This document describes various timers used on the network side in GSM. It lists the timer name, description of what each timer is used for, and typical values. Many of the timers are used to keep radio resources allocated for a period of time while waiting for a mobile station to respond to a message or successfully access a channel. The values range from 50ms to several seconds and are set by the network to allow enough time for procedures while avoiding keeping resources allocated indefinitely if the mobile station fails to respond.

1. GSM Timers
Timer Name Description Value
T100 RADIO-LINK-
TIMEOUT
Detects the presence of the radio link by detecting SACCH frames every
480 ms.
4 SACCH multiframes.
That is 1.92 seconds if
the SACCH is
completely absent.
T200 Data link timer
Used for re-transmission on the data link. The value varies depending on
the message type.
155 ms for FACCH
T301 Alerting
(ringing) timer
Timer used to limit the amount of time a user has to answer a call. 20 seconds
T303 Mobility
Management
connection timer
Time the network waits after sending a CM SERVICE REQUEST until
receiving a response. This occurs before initiating call clearing procedures
towards the MS.
10 seconds
T305 Release timer
Time the network waits after transmitting a DISCONNECT message until
receiving a RELEASE message.
10 seconds
T306 In-band tones
release timer
Time the network waits after transmitting a DISCONNECT message while
in-band tones/announcements are provided, until receiving a RELEASE
message.
10 seconds
T308 Release timer
Time the network waits after sending a RELEASE message until receiving
a RELEASE COMPLETE message. This occurs before re-transmitting the
RELEASE or releasing the Mobility Management connection.
10 seconds
T310 Call
proceeding timer
Time the network waits after receiving a CALL CONFIRMED message
until receiving a ALERTING, CONNECT, or DISCONNECT message
before initiating clearing procedures towards the MS.
10 seconds
T313 Connect
acknowledge timer
Time the network waits after transmitting a CONNECT message until
receiving the CONNECT ACKNOWLEDGE message before performing
clearing procedures with the MS.
10 seconds
T323 Modify
complete timer
Time the network waits after sending a MODIFY message during call
mode changes, until receiving a MODIFY COMPLETE or MODIFY
REJECT message before initiating call clearing procedures.
10 seconds
T3101 Immediate
assignment timer
Time the network waits after sending the IMMEDIATE ASSIGNMENT or
IMMEDIATE ASSIGNMENT EXTENDED message until the main
signalling link is established before releasing the newly allocated
channels.
1 second
T3103 Handover
timer
Time the network waits after transmitting a HANDOVER COMMAND
message until receiving HANDOVER COMPLETE or HANDOVER
FAILURE or the MS re-establishes the call before the old channels are
released. If the timer expires and the network has not received a correctly
decoded L2 (format A or B) or TCH frame, then the newly allocated
channels are released.
2 seconds
T3105 Physical
information
repetition timer
Time the network waits after sending the PHYSICAL INFORMATION
message until receiving a correctly decoded L2 (format A or B) or TCH
frame. This occur before re-transmitting the PHYSICAL INFORMATION
message or releasing the newly allocated channels.
50 ms
T3107 Channel
assignment timer
Time the network waits after transmitting an ASSIGNMENT COMMAND
message until receiving the ASSESSMENT FAILURE message or the MS
re-establishes the call before releasing the old and the new channels.
3 seconds
T3109 Signaling
disconnection timer
Time the network waits after sending the CHANNEL RELEASE message
before disconnecting the signalling link.
5 seconds
T3111 Channel
deactivation after
disconnection timer
Time the network waits after disconnecting the signalling link before
deactivating the channel.
500 ms
T3113 Paging timer Time the network waits after transmitting the PAGING REQUEST
message until receiving the PAGING RESPONSE message. This occurs
before re-transmitting the PAGING REQUEST (if the maximum number of
5 seconds

