3g dropped & blocked call specifications

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RANT Dropped and Blocked Calls Classification Summary (WCDMA Network MTN South Africa) 1 Introduction......................................2 2 Dropped Calls Classification......................3 2.1 Missing Neighbours................................3 2.2 Poor Coverage.....................................4 2.3 Bad Radio Environment.............................5 2.4 Congestion........................................6 2.5 Not Radio.........................................7 2.6 Equipment Fault...................................8 3 Blocked Calls Classification......................9 3.1 Missing Neighbour................................10 3.2 Poor RF (Bad Coverage and Radio Environment).....11 3.3 Equipment Fault (UE).............................12 3.3.1 Security and Authentication Mode Failure.........12 3.3.2 UE Freeze........................................13 3.4 Not Radio........................................14 3.4.1 Disconnect on RAB Setup..........................14 3.4.2 Resources Unavailable (Congestion)...............15 3.4.3 UE Sensitivity Fault.............................16 3.5 Abnormal blocked calls...........................17 3.5.1 Unclassified - Unanswered RRC requests...........17 3.5.2 Faulty Block Recording - Barred Network..........18 3.5.3 Call Initialisation during L.U. signalling.......19

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Page 1: 3G Dropped & Blocked Call Specifications

RANT Dropped and Blocked Calls Classification Summary

(WCDMA Network MTN South Africa)

1 Introduction..........................................................................................22 Dropped Calls Classification................................................................32.1 Missing Neighbours.............................................................................32.2 Poor Coverage.....................................................................................42.3 Bad Radio Environment.......................................................................52.4 Congestion...........................................................................................62.5 Not Radio.............................................................................................72.6 Equipment Fault...................................................................................83 Blocked Calls Classification.................................................................93.1 Missing Neighbour.............................................................................103.2 Poor RF (Bad Coverage and Radio Environment)............................113.3 Equipment Fault (UE)........................................................................123.3.1 Security and Authentication Mode Failure.........................................123.3.2 UE Freeze..........................................................................................133.4 Not Radio...........................................................................................143.4.1 Disconnect on RAB Setup.................................................................143.4.2 Resources Unavailable (Congestion)................................................153.4.3 UE Sensitivity Fault............................................................................163.5 Abnormal blocked calls......................................................................173.5.1 Unclassified - Unanswered RRC requests........................................173.5.2 Faulty Block Recording - Barred Network..........................................183.5.3 Call Initialisation during L.U. signalling..............................................19

Page 2: 3G Dropped & Blocked Call Specifications

1 Introduction

This document describes some of the typical dropped/blocked call classifications encountered during several RAN Tuning Projects for WCDMA networks. The purpose of the document is for RAN Consultants to understand some of the problems to make the UE analysis and classification easier. The analysis has been based on limited data (for example no UETR data or data based on similar tool, no usage of RBS and RNC tracers) and for this result there could be a deviation in the results. Some of these classifications are only a guideline and should be viewed merely as documenting the typical problem until the correct reason behind the dropped call is established.

All these dropped/blocked calls categories are adapted to the radio environment evaluation thresholds set up for the MTN 3G RAN Tuning project in the post-processing tool TEMS Deskcat 5.6.

In the table below are listed the main causes that must be considered during the analysis, with the explanation for each cause.

CLASSIFICATION CRITERIA

Poor CoverageThe Drop occurs in regions where conditions CPICH RSCP and/or CPICH Ec/No are measured in critical values not suitable for a proper connection.

Bad Radio Environment

Every drop that occurs when Best Server is Missing (Mostly in good CPICH RSCP conditions). The UE active set update cannot follow the quick coverage changes. In this case Pilot Pollution situations are included as well (3 cells in AS and more than 1 strong SCs is interfering the connection within a range of 5 dB - Ec/No basis evaluation).

CongestionEvery drop that occurs when there are no more available radio resources for the connection. The network sends an RRC Connection Release when the RBS reaches the maximum available Power in DL.

Not Radio

Every drop that occurs when the radio conditions are good, the logging equipment is working properly and the RRC connection release cause (marked usually as "Unspecified") could be attributed to a RBS/Network fault, (including UL UE power going to maximum even if the CPICH RSCP is measured at good values, crossed feeders causing false missing neighbours, crossed UL-DL feeders, wrong parameter settings that can affect accessibility/SHOs in the cell).

Equipment FaultEvery drop that occurs when TEMS Investigation/UE are Blocking or Freezing and/or SW is crashing, so that it's not possible to maintain the connection.

Missing NeighboursEvery drop that occurs when there are poor RSCP and/or Ec/No levels/quality on the Best Server/AS, with the contemporary possibility for the UE to perform a SHO on a better cell that is not declared as a Neighbour for the AS cells themselves.

2 Dropped Calls Classification

The main cases and dropped call causes are listed below.

Page 3: 3G Dropped & Blocked Call Specifications

2.1 Missing Neighbours

Every drop that occurs when there are poor RSCP and/or Ec/No levels/quality on the Best Server/AS, with the contemporary possibility for the UE to perform a SHO on a better cell that is not declared as a Neighbour for the AS cells themselves. An example of dropped call for missing neighbour problem is shown in figure below.

