources are available in a given

system• The calculation input is a pre-defined system configuration• The calculation output is the available traffic capacity• Alternatively, the available capacities for different alternative

configurations can be calculated

– Required capacity:• It is calculated to design a network that supports the defined amount of

traffic and targeted performance level• The inputs are additional traffic volume, type, and performance

requirements• The output is the needed amount of traffic dependent hardware and

associated software configurations

7

Air interface Capacity Calculations – Available Capacity

• The available capacity for data services can be estimated when the existing BTS hardware and the current voice traffic load is known.

• The next step is to calculate the capacity of the air interface related to the different cell / segment options analyzed before.

• The air interface capacity calculation contains the following items:– TSL data rate estimation– PSW Multislot usage (with CSW traffic volume and free TSLs)

• The TSL data rate calculations and the territory figures together for all the cells/segments can give the calculation results of available air interface capacity

Load CS - (Erlang-B) MarginAvailable for

(E)GPRS

Total Capacity = CS + Margin (free TSL in CS) + (E)GPRS Traffic x Territory Occupancy

8

Air Interface Capacity Planning – Required Capacity

• The required capacity calculation is the calculation of number of TSLs needed for both circuit switched traffic and packet switched traffic in each cell in order to achieve a given blocking probability for circuit switched traffic and required throughput for packet switched traffic. Using subscriber information is more complicated, data user penetration must be known and user data amount per busy hour must be estimated– User profile for BH (example)

• PSW BH traffic in kbps and in MB• CSW BH traffic in Erlang • Service Mix: e.g. 45 % Voice, 10 % Video Streaming, 20 % PoC, et

– Traffic distribution• Number of users• Traffic density • GPRS/EGPRS multiplexing

•32kbps•0.45 /2.8•1(UL)/32 (DL) kbps•Video (Streaming) GBR•8kbps•1.8 /1.8•8 (UL)/8 (DL) kbps•PoC•THP=ARP=1 NBR

•0.1(UL)/0.1(DL) kbps•0.25(UL)/1(DL) kbps•0.5 (UL)/3(DL) kbps

•12•mErl•BH Traffic

•0.045/0.045•0.1125/0.45•0.225/1.35

•Voice•BH Traffic in MB

•NRT•MMS (Background) NBR•NRT•Email (Background) NBR•NRT•Browsing (Interactive) NBR

•Voice channel•Voice•Bearer•Application

•32kbps•0.45 / 2.8•1(UL)/32 (DL) kbps•Video (Streaming) GBR•8kbps•1.8 /1.8•8 (UL)/8 (DL) kbps•PoC•THP=ARP=1 NBR

•0.1(UL)/0.1(DL) kbps•0.25(UL)/1(DL) kbps•0.5 (UL)/3(DL) kbps

•12•mErl•BH Traffic

•0.045/0.045•0.1125/0.45•0.225/1.35

•Voice•BH Traffic in MB

•NRT•MMS (Background) NBR•NRT•Email (Background) NBR•NRT•Browsing (Interactive) NBR

•Voice channel•Voice•Bearer•Application

•GBR = Guaranteed Bit Rate = RT THP = Traffic Handling Priority•NBR = Non-Guaranteed Bit Rate = NRT ARP = Allocation Retention Priority

9

•Peak throughput• 12 Kbps (GPRS CS1-2)

•1 TSL

•TSL Capacity

•C/I distribution

•TSL sharing•User throughput•per allocated TSL

TSL Sharing

• TSL sharing reduces data pipeline capacity if there is not enough TSL available for GPRS.

• As GPRS traffic increases there will the need to introduce new TRX's in order to avoid excessive TSL sharing.

•Reduces data pipeline capacity

10

Rate Reduction

• CSW and GPRS traffic levels (offered loads) vary dynamically.

•TRX 1•TRX 2

•CCCH•TS •TS •TS •TS •TS •TS •TS

•TS •TS •TS •TS •TS •TS •TS•TS

•Circuit Switched•Packet Switched

•Circuit Switched

•TRX 1

•TRX 2

•CCCH•TS •TS •TS •TS •TS •TS •TS

•TS •TS •TS •TS •TS •TS •TS•TS •Packet Switched

•A)

•B)

•GPRS Territory = 6 TSLs

•GPRS Territory = 1 TSL

•Time = T1

•Time = T2

•Two 3 TS mobiles each achieve•3*12kb/s = 36kb/s DL•(CS-2 @ 10% BLER)

