GPRS/EDGE GPRS/EDGE

•• GPRS Network OverviewGPRS Network Overview

•• Scope of GPRS/EDGE OptimizationScope of GPRS/EDGE Optimization

•• GPRS/EDGE TestingGPRS/EDGE Testing

•• Monitoring GPRS/EDGE KPI Monitoring GPRS/EDGE KPI ’’ss

•• GPRS/EDGE ParametersGPRS/EDGE Parameters

•• GPRS/EDGE Common issuesGPRS/EDGE Common issues

GPRS Network OverviewGPRS Network Overview

Data Network ArchitectureData Network Architecture

GPRS TransmissionGPRS Transmission

GPRS NW ElementsGPRS NW Elements• PCU

• Packet Control Unit (PCU) functionalities include handling Network Services Signaling, BSSGP Signaling, routing of signaling messages, Radio Link Control (RLC) and Media Access Control (MAC) preload and transferring of user data.

• It further performs the channel access control functions, radio channel Management functions like power control congestion control, scheduling data transmission and protocol conversion between Gb and Um interfaces.

• SGSN

• Authentication, ciphering, location updating, GPRS Attach, Paging, Packet routing, transfer and traffic management etc.

• GGSN

• Activation of GPRS Packet Data Protocol (PDP) contexts.

• Routes Mobile originated packets to the right destination.

• It translates data formats, signaling protocols and address information for communication.

Scope of GPRS/EDGE Scope of GPRS/EDGE OptimizationOptimization

GPRS/EDGE OptimizationGPRS/EDGE Optimization

Optimizations possible for network operatorsOptimizations possible for network operators

Many of optimizations that can be done, especially with the TCP protocol, are optimizations that are out of the scope for network operators. Some of the optimizations are however up to the network operator to deal with:

• Latency decreasing

• TBF release time counter, i.e. not released immediately when sending or receiving stops

• Time-slot usage in GPRS

• Using the optimal coding scheme

GPRS/EDGE OptimizationGPRS/EDGE OptimizationOptimizations not possible for network operatorsOptimizations not possible for network operators• TCP window size

Since TCP is a reliable transport, if any data is lost in transmission, TCP must be able to retransmit it. Thus TCP remembers all the sent data in a buffer until the other side acknowledges receiving it. The size of this buffer is the TCP window size.

• Increased initial window (TCP)

MSS (Maximum segment size) follows window size: If (MSS <= 1095 bytes) then win <= 4 * MSS; If (MSS >1095 bytes & < 2190 bytes) then win <= 4380; If (MSS<=2190 bytes) then win <= 2 * MSS; Draw back: Can cause congestion at TCP layer for large packets

• TCP segment sizes

The default IP Maximum Datagram Size is 576The default TCP Maximum Segment Size is 536The default Header size is 20

• Selective Acknowledgments (TCP)

TCP may experience poor performance when multiple packets are lost from one window of data. With the limited information available from cumulative acknowledgments, a TCP sender can only learn about a single lost packet per round trip time. An aggressive sender could choose to retransmit packets early, but such retransmitted segments may have already been successfully received. A Selective Acknowledgment (SACK) mechanism, combined with a selective repeat retransmission policy, can help to overcome these limitations. The receiving TCP sends back SACK packets to the sender informing the sender of data that has been received. The sender can then retransmit only the missing data segments. This memo proposes an implementation of SACK and discusses its performance and related issues.

GPRS/EDGE TestingGPRS/EDGE Testing

GPRS/EDGE TestingGPRS/EDGE Testing•• Drive TestingDrive Testing

•• Moving TestMoving Test•• How to analyze the DTHow to analyze the DT

•• Test Case Test Case D:\GPRS Activities\Reports\Test Case GPRS- EDGE.ppt

•• Factors affecting data rates for moving usersFactors affecting data rates for moving users

•• Static Testing Static Testing •• GPRS attach/detachGPRS attach/detach

•• PDP Context activation/deactivationPDP Context activation/deactivation

•• Ping test (Ping test (A ping is a test to see if a system on the Internet is working. A ping is a test to see if a system on the Internet is working. "Pinging" a server "Pinging" a server tests and records the response time of the server. Pinging multitests and records the response time of the server. Pinging multiple computers can be helpful in ple computers can be helpful in finding Internet bottlenecks, so that data transfer paths can befinding Internet bottlenecks, so that data transfer paths can be rerouted a more efficient way.)rerouted a more efficient way.)

•• HTTP test HTTP test

•• UL/DL Throughput using FTP server UL/DL Throughput using FTP server ((TheThe amount of data transmitted amount of data transmitted through the Internet connectors in response to a given request. through the Internet connectors in response to a given request. The more "throughput" you deliver The more "throughput" you deliver

to your customers, the better (if you're charging enough).to your customers, the better (if you're charging enough).