2. Timer Name Description Value
re-transmissions have not been exceeded).
T3212 Location
update timer
The location update timer is set to zero, periodic location update by the
MS are disabled. If the MS camps to the BCH and decodes a new MCC
or MNC from the one it last camped on, it should perform a location
update.
zero = infinite time
T3250 TMSI
reallocation timer
Time the network waits after sending the TMSI REALLOCATION
COMMAND until receiving TMSI REALLOCATION COMPLETE. This
occurs before aborting the procedure and releasing the Radio Resource
connection.
5 seconds
T3260
Authentication
response timer
Time the network waits after an AUTHENTICATION REQUEST until
receiving AUTHENTICATION RESPONSE. This occurs before aborting
the procedure and releasing the Radio Resource connection.
5 seconds
GSM Frame Erasure Rate (FER) Measurement Description
This section is only applicable to the lab applications and is not applicable to GPRS or EGPRS.
You can use the GSM Frame Erasure Rate (FER) measurement to verify the mobile station's reference sensitivity for
control channels.
How is the FER Measurement Made?
The test set measures FER by sending a Layer 3 message that does not require a Layer 3 response from the mobile
station. It does require acknowledgment in the form of an RR frame from the mobile station. When the test set does
not receive the RR frame in acknowledgment, it retransmits the Layer 2 message. The test set counts the number of
times it resends Layer 2 messages.
The test set uses an MM Information message with all the optional fields omitted for the Layer 3 message.
You can make the Frame Erasure Rate Measurement on a full-rate FACCH channel (FACCH/F) or a half-rate
FACCH channel (FACCH/H).
Operating Considerations
The FER measurement can only be performed in Active Cell Operating Mode.
The connection type must be Auto.
FER Measurement Parameters
• Samples to Test - The number of samples to be taken by the measurement.
• Minimum Frame Interval (FACCH/F)- The minimum interval between FACCH frames (full rate) being sent to
the mobile station.
• Minimum Frame Interval (FACCH/H)- The minimum interval between FACCH frames (half rate) being sent
to the mobile station.
• Trigger Arm
• Measurement Timeout

3. FER Measurement Results
• Integrity Indicator -
• Frames Sampled - The count of samples tested.
• Frames Erased - The count of frames requiring retransmission by the test set.
Frame Erasure Rate - The ratio of Frames Erased to Frames Sampled
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GSM Timers-Network side
Timers on the network side
T3101: This timer is started when a channel is allocated with an IMMEDIATE ASSIGNMENT message. It is stopped
when the MS has correctly seized the channels. Its value is network dependent. NOTE: It could be higher than the
maximum time for a L2 establishment attempt.
T3103: This timer is started by the sending of a HANDOVER message and is normally stopped when the MS has
correctly seized the new channel. Its purpose is to keep the old channels sufficiently long for the MS to be able to
return to the old channels, and to release the channels if the MS is lost. Its value is network dependent. NOTE: It
could be higher than the maximum transmission time of the HANDOVER COMMAND, plus the value of T3124, plus
the maximum duration of an attempt to establish a data link in multiframe mode.)
T3105: This timer is used for the repetition of the PHYSICAL INFORMATION message during the hand-over
procedure. Its value is network dependent. NOTE: This timer may be set to such a low value that the message is in
fact continuously transmitted.
T3107: This timer is started by the sending of an ASSIGNMENT COMMAND message and is normally stopped when
the MS has correctly seized the new channels. Its purpose is to keep the old channel sufficiently long for the MS to be
able to return to the old channels, and to release the channels if the MS is lost. Its value is network dependent.
NOTE: It could be higher than the maximum transmission time of the ASSIGNMENT COMMAND message plus twice
the maximum duration of an attempt to establish a data link multiframe mode.
T3109: This timer is started when a lower layer failure is detected by the network, when it is not engaged in a RF
procedure. It is also used in the channel release procedure. Its purpose is to release the channels in case of loss of
communication. Its value is network dependent. NOTE: Its value should be large enough to ensure that the MS
detects a radio link failure.
T3111: This timer is used to delay the channel deactivation after disconnection of the main signalling link. Its purpose
is to let some time for possible repetition of the disconnection. Its value is equal to the value of T3110.
T3113: This timer is started when the network has sent a PAGING REQUEST message and is stopped when the
network has received the PAGING RESPONSE message. Its value is network dependent. NOTE: The value could
allow for repetitions of the Channel Request message and the requirements associated with T3101.
T3115: This timer is used for the repetition of the VGCS UPLINK GRANT message during the uplink access
procedure. Its value is network dependent. NOTE: This timer may be set to such a low value that the message is in
fact continuously transmitted.
T3117: This timer is started by the sending of a PDCH ASSIGNMENT COMMAND message and is normally stopped
when the MS has correctly accessed the target TBF. Its purpose is to keep the old channel sufficiently long for the

