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White Paper
Performance Management and Optimization Method for
Mature GPRS Networks
Prepared by
Mehmet BEYAZ
TTG International, L.T.D.
www.ttgint.com
3/10/2015
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Contents
GPRS PERFORMANCE MANAGEMENT....................................................................................................5
GPRS KPIs ................................................................................................................................................6
GPRS BSS KPIs..........................................................................................................................................8
BSS Accessibility..................................................................................................................................8
BSS Retainability .................................................................................................................................9
BSS Integrity......................................................................................................................................10
GPRS CN KPIs.........................................................................................................................................11
CN Accessibility .....................................................................................................................................11
CN Quality and Mobility....................................................................................................................12
GPRS NETWORK OPTIMIZATION...........................................................................................................13
GPRS RAN/BSS.......................................................................................................................................13
CONCLUSIONS.......................................................................................................................................14
ABBREVIATIONS, ACRONYMS, AND TERMS..........................................................................................16
REFERENCES..........................................................................................................................................19
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Abstract
This paper discusses performance management and optimization method for mature GPRS networks. A
selection of GPRS KPIs based on network performance counters, measurement systems, as well as possible
threshold values and their analysis and interpretation.
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INTRODUCTION
Today, many wireless operators are focused on providing mobile internet access. A large
variety of technologies has contributed to the operators’ vision of true mobility and seamless
roaming. The currently prevailing technology providing true mobile Internet access on a
European scale is general packet radio service (GPRS).
The popularity of Short Messaging (SMS), MMS and the growing demand for mobile data
services prompted the implementation of a Packet Switched (PS) overlay on Circuit Switch
(CS) network, opening the public Land Mobile Network (PLMN) operators to the data
networking market and internet-based services. However, voice services stil remains the core
business for many operators. This trend and some other factors have bringup the factor of
growing requirement to optimize GPRS.
This paper covers the performance management and optimization of GPRS networks. A
performance management overview is presented, including proposed Key Performance
Indicators (KPIs) for the RAN as well as the Core Network (CN).
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GPRS PERFORMANCE MANAGEMENT
Performance management involves collecting and analyzing performance data from different
resources and constitute set of KPIs. Network operators typically define a set of KPIs and
stratified target thresholds in line with planning, marketing and businesspriorities.
Performance management teams which are responsible, for example, for certain districts of
major cities, towns of a certain size, or large rural areas, as well as routing areas or IP
backbones periodically monitor various KPIs to isolate areas not achieving target
performance. Optimization method/s are then kick off to ensure that performance targets are
met. KPIs are usullay forumed by using performance counters provided by network elements.
Statistics based on network element counters can be verified and supplemented by additional
measurements obtained by active testing with test Mobile Station (MS), protocol analyzers at
different interfaces in the network. Such additional performance measurement systems can
emphasize aspects of GPRS performance not evident from network counters alone.
The figure 1 shows the GPRS network architecture as well possible measurement points for
network counters and protocol analyzers. Standard network surveillance or alarm monitoring,
as well as long-term trending and analysis of KPIs, can assist in identifying problems and
helping to achive desired performance.
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Figure 1. GPRS Network and interfaces
GPRS KPIs
Selecting meaningful KPIs is a pioneer to continuous performance monitoring. GPRS KPIs
should cover the Base Station System (BSS) and the CN to account for end-to-end
performance, i.e., from the MS to the Gi interface on the gateway GPRS support node
(GGSN). Typically, KPIs for the BSS and the RAN reflect accessibility, retainability, and
integrity. CN KPIs focus on Routing Area Update (RAU) behavior, congestion metrics on
several interfaces, and system accessibility. Table 1 provides an overview of GPRS KPIs.
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Network Element Attribute KPI
BSC/PCU Accessibility PRACH
BSC/PCU Accessibility PAGCH (immediate assignment
rejection rate)
BSC/PCU Accessibility Congestion time
BSC/PCU Accessibility PDCH availability
BSC/PCU Accessibility DL/UL data throuhput
BSC/PCU Accessibility PDTCH Allocation Failure Rate
BSC/PCU Accessibility TBF Set-up Failure rate
BSC/PCU Quality TBFs per PDTCH
BSC/PCU Integrity RLC BLER
BSC/PCU Quality RLC Re-transmission
BSC/PCU Quality CELL Re-selection Time
BSC/PCU/SGSN Accessibility GBL data throuhput
BSC/PCU Retainability % of TBF Preemtion
SGSN Accessibility GPRS Attached Success Rate
SGSN Accessibility GPRS Attached Time
SGSN/GGSN Quality GPRS RAU Success Rate
SGSN/GGSN Quality GPRS RAU Success Time
SGSN Accessibility PDP Context Activation on Success
Rate
SGSN Accessibility PDP Context Activation Time
SGSN/GGSN Quality Congestion on Gi, Gb and Gn
End-to-End Quality Delay
End-to-End Quality Application Throughput
Table 1. KPIs and Thresholds for GPRS System Performance
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GPRS BSS KPIs
BSS Accessibility
The RAN has an important role in overall system performance, since it typically represents
the bottleneck in terms of resources and available physical transmission rates on the air
interface as well as phishical links and PDCH. Accessibility from a RAN/BSS perspective is
mainly a function of radio resources, signaling capacity, links (Gb) and BSS parameter
configuration. Packet channel requests on the Packet Random Access Channel (PRACH),
which establish the first contact of an MS with the network. Unsuccessful access requests due
to congestions can indicate poor radio conditions.
The total number of PRACH requests may include instances where the MS sends multiple
consecutive access bursts. Immediate assignment the BSS’ response to the packet channel
request from the MS is indication for identifying congestion; the immediate assignment
rejection rate is based on the number of immediate assignment rejections over the total
number of PRACH requests. Such rejections are due mainly to the lack of Packet Data
Channel (PDCH) resources in the cell. Although extreme delays on the Um interface or lack
of resources in the Base Station Controller (BSC), Packet Control Unit (PCU), or other nodes
may cause rejections.
Cell congestion levels can be calculated as no PDCH available for a certaion time period
within the GPRS busy hour, which may be expressed as a percentage of 60 minutes. GPRS
congestion levels should be think of Traffic Channel (TCH) demand point of view for CS. On
the other hand, CS busy hour traffic can affect PS available resources for connections. This is
clearly depends on the BSS configuration in terms of preemption and the allocation of fixed
PDCHs.