• Objective : Objective : Performance at BTS,PCU/Performance at BTS,PCU/GbGb, SGSN/, SGSN/GnGn, GGSN/, GGSN/GiGi, IP cloud, IP cloud

GPRS Attach Flow DiagramGPRS Attach Flow Diagram

GPRS Detach Flow DiagramGPRS Detach Flow Diagram

PDP Context activation Flow PDP Context activation Flow DiagramDiagram

Successful GPRS Attach/Detach Successful GPRS Attach/Detach

Attach Detach Process

GPRS Attach/Detach Failure GPRS Attach/Detach Failure

Attach Detach Failure

GPRS Attach Success vs. Failure GPRS Attach Success vs. Failure

vs.

PDP Activation SuccessPDP Activation Success

Network/User released PDPNetwork/User released PDPUser deactivated PDP context

PDP Activation failurePDP Activation failure

Attach accept missing so no PDP context activation takes place

Ping TestPing Test

GPRS/EDGE TestingGPRS/EDGE Testing•• End To End Data Network Testing. Trouble shooting

• Performance Logs at MS

• Configuring performance log *

• K-12 analyzer trace at BSC/PCU

• Signaling links of BSCs are tapped with a “T” connector and

trace is recorded in protocol analyzer

• Ethereal Trace at SGSN & GGSN

* Useful for every one using Data services for checking throughput

Performance LogPerformance Log

* Useful for every one using Data services for checking throughput

K12 Trace K12 Trace

* Useful for every one using Data services for checking throughput

Ethereal TraceEthereal Trace

* Useful for every one using Data services for checking throughput

Monitoring GPRS/EDGE KPI Monitoring GPRS/EDGE KPI ’’ss

Monitoring GPRS/EDGE KPI Monitoring GPRS/EDGE KPI ’’ssKey performance indicators, or simply KPI, are indicators which are particularly important for a services performance. First one has to define the KPIs associated to a service, and then one has to determine how to measure the KPIs.

· Accessibility (Accessibility has to do with the users being able to set up a call and access radio resources)

· Retainability (Retainability covers the ability to keep up a call)

· Quality (Quality deals with how good the connection is)

GPRS KPIs• TBF

• Throughput

• PayloadThe payload is the bits that get delivered to the end user at the destination without header.

Monitoring GPRS/EDGE KPI Monitoring GPRS/EDGE KPI ’’ss

GPRS %UL/DL CS1, 2 Usage(%)

EDGE %UL/DL MCS 5~9 Usage(%)

EDGE %UL/DL MCS 1~4 Usage(%)

GPRS/EDGE %Packet territory upgrade reject(%)

GPRS/EDGECountShare of rejected allocations due to lack of resources

GPRS/EDGECountsTBF Drop due to radio, high CS traffic, ABIS Congestion, Flush

GPRS/EDGE %TBF Drop Rate(%) UL + DL

GPRS/EDGE %TBF success rate(%) UL + DL

GPRS/EDGEKb/sUL + DL RLC throughput (GPRS & EDGE)

GPRS/EDGEKBTotal Packet payload UL + DL (GPRS & EDGE)

The flush procedure is used, for example, when the MS has stopped data sending in a given cell and has moved to another cell. The SGSN sends a FLUSH-LL PDU to the BSC to ensure that LLC PDUs queued for transmission in a cell for an MS are either deleted or transferred to the new cell.

GPRS/EDGE ParametersGPRS/EDGE Parameters

GPRS/EDGE ParametersGPRS/EDGE Parameters

With this parameter you define whether the GPRS capability is enabled in the BTS during the normal operation of the cell.gprsEnabled

With this parameter you enable or disable the EGPRS capability in the BTS. All TRXs of the BTS have to be EDGE capableegprsEnabled

With this parameter you define which BTSs in the SEG may be used for GPRS or EGPRS without signal level measurements. This parameter defines the signal level compared to non BCCH layer offset. When the value of this parameter is higher than the value of the parameter non BCCH layer offset the direct GPRS access to non BCCH layer BTS is applied. This is used in initial channel allocation and reallocation.

directGPRSAccessBts

With this parameter you determine the amount of PSW-only channels in a cell. The value of the default GPRS capacity parameter must be higher than or equal to the value of the dedicated GPRS capacity parameterdefaultGPRScapacity(CDEF)

With this parameter you determine the amount of PSW-only channels in a cell. The value of the dedicated GPRS capacity parameter must be smaller than or equal to the value of the default GPRS capacity parameterdedicatedGPRScapacity(CDED)

With this parameter you indicate typical throughput per timeslot in the BTS, depending on the direction and (M)CS. The parameter is used when comparing the TSL capacities between different BTSs.throughputFactor_mcs1mcs9ulcs

With this parameter you indicate typical throughput per timeslot in the BTS, depending on the direction and (M)CS. The parameter is used when comparing the TSL capacities between different BTSs.throughputFactor_mcs1mcs9dlcs