4. MS to be able to return to the old channels, and to release the channels if the MS is lost. Its value is network
dependent. NOTE: It could be higher than the maximum transmission time of the PDCH ASSIGNMENT COMMAND
message plus T3132 plus the maximum duration of an attempt to establish a data link in multiframe mode.
T3119: This timer is started by the sending of a RR-CELL CHANGE ORDER message and is normally stopped when
the MS has correctly accessed the new cell. Its purpose is to keep the old channels sufficiently long for the MS to be
able to return to the old channels, and to release the channels if the MS is lost. Its value is network dependent.
NOTE: It could be higher than the maximum transmission time of the RR_CELL CHANGE ORDER, plus T3134, plus
the maximum duration of an attempt to establish a data link in multiframe mode.
T3141: This timer is started when a temporary block flow is allocated with an IMMEDIATE ASSIGNMENT message
during a packet access procedure. It is stopped when the mobile station has correctly seized the temporary block
flow. Its value is network dependent.
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GSM Timers-MS side
GSM Timers
Timers on the mobile station side
T3122: This timer is used during random access, after the receipt of an IMMEDIATE ASSIGN REJECT message. Its
value is given by the network in the IMMEDIATE ASSIGN REJECT message.
T3124: This timer is used in the seizure procedure during a hand-over, when the two cells are not synchronized. Its
purpose is to detect the lack of answer from the network to the special signal. Its value is set to 675 ms if the channel
type of the channel allocated in the HANDOVER COMMAND is an SDCCH (+ SACCH); otherwise its value is set to
320 ms.
T3126:This timer is started either after sending the maximum allowed number of CHANNEL REQUEST messages
during an immediate assignment procedure. Or on receipt of an IMMEDIATE ASSIGNMENT REJECT message,
whichever occurs first. It is stopped at receipt of an IMMEDIATE ASSIGNMENT message, or an IMMEDIATE
ASSIGNMENT EXTENDED message. At its expiry, the immediate assignment procedure is aborted. The minimum
value of this timer is equal to the time taken by T+2S slots of the mobile station's RACH. S and T. The maximum
value of this timer is 5 seconds.
T3128: This timer is started when the mobile station starts the uplink investigation procedure and the uplink is busy. It
is stopped at receipt of the first UPLINK FREE message. At its expiry, the uplink investigation procedure is aborted.
The value of this timer is set to 1 second.
T3130: This timer is started after sending the first UPLINK ACCESS message during a VGCS uplink access
procedure. It is stopped at receipt of a VGCS ACCESS GRANT message. At its expiry, the uplink access procedure
is aborted. The value of this timer is set to 5 seconds.
T3110: This timer is used to delay the channel deactivation after the receipt of a (full) CHANNEL RELEASE. Its
purpose is to let some time for disconnection of the main signalling link. Its value is set to such that the DISC frame is

5. sent twice in case of no answer from the network. (It should be chosen to obtain a good probability of normal
termination (i.e. no time out of T3109) of the channel release procedure.)
T3134:This timer is used in the seizure procedure during an RR network commanded cell change order procedure.
Its purpose is to detect the lack of answer from the network or the lack of availability of the target cell. Its value is set
to 5 seconds.
T3142: The timer is used during packet access on CCCH, after the receipt of an IMMEDIATE ASSIGNMENT
REJECT message. Its value is given by the network in the IMMEDIATE ASSIGNMENT REJECT message.
T3146:This timer is started either after sending the maximum allowed number of CHANNEL REQUEST messages
during a packet access procedure. Or on receipt of an IMMEDIATE ASSIGNMENT REJECT message during a
packet access procedure, whichever occurs first. It is stopped at receipt of an IMMEDIATE ASSIGNMENT message,
or an IMMEDIATE ASSIGNMENT EXTENDED message. At its expiry, the packet access procedure is aborted. The
minimum value of this timer is equal to the time taken by T+2S slots of the mobile station's RACH. S and T are
defined in section 3.3.1.2. The maximum value of this timer is 5 seconds.
T3164: This timer is used during packet access using CCCH. It is started at the receipt of an IMMEDIATE
ASSIGNMENT message. It is stopped at the transmission of a RLC/MAC block on the assigned temporary block flow,
see GSM 04.60. At expire, the mobile station returns to the packet idle mode. The value of the timer is 5 seconds.
T3190: The timer is used during packet downlink assignment on CCCH. It is started at the receipt of an IMMEDIATE
ASSIGNMENT message or of an PDCH ASSIGNMENT COMMAND message when in dedicated mode.It is stopped
at the receipt of a RLC/MAC block on the assigned temporary block flow, see GSM 04.60. At expiry, the mobile
station returns to the packet idle mode. The value of the timer is 5 seconds.
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Basic Antenna Definitions
Beamwidth
- Defined by –3dB power points on both vertical and horizontal planes.
- Usually affects the physical size of the antenna.
Gain
- Defined as the power output relative to an isotropic antenna (Gain 0dB) or Dipole antenna (Gain
2.2dB).
Front-to-Back Ratio
- Defined as the amount of power in Front direction relative to Back direction.
- Usually approximately 20-25dB.