The number of packet access requests and the transmitted data volume during CS busy hour
can be used to determine whether the CS resource requirements are pushing the PS traffic
into congestion or whether the GPRS traffic demand is high. On the other hand, it should be
noted that GPRS busy hour are not necessarily matching, but are offset to those of the CS. It
may, therefore, be useful to consider PS traffic expressed as bytes at the busy hour statistics
when evaluating GPRS congestion. The PDCH allocation failure rate sometimes referred as
GPRS blocking and the Temporary Block Flow (TBF) setup failure rate are additional KPIs
that can indicate congestion. A certain amount of GPRS blocking may be acceptable
considering that CS orianted cell dimensioning strategies may allow for approximately %2
blocking rate or quality of service (QoS).
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BSS Retainability
RAN CS congestion, high volumes of data traffic, or a combination of both can give rise to a
series of other symptoms that may affect not only the system accessibility but also the
retainability and quality for ongoing TBFs connections. TBFs are subscriber-specific,
bothway, logical connections associated with a varying number of PDCHs, established to
facilitate data transfer between the MS and the BSC/PCU. In other words, the data service
may be accessed successfully, but the connection quality can range from unacceptably bad to
very good. The PCU reserves the requested number of PDCHs for new connections during
the packet allocation procedure. PDCHs available in the Packet Switch Domain (PSD) at any
given moment are used for the assignment, although more than one TBF may be assigned to a
PDCH. The GPRS multiplexing capability can support multiple TBFs per PDCH and allocate
new TBFs on already used PDCHs.
Note that: The number of PDCHs requested by an MS is determined mainly by its multislot
class. On-demand PDCHs make temporary use of idle CS TCHs, which are swithed back to
the CSD when they have not been used for a defined period of time.
New GPRS users can be blocked if the PSD cannot be expanded to accommodate new TBFs
when the TBF-per-PDCH reached the limit, where resulting in PDCH allocation failures
(packet access reject) and TBF set-up failures.
Note that: The PDCH allocation failures may occur after successful immediate assignment.
These failure rates can be biased by TBF upgrade failures. System vendors may provide a
feature that allows the TBF to request additional PDCHs if it has been set up initially with
fewer PDCHs than the multislot class of the MS allows.
While TBF multiplexing and the allocation of fewer resources than the MS can support work
together to provide flexible system accessibility, both mechanisms can have an undesirable
effect on throughput performance and Bandwidth Delay Product (BDP) per user. In addition,
the absolute or average number of allocated PDCHs per TBF in a given cell provides another
standpoint on GPRS QoS. Multiplexing is point out when this KPI increases beyond 1.
Because the Logical Link Control (LLC) throughput performance per TBF is affected by the
multislot class of an MS, the distribution of different multislot MSs in the network should be
identified to set reachable throughput targets.
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BSS Integrity
The changeable radio propagation and RAN interference conditions are the main factors
affecting the BSS. The Carrier-to-Interference (C/I) ratio has a critical impact on the
maximum physical transmission rate of a PDCH and TCH. The GPRS coding schemes,
whose ranges of optimum performance are related to the C/I ratio, help to
lower the impact of radio interference on the radio channel’s BLock Error Eate (BLER).
Remaining uncorrectable bits and corrupted radio blocks set off the Radio
Link Control (RLC) Automatic Repeat Request (ARQ) mechanism if the TBF is operated in
RLC-acknowledged mode. The probability of RLC retransmissions hence reduces the
physical transmission rate of the channel, adds additional delays to the air interface, and
affects the end-to-end RoundTrip Time (RTT) of higher layer protocols. The Bit Error Rate
(BER) of a radio channel (also categorized into receive/transmit quality (Rx/TxQual) levels
ranging from 0 to 7 and the percentage of RLC retransmissions should be tightly monitored.
Desirable RLC retransmission rates are generally below %1. Moreover, TCP window sizes,
TCP retransmission time-outs, typical IP packet size distributions, and the application
protocol affect the effective throughput on the application layer.
BSS Quality and Mobility Cell reselection, as well as possible Location and Routing Area
Updates (LAUs and RAUs), has a weakening effect on throughput performance. During cell
reselection, the MS releases all channels to read the system information of the destiontion
cell. The radio outage time begins with the channel release and ends with the completion of
the cell reselection process and the establishment of downlink and uplink TBFs on PDCHs of
the destination cell. Cell reselection may also require LAUs and RAUs if the destination cell
is part of another location and routing area. This introduces extra signaling in the network as
and increases the time until new TBFs are established on the destination cell.
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GPRS CN KPIs
In the GPRS optimization CN GPRS plays a fundamental role in assessing overall system
performance. Along with the key elements of CN performance assessments are success rates
for GPRS are;
1. Attached
2. Packet Data Protocol (PDP) context activation
3. RAU
4. Paging
CN Accessibility
The GPRS attach request message is the first contact of the MS with the serving GPRS
Support Node (SGSN) then a TBF has been established successfully. It contains the
Temporary Mobile Subscriber Identity (TMSI), Mobile Network Code (MNC), and Mobile
Country Code (MCC), as well as Location and Routing Area Identity. Following identity
checks of the International Mobile Equipment Identity (IMEI) or the International Mobile
Subscriber Identity (IMSI), as well as authentication and ciphering request messages, may be
issued by the SGSN. In order to retrieve the IMSI if no entry is found for it, the SGSN uses
the old location area information to
identify the old SGSN where this terminal was last served. The SGSN may require Home
Location Register (HLR) signaling over the Gr interface to identify profiles for unknown
IMSIs. Unsuccessful authentication and ciphering may also contribute to the attach rejects.
SGSN counter statistics for the Gb interface can be used to establish the probability of attach
failures and the distribution of failure reasons. Some of the common failure reasons are:
1. Attach requests from users who are not subscribed to the GPRS network
2. International roamers from networks without roaming agreements
3. Software and hardware levels on specific MSs
4. Attach time-outs (excessive delays, failed responses from the MS)
5. Network failures.
Gb interface congestion and dimensioning should be taken in accout when assessing the
GPRS attach success rate. The Gb interface interconnecting the BSS with the SGSN is a
Frame Relay (FR) connection over an E1/T1 link. Ofcours this is depending on the CN
design strategy, this FR connection may be transported over
intermediate networks, such as Asynchronous Transfer Mode (ATM) backbones supporting
FRF5 (FR over ATM). FR congestion control and discard mechanisms, can be monitored to
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identify congestion levels on the FR data Link Connection Identifier (DLCI) carrying the
BSS GPRS protocol (BSSGP) protocol Data Units (PDUs). Measuring the PDP context
activation Success Rate (SR) is also important.