•Two 3 TS mobiles now each •achieve 12/2 kb/s = 6kb/s DL

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Abis Basic Concepts-PCM frame (E1)

One 64 kbit/s (8 bits) channel in PCM frame is called timeslot (TSL)One 16 kbit/s (2bits) channel timeslot is Sub-TSLPCM frame has 32 (E1) or 26 (E1) TSLs

•One Radio timeslot corresponds one 16 kbit/s Sub-TSL (BCCH, TCH/F etc.) and one TRX takes two TSLs from Abis

0 MCB LCB123456789

101112131415161718 TCH 0 TCH 1 TCH 2 TCH 319 TCH 4 TCH 5 TCH 6 TCH 7202122232425 TRXsig2627 BCFsig28293031 Q1-management

•TRX Signalling

•Site Level Signalling •TRX1

•Q1-management needed if TRS management under BSC

•MCB/LCB required if loop topology is used

12

• Coding scheme Data rate

• MCS-1 8.8 kbit/s

• MCS-2 11.2 kbit/s

• MCS-3 14.8 kbit/s

• MCS-4 17.6 kbit/s

• MCS-5 22.4 kbit/s

• MCS-6 29.6 kbit/s

• MCS-7 44.8 kbit/s

• MCS-8 54.4 kbit/s

• MCS-9 59.2 kbit/s

•Abis PCM allocation (fixed + pool)

Transmission req. for EGPRS coding schemes in Abis

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Abis PCU-PCU Connectivity Capacity Planning

•Abis Capacity of PCU or PSE

•Abis 2

•Abis3 •Abis4

•Abis 1

•75%

•In EGPRS networks the main limitation defining the number of PCUs is the Abis channels limits. The available capacity depends on the PCU version, in case of PCU pooling the amount of pooled PCUs. In this case one has to assume the summed capacity of all PCUs in the pool. The 75% connectivity limit should still be considered. The distribution of the individual Pools along with the associated Radio resources between the PCUs will be done by the system.

•BTS 1

•BTS 1 •From planning's point of view the Default Capacity is used for each BTS(Cell), •1 RTSL = 1 Abis channel

•BTS 2

•BTS 5 •BTS 6 •BTS 7

•BTS 3 •BTS 4

•BTS 8

•BTS 9

•Abis 5•BTS 11•BTS 9 •BTS 10

•BTS 19

•BTS 12 •BTS 13 •BTS 14 •BTS 15

•BTS 16 •BTS 18

•BTS 20

•BTS 17

•BTS 21

•Capacity for dynamic territory upgrades in a certain BTS(cell)

14

PCU Connectivity Planning

• The connectivity planning for maximum capacity is based on the proper set of DEFAULT and Abis size

– To provide enough capacity for territory upgrade the 75 % utilization in the connectivity limits

– The DEFAULT* is allocated to the cells (BTSs(cells) in segment)- if the default capacity is too big more PCUs are needed.

– The Abis Pool ** is allocated to the sites (BCFs). Higher Abis pool size provides more MCS9 capable TSLs on air interfaces, but on the other side, higher DAP size needs more capacity on E1s and more PCUs as well.

• Abis channels limits for different logical PCUs, in brackets 75%:

15

Gb Interface Protocol Stack

FRFR

NS NSMAC

BSSGPBSSGP

RLC

RELAY

BSS Gb SGSN

LLC

GSM RF

SNDCP

•Physical layer : PCM frame of 32 or 24 TSL, each 64kbit/s

•FR layer : end to end logical virtual circuit are created for data transmission (PVC, SVS). They addressed by e-to-e PVCI and node to node DLCI. FR provides NS with DLCI & FR bearer channel.

•NS :

