advanced ranop chapter 4 - drop call ratio

5/21/2018 Advanced RANOP Chapter 4 - Drop Call Ratio

1/121 NOKIA Training Center / RDM

Chapter 4: Drop Call Ratio



Objectives

Objectives: This section explains the DCR8 Drop Call Rate formula and why it is better that the DCR 3G. It also

explains how the new DCR BREAKDOWN OBSERVATION can be used as an effective tool to

troubleshoot drop calls. There is also a brief description about AMR drops and RLT with AMR.

References: Michael Ledesma



Drop Call Rate Formula

The common formula is DCR3G and it is composed of the following counters :tch_abis_fail_call

tch_abis_fail_old

tch_lapd_fail

tch_bts_fail

tch_a_if_fail_call

tch_a_if_fail_oldtch_act_fail_call

tch_tr_fail

tch_tr_fail_old

tch_user_act

tch_bcsu_reset

tch_netw_act

tch_radio_failtch_rf_old_ho

The new drop call counter 1202 counts customer perceived drops. These are TCHfailures that happens between ASSIGNMENT COMPLETE and DISCONNECT.

This new counter has a smaller supervision period than the DCR3G countersthus

lesser drop call counts but measures the exact user experience The succeeding slides shows the difference between DCR3G and the new formula

DCR8E and why is it better to use



1202 (DCR8E) Counter Supervision Time

DCR3G

Start Point : Channel ActivationChannel Activation command from the BSC. Voice Callhas not yet been successfully established

End Point : RF Channel Release Ack

RF Channel Rel Ack received from the BTS

1202 (DCR8E)

Start Point : Assignment CompleteThis implies that the voice or data call has beensuccessfully established.

End Point : Disconnect

BSS and MS are aware of the disconnection. Callrelease continues.

SupervisionPeriod of DCR3G

Supervision Period

of DCR8E



Advantages

The 1202 counter is much closer to customer experience when it

comes to drop calls

The counter has been verified and mapped together with the DCRBREAKDOWN OBSERVATION measurement (S11). This will giveyou the ability to drill down on the DCR investigation.

Better drop call details in S11.5 with the enhanced DCRBREAKDOWN OBSERVATION

This drop call counter was developed to match the drop call countersof other GSM vendors

The counter is already available in S10.5 and S11 as 57044 and 1202respectively



Drop Call Breakdown Observation in S11

Detail Information per drop call

This observation can be activated in the BSC with noconstraints of overload.

It can be activated and available across all the network 24/7.

In S11, this observation provides:

TRX Information Phase In and Cause In Phase Out and Cause Out

The information above is already available and helps to bettertroubleshoot network incidents.

This observation currently is not integrated in OSS, therefore it isrequired to FTP the BSCto access this information.

Length : 25

Type : 29

Tracing Status : 0

Tracing Reference (hex) : 0000Header Version : 13

Compatibility Version : 1

BTS ID : 20

Release time : 2005-05-13

10:48:50,63

Phase out : 2

Cause out : 368

TRX ID : 2

Phase In : 3

Cause in : 43

Drop Call Observation Example

One drop call event, c1202 = 1



Example of DCR Breakdown Observation

Length : 25

Type : 29

Tracing Status : 0

Tracing Reference (hex) : 0000

Header Version : 13

Compatibility Version : 1

BTS ID : 20

Release time : 2005-05-13 10:48:50,63

Phase out : 15

Cause out : 317

TRX ID : 2

Phase In : 3

Cause in : 43

In S11 you can have the time, Phase

out, Cause Out, Phase in, Cause inand TRX ID of the drop call

Using the Call Related DX Causes in

BSCdocument you can narrow down

the cause of the drop call

This gives you better information onfinding a solution to improve your drop

call rate.

Drop occurred during conversation

The Abis interface receives a CONNECTION FAILUREmessage and its cause is radio link failure

Counter 1013 from the traffic table is pegged



S11.5 DCR Breakdown ObservationEnhancements

The purpose of Breakdown of counter 1202 is to get more accurate data on

dropped calls for BSC counter 'Drop After TCHAssignment. With the data providedby new observation, TCH drops happening after TCH is assigned can be analysed inTRX level with the actual reason for the drop. When the observation is activated inBSC, it will collect data from the whole BTSsunder BSC.

SUDDEN DROPADJ CELL PLMN ID 1

ADJ CELL LAC 1

ADJ CELL ID 1

RX LEVEL ADJ 1

.

.

.

ADJ CELL PLMN ID 6

ADJ CELL LAC 6ADJ CELL ID 6

RX LEVEL ADJ 6

BTS ID

RELEASE TIME

PHASE OUT

CAUSE OUT

PHASE IN

CAUSE IN

TIMING ADVANCE

DL RX LEVEL

UL RX LEVEL

DL RX QUALITY

UL RX QUALITY

DL FER

UL FER

DL LAST USED BIT RATE

UL LAST USED BIT RATE

Drop

call

DetailInformationper Drop



5 Minute DCR BD OBS S11.5 Exercise



Activity

Attached is a DCR BD OBS file in txt format

Using the Call Related DX Causes in BSCdocument. Try to figure outwhat caused the call to drop.



AMR and Drop Calls

The introduction of the AMR codec gives us the MS the ability to carry

a conversation in C/I conditions where EFR cannot.

This improvement in the speech codices bring it closer to the robustperformance of the SACCH and at the worst conditions evenoutperform the SACCH.

This can result in more radio related drops as the customer can carrythe conversation but the signaling is lost (measurement reports)

It is imperative then that we consider how we use AMR and theparameterization that it requires to operate without sacrificing the user

perceived gains and still maintaining reasonable KPIs. More details about AMR will be discussed in the succeeding chapters.



AMR and Radio Link Time Out

Recommendations:

EFR 20 SACCH periods

AMR FR 32 to 44 SACCH periods

AMR HR 20 to 32 SACCH periods

AMR HR is not as robust as AMR FR. It is generally used in good C/Iconditions. At RXQUAL 4, AMR HR is already giving poor voiceperformance that an extremely long RLT will artificially improve yourDCR as the subscriber will terminate the call due to bad voice quality.

advanced ranop chapter 4 - drop call ratio

Documents

new drop

better drop

new counter

nokia training center

new dcr breakdown observation

end point

rate formula

new formuladcr8e