GGSN provides the allocated IP address to the SGSN via the create PDP context response,
which, in turn, sends the activate PDP context accept message to the MS. Hance, a successful
PDP context activation establishes IP connectivity between the MS and the GGSN, which
then forwards or routes the traffic to external networks. Common reasons of PDP context
activation failure include network link failures, incorrect DNS records, and inappropriate
configuration of MSs. Counters on the SGSN and GGSN provide the basis for establishing
the PDP context activation failure rates and the distribution of the causes. The IP backbone
can be based on different network architectures, QoS-aware, high-capacity backbones. When
a PDP context is in active state, GPRS tunneling protocol (GTP) encapsulation is used to
create Virtual Circuit (VC) connections between GPRS support nodes (GSNs) supporting the
data flow across the backbone. The GTP VC connection is released as soon as the context
becomes inactive.
CN Quality and Mobility
The RAU Success Rate (RAUSR) is an another important key metric for GPRS system
performance. All idea about this KPI contributes to the understanding of end user throughput
performance. A GPRS-attached MS can issue periodic, intra-SGSN and inter-SGSN RAUs,
depending on its situation. Periodic RAUs are used to ensure that the MS is stil reachable and
are so treated as a intra-SGSN updates. The non-periodic update requests can be triggered
when the MS transcends a routing area
boundary during cell reselection. The intra-SGSN RAU procedure is used when the new
routing area of the target cell is administered by the same SGSN. RAU rejects can reasons of
authentication and ciphering failures, RAU time-outs due to excessive delays, lower layer
link failures, and/or protocol failures. Performance metrics can be used for GPRS attach,
context activation, authentication time, DNS response time, TCP connection establishment
time, and additional application-specific indicators.
Throughput RTT DELAY RLC Re-
transmission
TBF Multiplexing TBF / PDTCH PS Immediate
Assignment
Reject
PDTCH
Allocation
Failures
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B
S
S
Mobility Mobility
CS Congestion PS Congestion
Poor Coverage Poor Coverage Poor Coverage PCU Capacity PCU Capacity
N-Cell Definitions N-Cell
Definitions
N-Cell Definitions CS Congestion CS Congestion CS Congestion CS Congestion
Interface Interface Interface PS Congestion PS Congestion PS Congestion PS Congestion
Fault Fault Fault Fault Fault Fault Fault
C
N
Transmission Transmission GSN Configuration GSN Configuration GSN
Configuration
GSN
Configuration
IP Backbone
Gb Congestion Gb Congestion Gb Congestion Gb Congestion Gb Congestion Gb Congestion RADIUS
Gn Congestion Gn Congestion Gn Congestion Gn Congestion Gn Congestion Gn Congestion
Packet Loss Packet Loss Gr Congestion Gr Congestion Packet Loss Packet Loss
Packet Loss Packet Loss MS
DHCP DHCP
RADIUS RADIUS
DNS DNS
PDP Context
Activation Time
PDP Context
Activation Success
RAU Time RAU Success Authentication
Figure 3. KPI Effect Matrix
GPRS NETWORK OPTIMIZATION
GPRS network optimization plans can vary from operator to operator and may be tied to
specific circumstances, although certain practices and approaches have a more universal
nature. On the one hand, optimization should be understood as an ongoing activity in the
perspective of network rollout and expansion, and one that is concerned mainly with an
optimal integration of new base stations, BSCs, and CN elements. The RAN, however, more
than any other part of the GPRS system, changes constantly as new cells are introduced and
existing ones are reconfigured, relocated, or modified. Optimization staffs are also support
network operations on an ongoing basis. On the other hand, optimization activities may be
triggered when certain areas of the network fail to meet performance thresholds.
GPRS RAN/BSS
The RAN has a leading role in GPRS optimization. Coverage planning, frequency planning,
and neighbor cell definitions and configuration have a clear impact on radio conditions and
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interference levels, where they should be carefully controlled. Such as frequency retunes and
neighbor cell corrections often improve high percentages of intra-cell and vital inter-cell
handovers or TCH drops and handovers due to downlink quality. Sufficient channel
dimensioning strategies of Base Transceiver Stations (BTSs) for CS and PS services should
make sure minimum congestion levels about %2 or less. BSS features and parameter
optimization also further improve system performance. An important feature that can be
offered by PS broadcasts, is network assisted cell change, which allows a considerably
reduced radio outage time during cell reselection process. When in packet transfer mode, the
MS sends packet cell change notifications to the BSS before entering the cell reselection
procedure. The network’s response contains minimum required system information about the
destination cell, which allows the MS to initiate TBF connections in the destination cell
before cell reselection is actually completed.
Depending on GPRS priority and preemption parameters, on-demand PDCHs can be treated
as available or blocked for CS connections, regardless of a PDCH’s current usage state.
Generally, priority and preemption algorithms are affected by using dynamic allocation or
adapting half-rate channels for CS connections, implementation vary from vendor to vendor.
Operators typically allow the preemption of on-demand PDCHs to allocate new CS
connections when needed.This methodology, conflict with a performance guarantee for
GPRS users in congested situations. Where TCH requirements are high and PDTCH
preemption causes GPRS blocking (packet immediate assignment rejects) to be %2 or higher
during the CS busy hour, a strategy for allocating FPDCHs can improve accessibility
performance. FPDCHs may not be preempted, so the defined number of time slots is
guaranteed for GPRS users. Additionally, if GPRS blocking is % 2 or higher during the
GPRS busy hour, the allocation of FPDCHs can be considered. The FPDCHs can also
increase throughput performance during blocked and congested situations. Ensuring an
acceptable level of GPRS performance without significantly affecting the CS service
becomes part of the operator’s FPDCH allocation methodology.
CONCLUSIONS
GPRS system performance depends on performance management method, which identify
performance shortcomings, and on network optimization, which is conducted continuously
and also when triggered by problems. GPRS performance optimization activities should focus
on;
 C/I
 BLER
 Radio capacity
 PCU
 GSN dimensioning
 RADIUS
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 DNS
 DHCP
 Mobility
 Usage of BSS
 Usage of CN features
 Configuration
All these contribute to the end-to-end performance experienced by the user. Active
measurement systems can be used to accurately capture application throughput and RTTs.
