UE Drop and Block Call Analysis Guidelines

1 (45) Prepared (also subject responsible if other) No.

Approved Checked Date Rev Reference

2006-08-01 PA1

UE Drop and Block Call analysis Guidelines

Abstract The following document is an aid for use by RF engineers in analysing UE dropped and blocked calls from drive data collected during the initial tuning phase of the Network.

Scope

The UE analysis in this document does not include UE dropped or blocked calls related to IRAT, IFHO, IFLS.



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Contents

1 Introduction .......................................................................................... 3

2 UE ANALYSIS (CS) ............................................................................... 4 2.1 Missing neighbour relationship ................................................. 4 2.2 Poor coverage .......................................................................... 5 2.3 Rapidly decreasing Ec/No ........................................................ 6 2.4 Site/System problem ................................................................ 7 2.5 ASU without MR ....................................................................... 8 2.6 Congestion ............................................................................... 9 2.7 Not classified .......................................................................... 10 2.8 UE stops Tx Power ................................................................. 11

3 Poor coverage - Short call ................................................................ 12 3.1 Bad Ec/No .............................................................................. 13 3.2 Site/System problem .............................................................. 14 3.3 UE Problem ............................................................................ 15 3.4 Call attempt to the worst cell................................................... 16 3.5 Only one RRC Connection Request. ...................................... 17 3.6 Best SC removed from the AS ................................................ 18 3.7 Not classified .......................................................................... 19 3.8 RRC Connection Request with no AICH ................................. 20 3.9 RRC Connection Release after Radio Bearer Reconfiguration

Complete. ............................................................................... 22 3.10 Out of synchronization RL ...................................................... 23 3.11 Other ...................................................................................... 24 3.12 Abnormal blocked calls ........................................................... 25

4 Packet Call Analysis .......................................................................... 28 4.1 Long call ................................................................................. 29 4.2 Radio Frequency .................................................................... 31 4.3 Poor coverage ........................................................................ 32 4.4 Ec/No dropping very fast ........................................................ 33 4.5 Not classified .......................................................................... 34 4.6 Downswitch to FACH due to low throughput ........................... 35 4.7 Throughput lost after ASU ...................................................... 36 4.8 Site / System Problem ............................................................ 37 4.9 Application Errors ................................................................... 38 4.10 RAS Error ............................................................................... 40 4.11 Short call ................................................................................ 41 4.12 User Authentication Failed ..................................................... 42 4.13 Radio Bearer setup then PDP rejected ................................... 43 4.14 PPP Link Control terminated .................................................. 44



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1 Introduction

The purpose of this document is aid the RF engineer in classifying UE blocked and dropped calls. It describes common block and drop causes and symptoms. The document is divided into the following main categories:

1. UE analysis CS ( Voice and Video)

2. UE analysis PACKET



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2 UE ANALYSIS (CS)

2.1 Missing neighbour relationship

Based on Long call UE

Classification: Radio Frequency

When the Ec/No of the serving cell becomes very bad and another SC becomes better than the best serving cell in terms of Ec/No and the UE detects it as a “DN” (Detected Neighbour), then this is a missing neighbour relationship.

DL BLER becomes worse and CPICH RSCP could be either good or bad. Sometimes the UE release the call because very bad Ec/No of the serving cell and sometimes the system release the call (to avoid UL interference) by sending RRC Connection release message with cause unspecified.

“DN” cell better than the serving cell

DL BLER gets worse

“DN” cell better than the serving cell

DL BLER gets worse



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Poor coverage

Classification: RF

The UE enters to a very bad coverage area, i.e. an area where RSCP > -105 dBm. Ec/No can be either good or bad, the UE ramps up its transmitting power to the maximum, DL BLER starts to increase and finally the call drops.

Very bad RSCP

UE max Tx power

andhigh DL BLER

Very bad RSCP

UE max Tx power

andhigh DL BLER



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2.2 Rapidly decreasing Ec/No

Classification: RF

It seems like the phone call is on going with no problems but suddenly the CPICH Ec/No drops very fast and the UE stops its Tx power. Sometimes the UE stops its Tx Power even before the Ec/No drops. Usually only UE2 drops because it has only one SC in the AS and UE1 has two, but when UE2 has one SC in the AS too, it also drops at the same time than UE1. In the Uplink Signal Strength and Power Control Report inside the Mode Reports window, the message Disable UL Power Control can be found, as shown in the figure below.