With this parameter you indicate typical throughput per timeslot in the BTS, depending on the direction and (M)CS. The parameter is used when comparing the TSL capacities between different BTSsthroughputFactor_mcs1mcs4ulcs

With this parameter you indicate typical throughput per timeslot in the BTS, depending on the direction and (M)CS. The parameter is used when comparing the TSL capacities between different BTSs.throughputFactor_cs1cs4ulcs

With this parameter you indicate typical throughput per timeslot in the BTS, depending on the direction and (M)CS. The parameter is used when comparing the TSL capacities between different BTSs.throughputFactor_cs1cs4dlcs

With this parameter you define whether the BCCH TRX or other TRXs are preferred in GPRS channel allocation preferBCCHfreqGPRS2

With this parameter you can define whether CS3&CS4 is used in the BTS.cs3Cs4Enabled

With this parameter you indicate the GPRS cell reselection criterion c31Hysteresis

CDED = 20 means that (20/100*6) = 1.2 TSs as it will round down Dedicatied TS i.e.1 TSs (here 6 is No of TCH TSs in a TRX – 8 minus BCCH TS– SDCCH TS = 6)CDEF = 70 means that (70/100*6) = 4.2 TSs as Packet switch territory. It will round down i.e.4 TSs (including the Static TS) (here 6 is No of TCH TSs in a TRX – 8 minus BCCH TS– SDCCH TS = 6)

GPRS/EDGE Parameters GPRS/EDGE Parameters ((contdcontd))

With this parameter you define the negative offset of the C32 reselection criterion for the duration of the GPRS penalty time (GPET) after the MS has placed the cell on the list of the strongest carriers. It is used by the mobile station as part of its calculation of C32 for the cell reselection process. The parameter can be changed in 10 dB steps. Value 70 dB means infinity

GPRS temporary offset (GTEO)

With this parameter you define the offset of the C32 reselection criterion for a adjacent cell.GPRS reselect offset

With this parameter you define the duration for which the GPRS temporary offset (GTEO) appliesGPRS penalty time

With this parameter you define the minimum power level the MS has to receive to allocate resources from the BTSgprsNonBCCHRxlevUpper

With this parameter you define the threshold when a reallocation to a better BTS must be made. BTS with the direct GPRS access BTS option on is selected. If there are no BTSs with direct GPRS access BTS set to on.gprsNonBCCHRxlevLower

With this parameter you define the maximum transmission power level a mobile station can use when accessing a packet control channel in the cell for GSM 1800/1900 bands.gprsMsTxPwrMaxCCH1x00

With this parameter you define the maximum transmission power level a mobile station can use when accessing a packet control channel in the cell.gprsMsTxpwrMaxCCH

With this parameter you indicate the maximum number of retransmissions allowed on the PRACH.gprsMaxRetrans

With this parameter you define additional hysteresis applied in READY state for selecting a cell in the same routing area.gprsCellReselHysteresis

With this parameter you can adjust the MCS and modulation preferences. This is the offset added to reported GMSK mean BEP values before BEP table lookups. The value applies to both uplink and downlink directions. The parameter is used in EGPRS link adaptation.

egprsMeanBepOffsetGmsk

With this parameter you can adjust the MCS and modulation preferences. This is the offset added to reported 8PSK mean BEP values before BEP table lookups. The value applies to both uplink and downlink directions. The parameter is used in EGPRS link adaptation.

egprsMeanBepOffset8psk

With this parameter you indicate the maximum block error rate in unacknowledged mode. The unit is parts per thousand. The parameter is used in EGPRS link adaptation.egprsMaxBlerUnAckMode

With this parameter you indicate the maximum block error rate of first transmission in acknowledged mode. The parameter is used in EGPRS link adaptation.egprsMaxBlerAckMode

With this parameter you enable or disable EGPRS link adaptation on cell level. If disabled the system uses the MCS value defined by initial MCS for acknowledged mode or initial MCS for unacknowledged mode parameters or a lower MCS.egprsLinkAdaptEnabled

With this parameter you indicate the MCS used at the beginning of a TBF for unacknowledged mode. The parameter is used in EGPRS link adaptation.egprsInitMcsUnAckMode

With this parameter you indicate the Modulation and Coding Scheme (MCS) used at the beginning of a TBF for acknowledged mode. The parameter is used in EGPRS link adaptationegprsInitMcsAckMode

With this parameter you define the minimum power level an MS has to receive before it is allowed to access the adjacent cell.gprsRxlevAccessMin

GPRS/EDGE Common issuesGPRS/EDGE Common issues

• RAC Mismatch (BSS & CORE)

• Wrong Parameter settings & Dedicated time slot

• HR on all TRXs of a segment

• NO GPRS capable TRX

• TXN issues

• PCU rejections

• Operational Issue

• Rare cases

• Poor radio condition

• SGSN rejections

• GGSN rejections

• IN rejections

Thanks