Network operators should ensure that GSM and GPRS networks are balanced in terms of
capacity performance management and optimization, acknowledging the increasing
importance of GPRS in the context of supplementing IP services over UMTS.
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ABBREVIATIONS, ACRONYMS, AND TERMS
3G: Third generation
APN: Access point name
ARQ : Automatic repeat request
ATM : Asynchronous transfer mode
BCCH: Broadcast control channel
BDP : Bandwidth delay product
BECN : Backward explicit congestion notification
BER : Bit error rate
BLER : Block error rate
BSC : Base station controller
BSS : Base station system
BSSGP: BSS GPRS protocol
BTS : Base transceiver station
CCCH : Common control channel
C/I : Carrier-to-interference (ratio)
CN : Core network
CPU : Central processing unit
CS : Circuit switch(ed)
CSD : Circuit switch domain
DE : Discard eligible
DHCP : Dynamic host configuration protocol
DLCI: Data link connection identifier
DNS: Domain name service
FECN: Forward explicit congestion notification
FPDCH : Fixed packet data channel
FR : Frame relay
FRoATM : FR over ATM
FTP :file transfer protocol
GGSN: Gateway GPRS support node
GPRS :General packet radio service
GSM : Global system for mobile communication
GSN : GPRS support node
GTP : GPRS tunneling protocol
HLR : Home location register
IMEI : International mobile equipment identity
IMSI : International mobile subscriber identity
IP : Internet Protocol
IPoA : IP over ATM
ISP : Internet service provider
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KPI : Key performance indicator
LAN : Local area network
LAU : Location area update
LLC : Logical link control
MCC : Mobile country code
MNC : Mobile network code
MS: Mobile station
MSC: Mobile switching center
multi-RAT: Multi-radio access technology
N-cell : Neighbor cell
NMS : Network management system
NTE : Network termination equipment
PAGCH: Packet access grant channel
PBCCH : Packet broadcast control channel
PCU : Packet control unit
PDA : Personal digital assistant
PDCH : Packet data channel
PDP : Packet data protocol
PDU : Protocol data unit
PLMN : Public land mobile network
PRACH: Packet random access channel
PS : Packet switch(ed)
PSD : Packet switch domain
QoS : Quality of service
RADIUS : Remote authentication dial-in user service
RAN : Radio access network
RAND : Random number
RAU : Routing area update
RLC : Radio link control
RTT : Roundtrip time
Rx/TxQual : Receive/transmit quality
RxQual : Receive quality
SGSN : Serving GPRS support node
SI : System information
SIM : Subscriber identity module
SNMP : Simple network management protocol
SQI : Speech quality index
SRES : Signed response
TBF : Temporary block flow
TCH : Traffic channel
TCP : Transmission control protocol
TMSI : Temporary mobile subscriber identity
UMTS : Universal mobile telecommunications system
UTRAN : UMTS terrestrial radio access network
VC : Virtual circuit
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VLR : Visitor location register
WAN : Wide area network
WiMAX: Worldwide interoperability for microwave access
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Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760
TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996
www.ttgint.com
REFERENCES
1. 3GPP, TS 44.060 V6.10.0 (2004–11), Technical Specification 3rd Generation Partnership Project.
2. Technical Specification Group GSM/EDGE Radio Access Network; General Packet Radio Service (GPRS); Mobile Station (MS) –
Base Station System (BSS) Interface; Radio Link Control/Medium Access Control (RLC/MAC) Protocol.
3. 3GPP, TS 03.64 V8.11.0 (2003–04), Technical Specification Group GSM/EDGE Radio Access Network; General Packet Radio
Service (GPRS); Overall Description of the GPRS Radio Interface.
4. 3GPP, TS 04.60 V8.23.0 (2004–05), Technical Specification Group GSM/EDGE Radio Access Network; General Packet Radio
Service (GPRS); Mobile Station (MS) – Base Station System (BSS) Interface; Radio Link Control/Medium Access
5. Control (RLC/MAC) Protocol .
6. R. Chakravorty and I. Pratt, “Performance Issues with GPRS,” Journal of Communications and Networks (JCN), Vol. 4, No. 2,
December 2002, pp. 226–281.
7. S. Hoff, M. Meyer, and A. Schieder, “A Performance Evaluation of Internet Access via the General Packet Radio Service of GSM,”
Vehicular Technology Conference (VTC) ’98, May 1998, Ottawa, ON, Canada.
8. D.E. Comer, “Internetworking with TCP/IP – Principles, Protocols, and Architectures,” 4th Edition, Prentice Hall, 2000.
9. D. Michel and N. Ramasarma, “GPRS Measurement Methodologies and Performance Characterization for the Railway
Environment,” Wireless Communications and Networking Conference (WCNC) 2005, March 2005, New Orleans, LA.
10. G. Heine, “GSM Networks: Protocols, Terminology, and Implementation,” Artech House Publishers, 1999.
11. 3GPP, TS 04.64 V8.7.0 (2001–12), Technical Specification Group Core Network; Digital Cellular Telecommunications System
(Phase 2+); General Packet Radio Service (GPRS); Mobile Station – Serving GPRS Support Node
12. (MS-SGSN) Logical Link Control (LLC) Layer Specification (Release 1999).
13. 3GPP, TS 48.016 V6.1.0 (2004–11), Technical Specification Group GSM EDGE Radio Access Network; General Packet Radio
Service (GPRS); Base Station System (BSS) – Serving GPRS Support Node (SGSN) Interface; Network Service (Release 6).
14. 3GPP, TS 07.60 V7.2.0 (2001–03), Technical Specification Group Core Network; General Packet Radio Service (GPRS); Mobile
Station (MS) Supporting GPRS (Release 1998).
15. IIR conference on “Developing An Interference Matrix to Improve GSM/GPRS Network Planning and Management”
by Mehmet BEYAZ London December 2001.