It could be the case that this kind of drop is a UE fault, for example, when the UE has the time to send the MR to add the SC which is becoming better to the AS, but the UE does not send it or takes longer than it should. Another case of UE fault in this kind of drops is when the UE that drops the call measures totally different values of RSCP and/or Ec/No than the UE that does not drop and the scanner.

Whenever is a UE fault, this drop should be classified as “Ec/No dropping very fast – UE”.

Ec/No drops very

fast and the UE

stops its Tx power

Only one SC in the AS

Ec/No drops very

fast and the UE

stops its Tx power

Only one SC in the AS



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2.3 Site/System problem

Unable to add/remove SC to/from the AS

The UE sends many Measurement Reports to add or remove a SC to or from the AS, but the system does not respond. Finally, the UTRAN finish the call by sending the RRC Connection release message with cause unspecified.

Many MR to add SC274Many MR to add SC274



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2.4 ASU without MR

The UE sends a MR to add an SC to the AS, but immediately after this SC is added, and even though the UE does not send any other MR, the system sends another Active Set Update to remove the SC that was just added to the AS.

This can happen several times until the system sends the RRC Connection Release with cause unspecified.

SHO to add SC

359 to the AS

ASU to remove

SC359 but no MR

was sent by the UE

SHO to add SC

359 to the AS

ASU to remove

SC359 but no MR

was sent by the UE



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2.5 Congestion

Drops that occur 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.

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”.



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2.6 Not classified

UE Tx Power down after RL removal

Immediately after only one SC remains in the AS, the UE drops its transmitting power very fast. It is important to note that the UE does not stop its Tx power.

UE Tx power goes

down when only one

SC remains in the ASRF Conditions are very good

UE Tx power goes

down when only one

SC remains in the ASRF Conditions are very good



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2.7 UE stops Tx Power

All the RF conditions are good or not so bad. Suddenly DL SIR drops sometimes up to –40 and the UE stops its Tx power. In the Uplink Signal Strength and Power Control Report inside the Mode Reports window, the value of Measured SIR can be found.

RF Conditions are OK

The UE stops its Tx

PowerRF Conditions are OK

The UE stops its Tx

Power



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3 Poor coverage - Short call

Classification RF

The UE sends out 6 RRC Connection request messages but it does not get any answer from the UTRAN. The RF Conditions are very bad and the UE ramps up its power to the maximum. The UTRAN does not answer because the UE cannot reach the BTS.

6 RRC Connection request

Very bad RF Conditions UE max Tx power


Very bad RF Conditions UE max Tx power



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3.1 Bad Ec/No

Classification RF

The UE makes a call attempt in a very bad Ec/No area, maybe the system answers the UE attempt but it cannot decode the answer because Ec/No is very bad. RSCP is good or at least no so bad, i.e. RSCP > -100 dBm, then this is not poor coverage.

Very bad Ec/No and good RSCPVery bad Ec/No and good RSCP



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3.2 Site/System problem

CM service reject

During the call setup, the UE receives the CM service reject message with cause network failure, just after that, the system sends the RRC Connection release message. This is not an RF problem, is a network problem.

CM Service reject with cause:

Network failure

CM Service reject with cause:

Network failure



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3.3 UE Problem

UE freeze

During the call setup the UE freeze, i.e. all the RF measurements are frozen. This is a UE problem.

All measurements are frozen

All measurements are frozen



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3.4 Call attempt to the worst cell

The UE attempts to make a call on a SC that is not the best server and later it does not have time make the HO because the Ec/No is very bad. This is a cell reselection problem because the UE should make the attempt to the best cell.

Attempt to SC122, but SC267 is the

best server

The UE has no time to HO to the best

server

Attempt to SC122, but SC267 is the

best server

The UE has no time to HO to the best

server



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3.5 Only one RRC Connection Request.