6. Polarization
- Electromagnetic wave consists of both an E Field and H Field.
Polarisation usually refers to the direction of the Electric field relative to the intended direction of use for the antenna.
Downtilt
- Downtilt is required to focus max.power where signal is desired (Coverage).
-Downtilt is required to prevent interference to other coverage areas (Interference).
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Timing Advance With Calculation
A Timing Advance (TA) is used to compensate for the propagation delay as the signal travels between the Mobile
Station (MS) and Base Transceiver Station (BTS). The Base Station System (BSS) assigns the TA to the MS based
on how far away it perceives the MS to be. Determination of the TA is a normally a function of the Base Station
Controller (BSC), bit this function can be handled anywhere in the BSS, depending on the manufacturer.
Time Division Multiple Access (TDMA) requires precise timing of both the MS and BTS systems. When a MS wants
to gain access to the network, it sends an access burst on the RACH. The further away the MS is from the BTS, the
longer it will take the access burst to arrive at the BTS, due to propagation delay. Eventually there comes a certain
point where the access burst would arrive so late that it would occur outside its designated timeslot and would
interfere with the next time slot.
Access Burst
As you recall from the TDMA Tutorial, an access burst has 68.25 guard bits at the end of it.
This guard time is to compensate for propagation delay due to the unknown distance of the MS from the BTS. It
allows an access burst to arrive up to 68.25 bits later than it is supposed to without interfering with the next time slot.

7. 68.25 bits doesnt mean much to us in the sense of time, so we must convert 68.25 bits into a frame of time. To do
this, it is necessary to calculate the duration of a single bit, the duration is the amount of time it would take to transmit
a single bit.
Duration of a Single Bit
As you recall, GSM uses Gaussian Minimum Shift Keying (GMSK) as its modulation method, which has a data
throughput of 270.833 kilobits/second (kb/s).
Calculate duration of a bit.
So now we know that it takes 3.69µs to transmit a single bit.
Propagation Delay
Now, if an access burst has a guard period of 68.25 bits this results in a maximum delay time of approximately 252µs
(3.69µs × 68.25 bits). This means that a signal from the MS could arrive up to 252µs after it is expected and it would
not interfere with the next time slot.

9. The next step is to calculate how far away a mobile station would have to be for a radio wave to take 252µs to
arrive at the BTS, this would be the theoretical maximum distance that a MS could transmit and still
arrive within the correct time slot.
Using the speed of light, we can calculate the distance that a radio wave would travel in a given time frame.
The speed of light (c) is 300,000 km/s.
So, we can determine that a MS could theoretically be up to 75.6km away from a BTS when it transmits its
access burst and still not interfere with the next time slot.
However, we must take into account that the MS synchronizes with the signal it receives from the BTS. We
must account for the time it takes for the synchronization signal to travel from the BTS to the MS.
When the MS receives the synchronization signal from the BTS, it has no way of determining how far
away it is from the BTS. So, when the MS receives the syncronization signal on the SCH, it
synchronizes its time with the timing of the system. However, by the time the signal arrives at the MS,
the timing of the BTS has already progressed some. Therefore, the timing of the MS will now be
behind the timing of the BTS for an amount of time equal to the travel time from the BTS to the MS.

10. For example, if a MS were exactly 75.6km away from the BTS, then it would take 252µs for the signal to travel
from the BTS to the MS.
The MS would then synchronize with this timing and send its access burst on the RACH. It would take 252µs for this
signal to return to the BTS. The total round trip time would be 504µs. So, by the time the signal from the MS arrives
at the BTS, it will be 504µs behind the timing of the BTS. 504µs equals about 136.5 bits.
The 68.25 bits of guard time would absorb some of the delay of 136.5 bits, but the access burst would still cut into the
next time slot a whopping 68.25bits.

11. Maximum Size of a Cell
In order to compensate for the two-way trip of the radio link, we must divide the maximum delay distance in half. So,
dividing 75.6km in half, we get approximately 37.8 km. If a MS is further out than 37.8km and transmits an access
burst it will most likely interfere with the following time slot. Any distance less than 37.8km and the access burst
should arrive within the guard time allowed for an access burst and it will not interfere with the next time slot.
In GSM, the maximum distance of a cell is standardized at 35km. This is due mainly to the number of timing
advances allowed in GSM, which is explained below.
How a BSS Determines a Timing Advance
For each 3.69µs of propagation delay, the TA will be incremented by 1. If the delay is less than 3.69µs, no adjustment
is used and this is known as TA0. For every TA, the MS will start its transmission 3.69µs (or one bit) early. Each TA
really corresponds to a range of propagation delay. Each TA is essentially equal to a 1-bit delay detected in the
synchronization sequence.