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GPRS KPIs based on network performance

  • 1. TTG Int. LTD Proprietary & Confidential Page 1 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com White Paper Performance Management and Optimization Method for Mature GPRS Networks Prepared by Mehmet BEYAZ TTG International, L.T.D. www.ttgint.com 3/10/2015
  • 2. TTG Int. LTD Proprietary & Confidential Page 2 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com Contents GPRS PERFORMANCE MANAGEMENT....................................................................................................5 GPRS KPIs ................................................................................................................................................6 GPRS BSS KPIs..........................................................................................................................................8 BSS Accessibility..................................................................................................................................8 BSS Retainability .................................................................................................................................9 BSS Integrity......................................................................................................................................10 GPRS CN KPIs.........................................................................................................................................11 CN Accessibility .....................................................................................................................................11 CN Quality and Mobility....................................................................................................................12 GPRS NETWORK OPTIMIZATION...........................................................................................................13 GPRS RAN/BSS.......................................................................................................................................13 CONCLUSIONS.......................................................................................................................................14 ABBREVIATIONS, ACRONYMS, AND TERMS..........................................................................................16 REFERENCES..........................................................................................................................................19
  • 3. TTG Int. LTD Proprietary & Confidential Page 3 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com Abstract This paper discusses performance management and optimization method for mature GPRS networks. A selection of GPRS KPIs based on network performance counters, measurement systems, as well as possible threshold values and their analysis and interpretation.
  • 4. TTG Int. LTD Proprietary & Confidential Page 4 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com INTRODUCTION Today, many wireless operators are focused on providing mobile internet access. A large variety of technologies has contributed to the operators’ vision of true mobility and seamless roaming. The currently prevailing technology providing true mobile Internet access on a European scale is general packet radio service (GPRS). The popularity of Short Messaging (SMS), MMS and the growing demand for mobile data services prompted the implementation of a Packet Switched (PS) overlay on Circuit Switch (CS) network, opening the public Land Mobile Network (PLMN) operators to the data networking market and internet-based services. However, voice services stil remains the core business for many operators. This trend and some other factors have bringup the factor of growing requirement to optimize GPRS. This paper covers the performance management and optimization of GPRS networks. A performance management overview is presented, including proposed Key Performance Indicators (KPIs) for the RAN as well as the Core Network (CN).
  • 5. TTG Int. LTD Proprietary & Confidential Page 5 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com GPRS PERFORMANCE MANAGEMENT Performance management involves collecting and analyzing performance data from different resources and constitute set of KPIs. Network operators typically define a set of KPIs and stratified target thresholds in line with planning, marketing and businesspriorities. Performance management teams which are responsible, for example, for certain districts of major cities, towns of a certain size, or large rural areas, as well as routing areas or IP backbones periodically monitor various KPIs to isolate areas not achieving target performance. Optimization method/s are then kick off to ensure that performance targets are met. KPIs are usullay forumed by using performance counters provided by network elements. Statistics based on network element counters can be verified and supplemented by additional measurements obtained by active testing with test Mobile Station (MS), protocol analyzers at different interfaces in the network. Such additional performance measurement systems can emphasize aspects of GPRS performance not evident from network counters alone. The figure 1 shows the GPRS network architecture as well possible measurement points for network counters and protocol analyzers. Standard network surveillance or alarm monitoring, as well as long-term trending and analysis of KPIs, can assist in identifying problems and helping to achive desired performance.
  • 6. TTG Int. LTD Proprietary & Confidential Page 6 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com Figure 1. GPRS Network and interfaces GPRS KPIs Selecting meaningful KPIs is a pioneer to continuous performance monitoring. GPRS KPIs should cover the Base Station System (BSS) and the CN to account for end-to-end performance, i.e., from the MS to the Gi interface on the gateway GPRS support node (GGSN). Typically, KPIs for the BSS and the RAN reflect accessibility, retainability, and integrity. CN KPIs focus on Routing Area Update (RAU) behavior, congestion metrics on several interfaces, and system accessibility. Table 1 provides an overview of GPRS KPIs.
  • 7. TTG Int. LTD Proprietary & Confidential Page 7 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com Network Element Attribute KPI BSC/PCU Accessibility PRACH BSC/PCU Accessibility PAGCH (immediate assignment rejection rate) BSC/PCU Accessibility Congestion time BSC/PCU Accessibility PDCH availability BSC/PCU Accessibility DL/UL data throuhput BSC/PCU Accessibility PDTCH Allocation Failure Rate BSC/PCU Accessibility TBF Set-up Failure rate BSC/PCU Quality TBFs per PDTCH BSC/PCU Integrity RLC BLER BSC/PCU Quality RLC Re-transmission BSC/PCU Quality CELL Re-selection Time BSC/PCU/SGSN Accessibility GBL data throuhput BSC/PCU Retainability % of TBF Preemtion SGSN Accessibility GPRS Attached Success Rate SGSN Accessibility GPRS Attached Time SGSN/GGSN Quality GPRS RAU Success Rate SGSN/GGSN Quality GPRS RAU Success Time SGSN Accessibility PDP Context Activation on Success Rate SGSN Accessibility PDP Context Activation Time SGSN/GGSN Quality Congestion on Gi, Gb and Gn End-to-End Quality Delay End-to-End Quality Application Throughput Table 1. KPIs and Thresholds for GPRS System Performance
  • 8. TTG Int. LTD Proprietary & Confidential Page 8 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com GPRS BSS KPIs BSS Accessibility The RAN has an important role in overall system performance, since it typically represents the bottleneck in terms of resources and available physical transmission rates on the air interface as well as phishical links and PDCH. Accessibility from a RAN/BSS perspective is mainly a function of radio resources, signaling capacity, links (Gb) and BSS parameter configuration. Packet channel requests on the Packet Random Access Channel (PRACH), which establish the first contact of an MS with the network. Unsuccessful access requests due to congestions can indicate poor radio conditions. The total number of PRACH requests may include instances where the MS sends multiple consecutive access bursts. Immediate assignment the BSS’ response to the packet channel request from the MS is indication for identifying congestion; the immediate assignment rejection rate is based on the number of immediate assignment rejections over the total number of PRACH requests. Such rejections are due mainly to the lack of Packet Data Channel (PDCH) resources in the cell. Although extreme delays on the Um interface or lack of resources in the Base Station Controller (BSC), Packet Control Unit (PCU), or other nodes may cause rejections. Cell congestion levels can be calculated as no PDCH available for a certaion time period within the GPRS busy hour, which may be expressed as a percentage of 60 minutes. GPRS congestion levels should be think of Traffic Channel (TCH) demand point of view for CS. On the other hand, CS busy hour traffic can affect PS available resources for connections. This is clearly depends on the BSS configuration in terms of preemption and the allocation of fixed PDCHs. The number of packet access requests and the transmitted data volume during CS busy hour can be used to determine whether the CS resource requirements are pushing the PS traffic into congestion or whether the GPRS traffic demand is high. On the other hand, it should be noted that GPRS busy hour are not necessarily matching, but are offset to those of the CS. It may, therefore, be useful to consider PS traffic expressed as bytes at the busy hour statistics when evaluating GPRS congestion. The PDCH allocation failure rate sometimes referred as GPRS blocking and the Temporary Block Flow (TBF) setup failure rate are additional KPIs that can indicate congestion. A certain amount of GPRS blocking may be acceptable considering that CS orianted cell dimensioning strategies may allow for approximately %2 blocking rate or quality of service (QoS).
