Service Setup Failure

1.1 Fault DescriptionCS/PS services cannot be set up after the cell is set up. Users cannot use the AMR voice service or the PS dial-up service.

1.2 Possible Fault CausesEmergency faults are as follows:

Receives user complaints that the call quality and access for many users in a live network are affected.

KPIs, such as the call drop rate and the access success rate, deteriorate so serverely, affecting that the call quality and network access for a large number of users in a live network.

The services in one subsystem, one subrack, or the entire RNC are affected. All services in one interface board are affected.

Possible causes for non-emergency faults are as follows:

Cell activation failure

Power congestion

Code resource congestion

Transmission congestion

CE congestion

DSP soft failure

1.3 Troubleshooting Method

1.3.1 Service Setup FailureIf the fault is not an emergency service problem, you can infer that only some users cannot make calls or access the network. To rectify the fault, do as follows:

                               Step 1     Check whether the cell status is normal, namely, whether cell setup is normal, whether the cell is available, and whether the cell uplink or downlink traffic is congested. Run the following commands to query the cell status:

DSP UCELL

DSP UCELLCHK

If the cell is not activated, run the command ACT UCELL to activate the cell. If the cell activation fails, run the command DSP UCELL to query the failure cause.

If the cell is successfully set up, run the command LST UCELLACCESSSTRICT to check whether the cell or the user AC is barred. If the cell is barred, unbar the cell.

Run the DSP UCELLCHK to check whether the cell is in congested state, including power congestion, code resource congestion, transmission congestion, and CE congestion.

Power congestion:

Power congestion is classified into uplink power congestion and downlink power congestion. Usually, algo-rithm 1 is used as the downlink connection admission control (CAC) algorithm, whereas the uplink CAC al gorithm 2.

If the access failure is due to uplink power congestion, run the command DSP UCELLCHK to check whether the RTWP is within the valid range (–96.5 dB to –105.5 dB). Run the command LST UCELLCAC to check whether the auto-adaptive background noise update switch is ON. If the auto-adaptive background noise update switch is ON, deactivate the cell, and then re-activate the cell to check whether the RTWP is normal.

 

If the auto-adaptive background noise update switch is OFF, turn off the uplink CAC switch or reset the back-ground noise. You can use the following command to turn off the uplink CAC switch:

MOD UCELLALGOSWITCH: NBMUlCacAlgoSelSwitch=ALGORITHM_OFF;

Check the average RTWP value (vs-meanrtwp) in the traffic statistics, and set the background noise to the minimum vs-meanrtwp.

The command is as follows:

MOD UCELLCAC: BackgroundNoise=61;

UL Power congest check RTWP and background noise

DL Power congest check TCP (Lastest TxPwr Measure)

Code congest check Code used rate

IUB congest check Iub congest rate

CE congest check Cell Credit used rate

Note :

The parameter value depends on the site requirements. By default, it is set to 61.

Actually configured noise floor = 112 + BackgroundNoise x 0.1

If the access failure is due to downlink power congestion, run the command DSP UCELLCHK to check whether the latest TCP value is normal (<75%). To query the admission threshold of a specific service, you can run the command LST UCELLCAC. If the TCP value exceeds the threshold, the access fails. Check whether the admission threshold is configured according to the baseline data or radio parameters for network planning, and modify the obvious errors. For example, the admission threshold is configured to 30%. If the threshold is configured according to the baseline data or radio parameters for network planning, the network planners should negotiate with the customer on whether to adjust the threshold to admit more users or expand the capacity.

Code congestion:

Run the command DSP UCELLCHK to check whether the cell used rate of code resources is normal and trace the code tree to check whether the cell uses too many code words. If the minimum available code words are more than the reserved code words, the cell capacity is limited and needs expansion. The fewer the code words, the greater the service rate. For example, the available minimum code word is SF32 but the configured reserved code word is only SF16, the admission fails.

Alternatively, you can run the command LST UCELLCAC to check whether the reserved code word of the cell is configured according to the baseline data or the radio parameters for network planning. Newly admitted users cannot use reserved code words. As a result, the more the reserved code words, the fewer code words available for new users. If the configured value is too small (SF4), you can modify it according to the baseline data. Otherwise, the network planners should negotiate with the customer on whether to adjust the threshold to admit more users or to expand capacity.

If the cell's number of users is too small and available minimum code words are fewer than reserved code words, no congestion occurs. You can deactivate the cell and then re-activate the cell to view the test result.

Transmission congestion:

Run the command DSP UCELLCHK to check whether Iub interface of the cell is in congested state.

If the Iub interface is in congested state, check whether the reserved bandwidth for the IPPATH is too high. By default, the reserved bandwidth is 0. That is, no bandwidth is reserved.

UL/DL Reserve code for HO

Run the command LST TRMFACTOR to check whether the values configured for service activation factors are within the valid ranges. Usually, these parameters should be configured with recommended values.

For the PS services, you should also check whether the GBR (LST UUSERGBR) is configured according to the baseline data. If the GBR value is obviously inappropriate (such as 384 KB), the network planners should negotiate with the operator on whether to decrease the GBR to admit more users or adjust the bandwidth.

CE congestion:

Run the command DSP UCELLCHK to check whether the CEs of the cell are congested.

   Step 2     Check whether the LAC/SAC/RAC data is configured and activated on the CN side (MSC/SGSN). If this data is not configured, UEs cannot register to or attach themselves to the network. You can trace the intelligent optimum sample (IOS) of the cell to check whether a UE can register on or attach to the network normally.

 

When the SAC data is not configured on the CN side, the RNC fails to send the initial direct transfer message for setting up signaling connection control part (SCCP) connection. As a result, the UE cannot access the net-work.

                               Step 3     Check whether the IPPATH is available and configured correctly.

Run the command LST TRMMAP to check whether the transmission mapping is set correctly.

Run the command LST PHBMAP to check whether the Interface board transmission mapping is set correctly.

Run the command LST IPPATH to check whether the mapped path in the TRMMAP is actually configured.

IP PATH on RNC

 

IP PATH on Node B

According to the preceding result, the AMR service can be set up only an EF type IP path is configured.

  Step 4     Check whether the call setup failure is caused by the soft failure of a certain DSP.

Run the command DSP UCELLCHK to check which is the DSP that process the cell service.

Operations (such as DSP resetting) in this section are complicated and highly risky. Therefore, this sec-tion serves as the reference for experienced engineers only. Once such a problem occurs, inform the maintenance department and work together with them on a solution.

Run the command DSP UDSPRESOURCE to check cell list is processed by the DSP.

Run the command RST DSP to reset the related DSP in the DPU .