The UE sends only one RRC Connection Request and does not receive the RRC Connection setup from the UTRAN. Immediately after this, the UE starts to read SIB. RF conditions are good. It is a UE problem because the UE does not re-transmit the RRC Connection Request.

Good RF Conditions

Only one RRC Connection Request

and the UE reads SIBGood RF Conditions

Only one RRC Connection Request

and the UE reads SIB



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3.6 Best SC removed from the AS

The UE sends a MR to remove the best SC from the AS. After this SC is removed the other ones in the AS become very bad in terms of Ec/No and the UE has no time to add it back to the AS.

The UE sends a MR to remove SC204,which is the best server SC.

The UE sends a MR to remove SC204,which is the best server SC.



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3.7 Not classified

L1 Synchronization problem

The UE sends the RRC Connection request message and it receives the RRC Connection setup, after this the UE must send the RRC Connection setup complete message, but it does not, and then the UE ramps up its transmitting power to the maximum.

The UE ramps up its power to the maximum.

The UE ramps up its power to the maximum.



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3.8 RRC Connection Request with no AICH

The UE sends out 6 RRC Connection request but it does not receive the RRC Connection setup from the UTRAN. The RF conditions could be very good or at least not very bad. There is not cell reselection and the UE does not ramp up the Tx power to the maximum, so it is not UL poor coverage. However, the UE does not get the AICH. It can be seen in the Random access reports, in the mode reports window.


RF conditions not very bad


RF conditions not very bad



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Very good RF conditions


Very good RF conditions



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3.9 RRC Connection Release after Radio Bearer Reconfiguration Complete.

Immediately after the UE sends the Radio Bearer Reconfiguration Complete, it receives the RRC Connection Release from the System with cause unspecified. The RF conditions does not matter, they can be good or bad.

RF Conditions are good or not so badRF Conditions are good or not so bad



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3.10 Out of synchronization RL

In the AS there are two SC’s, RF conditions become very good for one of them and bad for the other, UE Tx power is low. It is assumed that the good radio link is out of synchronization because the DL BLER is increasing while the RF conditions become better for one SC. Finally the call drops because high DL BLER.

DL BLER increases while SC183 is gets better and

SC308 is gets worse

DL BLER increases while SC183 is gets better and

SC308 is gets worse



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3.11 Other

RACH error

When a sequence is used to trigger a phone call during the drive test, sometimes the UE generates an internal message called “RACH error” and the UE does not send the RRC Connection request message, i.e. there is no call attempt, and then this is not a call setup failure. Anyway, the message is recorded by TEMS investigation (older versions of TEMS) and TEMS RANT detects it as a call setup failure, it can be checked in the events window.

There is no call attemptThere is no call attempt



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3.12 Abnormal blocked calls

Unclassified - Unanswered RRC requests

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.



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3.12.1 Faulty Block Recording - Barred Network

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). TEMS RA 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.



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3.12.2 Call Initialisation during L.U. signalling

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.



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4 Packet Call Analysis

Definitions

Remote Access Service (RAS) – A feature built into Windows that enables users to log into a remote network by using a client program such as Dial-up Networking. It provides a set of features and instructions that allow clients to establish RAS sessions to access network services such as file and printer sharing, electronic mail, scheduling, etc.

It is important to note that RAS is a Microsoft defined term with no relation to the WCDMA system whatsoever. Thus RAS events must never be used to estimate figures for accessibility or retainability. The reason why they are used during this document is because Dial-up networking is used by TEMS Investigation to access the Packet Data Network and establish the FTP sessions used for testing.

RAS Session Start – An FTP session has been established.

RAS Session End – An FTP session has ended, i.e. the file download/upload has been successfully terminated.

RAS Session Error – An FTP session was interrupted because of an error.



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4.1 Long call

During the long call Packet Data Testing a GET FTP session is started and the RLC throughput behaviour is monitored. In case the throughput goes to zero for a certain time, previously defined in the TEMS Investigation Sequence, the Session Error event is triggered and the TEMS sequence will deactivate the PDP Context and start the whole procedure again. If that is the case the Session Error will present the cause “Connection timeout”.

Figure 1 below shows the point where throughput is lost and the session error timer starts.

