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In GRPS, the KPIs mainly define the quality level of a connection from the MS to the GGSN; therefore,they focus on the core network, rather than on the physical layer. The GPRS KPIs are classified in the

following categories:

Reliability; Delay Peak throughput; Mean throughput; GPRS utilization; Attach attempts failure rate

What is TBF:A Temporary Block Flow (TBF) is a logical connection used by two General Packet Radio

Service (GPRS) entities to support the unidirectional transfer of lower layer compatibility (LLC) protocol

data units (PDUs) on packet data physical channels(PDCHs)(or timeslots). In a typical GPRS system, the

network needs to establish a downlink (DL) TBF to transfer data in the DL direction and an uplink (UL)

TBF to transfer data in the UL direction. TBFs are typically short-lived and are generally only active

during data transfers.

The GPRS blocking of resources is linked with the temporary block flow (TBF) set up failure, due to the

lack of PDTCH resources. TBF is the physical connection that is used to support the unidirectional

transfer of LLC PDU on packet data physi-cal channels. TBF is allocated in one or more TCH channels and

comprises a number of RLC/MAC blocks carrying one or more LLC PDUs. A TBF is temporary as its

name denotes and is maintained as long as data is transferred. PDTCH access failure can be separated in

two types. The first type is called hard blocking, and the second one is called soft blocking.

Hard GPRS blocking. Hard blocking describes the situation when no radio resources are assigned after

the GPRS service request. For instance, if we consider the case when a user requests three time slots

(TSLs) to download a file using ftp and no resources at all are assigned, this is characterized as hard GPRS

blocking.

Soft GPRS blocking. Network operators usually operate their GPRS networks using at least one dedicated

channel. For that reason hard blocking occurs rarely, and a more common situation is the soft GPRS

blocking where users are assigned a portion of the resources they request. For example a user who

requests three time slots for a service will finally receive one or two.

Session Release Success Rate

This KPI discriminates the various reasons for abnormal TBF release expressing the

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percentage of TBF dropped sessions due to bad radio conditions as well as due to

high circuit-switched traffic, where the prioritized voice requests are served by

assigning traffic slots from the default GPRS territory. The session release success

rate indicates the impact of circuit-switched (CS) traffic on packet-switched (PS)

traffic (TBF drops) when radio resources (TCHs) are not sufficient, and CS accom-modated traffic is

served also by using traffic slots from the default GPRS territory.

Data Connection Success Rate

Whenever a mobile station is admitted to access the GPRS channels and requests a

service, the network will establish a connection that supports the unidirectional

transfer of LLC PDU. This connection is the TBF one that was described in the previ-ous section. There

are three TBF types when a mobile station is in data transfer:

Uplink TBF;

Downlink TBF;

Simultaneous uplink and downlink TBF.

The TBF is assigned to the radio resources of one or more PDTCH and com-prises a number of RLC/MAC

blocks carrying one or more LLC PDU. The TBF set up failure due to the lack of PDTCH resources results

in soft or hard blocking in GPRS. The following formulas present the uplink and downlink hard blocking

rate in PDTCH.

Delay

The delayis another critical KPI that does not occur due to congestion in the radio resources, but it

appears and is considered in the core network. It specifies the end-to-end transfer delay measured in

the transmission of SDUs through the GPRS net-work. This KPI has direct interaction with the use of the

CCCH of the CS channels, such as RACH, AGCH, and PCH (which are called PRACH, PAGCH, and PPCH

when they are used in GPRS). A big delay is strongly linked with congestion in the above resources.

GPRS Utilization

Another very useful KPI, especially in this early working phase of the GPRS net-work, is the monitoring of

usage of the related resources as well as the total amount

of data transmitted in a specific period of time. It indicates how many time slots the

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GPRS traffic consumes on average during this period. This information is useful, for

example, in forecasting the need for applying capacity extensions, and it represents

Erlangs on PDTCH. The idea behind this indicator is the amount of GPRS territory

resources usage measured in Erlangs or TSLs, meaning how many TSLs were occu-pied during a specific

period of time in order for a known amount of data to be

transferred.

The allocation of physical channels for GPRS usage can be done for transferring

either normal data or signaling data. The calculation of the traffic is made on the

basis of the number of RLC layer blocks transmitted in a specific period of time

based on the data that can be sent in one TSL for the same period

Method for the early establishment of uplink TBFs:-

A mobile station operating in EGPRS mode needs to the early establishment of an uplink TBF although

has not data to send, at the only precautionary purpose of preventing an intolerable latency negatively

affecting the subsequent delay-sensitive transmissions. To this aim, the mobile sends a Packet Channel

Request message in one phase access mode including a new establishment cause called "Early TBF

establishment". The network establishes an uplink TBF indicating the requester and assigns a radio

resource on one PDCH channel or more. Then the network schedules the transmission from the mobile

station also when it does not have data to transmit other than dummy packets. This is performed

through the USF flags in the usual manner. As soon as actual data become available for transmission, themobile send them instead of dummy packets. In an alternative embodiment the mobile sends the

Packet Channel Request message in two phase access mode. As soon as the Packet Uplink Assignment

message is received by the mobile station, it sends a Packet resource Request message including

Extended Uplink TBF information

How to fix high TBF block rate:

Try use most BCCH TRX TS for PDCH Make sure (E)GPRS link adaptation is enabled. If frequency change doesn't get good result limit the (E)GPRS coding

scheme up to MCS7 instead of MCS9. MCS7 is more robust thanMCS9

Reduce no. of users per PDCH Check PCU congestion/Utilization

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