Alarm 7743_Mean Holding Time Below Threshold

 Mean holding time below threshold

Alarm 7743

Contents

• Alarm Definition as per NED 

• Reasons for Alarm 

• Troubleshooting 

Alarm Definition as per NED 

• 7745 MEAN HOLDING TIME BELOW DEFINED THRESHOLD Meaning : Mean holding time on a channel is below the operator-defined minimum during the measurement period. The alarm is used to supervise the functioning of traffic channels and to detect the possible faulty channels. 

      Parameters, with their default values, affecting the alarm: 

ZEEN:MINHTT = minimum mean holding time for a TCH (10 s) 

 PRDMHT = length of TCH supervision measurement (120 min) 

 CS = channel seizure threshold value 

Reasons for Alarm

• Hardware Issues: – BTS unit hardware failures (DTRX, TRX. DDU,BB2F,WCxA,DVxA) – Crossed feeder cables. – Bad SMA cables and RF cables used for connection between DTRX/DDU. – RSSI values on the main and diversity paths are differing a lot. – High VSWR 

• RF Issues: – BCCH Frequency used in MAL list – Some segments in the network using same BCCH Frequency – Value of TSC parameter is same as BCC value – High Interference in the network. – Large number of intracell handovers (AMR packing/unpacking, interference) 

• BSC/Network Issues :– LAPD message distribution problem due to unused (floating) TRX signaling links on the BCSU concerned – Telecom links overloading the BCSU – Repeated Transmission Failures 

Troubleshooting

1. Check the BTS alarms for presence of degradation alarms TRX FAULTY, 7745 Channel Failure rate above threshold, TRX Operation degraded etc. 

2. Check the hardware showing that alarm and trouble shoot for the alarm as per NED. 

3. Recommissioned particular BTS with RFCAD. 

4. Make sure all the TRX test are passed during the commissioning. 

5. Check for any High VSWR or RF feeder swapping in the sector. Once the troubleshooting for the BTS HW part is done and verified and all issues were addressed. Please start for the verification on RF part. 

1. Check for alarm 7744: HIGH TCH INTERFERENCE showing high interference in the cell. 

2. Verify for any adjacent cells having same BCCH frequency using ZEAT command. 

3. Use ND reports and KPI data to for high UL interference and radio drops. 

4. KPI analysis of the affected cells for large number of intracell handovers causing shorter duration TCH seizures

Troubleshooting

Incase of large handover attempts in the segment follow following guidelines 

1. Check the handover parameters in the cells for intracell handover thresholdsand margins. 

2. Tune the TCH access parameters for 1800 band from 900 band i.e LAR,LER and NBL for segments. 3. Tune the FRL/FRU and LSEG parameters for TCH load distribution in both BTSs in Segment 

Note : Changes in the handover parameters should be done inconsultation with local RF team as per their recommendation

Note 

• MHT is the duration during which a MS is using the TCH in the cell. So if it is too short, it means either the calls are dropped as soon as the TCH is seize... or there is a HO taking place immediately. Check your drops and your outgoing HO : are they high ? 

                  If drops : HW problem, probably 

                  If HO : settings are done in such a way that HO are triggered quickly from this cell. 

• The Mean Holding Time for TCH reflects the average duration of calls on traffic channel. 

formula: (Traffic * Time duration(s) ) / (Number of Calls + Incomming Handovers) 

This statistics is depending much more on users behaviors, it's not really reflect a specific problem in the cell. To be sure you need to correlate the MHT with drop call rate for example