Problem Description: The Active Set best server is cell 61888 (SC = 205). During the call sector 62096 (SC = 293) becomes the strongest sector but is not added to the active set, as the two cells are not defined neighbours. This can be seen in the Serving/Active Set window in TEMS. The cell 62096 act as an increasing interferer until eventually the call is released. The release cause is classified as unspecified.

2.2 Poor Coverage

The Drop occurs in regions where conditions CPICH RSCP and/or CPICH Ec/No are measured in critical values not suitable for a proper connection. In the table below an example is shown.

Page 4: 3G Dropped & Blocked Call Specifications

Problem Description: In this case the RF environment as reported by the UE is very poor before the call is dropped. The best server RSCP=-127dBm and Ec/No=-32dB. The scanner also reports poor radio conditions for the same SC at the same instant i.e. RSCP = -11.97dBm and Ec/Io = -10.69dB. The last message sent is the UL Active Set Complete message sent by the UE. The UE then goes into idle mode.

2.3 Bad Radio Environment

Every drop that occurs when Best Server is Missing (Mostly in good CPICH RSCP conditions). The UE active set update cannot follow the quick coverage changes. In this case Pilot Pollution situations are included as well (3 cells in AS and more than 1 strong SCs is interfering the connection within a range of 5 dB - Ec/No basis evaluation).

Page 5: 3G Dropped & Blocked Call Specifications

Problem Description: The Active Set best servers are cells with SCs 49 and 303, and all MN (SCs 304, 179 and 180) are close to them on a RSCP basis (from –70dBm to –79 dBm). During the call UE is performing a continuous number of SHOs, affecting both the service continuity and the quality of the connection (low values of Ec/No on each cell). So, the Radio Environment is not suitable for a good connection and therefore the dropped call occurs. Sometimes the TEMS Inv. doesn’t show the event on the chart, like in this case, so it’s advisable to check the Events and Layer 3 messages: In the L3 table the RRC Connection Release DL corresponds (into the Event table) to an RRC Connection Abnormal Release with the specification “Unspecified”.

2.4 Congestion

Every drop that occurs when there are no more available radio resources for the connection. The network sends an RRC Connection Release when the RBS reaches the maximum available Power in DL. In the corresponding DL Layer 3 message “RRC Connection Release” when the drop happens, the release cause is clearly marked as “Congestion”. An example is shown in figure below.

Page 6: 3G Dropped & Blocked Call Specifications

Problem Description: In this case the radio environment doesn’t show any critical issue: the AS is full, and there is a Best Server cell (SC 352) with two more cells that are carrying the service. Also the MN set is good, and the Layer 3 messages sequence is regular.

The radio resource unavailability pops up suddenly after a certain number of fast SHOs, and an “RRC Connection Release” message from the network comes to interrupt the call. In the TEMS L3 messages window details the release cause is clearly marked as “Congestion”.

2.5 Not Radio

Every drop that occurs when the radio conditions are good, the logging equipment is working properly and the RRC connection release cause (marked usually as "Unspecified") could be attributed to a RBS/Network fault, (including UL UE power going to maximum even if the CPICH RSCP is measured at good values, crossed feeders causing false missing neighbours, crossed UL-DL feeders, wrong parameter settings that can affect accessibility/SHOs in the cell).

This case also includes the “UE Sensitivity” drop, as shown in figure below.

Page 7: 3G Dropped & Blocked Call Specifications

Problem Description: The radio environment as reported by the UE is very poor just before the call dropped i.e. Best server RSCP=-127dBm and Ec/No=-27dB. The scanner reports much better radio conditions for the same SC at the same instant i.e. RSCP =-93.57dBm and Ec/Io = -8.66dB. Although the drop is as a result of low RSCP as measured by the UE it should not be classified, as a poor coverage drop since the scanner indicates the radio conditions should be ok to maintain the call.

2.6 Equipment Fault

Every drop that occurs when TEMS Investigation/UE are Blocking or Freezing and/or SW is crashing, so that it's not possible to maintain the connection.

An example of UE freezing dropped call is shown in figure below.

Page 8: 3G Dropped & Blocked Call Specifications

Problem description: In the example the network sends a DL Measurement Control message and then the UE freezes. There are no further massages sent between the network and the UE. The RF environment was good at the time of the drop as can be seen from the scanner information i.e. RSCP =-82.72dBm and Ec/Io = -5.44dB.

Page 9: 3G Dropped & Blocked Call Specifications

3 Blocked Calls Classification

The main cases and blocked call causes are listed below. In this situation the cases of Blocked Calls are pretty equal to the corresponding ones in the dropped calls list. It’s advisable to consider that it is intended as “blocked call” a connection interrupted for the same problems shown in section 2 (with some obvious exceptions shown in the following paragraphs) and according the Classification Criteria table shown in section 1. It’s crucial to consider that the blocked call event always happens during the call setup phase.

Due to these differences, the classification for the blocked calls is different for the dropped calls’ one.

