C O M PILA T I O N O F RFOPTIMIZATION P R OBL E M C AS E AN D AN AL Y S IS ( C E L L U L AR 2 G N ETW OR KS ) c ompiled by Hery S upriya nto [email protected][email protected]http:// www.linkedin.com / in / her ysup riya n t o these document compilation from many resource feel free to share for knowledges purpose 1 s t Edition Marc h 10 , 20 10 Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer
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Compilation Case and Analysis Rf Optim 2g 1stedition
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8/9/2019 Compilation Case and Analysis Rf Optim 2g 1stedition
TCHDropreason(1)The classification of TCH Drop Reasons are arranged in the order of priority:
1.Excessive Timing Advance
2.Low Signal Strength
3.Bad Quality
4.Sudden Loss of Connection5.Other Reasons
Excessive TimingAdvanceThe 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.
TCHDrop Reasons(2)Low Signal Strength onDown or Uplink or Both LinksThe 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.
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
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TCHDrop Reasons(3)Poor Quality on Down or Uplink or Both LinksThe 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 isused only for statistics purposes and does not affect thebehavior 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.
TCHDrop Reasons(4)Sudden Lossof ConnectionDrops 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.
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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
TCHDrop Reasons(5)TCHDropsdue to Other ReasonsTCH 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 withhardware 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).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 reasonof drop in SDCCHLow Signal Strength onDown or UplinkThe reason for poor coverage could be too few sites, wrong output power, shadowing, no
Subscriber BehaviorPoorly 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 FlawWhen a subscriber runs out of battery during a conversation, the call will be registered as
dropped call due to low signal strength or others.
Action: Check if MS power regulation is used. Check if DTX uplink is used.
Congestion on TCHThe 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
TCH ASSIGNMENT SUCCESSRATE
Probable Reason:1) No dominant serving cell: The serving cell cannot cope with the TCH traffic.
2) Severe congestion on TCH: Failing TCH allocation for assignment or handover due to
congestion
3) Low signal strength for call access: The signal strength might be higher on the BCCH than onthe TCH.
4) Interference: Disturbance on SDCCH or target TCH
5) Faulty transceiver: Faulty equipment
Probable Reasonsof SDCCH Congestion
---Low AvailabilityAction: Check SDCCH Availability. Check if the channels are manual, control or automatic
blocked.
---IncreasingTrafficDemandThe high traffic could be related to an occasional event or due to a long term growth.
Action: Check if short term traffic growth. Make trend comparisons. Check if combined SDCCH is
used. Check SDCCH dimensioning.
---Bad use of Adaptive configuration of Logical ChannelsBy using the Adaptive configuration of logical channels feature, the basic SDCCH configuration in
a cell will be under-dimensioned. If this feature is not used correctly, it will cause SDCCH
congestion.
Action: Check if ACSTATE is on. Check parameters related to Adaptive configuration of logical
channels
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The actual ping pong handover is easily identified through drive test with sense of optimization
engineer without require any calculation. Coverage holes might lead to Ping-Ponghandover
especially for slow moving mobiles. It may be cause by shadowing by high building. Several
possible equal signals from two or more base stations might lead to Ping-Ponghandover as well
which is so called not optimized cell dominance.
The following action items shall be used for optimization solutions:
• Check the parameter setting such as hysteresis, offset, priority layer in dual-band case,
etc. If poor parameters setting found, then correct the related parameters. Compare to
default parameters design.
• Check the output power BSPWR and BSPWRT which normally put on maximum value or
compare to design.
• Check path balance on transceiver link, e.g. loss in uplink and downlink chain. Defective
RF modules might be the reason of imbalanced link.
• Check the site location such as possible coverage holes or no dominant cells.
• Perform drive test on that particular area to check the signal strength, if the average of signalstrength of the neighbors are the same, no dominant cell is found.
• For Long term action if no dominant cell shall be adding new site, while short term action shall
be uptilt the most dominant cell as the serving cell for that area and reduce coverage for others.