12. In order to determine the propagation delay between the MS and the BSS, the BSS uses the synchronization
sequence within an access burst. The BSS examines the synchronization sequence and sees how long it arrived
after the time that it expected it to arrive. As we learned from above, the duration of a single bit is approximately
3.69µs. So, if the BSS sees that the synchronization is late by a single bit, then it knows that the propagation delay is
3.69µs. This is how the BSS knows which TA to send to the MS.
The Distance of a Timing Advance
When calculating the distances involved for each TA, we must remember that the total propagation delay accounts
for a two-way trip of the radio wave. The first leg is the synchronization signal traveling from the BTS to the MS, and
the second leg is the access burst traveling from the MS to the BTS. If we want to know the true distance of the MS
from the BTS, we must divide the total propagation delay in half.
For example, if the BSS determines the total propagation delay to be 3.69µs, we can determine the distance of the
MS from the BTS.

13. We determined earlier that for each propagation delay of 3.69µs the TA is inceremented by one. We just learned that
a propagation delay of 3.69µs equals a one-way distance of 553.5 meters. So, we see that each TA is equal to a
distance of 553.5 meters from the tower. Starting from the BTS (0 meters) a new TA will start every 553.5m.
The TA becomes very important when the MS switches over to using a normal burst in order to transmit data. Thenormal burst does not have the 68.25 bits of guard time. The normal burst only has 8.25 bits of guard time, so the MSmust transmit with more precise timing. With a guard time of 8.25 bits, the normal burst can only be received up to30.44µs late and not interfere with the next time slot. Because of the two-way trip of the radio signal, if the MStransmits more than 15.22µs after it is supposed to then it will interfere with the next time slot.

14. Excessive Timing Advance (TA)
Another Problem
ExcessiveTimingAdvance(TA)
Drop call due to excessive TA happens when the TA value at drop call connection is higher than the cell parameter
TALIM (TADROP > TALIM) and from this counter TFDISTA is incremented.
Probable Reason
Location High sites or sites next to water pick up traffic from far away
Parameter setting Very low TALIM setting, which would indicate a ‘false’ excessive timing advance
How to analyze:
· Check cell parameter MAXTA and TALIM. If it covers far coverage, it is possible to setting of the cell parameters
MAXTA and TALIM to a higher value (for e.g. MAXTA=63, TALIM=62)
· If the cell is really covering far away from the site, other options are reducing the coverage by down tilting the
antennas, reducing antenna height, changing antenna or reducing output power
· If it is a rural area and need to cover a larger area, Extended Range feature might be useful to be considered.
Other Reason
Drop due other reason equal to total number of drops subtracts all drops with reason. If any of the above drop reason
didn’t meet the criteria, the reason for drop will be in the ‘Other Reason’.
Probable Reason
H/W fault Hardware Problem (Managed Object in BTS)
Disturbance Link/ Transmission disturbance problem
Parameter Setting Wrongly defined setting (for e.g. LAC – Location Area Code)
Mobile Station MS problem
Interference Interference problem (Uplink)
How to analyze:
· Check the BTS error log for hardware faults. (run commands: RXELP & RXMFP to look the hardware faults log)
· Check if ICM is indicating uplink interference in the cell.

15. · Check with O&M regarding transmission problems, HW problems and service affecting maintenance work during the
time period. The average cell downtime and TCH availability should also be check. It might be intermittent link
connection.
· Check object type MOTS, which is based on drop on Timeslot (TS) in order to find faulty devices.
Happy Learning :)
mail me At cellular.planning.optimization@gmail.com
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Congestion Analysis
Hi all
This is second topic for today that is "Congestion Analysis" a well known word for Telecom professionals .
Traffic congestion is one of the major network problems in a mobile system. A high congestion deteriorates the
overall performance of the network and should be minimized.
· 1: Short term growth
If the high traffic related to an occasional event, like sports event, fairs, conference, a temporary solution might be
considered.
· 2: Long term growth
If there is a long-term growth the network capacity has to grow according to the demand.
Type of Congestion
The congestion analysis begins by identifying if there is only SDCCH or TCH congestion or both. Congestion on both
SDCCH and TCH may mean that the only way to get rid of the congestion is to add more physical capacity in terms
of transceivers or sites.
Consider how many channels that are allocated in the cell. If possible, expand the capacity with new transceivers,
otherwise a new site must be implemented. Frequency planning schemes such as MRP and FLP could be used to
relieve congestion. Microcells could be used to take traffic in severe congested areas.
SDCCH Congestion

16. In R8, the time congestion should be used instead of congestion based on access attempts as there is no way to
estimate the number of access attempts a single mobile does.
The flowchart below, explains a general approach to investigate SDCCH Congestion. The next section describes the
action points in this flowchart. The reference to each action point is indicated on the flow chart as well.
Let me know your suggestions and feedback
Happy learning
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Low Signal Strength Analysis
lets starts todays topic that is Low signal strength analysis
What could be the probable cause of low signal while you drive or optimize.
First see the following flow chat and try to understand the things

