Directed Retry

Nokia Siemens Networks GSM/EDGE BSS, rel. RG10(BSS), operating documentation, issue 04

Feature description

Directed Retry in BSC

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Issue 11-1Approval Date 26/02/2007 00:00:00

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Table of ContentsThis document has 18 pages.

Summary of changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1 Overview of Directed Retry in BSC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Directed Retry handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.1 BSC internal Directed Retry handover. . . . . . . . . . . . . . . . . . . . . . . . . . . 82.2 BSC external Directed Retry handover on the source cell side . . . . . . . 112.3 BSC external Directed Retry handover on the target cell side. . . . . . . . 12

3 Functionality of Directed Retry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4 User Interface of Directed Retry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

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List of FiguresFigure 1 Directed Retry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Figure 2 BSC internal Directed Retry handover (mobile-terminating call with Direct-

ed Retry; non-synchronized). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Figure 3 BSC external Directed Retry handover (mobile-terminating call on source

cell side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Figure 4 BSC external Directed Retry handover (mobile-terminating call on target

cell side) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

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Directed Retry in BSC Summary of changes

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Summary of changesChanges between document issues are cumulative. Therefore, the latest document issue contains all changes made to previous issues.

Changes made between issues 11-1 and 11The use of the timers MADR and T10 has been clarified in Functionality of Directed Retry.

Changes made between issues 11 and 10Material related to Directed Retry and target cell evaluation in the RF Power Control and Handover Algorithm document has been moved to this document.

In Overview of Directed Retry in BSC, a list of related topics has been added.

Changes made between issues 10 and 9The document has been revised throughout to comply with the latest documentation standards. No changes have been made due to changes in software.

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Overview of Directed Retry in BSC

1 Overview of Directed Retry in BSCDirected Retry for Nokia DX 200 Base Station Controller (BSC) is a procedure used when there is congestion in the network in the call set-up phase and the mobile station (MS) is assigned to a traffic channel in a cell other than the serving cell.

By using the Directed Retry procedure, it is possible to avoid the loss of a call if the serving cell is temporarily congested. The Directed Retry is triggered by an assignment procedure and can be used either in a mobile-originating call (MOC) or a mobile-termi-nating call (MTC) attempt.

The Directed Retry function is effective in mobile stations (MS), base station controllers (BSC), and DX MSCs (MSC). This is a description of the Directed Retry procedure in the BSC.

Directed Retry is an application software.

Related topics in Directed Retry

• Directed Retry handover • Functionality of Directed Retry • User interface of Directed Retry

Other related topics in BSC/TCSM documentation

• Test and Activate • Radio Network Performance

• BSS6115: Directed Retry in BSC • Activating and Testing BSS6115: Directed Retry in BSC

• Reference • Counters/Performance Indicators

• Call Control Measurements (CSW) • 4 Handover Measurement

• Parameters • BSS Radio Network Parameter Dictionary

• Descriptions • Functional Area Descriptions

• Radio Network Performance • Handover Signalling in BSC • RF Power Control and Handover Algorithm • Radio Channel Allocation

• Feature Descriptions • Value Added Services

• Radio Resource Pre-emption and Queuing in BSC

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Directed Retry in BSC Directed Retry handover

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2 Directed Retry handover Directed Retry is an application software designed to allow the mobile station to make a second attempt at gaining access if the first one fails because of the TCH congestion.

When the Directed Retry is enabled, the BSC may perform an inter-cell handover from an SDCCH of the serving cell to a TCH of an adjacent cell if there are no TCHs available in the serving cell. The parameter directed retry used (DR) indicates whether a handover caused by the directed retry is enabled. The handover is enabled when the value is 'yes'.

The following figure shows the process leading to the handover.

Figure 1 Directed Retry

Directed Retry (DR) handovers are functionally divided into three types:

• BSC internal, inter-cell Directed Retry handover • BSC external Directed Retry handover (source cell side) • BSC external Directed Retry handover (target cell side)

The examples in BSC internal Directed Retry handover, BSC external Directed Retry handover on the source cell side, and BSC external Directed Retry handover on the target cell side are from a mobile-originating call. It is assumed that the procedure for a mobile-terminating call is similar.

Interval between handovers and handover attempts

IF

DirectedRetryUsed = Yes

Handover from SDCCH of the serving cell to

TCH of an adjacent cell due to congestion.