Drive Testing
ThePurpose of Drive Testing
Drive testing is principally applied in both the planning and optimisation stage of network
development. However, there are other purposes for which drive testing can be used:
•To provide path loss data for initial site survey work
•To verify the propagation prediction during the initial planning of the network.
•To verify the network system parameters, as defined in the EG8: GSM/DCS
System-Specific Parameters.
•To provide the initial test parameters used in Benchmarking (as defined in the
“Analysis” section of the Network Performance and Monitoring Guideline).
•To verify the performance of the network after changes have been made e.g.When a new TRX is added; the removal or addition of a new site; any power
Adjustments or changes to the antenna; any changes in clutter or traffic habits
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•To measure any interference problems such as coverage from neighboring
Countries.
•To locate any RF issues relating to traffic problems such as dropped or blocked
calls.
•To locate any poor coverage areas.
•To monitor the network against a slow degradation over time, as well as
Monitoring the network after sudden environmental conditions, such as gales
or electrical storms.
•To monitor the performance of a competitor’s network.
Whento Drive Test
Drive testing can take place during the day or at night and is dependant upon the
Operator’s requirements and subscriber habits.
Drive testing during the day will mimic the conditions as seen by subscribers, but may
clog up the network if call analysis is being performed.
Drive testing during the night will allow a greater area to be surveyed due to the reduction
in vehicular congestion. It will also allow for certain test signals to be transmitted and
tested, particularly when setting up a new site, without interrupting normal operation.
However, night-time testing does not mimic the conditions experienced by subscribers.
For planning purposes, drive testing is typically performed at night and for maintenance
purposes, drive testing is performed during the day.
Where to Drive Test
Some areas of a network will have greater performance problems than others. Drivetesting should not be uniform throughout the whole network, but should be weighted
towards areas where there are significant RF problems.
There may be other areas of the network that require temporary coverage during a certain
time of the year e.g. an exhibition centre or a sports stadium. These areas should be
examined and planned in greater detail.
It is important that a drive test is documented. This is specified by the Operator and can
either take the form of creating a new item of documentation or filling in an existing
document. All documentation will be passed to Analysts and Engineers, who will need
accurate records of any test work carried out.
----Route PlansThe area to be drive tested is ascertained before leaving the office. There are three levels
of drive testing depending on the purpose of the test:
Primary Route: This includes all major roads, highways and throughfares and should be
given priority to all other roads when conducting a coverage test, unless a new site is put
into service for a specific objective.
Secondary Route: This includes all streets, by-streets and compounds, where accessible,
such as a University Campus. Secondary routes are used in areas where problems have
been located during a primary route test and further investigation is needed.Miscellaneous Routes: This includes in-building and non-access routes to vehicles such
as shopping malls, golf courses, airports, hotels, conference centres etc.
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In GSM, this particular classification is very difficult to determine with great accuracy. It
should be noted that it is not enough to monitor just the RxLEV and the RxQUAL.
Troubleshooting
No Data CollectedOccasionally, the equipment fails to trigger the collection device to save the data to file.
Check • all cables
Ensure the Processing Unit is powered •
Re-start the laptop computer •
Re-start the equipment •
Re-drive the test. •
No Positional InformationCollectedIf data is collected using GPS only, it may be possible that satellite reception was lost
during a drive through a tunnel etc. It is important that back-up equipment is used, such asa Dead-Reckoning device, since a GPS receiver will re-transmit the last known position
until it receives an update. If the vehicle moves without GPS cover, the data will be
inaccurate and cannot be analysed.
Check the • GPS antenna cable to the receiver
Drive to an open area and ensure that the GPS system is working correctly •
If required, install a back-up positional device to safeguard against lost GPS •
Coverage Holes
If there are patches of poor coverage in unexpected areas, it may indicate the fringes of a
coverage hole. It is important to re-drive this particular area.