Figure 1: Throughput lost, Session Error timer started.

DL App Throughput = 0DL App Throughput = 0



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Figure 2 shows the moment when the session timer runs out and the Session Error event is triggered. Note how the PDP Context is deactivated and the process starts again.

Figure 2: Session Error triggered.

Since the Session Errors are the triggered when there is a lack of throughput they are used to identify possible network problems. The approach should be to look for Session Errors and then go back a few seconds and analyse the possible reasons for the loss of throughput.

Session Error TriggeredSession Error Triggered



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4.2 Radio Frequency

Missing Neighbour Relationship

A missing neighbour relationship is identified when the Ec/No of the serving cell decreases and that of another Scrambling Code becomes better with the UE detecting it as a “detected neighbour” (DN).

DL BLER and CPICH RSCP can be either good or bad. If the radio conditions are too bad the call is released by the UE due to low Ec/No. Another possibility consists on the system releasing the call by sending an RRC Connection Release message with cause unspecified. Both App and RLC DL throughput go to zero, and if the Radio Access Bearer and the throughput are not resumed the Session Error event is triggered with cause “session timeout”.

Figure 3: Session Error. Cause: Missing Neighbour relationship.

DN better than serving cellDN better than serving cellDN better than serving cell



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4.3 Poor coverage

The UE enters a very low coverage area, i.e. an area with RSCP below –105dBm. Ec/No can present both low and high values. The packet connection is carried on a 64/64 DCH Channel as consequence of the low coverage conditions. The UE ramps its transmitting power to the maximum, goes to Idle Mode and the Application and RLC throughputs go to zero.

At this point the RAS application will start the Session Timeout timer, if the throughput is not resumed the Session Error event is triggered with cause “session timeout”.

Figure 4: Session Error. Cause: Poor coverage.

App throughput ~64kbps

Very low RSCP

App throughput ~64kbps

Very low RSCP



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4.4 Ec/No dropping very fast

The radio conditions are stable when the CPICH Ec/No starts to drop very fast. The UE stops its Tx power. The Uplink Signal Strength and Power Control report inside the Mode Reports window presents a Disable UL Power Control indication. Throughput is lost and the Session Error event with cause “session timeout” is eventually triggered.

Figure 5: Session Error. Cause: Ec/No dropping very fast

Ec/No drops very fast and the UE

stops Tx power

Ec/No drops very fast and the UE

stops Tx power



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4.5 Not classified

Throughput lost after Channel Reconfiguration

A Transport Channel Reconfiguration message is sent to the UE to downswtich/upswtich the connection. The UE replies with a Transport Channel Reconfiguration Complete message and the throughput is lost. The Session Error event is triggered with cause “session timeout”.

Figure 6: Session Error. Cause: Throughput lost after channel reconfiguration.

DL App throughput lostDL App throughput lostDL App throughput lost



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4.6 Downswitch to FACH due to low throughput

The throughput is stable and suddenly it goes down without the channel being released. The UE goes to cell FACH due to lack of transfer, the session timeout expires and the Session Error event is triggered with cause “session timeout”.

Figure 7: Session Error. Cause: Downswitch to FACH due to low throughput

DL App throughput lost

UE goes from Cell_DCH to

Cell_FACH

DL App throughput lostDL App throughput lost


Cell_FACH


Cell_FACH



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4.7 Throughput lost after ASU

The throughput is stable and a normal handover is performed. After the UE sends the Active Set Update Complete message the transfer goes down and not resumed. The session timer expires and the Session Error event is triggered with cause “session timeout”.

Figure 8: Session Error. Cause: Throughput lost after ASU.

DL App throughput lostDL App throughput lostDL App throughput lostDL App throughput lost



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4.8 Site / System Problem

ASU without Measurement Report

The UE sends a Measurement Report to add a SC to the Active Set. After the handover is finished the system sends an Active Set Update to delete the same SC without the UE sending the corresponding Measurement Report.

The above cycle can be repeated many times before the system sends the RRC Connection Release message with cause unspecified. Throughput is lost and the Session Error event is triggered after the session timeout expires.