17. Remember that
Low Signal strength is one of the reason of drop call. It can be indicated by many calls disconnected at low
signal strength by subscriber, drop calls due to excessive TA, poor handover performance and poor call
setup performance.
What could be the probable reasons
Probable Reason
Poor BSC
Exchange
Property setting
High LOWSSDL & LOWSSUL will give
more drop reason due to SS and this might
not show the actual drop. It is because drop
due to SS is more priority than Quality.
No dominant cell Cell might be isolated or standalone.
Antenna tilt &
orientation
Too much downtilt sometimes might not
cover a larger area and the subscriber
might lose the SS.
Output Power Low output power might cause smaller
border cell.
Just try to observed what could be the right cause :-
The following procedure should be performed for low signal strength
analysis:
1:
Identify the baseline requirement of design and BSC exchange property (setting for LOWSSUL/LOWSSDL).
2:

18. Check the value for LOWSSDL & LOWSSUL. If it is higher than ACCMIN, change the parameter to a reasonable
value since the drop reason will be more priority to SS compared to Quality.
3:
Check the site position, antenna direction, position etc. This is to ensure the possible location is open to interference
(open water environment) or isolated. Good map is needed for this.
4:
Check if the site is sectorized or Omni. If it is Omni, set the cell into sectorized cell.
5:
Check if the signal strength is uplink or downlink limited. Mostly, It is designed to be downlink limited.
6:
Check the coverage cover expected area from the planet. If it is not, check the antenna tilt and orientation. Change
the direction or tilt if it is too much downtilt or pointing to a wrong direction.
7:
Sometime, low output power might cause low SS. Check output power and if it is low, increase the output power.
8:
Check cell whether it has hotspots from drivetests. If found, adding new site is recommend.
9:
In order to check power distribution, run Cell Traffic Recording (CTR) to that particular cell.
10:
Check if the cell has indoor coverage problem. If yes, add micro site instead.
Need Your suggestions and doubts and let me know if problem is still there...
happy learning
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TCH Drop Analysis
1. Radio Link Time-Out

19. Every time a SACCH message can not be decoded the radio link time-out counter is decreased by 1. If the message
can be decoded the counter is incremented by 2. However, the value can not exceed the initial value. The initial value
is set by the parameter RLINKT for radio link time-out in the mobile station and by RLINKUP for timeout in the BSC. If
the mobile moves out of coverage and no measurement reports are received in the BSC, there will be a radio link
time-out and the message Channel Release (cause: abnormal release, unspecified) is sent to the mobile station and
the SACCH is deactivated in the BTS. A Clear Request message is sent to the MSC. To be sure that the mobile has
stopped transmitting, the BSC now waits RLINKT SACCH periods before the timeslot is released and a new call can
be established on the channel.
2. Layer 2 Time-Out
If the BTS never get an acknowledge on a Layer 2 message after the time T200XN200, the BTS will send Error
Indication (cause: T200 expired) to the BSC, which will send Channel Release (cause: abnormal release, timer
expired) to the mobile station and a Clear Request to the MSC. The SACCH is deactivated and the BSC waits
RLINKT SACCH periods before the timeslot is released and a new call can use the channel. This is only valid if the
call is in steady state, i.e. not during handover or assignment.

20. 3. Release Indication
When the BTS received a layer 2 DISC frame from the mobile it replies with a Layer 2 UA frame to the mobile station
and a Release Indication to the BSC. The system does only react on Release Indication if it is received during a
normal disconnection situation. If such a message is received unexpectedly this will usually cause radio link time-out
or timer T200 expiration as the mobile station stops the transmitting of measurement reports. It is also possible that
the release will be normal depending on when the Release Indication is received.
4. MSC Time-Out
Normal Release:
If the MSC never received a response on a message (e.g. Identity Request) and there is no radio link time-out or
layer 2 time-out, the MSC will send a Clear Command to the BSC. The time-out is depending on the message. When
receiving Clear Command, the BSC will send a Channel Release (cause: normal release) and then deactivates the
SACCH.
Reject (only SDCCH):
If the MSC never receives a response on the first message after Establish Indication, the MSC will send a reject
message. If the connection was a Location Update it will be a Location Update Reject (cause: network failure) and if
the connection was a mobile originating call (CM Service Request) a CM Service Reject (cause: network failure) will
be sent. The MSC will then send a Clear Command to the BSC and the call is cleared by Channel Release (cause:
normal release).
5. Assignment to TCH
Before sending an Assignment Command from the BSC at TCH assignment, the following two criterion have to be
fulfilled:

21. a. There must be a TCH channel available, i.e. no congestion
b. The locating algorithm must have received at least one valid measurement report.
If either of the criterion is not fulfilled, Assignment Command will not be sent and a Channel Release (cause:
abnormal release, unspecified) will be sent to the mobile station and a Clear Request to the MSC.
TCH Drop reason (1)
The classification of TCH Drop Reasons are arranged in the order of priority:
1.ExcessiveTiming Advance
2.Low Signal Strength
3.Bad Quality
4.Sudden Loss of Connection
5.Other Reasons
Excessive Timing Advance
The TCH Drop counters due to Excessive Timing Advance will pegged when the during the time of disconnection, the
last Timing Advance value recorded was higher than the TALIM Parameter. This drop reason is commonly apparent
to isolated or island sites with a wide coverage area.
Action:
Check if the cell parameter TALIM is < "63" Solution:
Set TALIM to a value close to 63.
Tilt antenna/reduce antenna height/output power, etc. for co-channel cells.
TCH Drop Reasons (2)
Low Signal Strength on Down or Uplink or Both Links
The drops counters due to Low Signal Strength will be pegged when the Signal Strength during the last Measurement
Report before the call dropped is below the LOWSSDL and/or LOWSSUL Thresholds. LOWSSDL and LOWSSUL
are BSC Exchange Property parameters which is used only for statistics purposes and does not affect the behavior of
calls. If both UL and DL Signal Strength are below the thresholds, only Drop due to Low SS BL will pegged. Normally
a call is dropped at the border of large rural cell with insufficient coverage. Bad tunnel coverage cause many dropped
calls as well as so called coverage holes. Bad indoor coverage will result in dropped calls. Building shadowing could
be another reason.
Action:
Check coverage plots.
Check output power.
Check power balance and link budget.

22. Check if Omni site.
Check antenna configuration & type.
Check antenna installation.
Perform drive tests & site survey.
Check TRX/TS with high CONERRCNT.
Solution:
Add a repeater to increase coverage in for example a tunnel.
Change to a better antenna (with higher gain) for the base station.
Add a new base station if there are large coverage holes.
Block/Deblock TRX
TCH Drop Reasons (3)
Poor Quality on Down or Uplink or Both Links
The drops counters due to Bad Quality will be pegged when the Signal Strength during the last Measurement Report
before the call dropped is above the BADQDL and/or BADQUL Thresholds. BADQDL and BADQUL (expressed in
DTQU) are BSC Exchange Property parameters which is used only for statistics purposes and does not affect the
behavior of calls. If both UL and DL Quality are above the thresholds, only Drop due to BAD Quality BL will pegged.
Problem on Bad Quality is usually associated with Co-channel Interference on BCCH or TCH. Faulty MAIO
assignment can cause frequency collisions on co-sited cells especially on 1x1 Reuse. External interference is also
one possible cause of problem on quality.
Action:
Check C/I and C/A plots.
Check Frequency Plan (Co-BCCH or Co-BSIC Problem).
Check MAIO, HOP, HSN parameters.
Check FHOP if correctly configured (BB or SY).
Check for External Interference.
Perform drive tests.
Solution:
Change BCCH frequency.
Change BSIC.
Change MAIO, HOP, HSN.
Change FHOP.
Record RIR or on-site Frequency Scanning to identify source of interference.
Use available radio features.

23. TCH Drop Reasons (4)
Sudden Loss of Connection
Drops due to Sudden Loss are drops that have not been registered as low signal strength, excessive timing advance,
bad quality or hardware (other) reasons, and the locating procedure indicates missing measurement results from the
MS.
There are some common scenarios that could lead to Sudden Loss of connections such as very sudden and severe
drops in signal strength, such as when subscribers enter into buildings, elevators, parking garages, etc., very sudden
and severe occurrence of interference, MS runs out of battery during conversation, Handover Lost, BTS HW faults,
Synchronization or A-bis link fault (transmission faults), and
MS Faults.
Action:
Check BTS Error Logs, Alarms and Fault Codes.
Check CONERRCNT per TRX and TS.
Check Transmission Link (A-bis).
Check for DIP Slips.
Check LAPD Congestion.
Correlate Handover Lost to Drops due to Sudden Loss
Solution:
Fix Hardware Faults and Alarms.
Reset TRX with high CONERRCNT.
Ensure that Synchronization and A-bis Link are stable.
Change RBLT with high DIP Slips.
Change CONFACT or increase Transmission Capacity
Investigate HO Lost Problem
TCH Drop Reasons (5)
TCH Drops due to Other Reasons
TCH drops due to Other Reasons are computed by subtracting the sum of drops due to Excessive TA, Low SS, Bad
Quality and Sudden Loss from the Total TCH Drop Counts. Drops due to Other Reasons are generally associated
with hardware problems, transmission link problems on A-bis, Ater or Ainterfaces, and sometimes Handover Lost.
Action:
Check BTS Error Logs.
Check Alarms and Fault Codes.
Check CONERRCNT per TRX and TS.
Check Transmission Link (A-bis).