MinTimeLimitDR - target cell evaluation started.

MaxTimeLimitDR - target cell evaluation stopped.

Target cell evaluation

IF

DirectedRetryMethod = 1

THEN

AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa) (1)

AND

AV_RXLEV_NCELL(n) > DRThreshold(n) (4)

ELSE

AV_RXLEV_NCELL(n) > RxLevMinCell(n) + MAX(0, Pa) (1)

where

P = maximum power of MS

Pa = (MsTxPwrMaxGSM(ADJ)(n) - P) if adjacent cell is GSM 900 or GSM 850

Pa = (MsTxPwrMaxGSM1x00(ADJ)(n) - P) if adjacent cell is GSM 1800 or GSM 1900

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Directed Retry handover

2.1 BSC internal Directed Retry handoverThe normal call set-up procedures are followed until the BSC receives an ASSIGNMENT REQUEST message from the MSC. The BSC tries to allocate a traffic channel (TCH) of a requested type for a BTS (for more information, see Radio Channel Allocation). When traffic channels are congested, the Directed Retry procedure is initiated.

At this point it is also possible to put the call attempt in a queue in the BTS, provided that the following queueing conditions are met:

• MSC allows queueing for this transaction • queueing procedure is active in the BTS (defined by a BSC user parameter) • call attempt queueing is active in the BTS (defined by a BSC user parameter) • queueing is possible and the item can be placed successfully in the BTS queue

For more information on queueing, see Radio Resource Pre-emption and Queuing in BSC.

When the call is to be put in a queue, the BSC sends the QUEUEING INDICATION message to the MSC to inform the MSC about the delay in the allocation of radio resources. The message will only be sent when the real queueing procedure is initiated at this phase of the call set-up procedure.

Call attempt queueing in the initial BTS during the creation of the candidate cell list improves the possibility of obtaining the needed TCH quickly so that the call set-up can be continued.

After the Directed Retry procedure has started, there is a period during which the DR handover is not allowed. This period is allowed for the mobile station (MS) to decode the base station identity code (BSIC) of the adjacent cells before the target cell evaluation. If the radio resource queueing and the Directed Retry procedure are active simultane-ously in the serving cell, this period also increases the possibility of allocating a TCH from the serving cell before the execution of the DR handover. The BSC can start the target cell evaluation for the DR handover after the time supervision has expired. The time supervision is controlled on a cell-by-cell basis with the parameter min time limit directed retry (MIDR).

The BSC starts processing the measurement reports it has received from a MS. The measurement reports contain the signal strength values of the adjacent cells when the MS is in a standalone dedicated control channel (SDCCH). The procedure makes a real-time target cell list which is required in the Directed Retry.

The min time limit directed retry (MIDR) parameter determines the period starting from the assignment request (this message is sent from the MSC to the BSC in order to request the BSC to allocate a radio resource) during which the target cell eval-uation for the directed retry procedure is not allowed. The BSC starts the target cell eval-uation procedure after this time supervision has expired. The range of the MIDR parameter is from 0 to 14 seconds. The period is allowed for the mobile station to decode the BSIC of the adjacent cells before the HO decision. The period also increases the possibility of allocating a TCH from the serving cell before the execution of handover to an adjacent cell.

The BSC is able to evaluate the target cells by two alternative methods. The method is selected with the parameter directed retry method.The alternative values are the following:

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0 The measurement results of the adjacent cell must satisfy the basic equation (1) before the directed retry procedure is possible. For more information, see Target cell evaluation according to radio criteria.

1 The measurement results of the adjacent cell must satisfy both the basic equation (1) and the following equation (4) before the directed retry is possible.

EQUATION 4.AV_RXLEV_NCELL(n) > DRThreshold(n)

The parameter Directed Retry threshold (DRT) (set for each of the 32 adjacent cells) is the level which the signal level AV_RXLEV_NCELL(n) of the adjacent cell (n) must exceed before the directed retry to the adjacent cell (n) is possible. The range is from -110 dBm to -47 dBm.

The creation procedure of a handover candidate cell list is controlled with a timer. The BSC continues the target cell evaluation for the DR handover until it finds a target cell for the DR handover or the maximum time allowed for start of the DR handover expires. The time supervision is controlled on a cell-by-cell basis with the parameter max time limit directed retry (MADR).