  • 9. TTG Int. LTD Proprietary & Confidential Page 9 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com BSS Retainability RAN CS congestion, high volumes of data traffic, or a combination of both can give rise to a series of other symptoms that may affect not only the system accessibility but also the retainability and quality for ongoing TBFs connections. TBFs are subscriber-specific, bothway, logical connections associated with a varying number of PDCHs, established to facilitate data transfer between the MS and the BSC/PCU. In other words, the data service may be accessed successfully, but the connection quality can range from unacceptably bad to very good. The PCU reserves the requested number of PDCHs for new connections during the packet allocation procedure. PDCHs available in the Packet Switch Domain (PSD) at any given moment are used for the assignment, although more than one TBF may be assigned to a PDCH. The GPRS multiplexing capability can support multiple TBFs per PDCH and allocate new TBFs on already used PDCHs. Note that: The number of PDCHs requested by an MS is determined mainly by its multislot class. On-demand PDCHs make temporary use of idle CS TCHs, which are swithed back to the CSD when they have not been used for a defined period of time. New GPRS users can be blocked if the PSD cannot be expanded to accommodate new TBFs when the TBF-per-PDCH reached the limit, where resulting in PDCH allocation failures (packet access reject) and TBF set-up failures. Note that: The PDCH allocation failures may occur after successful immediate assignment. These failure rates can be biased by TBF upgrade failures. System vendors may provide a feature that allows the TBF to request additional PDCHs if it has been set up initially with fewer PDCHs than the multislot class of the MS allows. While TBF multiplexing and the allocation of fewer resources than the MS can support work together to provide flexible system accessibility, both mechanisms can have an undesirable effect on throughput performance and Bandwidth Delay Product (BDP) per user. In addition, the absolute or average number of allocated PDCHs per TBF in a given cell provides another standpoint on GPRS QoS. Multiplexing is point out when this KPI increases beyond 1. Because the Logical Link Control (LLC) throughput performance per TBF is affected by the multislot class of an MS, the distribution of different multislot MSs in the network should be identified to set reachable throughput targets.
  • 10. TTG Int. LTD Proprietary & Confidential Page 10 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com BSS Integrity The changeable radio propagation and RAN interference conditions are the main factors affecting the BSS. The Carrier-to-Interference (C/I) ratio has a critical impact on the maximum physical transmission rate of a PDCH and TCH. The GPRS coding schemes, whose ranges of optimum performance are related to the C/I ratio, help to lower the impact of radio interference on the radio channel’s BLock Error Eate (BLER). Remaining uncorrectable bits and corrupted radio blocks set off the Radio Link Control (RLC) Automatic Repeat Request (ARQ) mechanism if the TBF is operated in RLC-acknowledged mode. The probability of RLC retransmissions hence reduces the physical transmission rate of the channel, adds additional delays to the air interface, and affects the end-to-end RoundTrip Time (RTT) of higher layer protocols. The Bit Error Rate (BER) of a radio channel (also categorized into receive/transmit quality (Rx/TxQual) levels ranging from 0 to 7 and the percentage of RLC retransmissions should be tightly monitored. Desirable RLC retransmission rates are generally below %1. Moreover, TCP window sizes, TCP retransmission time-outs, typical IP packet size distributions, and the application protocol affect the effective throughput on the application layer. BSS Quality and Mobility Cell reselection, as well as possible Location and Routing Area Updates (LAUs and RAUs), has a weakening effect on throughput performance. During cell reselection, the MS releases all channels to read the system information of the destiontion cell. The radio outage time begins with the channel release and ends with the completion of the cell reselection process and the establishment of downlink and uplink TBFs on PDCHs of the destination cell. Cell reselection may also require LAUs and RAUs if the destination cell is part of another location and routing area. This introduces extra signaling in the network as and increases the time until new TBFs are established on the destination cell.