Complete a route plan using secondary roads as far as possible •
Make notes of any buildings / obstructions that may cause shadowing •
Take note of pedestrian / vehicular habits in the area •
Dropped Calls
Dropped calls can be caused by either RF environments or incorrect system parameters.
The following data should be checked to ensure that it has been collected properly.
Layer 3 Messages •
Neighbour Cell List (BA Table) •
RxLEV (Server • & Neighbour)
RxQUAL (Server • & Neighbour)
Finally, ensure that the automatic setting for the call length is not shorter than that for the
timer monitoring for unauthorised call drop-outs. The setting should be a minimum of 30
seconds.
Handover Problems
Handover problems are generally caused by inaccurate settings of the handover boundary.
This can cause ping-ponging, where the server will keep changing, and congestion at the
switch. Check the following.
The transceiver antenna is fitted correctly •
Collection of Layer 3 Messages •
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Also, ensure that the collection of data from the new serving cell immediately after the
handover has occurred (particularly RxLEV and RxQUAL) is not timed to occur prior tothe-synchronisation of the transceiver itself.
If a particular serving cell can be isolated as a potential cause of handover problems,
slowly drive around the cell in a radius of around 500m - 1km, checking when handovers
occur.
Blocked Calls/ System BusyIf calls are repeatedly classified as blocked, it is recommended that the drive test is
temporarily halted in order to try and locate the cause.
Check that the number called is fully functional •
Check that there is adequate coverage from the expected serving BTS •
Check the equipment transceiver is functioning correctly by using an ordinary •
mobile to call the office
If all appears functional, try to place calls through an alternative BTS. If this •
succeeds, inform the office immediately and re-suspend the drive test.
Timersandcountersfor Radio Resource Management
Timers on the Mobile Station Side
T3122: This timer is used during random access, after the receipt of an IMMEDIATE ASSIGNREJECT 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 IMMEDIATEASSIGNMENT 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.
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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 sent twice in case of no answer from thenetwork. (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 IMMEDIATEASSIGNMENT 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 mobilestation 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.
Timers on the network sideT3101: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 isnetwork 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 thehand-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.
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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 isnetwork 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 isnormally stopped when the MS has correctly accessed the target TBF. 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 isnetwork 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 isnetwork 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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?áThe PSTN subscriber dialsthe MS’stelephone number (MSISDN), the MSISDNisanalyzed inthe PSTN, which identifiesthat thisisa call to a mobile network subscriber. A connectionis
established to the MS’shome GMSC. The PSTN sendsan Initial Addressmessage(IAM) totheGMSC.?úThe GMSCanalyzesthe MSISDNto findout which HLR, the MSisregisteredin, and queriesthe HLRforinformationabout how to route the call to the servingMSC/ VLR. The HLRlooksupthe MSISDN and determinesthe IMSI and theSS7 addressfor the MSC/ VLRthat isservicingthe MS. The HLRalso checksif theservice, “call forwardingto C-number” isactivated, if so, thecall isrerouted bythe GMSCto that number.?‚ The HLRthencontactsthe servicingMSC/ VLRand asksit to assign a MSRN to thecall. [MSRN -MobileStationRoutingNumber].The MSC/ VLRreturnsanMSRN viaHLRto theGMSC.
?ÖThe GMSCsendsan Initial Addressingmessage(IAM) to the servicingMSC/ VLRand usestheMSRN to route the call to the MSC/ VLR. Once the servicingMSC/ VLRreceivesthe call, theMSRN canbe released and may be made available for reassignment.?+The MSC/ VLRthenordersallof itsBSCsand BTSsto page the MS. Since the MSC/ VLRdoesnot know exactly which BSCand BTSthe MSis monitoring, the page will besent out acrossthe entireLocationArea(LA).?{When the MSdetectsthe pagingmessage to the BTS’sin the desired LA. The BTS’stransmitthe message over the air interface usingPCH. To page the MS, the networkusesan IMSI orTMSI validonly in the current MSC/ VLRservice area.?ÐWhenthe MSdetectsthe pagingmessage, it sendsa request onRACH for a SDCCH.?ÛThe BSCprovides a SDCCH, usingAGCH.