16

•SGSN

•BSS 1

•Bearer Channel_1

•Bearer Channel_2

•DLCI_16

•DLCI_17

•DLCI_16

•DLCI_17

•DLCI_18

•Bearer Channel_3

•DLCI_16

•Bearer Channel_5

•Bearer Channel_6

•DLCI_16

•DLCI_17•PAPU 3

•PAPU 2

•PAPU 1•PCU 1

•PCU 2

•PCU 3

•LA

•RA 1

•BTS_6

•BTS_3

•RA 2•BTS_8

•BTS_22•Bearer Channel_4

•DLCI_16

•DLCI_17

•BSS 2

•PCU 3•LA

•RA

•BTS_22

•NSEI_7•NS-VCI_6

•NS-VCI_9

•NSEI_3•NS-VCI_4

•NS-VCI_1

•NS-VCI_11

•NSEI_2•NS-VCI_5

•NS-VCI_8

•NS-VCI_3

•NSEI_1•NS-VCI_7

•NS-VCI_2

•NSEI_7•NS-VCI_6

•NS-VCI_9

•NSEI_3 •NS-VCI_4

•NS-VCI_1

•NS-VCI_11

•NSEI_2 •NS-VCI_5

•NS-VCI_8

•NS-VCI_3

•BSSGP•NS•FR

•Signal•Data

•Data & Signal

•NSEI_1

•BVCI_22

•BVCI_0

•BVCI_22

•BVCI_0

•BVCI_8

•BVCI_8

•BVCI_6

•BVCI_0

•BVCI_0

•BVCI_22

•BVCI_6

•BVCI_0

•BVCI_0

•BVCI_3

•BVCI_22

•BVCI_0

•NS-VCI_7

•NS-VCI_2•BVCI_3

•BVCI_0

Gb, Logical Structure

17

Gb dimensioning

• The dimensioning of the Gb interface can be based on two different approaches:

• Gb EDGE dimensioning based on Abis pool:– Each PCU has typically one Gb link towards the SGSN. In case of redundant Gb, two

independent links are needed. – The Gb should be capable of supporting the instantaneous data traffic being carried by all

cells connected to a particular PCU.– Gb size = k * Maximum Abis pool size for that network area.– The k-factor is based on the estimate of the short term traffic distribution. If no specific

information about the distribution is available the minimum (k=1.25) may be used, which means one fully used Abis pool takes all the Gb capacity (can be seen as minimum)

– K-factor can range from 1.25, 1.4, 2, 3, ….(values above 2 are normally not used)

• Gb EDGE dimensioning based on traffic figures:– The basic dimensioning of the Gb interface depends mainly on EGPRS traffic. Because of

very different coding schemes and data rates, it is extremely relevant to know whether the traffic is GPRS or EDGE.

– Therefore, the main decision needed for Gb dimensioning is the amount of payload used, on average, for EGPRS traffic during a busy hour and the deviation of the traffic between the peak and minimum values.

– Data volume per PCU can be calculated (or estimated) as the total data volume per PCU or based on subscriber information.

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SGSN DimensioningDimensioning Rules

• Dimensioning criteria for the number of SGSN per basic/extension units:

1. Subscriber capacity: 30 000 subscribers simultaneously2. Data processing capacity: 12 Mbit/s3. Capacity of 64 kbit/s Gb interfaces: 256

ie. increment the number of units if any one of the above figures is exceeded until SGSN is fully equipped.

19

DIMENSIONING EXERCISE (NSN Case Study)

20

INPUT GIVEN FOR THE GPRS PLANNING

• No. of time slot required for the GPRS territory : DEDICATED TS=1 and DEFAULT TS=1

• No. of BTS(cells) per abis pool i.e the No. of sectors prevalent : 3

• No. of time slot used for abis pool on Abis (64 Kbps) : 3 Time slot

• % of upgrade is the Teritory upgrade for the future perspective : 10 %

• No. Of sites planned per BSC : 100

• Access rate (CIR) is the speed required at the GB interface : 256 Kbps

21

OUTPUT REQUIRED

• No. of sites per NSEI required

• No. of NSEI required in BSC

• No. of PCU or No. Of BCSU required

• No. Of Gb Link required

• No. of E1 required from the BSC to BTS

22

How to calculate what

• No. of EGPRS resources used in 1 sector * No. of sectors : 2 x 3 • No. of time slot/sector * no of time slot used for Abis pool :- 2 *

3 = 6 • So total time slots per site 6 + 6 = 12• 1 NSEI support 256 time slot with upgrade % as 10 so total no

of time slots which can be equipped is 256 - 10% of 256 = 230.4 ~ 230

• So no. of sites per NSEI is 230/12 = 19.16 ~ 19 • So no NSEI required / BSC : 100 / 19 = 5.2 +1 (for future use)

~ 6• If 2 NSEI supports 1 BCSU so then no. of PCU required : 6/2 = 3• No. of NSEI required is equivalent to the no. of Gb link = 3• On 1 E1 we can get 31x64 = 1984 , so access rate can be

given by 1 E1 = 1984/ access rate (256) = 1984 / 256 ~ 7

23

•BSC

•Metro •Hub

•SGSN

•GGSN

•ELECTRICAL ET

•GB LINK•GB LINK

Over view of GPRS Network

24

•NSEI 1 •NSEI 2

•NSEI 3

•NSEI 4

NSEI PLANNING