The BSC may monitor the signal level of the adjacent cells, and perform the handover from a dedicated control channel until the maximum period allowed for the directed retry procedure expires. The parameter max time limit directed retry (MADR) determines the maximum time period starting from the assignment request during which the target cell evaluation for the directed retry procedure is allowed. The range of the parameter from 1 to 15 seconds. If the call cannot be handed over from the dedicated control channel during the prescribed period, the BSC discontinues the call setup pro-cedure: the possibly ongoing queueing is terminated and the call attempt is cleared. Note that once the queuing has been started, it is no longer dependent on the value of the parameter max time limit directed retry (MADR). The queuing continues until the time set for the parameter time limit call (TLC) is exceeded, after which the call attempt is cleared. If queuing has not been started, the call attempt is cleared after the MADR value is exceeded.

Note also that if queueing has been started, the timer T10 is extended by the value of either the parameter MADR or TLC, depending on which parameter has the larger value. That is, when queueing is ongoing, T10 equals the value of the old T10 timer plus the value of MADR or TLC.

g The target cells for the directed retry procedure are ranked only according to radio link properties. Priority levels are not used.

g Radio resource queueing increases the possibility of allocating a TCH from the serving cell before the maximum period allowed for the directed retry procedure expires (for more information, see Radio Resource Pre-emption and Queueing). If a TCH of the serving cell can be assigned for the call, the BSC discontinues the Directed Retry Procedure.

When the BSC has successfully identified the new target cell, the possibly ongoing queueing is terminated in the BTS. When a traffic channel has been successfully allo-cated in the new target cell, the BSC sends a HANDOVER COMMAND message to the MS identifying both the target cell and the channel type. For more information, see Handover Signalling in BSC.

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When the BSC receives a HANDOVER COMPLETE message from the MS, it sends an ASSIGNMENT COMPLETE message to the MSC. This message informs the MSC of a successful Directed Retry procedure during the call set-up. It also informs the MSC of a new cell identity.

When Directed Retry is used in a mobile-terminating call, the MS sends the message ALERT to the BTS after the message HANDOVER COMPLETE. To be able to send the ALERT message autonomously, the MS has to be aware that the Directed Retry proce-dure is performed.

After a successful Directed Retry procedure, the SDCCH in the initial cell is released.

The main signalling during the BSC internal Directed Retry handover is presented in the figure BSC internal Directed Retry handover (mobile-terminating call with Directed Retry; non-synchronized).

Figure 2 BSC internal Directed Retry handover (mobile-terminating call with Directed Retry; non-synchronized)

MS BTS1 BTS2 BSC MSC

Normal call set-up procedures in BTS1

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assignment_request

physical_context_request

physical_context_confirm

(queueing_indication)

handover_command

handover_command

handover_access handover_detection

physical_info

sabm establish_indication

ua

handover_complete

rr

handover_complete

assignment_complete

rf_channel_release

rf_channel_release_ack

alert alert

connect connect

connect_ack connect_ack

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2.2 BSC external Directed Retry handover on the source cell sideAs with internal handover (see BSC internal Directed Retry handover), normal call set-up procedures are followed until the BSC receives an ASSIGNMENT REQUEST message from the MSC. The BSC then tries to allocate a TCH of the requested type for the BTS. In the case of a TCH congestion, the Directed Retry is initiated.

If the BSC starts queueing in the actual BTS, it sends the QUEUEING INDICATION message to the MSC in the same way as in the BSC internal Directed Retry. Similarly, measurement processing is carried out in order to make a handover candidate cell list for Directed Retry purposes.

When the BSC has successfully identified a new target cell, the possibly ongoing queueing is terminated in the initial BTS. If the chosen new target cell belongs to an adjacent BSC, the current BSC sends a HANDOVER REQUIRED message to the MSC with the cause 'Directed Retry'. The message with the specific cause informs the MSC of the Directed Retry procedure and allows the MSC to specify the required traffic channel in the subsequent handover signalling.

It would also be possible to send an ASSIGNMENT FAILURE message before the message HANDOVER REQUIRED with the cause 'Directed Retry'. However, in Nokia DX200 BSC Directed Retry function, the additional ASSIGNMENT FAILURE message is not implemented.

Handover signalling continues normally as described in Handover Signalling in BSC. After the successful Directed Retry handover signalling, the MSC sends a CLEAR COMMAND message to the initial BSC. The SDCCH of the initial cell is released.