24. Check for DIP Slips.
Correlate Handover Lost to Drops due to Other Reasons
Solution:
Fix Hardware Faults and Alarms.
Reset TRX with high CONERRCNT.
Ensure that Synchronization and A-bis Link are stable.
Change RBLT with high DIP Slips.
Investigate HO Lost Problem
Problem reason of drop in SDCCH
Low Signal Strength on Down or Uplink
The reason for poor coverage could be too few sites, wrong output power, shadowing, no indoor coverage or network
equipment failure.
Action: Check coverage plots.Check output power. Perform drive tests. Check BTS error log
Solution: Add new sites. Increase output power. Repair faulty equipment.
Poor Quality on Down or Uplink
Action: Check C/I and C/A plots. Check frequency plan. Perform drive tests.
Solution: Change frequency. Use available radio features.
Too High Timing Advance
Action: Check if the cell parameter TALIM is < style="font-weight: bold;">Solution: Set TALIM to a value close to 63.
Tilt antenna/reduce antenna height/output power, etc. for cochannel cells.
Mobile Error
Some old mobiles may cause dropped calls if certain radio network features are used. Another reason is that the MS
is damaged and not working properly.
Action: Check MS fleet.
Solution: Inform operator.
Subscriber Behavior
Poorly educated subscribers could use their handsets incorrectly by not raising antennas, choosing illadvised
locations to attempt calls, etc.
Action: Check customer complaints and their MS.
Battery Flaw
When a subscriber runs out of battery during a conversation, the call will be registered as dropped call due to low
signal strength or others.

25. Action: Check if MS power regulation is used. Check if DTX uplink is used.
Congestion on TCH
The SDCCH is dropped when congestion on TCH.
Action: Check TCH congestion
Solution: Increase capacity on TCH or using features like Assignment to another cell, Cell Load Sharing, HCS,
Dynamic Half-Rate Allocation and FR-HR Mode Adaptation etc
HOSR Analysis
Probable Reasons of Bad Handover Performance
---Neighboring Cell Relation
Action:Add neighbor cell relation.
---Missed measurement frequencies in BA-list
Action:Check measurement frequencies list.
---Permitted Network Color Code problem
Action:Check NCC Permitted
---HW faults.
Action: Check BTS error log.
---Blocking on Target Cell
Action:Remove Blocking on Tager Cell
---Congestion
A high congestion might lead to dragged calls (handover performed at a not intended location) and a lot of
unsuccessful handovers.
Action: Check TCH congestion.
---Timer Expire After MS is Lost
The MS never answers the base station.
Action: Check coverage. Check interference.
---Link Connection or HW Failure
Action: Check BTS error log. Perform site visit. Perform link performance measurements.
---Bad Antenna Installation
Action: Perform site survey and check antenna installation. Check antenna cabling.

26. ---Many Neighbors Defined
Many defined measurement frequencies defined (>16) will decrease the accuracy of the mobile measurements to
locate the best six servers. Many measurement frequencies mean few samples per frequency and problem for
mobiles to decode the BSIC.
Action: Check number of definitions.
---Delayed Handover Decision
A delayed handover decision can be due to congestion in the target cell.
Action: Check handover parameters.
---Wrong Locating Parameter Setting
Action: Check locating parameters.
---Bad Radio Coverage
Action: Check coverage plots.
---High Interference, Co-Channel or Adjacent
The potential handover candidate is disturbed by interference. Outgoing handover due to bad uplink quality may
indicate interference from co-channel another MS. On the border, the quality may be rather bad and the signal
strength low. Bad downlink quality may indicate interference from another co-channel base station.
Action: Check interference. Check if many handovers are performed due to downlink or uplink bad quality.
---Receiver Antenna Problem or RBS HW problems (in candidate cell)
Action: Check antenna installation. Check RBS HW and Error log of the target cell
---Poor Inter-MSC/BSC Handover Performance
For outer or external cell, wrong definitions in either MSC or BSC may be reason for the problem.
Action: Check inter-MSC/BSC handover performance.
---Incorrect Down Tilt
Action: Perform site survey and check antenna installation.
Solution: Correct antenna tilting