  • 11. TTG Int. LTD Proprietary & Confidential Page 11 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com GPRS CN KPIs In the GPRS optimization CN GPRS plays a fundamental role in assessing overall system performance. Along with the key elements of CN performance assessments are success rates for GPRS are; 1. Attached 2. Packet Data Protocol (PDP) context activation 3. RAU 4. Paging CN Accessibility The GPRS attach request message is the first contact of the MS with the serving GPRS Support Node (SGSN) then a TBF has been established successfully. It contains the Temporary Mobile Subscriber Identity (TMSI), Mobile Network Code (MNC), and Mobile Country Code (MCC), as well as Location and Routing Area Identity. Following identity checks of the International Mobile Equipment Identity (IMEI) or the International Mobile Subscriber Identity (IMSI), as well as authentication and ciphering request messages, may be issued by the SGSN. In order to retrieve the IMSI if no entry is found for it, the SGSN uses the old location area information to identify the old SGSN where this terminal was last served. The SGSN may require Home Location Register (HLR) signaling over the Gr interface to identify profiles for unknown IMSIs. Unsuccessful authentication and ciphering may also contribute to the attach rejects. SGSN counter statistics for the Gb interface can be used to establish the probability of attach failures and the distribution of failure reasons. Some of the common failure reasons are: 1. Attach requests from users who are not subscribed to the GPRS network 2. International roamers from networks without roaming agreements 3. Software and hardware levels on specific MSs 4. Attach time-outs (excessive delays, failed responses from the MS) 5. Network failures. Gb interface congestion and dimensioning should be taken in accout when assessing the GPRS attach success rate. The Gb interface interconnecting the BSS with the SGSN is a Frame Relay (FR) connection over an E1/T1 link. Ofcours this is depending on the CN design strategy, this FR connection may be transported over intermediate networks, such as Asynchronous Transfer Mode (ATM) backbones supporting FRF5 (FR over ATM). FR congestion control and discard mechanisms, can be monitored to
  • 12. TTG Int. LTD Proprietary & Confidential Page 12 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com identify congestion levels on the FR data Link Connection Identifier (DLCI) carrying the BSS GPRS protocol (BSSGP) protocol Data Units (PDUs). Measuring the PDP context activation Success Rate (SR) is also important. GGSN provides the allocated IP address to the SGSN via the create PDP context response, which, in turn, sends the activate PDP context accept message to the MS. Hance, a successful PDP context activation establishes IP connectivity between the MS and the GGSN, which then forwards or routes the traffic to external networks. Common reasons of PDP context activation failure include network link failures, incorrect DNS records, and inappropriate configuration of MSs. Counters on the SGSN and GGSN provide the basis for establishing the PDP context activation failure rates and the distribution of the causes. The IP backbone can be based on different network architectures, QoS-aware, high-capacity backbones. When a PDP context is in active state, GPRS tunneling protocol (GTP) encapsulation is used to create Virtual Circuit (VC) connections between GPRS support nodes (GSNs) supporting the data flow across the backbone. The GTP VC connection is released as soon as the context becomes inactive. CN Quality and Mobility The RAU Success Rate (RAUSR) is an another important key metric for GPRS system performance. All idea about this KPI contributes to the understanding of end user throughput performance. A GPRS-attached MS can issue periodic, intra-SGSN and inter-SGSN RAUs, depending on its situation. Periodic RAUs are used to ensure that the MS is stil reachable and are so treated as a intra-SGSN updates. The non-periodic update requests can be triggered when the MS transcends a routing area boundary during cell reselection. The intra-SGSN RAU procedure is used when the new routing area of the target cell is administered by the same SGSN. RAU rejects can reasons of authentication and ciphering failures, RAU time-outs due to excessive delays, lower layer link failures, and/or protocol failures. Performance metrics can be used for GPRS attach, context activation, authentication time, DNS response time, TCP connection establishment time, and additional application-specific indicators. Throughput RTT DELAY RLC Re- transmission TBF Multiplexing TBF / PDTCH PS Immediate Assignment Reject PDTCH Allocation Failures
  • 13. TTG Int. LTD Proprietary & Confidential Page 13 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com B S S Mobility Mobility CS Congestion PS Congestion Poor Coverage Poor Coverage Poor Coverage PCU Capacity PCU Capacity N-Cell Definitions N-Cell Definitions N-Cell Definitions CS Congestion CS Congestion CS Congestion CS Congestion Interface Interface Interface PS Congestion PS Congestion PS Congestion PS Congestion Fault Fault Fault Fault Fault Fault Fault C N Transmission Transmission GSN Configuration GSN Configuration GSN Configuration GSN Configuration IP Backbone Gb Congestion Gb Congestion Gb Congestion Gb Congestion Gb Congestion Gb Congestion RADIUS Gn Congestion Gn Congestion Gn Congestion Gn Congestion Gn Congestion Gn Congestion Packet Loss Packet Loss Gr Congestion Gr Congestion Packet Loss Packet Loss Packet Loss Packet Loss MS DHCP DHCP RADIUS RADIUS DNS DNS PDP Context Activation Time PDP Context Activation Success RAU Time RAU Success Authentication Figure 3. KPI Effect Matrix GPRS NETWORK OPTIMIZATION GPRS network optimization plans can vary from operator to operator and may be tied to specific circumstances, although certain practices and approaches have a more universal nature. On the one hand, optimization should be understood as an ongoing activity in the perspective of network rollout and expansion, and one that is concerned mainly with an optimal integration of new base stations, BSCs, and CN elements. The RAN, however, more than any other part of the GPRS system, changes constantly as new cells are introduced and existing ones are reconfigured, relocated, or modified. Optimization staffs are also support network operations on an ongoing basis. On the other hand, optimization activities may be triggered when certain areas of the network fail to meet performance thresholds. GPRS RAN/BSS The RAN has a leading role in GPRS optimization. Coverage planning, frequency planning, and neighbor cell definitions and configuration have a clear impact on radio conditions and
  • 14. TTG Int. LTD Proprietary & Confidential Page 14 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com interference levels, where they should be carefully controlled. Such as frequency retunes and neighbor cell corrections often improve high percentages of intra-cell and vital inter-cell handovers or TCH drops and handovers due to downlink quality. Sufficient channel dimensioning strategies of Base Transceiver Stations (BTSs) for CS and PS services should make sure minimum congestion levels about %2 or less. BSS features and parameter optimization also further improve system performance. An important feature that can be offered by PS broadcasts, is network assisted cell change, which allows a considerably reduced radio outage time during cell reselection process. When in packet transfer mode, the MS sends packet cell change notifications to the BSS before entering the cell reselection procedure. The network’s response contains minimum required system information about the destination cell, which allows the MS to initiate TBF connections in the destination cell before cell reselection is actually completed. Depending on GPRS priority and preemption parameters, on-demand PDCHs can be treated as available or blocked for CS connections, regardless of a PDCH’s current usage state. Generally, priority and preemption algorithms are affected by using dynamic allocation or adapting half-rate channels for CS connections, implementation vary from vendor to vendor. Operators typically allow the preemption of on-demand PDCHs to allocate new CS connections when needed.This methodology, conflict with a performance guarantee for GPRS users in congested situations. Where TCH requirements are high and PDTCH preemption causes GPRS blocking (packet immediate assignment rejects) to be %2 or higher during the CS busy hour, a strategy for allocating FPDCHs can improve accessibility performance. FPDCHs may not be preempted, so the defined number of time slots is guaranteed for GPRS users. Additionally, if GPRS blocking is % 2 or higher during the GPRS busy hour, the allocation of FPDCHs can be considered. The FPDCHs can also increase throughput performance during blocked and congested situations. Ensuring an acceptable level of GPRS performance without significantly affecting the CS service becomes part of the operator’s FPDCH allocation methodology. CONCLUSIONS GPRS system performance depends on performance management method, which identify performance shortcomings, and on network optimization, which is conducted continuously and also when triggered by problems. GPRS performance optimization activities should focus on;  C/I  BLER  Radio capacity  PCU  GSN dimensioning  RADIUS
  • 15. TTG Int. LTD Proprietary & Confidential Page 15 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com  DNS  DHCP  Mobility  Usage of BSS  Usage of CN features  Configuration All these contribute to the end-to-end performance experienced by the user. Active measurement systems can be used to accurately capture application throughput and RTTs. Network operators should ensure that GSM and GPRS networks are balanced in terms of capacity performance management and optimization, acknowledging the increasing importance of GPRS in the context of supplementing IP services over UMTS.