Figure 9: ASU without MR

ASU to remove SC318

without previous MR

UE sends MR to add

SC318, it receives ASU

ASU to remove SC318

without previous MR

ASU to remove SC318

without previous MR

UE sends MR to add


UE sends MR to add




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4.9 Application Errors

No FTP Initial Response

The PDP Context is activated and the Session starts. The UE moves to Cell_FACH but the transfer does not start, thus the Session Error event is triggered with cause “session timeout” or “no response”.

Figure 10: Session Error. Cause: No initial FTP response.

A variation of this type of Session Error occurs when there are Location Area Update and Routing Area Update procedures after the Session Start command has been executed. On this case the transfer cannot be initiated due to the ongoing signalling procedures and the Session Error is triggered with cause “session timeout” or “no response”.

This case is expected to happen on the borders between RNCs and will be classified as “No FTP Initial Response”. Please just add comments regarding the Routing Area and Location Area Updates.

No DL App ThroughputNo DL App ThroughputNo DL App Throughput



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Figure 11: Session Error. Cause: No initial FTP response. Comments: RAU and LAU

No DL App ThroughputNo DL App Throughput

RAU Performed

No DL App ThroughputNo DL App Throughput

RAU Performed



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4.10 RAS Error

Throughput is stable with good radio conditions and low BLER. A RAS Error with cause “unknown” is suddenly triggered without any previous signalling releasing the channel. The UE then sends an Uplink Direct Transfer message followed by a Deactivate PDP Context Request.

Figure 12: Session Error. Cause: RAS Error.

Signaling and DL App Throughput normal

Sudden Session Error triggered

Signaling and DL App Throughput normalSignaling and DL App Throughput normal

Sudden Session Error triggeredSudden Session Error triggered



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4.11 Short call

Not classified

Radio Bearer Setup not sent

The RRC has been established and the UE sends the Activate PDP Context Request message to the system. The Radio Bearer Setup message in the DL is never sent and the network eventually sends and Activate PDP Context Reject message with cause “unspecified”.

Figure 13: PDP Context Activation Failure. Cause: Radio Bearer Setup not sent.

Act. PDP Cont. Req. Sent RRC Established

Radio Bearer

Setup Message

never sent

PDP Context Activation Failure

Act. PDP Cont. Req. SentAct. PDP Cont. Req. Sent RRC EstablishedRRC Established

Radio Bearer

Setup Message

never sent

Radio Bearer

Setup Message

never sent

PDP Context Activation FailurePDP Context Activation Failure



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4.12 User Authentication Failed

The RRC has been established and the UE sends the Activate PDP Context Request message to the system. The Radio Bearer setup and Radio Bearer Reconfiguration are performed. The Downlink Direct Transfer message is sent to the UE followed by an Activate PDP Context Reject message with cause “User authentication failed”.

Figure 14: PDP Context Activation Failure. Cause: User Authentication Failed

Radio Bearer Setup Complete

User authentication

failed

Radio Bearer Setup CompleteRadio Bearer Setup Complete

User authentication

failed

User authentication

failed



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4.13 Radio Bearer setup then PDP rejected

The RRC has been established and the UE sends the Activate PDP Context Request message to the system. The Radio Bearer setup and Radio Bearer Reconfiguration are performed. The Downlink Direct Transfer message is sent to the UE followed by an Activate PDP Context Reject message with cause “unspecified”.

Figure 15: PDP Context Activation Failure. Cause: Radio Bearer setup then PDP rejected

Radio Bearer Setup Complete

Activation rejected,

unspecified

Radio Bearer Setup CompleteRadio Bearer Setup Complete


unspecified


unspecified



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4.14 PPP Link Control terminated

The RRC has been established and the UE sends the Activate PDP Context Request message to the system. A Downlink Direct Transfer message is sent to the UE followed by the Activate PDP Context Reject one with cause “The PPP link control terminated”.

Figure 16: PDP Context Activation Failure. Cause: PPP Link Control terminated

Radio Bearer Setup Not Sent

Activate PDP Context Reject

after DL Direct Transfer

Radio Bearer Setup Not SentRadio Bearer Setup Not Sent







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UE Drop and Block Call Analysis Guidelines

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