? SDCCH isused for the call set-up procedures. Over SDCCH all signalingprecedinga call takesplace. Thisincludes: Markingthe MSas“active” in the VLR. Authentication procedure (Startciphering, Equipment identification).?· The MSC/ VLRinstructs the BSC/ TRCto allocate an idle TCH. The BTSandMSare toldtotune to the TCH. The mobile phone rings. If the subscriber answers, the connectionisestablished.
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Note that it does not uniquely identify the operator. NCC is primarily used to distinguish
between operators on each side of border.
BCC = Base Station Colour Code (3 bits), identifies the Base Station to help distinguish between
BTS using the same BCCH frequencies
Location Number (LN)
Location Number is a number related to a certain geographical area, as specified by the network
operator by ”tying” the location numbers to cells, location areas, or MSC/VLR service areas.
The Location Number is used to implement features like Regional /Local subscription and
Geographical differentiated charging.
Dropped Call due to Sudden DropOn circuit switch service, when a call is abnormally disconnected, a Clear Message with cause
code Call Control be treated as normal Disconnection is sent to the MSC – named Clear Request
Message.
Refer to Ericsson system, the following Urgency condition is checked at that time and the
relevant counter is incremented as a consequence:
1. Excessive TA
2. Low Signal Strength
3. Bad Quality
4. Sudden Drop
As named, stright forward meaning for the dropped call is described for the first three items.
However, Sudden Drop is quite not easy to understand.
Sudden Loss are drops that have not been registered as bad quality, signal strength, timing
advance. The term Sudden Loss is used because if the network cannot establish a connection
with the lost MS after a pre-defined period, the sudden loss counter is incremented if the last
reported measurement from the MS does not fulfill any of the reasons mentioned.
A connection is marked as Sudden loss if none of the three types of urgency states (that isexcessive TA, low signal strength or bad quality) are indicated and the locating procedure
indicates missing measurement results from the MS.
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Drops due to ‘Other’ reasons are generally associated with hardware problems and
disturbances, number of drops due to ‘Other’ reasons is obtained by subtracting the drops with
known reasons from the total number of drops.
Main contributors in sudden and other TCH drop:
• Very sudden and severe drop in signal strength, such as when subscribers enter into
buildings, elevators, parking garages, etc.
•
Very sudden and severe occurrence of interference or bad quality.
MS running out of battery during conversation.
• Handover Lost.
• BTS HW faults.
• Synchronization or Abis link fault (transmission faults).
• MS Faults.
SMS(SHORTMESSAGESSERVICES)* *mostlyof term
SMS is a service that allows subscribers to send short messages (up to 160 characters) to other
mobile subscribers. Rather than having to set up a call on a traffic channel, SMS uses spare
capacity on the Standalone Dedicated Control Channel (SDCCH).
SMS is classified as a GSM Teleservice and three SMS teleservices (TS21-23) have been defined:· TS21 – Mobile terminated point-to-point messaging. A mobile can terminate an SMS
message either from another MS or from the fixed network.
· TS22 – Mobile originated point-to-point messaging. A mobile can send a message either to
another MS or into the fixed network (as an Email for example).
· TS23 – SMS Cell Broadcast (SMSCB). A more recent variation of SMS is SMSCB. SMSCB
messages are generally broadcast only in a specific network region. An MS cannot initiate such
a message and does not acknowledge receipt of one. Only MSs in idle mode can receive SMSCB
messages. These messages differ from standard SMS messages in that they are only 92
characters long. However, procedures exist to concatenate up to 15 SMSCB messages using a
special reassembly mechanism.In order to implement SMS, a network operator must establish a SMS Service Centre which
receives and processes SMS messages in a store-and-forward mode. Messages can be initiated
in the fixed or mobile network and delivered to either the fixed or mobile network.