  • 16. TTG Int. LTD Proprietary & Confidential Page 16 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com ABBREVIATIONS, ACRONYMS, AND TERMS 3G: Third generation APN: Access point name ARQ : Automatic repeat request ATM : Asynchronous transfer mode BCCH: Broadcast control channel BDP : Bandwidth delay product BECN : Backward explicit congestion notification BER : Bit error rate BLER : Block error rate BSC : Base station controller BSS : Base station system BSSGP: BSS GPRS protocol BTS : Base transceiver station CCCH : Common control channel C/I : Carrier-to-interference (ratio) CN : Core network CPU : Central processing unit CS : Circuit switch(ed) CSD : Circuit switch domain DE : Discard eligible DHCP : Dynamic host configuration protocol DLCI: Data link connection identifier DNS: Domain name service FECN: Forward explicit congestion notification FPDCH : Fixed packet data channel FR : Frame relay FRoATM : FR over ATM FTP :file transfer protocol GGSN: Gateway GPRS support node GPRS :General packet radio service GSM : Global system for mobile communication GSN : GPRS support node GTP : GPRS tunneling protocol HLR : Home location register IMEI : International mobile equipment identity IMSI : International mobile subscriber identity IP : Internet Protocol IPoA : IP over ATM ISP : Internet service provider
  • 17. TTG Int. LTD Proprietary & Confidential Page 17 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com KPI : Key performance indicator LAN : Local area network LAU : Location area update LLC : Logical link control MCC : Mobile country code MNC : Mobile network code MS: Mobile station MSC: Mobile switching center multi-RAT: Multi-radio access technology N-cell : Neighbor cell NMS : Network management system NTE : Network termination equipment PAGCH: Packet access grant channel PBCCH : Packet broadcast control channel PCU : Packet control unit PDA : Personal digital assistant PDCH : Packet data channel PDP : Packet data protocol PDU : Protocol data unit PLMN : Public land mobile network PRACH: Packet random access channel PS : Packet switch(ed) PSD : Packet switch domain QoS : Quality of service RADIUS : Remote authentication dial-in user service RAN : Radio access network RAND : Random number RAU : Routing area update RLC : Radio link control RTT : Roundtrip time Rx/TxQual : Receive/transmit quality RxQual : Receive quality SGSN : Serving GPRS support node SI : System information SIM : Subscriber identity module SNMP : Simple network management protocol SQI : Speech quality index SRES : Signed response TBF : Temporary block flow TCH : Traffic channel TCP : Transmission control protocol TMSI : Temporary mobile subscriber identity UMTS : Universal mobile telecommunications system UTRAN : UMTS terrestrial radio access network VC : Virtual circuit
  • 18. TTG Int. LTD Proprietary & Confidential Page 18 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com VLR : Visitor location register WAN : Wide area network WiMAX: Worldwide interoperability for microwave access
  • 19. TTG Int. LTD Proprietary & Confidential Page 19 of 19 Dikilitaş Mah. Dilek Sok. No: 10 Kat 3, Beşiktaş, 34387, Istanbul, Turkey Tel: +90 212 327 0757 Pbx Fax: +90 212 327 0760 TTG Uluslararsı LTD / Registered Office: as above / Registered Number in Turkey 461414-408996 www.ttgint.com REFERENCES 1. 3GPP, TS 44.060 V6.10.0 (2004–11), Technical Specification 3rd Generation Partnership Project. 2. Technical Specification Group GSM/EDGE Radio Access Network; General Packet Radio Service (GPRS); Mobile Station (MS) – Base Station System (BSS) Interface; Radio Link Control/Medium Access Control (RLC/MAC) Protocol. 3. 3GPP, TS 03.64 V8.11.0 (2003–04), Technical Specification Group GSM/EDGE Radio Access Network; General Packet Radio Service (GPRS); Overall Description of the GPRS Radio Interface. 4. 3GPP, TS 04.60 V8.23.0 (2004–05), Technical Specification Group GSM/EDGE Radio Access Network; General Packet Radio Service (GPRS); Mobile Station (MS) – Base Station System (BSS) Interface; Radio Link Control/Medium Access 5. Control (RLC/MAC) Protocol . 6. R. Chakravorty and I. Pratt, “Performance Issues with GPRS,” Journal of Communications and Networks (JCN), Vol. 4, No. 2, December 2002, pp. 226–281. 7. S. Hoff, M. Meyer, and A. Schieder, “A Performance Evaluation of Internet Access via the General Packet Radio Service of GSM,” Vehicular Technology Conference (VTC) ’98, May 1998, Ottawa, ON, Canada. 8. D.E. Comer, “Internetworking with TCP/IP – Principles, Protocols, and Architectures,” 4th Edition, Prentice Hall, 2000. 9. D. Michel and N. Ramasarma, “GPRS Measurement Methodologies and Performance Characterization for the Railway Environment,” Wireless Communications and Networking Conference (WCNC) 2005, March 2005, New Orleans, LA. 10. G. Heine, “GSM Networks: Protocols, Terminology, and Implementation,” Artech House Publishers, 1999. 11. 3GPP, TS 04.64 V8.7.0 (2001–12), Technical Specification Group Core Network; Digital Cellular Telecommunications System (Phase 2+); General Packet Radio Service (GPRS); Mobile Station – Serving GPRS Support Node 12. (MS-SGSN) Logical Link Control (LLC) Layer Specification (Release 1999). 13. 3GPP, TS 48.016 V6.1.0 (2004–11), Technical Specification Group GSM EDGE Radio Access Network; General Packet Radio Service (GPRS); Base Station System (BSS) – Serving GPRS Support Node (SGSN) Interface; Network Service (Release 6). 14. 3GPP, TS 07.60 V7.2.0 (2001–03), Technical Specification Group Core Network; General Packet Radio Service (GPRS); Mobile Station (MS) Supporting GPRS (Release 1998). 15. IIR conference on “Developing An Interference Matrix to Improve GSM/GPRS Network Planning and Management” by Mehmet BEYAZ London December 2001.