3.1 Missing Neighbour

Page 10: 3G Dropped & Blocked Call Specifications

Problem Description: An example of a blocked call caused by a missing neighbour is shown in figure above. The call is being set up on cell 49046 (SC = 387). During the set up sector 48007 (SC = 451) becomes the strongest sector but is not added to the active set as the two cells are not defined neighbours. This can be seen in the Serving/Active Set window in TEMS. The cell 48007 act as an increasing interferer until eventually the call itself is released. The release cause is classified as unspecified.

3.2 Poor RF (Bad Coverage and Radio Environment)

Page 11: 3G Dropped & Blocked Call Specifications

Problem Description: In this case the RF environment as reported by the UE is very poor when the UE attempts to initiate a call. The attempt is indicated by the event “Call Initialization” in TEMS Investigation, which is triggered at the start of a command sequence. The best server RSCP=-121dBm and Ec/No=-21dB. The scanner also reports poor radio conditions for the same SC at the same instant i.e. RSCP =-114.17dBm and Ec/Io = -11.29dB.

3.3 Equipment Fault (UE)

3.3.1 Security and Authentication Mode Failure

Page 12: 3G Dropped & Blocked Call Specifications

Problem Description: In this case there is a problem with the security and Authentication procedure, which causes the connection to be dropped and result in a blocked call. As can be seen in figure above the radio environment at the time of the blocked call is good i.e. Best server RSCP=-71dBm and Ec/No=-2dB.

The call is released normally during call set up and 6 seconds after the network sends the security command. There is a timer for the correct response to this security command, which is set to 6 seconds. This indicates a problem in the security and authentication response by the UE.

3.3.2 UE Freeze

Page 13: 3G Dropped & Blocked Call Specifications

Problem description: This type of dropped call classification is caused by the UE “freezing” which can be seen in figure below. In the example the UE sends a UL Active Set Update Complete message and then the UE freezes. There are no further massages sent between the network and the UE before the next call attempt, which is indicated by the Call initialisation event in TEMS Investigation. The RF environment was good at the time of the drop as can be seen from the scanner information i.e. RSCP =-94.17dBm and Ec/Io = -5.13dB.

3.4 Not Radio

3.4.1 Disconnect on RAB Setup

Page 14: 3G Dropped & Blocked Call Specifications

Problem description: In this case the radio environment is good as shown in figure above (i.e. Best server RSCP= -94dBm and Ec/No= -3dB). During call set up, after the “DL Call Proceeding” message the network sends a Disconnect message. This can be seen in the Layer 3 messages window below. The cause value is (127) Interworking, unspecified as shown in L3 message details window. The call is then released.

This case can include both DC Config Failure and RAB setup failure.

3.4.2 Resources Unavailable (Congestion)

Page 15: 3G Dropped & Blocked Call Specifications

Problem description: In this example the network sends a Disconnect message with the following message: cause value (47) Resources Unavailable, Unspecified. This can be seen in the Layer 3 messages window in figure above. The Disconnect message occurs after the Radio Bearer is set up. The radio environment is good at the time of the Disconnect message as seen in figure above.

Sometimes this example of blocked call can be also referred to Congestion problems in the measured cell.

3.4.3 UE Sensitivity Fault

Page 16: 3G Dropped & Blocked Call Specifications

Problem Description: In figure above, an example of a drop classified as UE sensitivity fault is shown. The radio environment as reported by the UE is very poor when the UE attempts to initiate a call (i.e. Best server RSCP=-122dBm and Ec/No=-18dB). The scanner reports much better radio conditions for the same SC at the same instant i.e. RSCP =-89.06dBm and Ec/Io = -2.65dB. Although the blocked call is as a result of low RSCP as measured by the UE it should not be classified, as a poor RF block since the scanner indicates the radio conditions should be sufficient to set up a call.

3.5 Abnormal blocked calls

3.5.1 Unclassified - Unanswered RRC requests

Page 17: 3G Dropped & Blocked Call Specifications

Problem description: In this example an RRC request is sent but the network never responds with an RRC connection setup message. It is not clear whether or not the network receives the RRC request. The radio environment in the downlink as seen by TEMS is good i.e. good RSPC, low CPICH Ec/No.

3.5.2 Faulty Block Recording - Barred Network

Page 18: 3G Dropped & Blocked Call Specifications

Problem description: This occurs when the UE attempts to initiate a call on a network other than the measured one (in our case MTN). In the serving/Active Set window in TEMS in figure above it can be seen that the DL UARFCN for the network the UE is camped on in idle mode is 10564. The example shows the case that happened for the Vodafone network (DL UARFCN 10712). DeskCat considers this a blocked call but since the blocked call does do not occur on the Vodafone network, it has to be excluded from our analysis.

3.5.3 Call Initialisation during L.U. signalling

Page 19: 3G Dropped & Blocked Call Specifications

Problem description: In this case the UE is involved in Location Update signalling. As seen in the RRC Connection Request message the establishment cause is registration and the Location Update request message is for Normal Location Updating. During the L.U. signalling a new call attempt is triggered by the command sequence in TEMS Investigation. This can be seen in the events window in figure above.