7745 Channel failure rate above defined threshold
7745 Channel failure rate above defined threshold
Meaning:
The rate of calls terminating in failure o The rate of calls terminating in failure on a chann n a channel is above the threshold value set by the el is above the threshold value set by the operator. The operator. The
alarm is used to supervise the functioning of t alarm is used to supervise the functioning of traffic and signaling channels, and to detect the po ic and signaling channels, and to detect the possible
faulty channels.
Parameters, with their default values, affecting the alarm:
ZEEN: TCHFR = TCH failure rate (20 %)
ZEEN: TCHFR = TCH failure rate (20 %)
SCHFR = SDCCH failure rate (80 %)
PRDCFR = length of supervision period (_60_ min)
CS = channel seizure threshold value (_10_)
When a SDCCH/TCH is released with t When a SDCCH/TCH is released with the following err he following error causes, the lost call counter is or causes, the lost call counter is
augmented.
Both SDCCHs and TCHs, release because of:
• a channel activation failure
• user actions
• a BTS failure
• an LAPD failure
•
a BSC signaling unit (BCSU) reset
• Abis problems
• A interface problems
• a radio failure
• a radio failure on an old channel during handover
• a radio failure on a new c a radio failure on a new channel during handover hannel during handover
• The counter for lost calls during a me The counter for lost calls during a measurement per asurement period is cleared at the end of each iod is cleared at the end of each
measurement period.
• The filtering of the alarm generation is The filtering of the alarm generation is achieved w achieved with a threshold value defined by the ith a threshold value defined by the
operator for the number of channel seizure operator for the number of channel seizure requests requests. The number of channel seizure requests . The number of channel seizure requests
during a measurement period must be gre during a measurement period must be greater than or ater than or equal to the threshold value for the equal to the threshold value for the
alarm to be generated. Although the alarm to be generated. Although the Channel failure Channel failure rate exceeded (SDCCH, TCH) supervis rate exceeded (SDCCH, TCH) supervision is
channel-specific, only one alarm per TRX and channel type is g l type is generated during one enerated during one
measurement period. In the alarm printout, more measurement period. In the alarm printout, more specified information is given of the channel cified information is given of the channel
with the greatest failure rate.
• The system cancels the alarm at The system cancels the alarm at the end of the firs the end of the first such measurement period during t such measurement period during
which conditions for alarm generation are no longer met or in connection with user's locking r in connection with user's locking
and unlocking commands.
• Hardware Issues:
1. BTS unit hardware failures (TRX, combiner, duplexer, connectors)
2. Crossed feeder cables.
3. Bad trx cabling, bad feeder quality or Bad trx cabling, bad feeder quality or their improp their improper connectivity. er connectivity.
4. RSSI values on the main and diversity paths are RSSI values on the main and diversity paths are differing a lot.
• RF Issues
1. BCCH Frequency used in MAL list
2. Some segments in the network using same BCCH Frequency
3. Value of TSC parameter is same Value of TSC parameter is same as BCC value as BCC value
4. High Interference caused in the network
• Detail Steps to check by RF
Check Neighbors
Every cell have some neighbors. Neighbors must be created and planned properly, in order to and planned properly, in order to
maintain every calls handover to its neighbors. Look at the k at the picture below. picture below.
From figure above, we see that cell A have neighbour cell B and cell C which is having same BSIC
and same Frequency Channel. Our experience shows that this condition will make whether TRx’s this condition will make whether TRx’s
under cell B or cell under cell B or cell C will have 7745 alarms. Becau C will have 7745 alarms. Because when MS from cell se when MS from cell A is going to handover, A is going to handover,
it detects two cells with same BSIC and Frequency. These two cells, will interfere each other. We
found this situation at some cells in Central Java. You can chec You can check this condition from MML using k this condition from MML using
comman ZEAT. And remember, check also neighbors of every cells which having 7745 alarms, cells which having 7745 alarms,
which can be perform with command ZEAO or which can be perform with command ZEAO or from RNW from RNW for its simplicity.
1.2 Check TRx’s TSC (Training Sequence Code)
TRx’s have TSC parameter as its Training Sequence Code of the carrier. We have to make sure,
that TSC must have same value with that TSC must have same value with its BCC. If TSC its BCC. If TSC is different with its BCC, it will is different with its BCC, it will raise 7745 raise 7745
alarms at the TRX’s. Check TRx’s alarms at the TRX’s. Check TRx’s TSC using ZERO com TSC using ZERO command. And check BCC of its cell u mand. And check BCC of its cell using ZEQO sing ZEQO
command. Make sure they have same value.
1.3 Switch BCCH Frequency to another TRX
7745 alarms can be raise in every different cases. Every case have different analysis and solutions. We will try to identify and analyze 7745 and 7604 alarms in some example situation
below.
7745 at one TRX only
Before you do the site visit, make sure that you have perform parameter check (TSC), neighbors
and perform the Trx test at the Trx remotely.If you go to do site visit, remember to check the
SMA cable at Tx connector to SMA cable at Tx connector to combiner of the TRx. Make sure it is properly tight connected.Replace the Trx, BB2F and SMA cables if needed.
7745 at two TRX.
Before you do the site visit, make sure that you ha sure that you have perform parameter check (TSC)
neighbors eighbors
and perform the Trx test at the Trx remotely.For example: we have 3 or 4 Trx under one cell,
which are Trx 1, 2, 3 and/or TRx4. If the alarms exist at Trx 1 and 2, and BCCH frequency is at TRX 1 or 2, try to switch the BCCH frequency to Trx 3 or Trx 4. If the alarms still appear at TRX1
or 2, then it is possible that TRX 1 and 2 have a partial cross feeder. It is just our temporary
conclusion.
. You have to do site visit to make sure. Replace Trx, system module( Combiner or
Duplexer) if needed.Also remember to check alarms on the other sector to ensure our analysis.
7745 at all TRX’s under same cell
Before you do the site visit,make sure that you have perform parameter check (TSC),neighbors
and perform the Trx test at the Trx remotely.Also remember to check alarms on the othersector. Many possibilities here,, including full partial cross feeder, bad feeder quality and its connection, interference,
broken Duplexer, etc.
• BSC/Network Issues:
1. LAPD message distribution problem due to unused (floating) TRX signaling links
on the BCSU concerned
2. Telecom links overloading the BCSU
3. Repeated Transmission Failures
• BSC/Network Issues refer the followings
• There are a number of BSC alarms and counters which may indicate that
BSC load is a problem, which Increase in counters 3005, 3038, 3039,
3040, 3041, 500627
(DAT files are needed to see (DAT files are needed to see these counters)
• Alarms 1014, 2133, 2478, 2720, 3164
• Alarms 2993 & 7745 may also be caused by BSC overload.
• Check the Transmission Links for any jitters, slips and BER.
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