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The Mobile StationThe mobile station (MS) is the wireless terminal capable of receiving and originating short
messages as well as voice calls. The wireless network signalling infrastructure is based on
signalling system 7 (SS7). SMS makes use of the mobile application part (MAP), which defines
the methods and mechanisms of communication in wireless networks, and uses the services of
the SS7 transaction capabilities application part (TCAP). An SMS service layer makes use of the
MAP signalling capabilities and enables the transfer of short messages between the peer
entities.
GSM Interfaces
Interface between the MSCand Base StationSystem (A-interface)The interface between the MSC and its BSS is specified in the 08-series of GSM Technical
Specifications. The BSS-MSC interface is used to carry information concerning:
· BSS management;
· call handling;
· mobility management.
A-BISINTERFACE(BSC- BTS)When the BSS consists of a Base Station Controller (BSC) and one or more Base Transceiver
Stations (BTS), this interface is used between the BSC and BTS to support the services offered tothe GSM users and subscribers. The interface also allows control of the radio equipment and
radio frequency allocation in the BTS.
This interface is specified in the 08.5x-series of GSM Technical Specifications.
BINTERFACE(MSC- VLR)The VLR is the location and management data base for the mobile subscribers roaming in the
area controlled by the associated MSC(s). Whenever the MSC needs data related to a given
mobile station currently located in its area, it interrogates the VLR. When a mobile station
initiates a location updating procedure with an MSC, the MSC informs its VLR which stores the
relevant information. This procedure occurs whenever an MS roams to another location area.Also, when a subscriber activates a specific supplementary service or modifies some data
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attached to a service, the MSC informs (via the VLR) the HLR which stores these modifications
and updates the VLR if required.
CINTERFACE(HLRand the MSC)The Gateway MSC must interrogate the HLR of the required subscriber to obtain routing
information for a call or a short message directed to that subscriber.
D INTERFACE(HLR- VLR)This interface is used to exchange the data related to the location of the mobile station and to
the management of the subscriber. The main service provided to the mobile subscriber is the
capability to set up or to receive calls within the whole service area. To support this, the
location registers have to exchange data. The VLR informs the HLR of the location of a mobile
station managed by the latter and provides it (either at location updating or at call set-up) with
the roaming number of that station. The HLR sends to the VLR all the data needed to support
the service to the mobile subscriber. The HLR then instructs the previous VLR to cancel the
location registration of this subscriber. Exchanges of data may occur when the mobile
subscriber requires a particular service, when he wants to change some data attached to hissubscription or when some parameters of the subscription are modified by administrative
means.
EINTERFACE(MSC– MSC)When a mobile station moves from one MSC area to another during a call, a handover
procedure has to be performed in order to continue the communication. For that purpose the
MSCs have to exchange data to initiate and then to realize the operation. After the handover
operation has been completed, the MSCs will exchange information to transfer A-interface
signalling as necessary. When a short message is to be transferred between a Mobile Station
and Short Message Service Centre (SC), in either direction, this interface is used to transfer themessage between the MSC serving the Mobile Station and the MSC which acts as the interface
to the SC.
FINTERFACE(MSCand EIR)This interface is used between MSC and EIR to exchange data, in order that the EIR can verify
the status of the IMEI retrieved from the Mobile Station.
GINTERFACE(VLR– VLR)When a mobile subscriber moves from a VLR area to another Location Registration procedure
will happen. This procedure may include the retrieval of the IMSI and authentication
parameters from the old VLR.
H INTERFACE(HLR- AuC)When an HLR receives a request for authentication and ciphering data for a Mobile Subscriber
and it does not hold the requested data, the HLR requests the data from the AuC. The protocol
used to transfer the data over this interface is not standardized.
Um INTERFACE(MS- BTS)The interface between the MS and the BSS is specified in the 04- and 05-series of GSM Technical
Specifications.
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