The main signalling in the BSC external Directed Retry handover in the source BSC is illustrated in the figure BSC external Directed Retry handover (mobile-terminating call on source cell side).

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Figure 3 BSC external Directed Retry handover (mobile-terminating call on source cell side)

2.3 BSC external Directed Retry handover on the target cell sideThe MSC sends a HANDOVER REQUEST message with the cause 'Directed Retry' to the target side BSC in the external Directed Retry handover. The cause value does not change the normal handover signalling procedures in the target BSC, rather it is used for statistical purposes.

When the BSC receives a HANDOVER COMPLETE message from the MS, it forwards the message to the MSC which interprets the message as ASSIGNMENT COMPLETE. This is how the BSC informs the MSC of a successful Directed Retry during the call set-up procedure.

In a mobile-terminating call with Directed Retry, the MS has to be aware of the started Directed Retry after the handover in order to be able to send the message ALERT auton-omously after the message HANDOVER COMPLETE to the BTS.

Main signalling in the BSC external Directed Retry handover in the target BSC is pre-sented in the figure BSC external Directed Retry handover (mobile-terminating call on target cell side).

MS BTS1 BSC MSC

Normal call set-up procedures in BTS1

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assignment_request

physical_context_request

physical_context_confirm

(queueing_indication)

handover_required(DR)

handover_command

handover_command

handover_command

clear_command

rf_channel_release

rf_channel_release_ack

clear_complete

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Figure 4 BSC external Directed Retry handover (mobile-terminating call on target cell side)

For an overview, see Overview of Directed Retry in BSC.

MS BTS2 BSC MSC

Call set-up procedures in source BSC

1

2

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handover_request(DR)

channel_activation

channel_activation_ack

handover_request_ack

handover_access

handover_detection

handover_detection

physical_info

sabm establish_indication

ua

handover_complete

rr

handover_completed

handover_completed

alert alert

connect connect

connect_ack connect_ack

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Functionality of Directed Retry

3 Functionality of Directed RetryGeneral concepts in Directed RetryNormal handover during assignment

A stand-alone dedicated control channel (SDCCH) handover cannot be started during the assignment (Directed Retry) procedure. If the Directed Retry has been started, the normal handover procedure cannot be started.

Creation procedure for the candidate cell list in Directed Retry

After the Directed Retry has been started, there is a period during which the DR handover is not allowed. The time supervision is controlled on a cell-by-cell basis with the parameter min time limit directed retry (MIDR).The time value param-eter can be changed with MML commands and it is controlled by the BSC.

The candidate cells in Directed Retry are examined in the same way as during the forced handover procedure. For more information on the user command to empty the defined cell, see RF Power Control and Handover Algorithm.

In this procedure, the criteria for selecting the possible candidate cells are not as strict as in the normal handover algorithm analysis. The following items are taken into account when creating the candidate list for Directed Retry handover:

• The RX signal level compared to the threshold value defined by the parameter RX lev min cell (SL)

• the MS classmark • the maximum power level in the cell

If the Directed Retry threshold method is in use, the minimum threshold value of the RX signal level is also taken into account when creating the candidate cell list. The minimum threshold value of the RX signal level is defined with the Directed Retry threshold (DRT) parameter. If the value of the Directed Retry threshold parameter has been set below the adjacent cell parameter RX lev min cell (SL), the measured signal strength is compared with the RX lev min cell instead.

If there are no neighbouring cells with satisfactory radio quality, the creation of a candi-date list is not possible and therefore it is not possible to continue the started Directed Retry.

Note that in order to implement a successful Directed Retry function, the user has to define the handover control and adjacent cell parameters for the cell.

The handover control parameter enable SDCCH handover (ESD) does not affect the Directed Retry procedure: the handover from an SDCCH to a TCH with Directed Retry can be performed even if the normal SDCCH handover (from SDCCH to SDCCH) is forbidden.

Note also that MS and BS power can be controlled during the creation of the candidate list if required.

Unsuccessful creation of a target cell list during DR

A time limit is given for the BSC handover algorithm that processes the measurement reports to make a real-time target cell list for Directed Retry. The user can change the time value parameter max time limit directed retry (MADR) with MML com-mands. The parameter is controlled by the BSC.

If no suitable candidate can be located within the time limit, the possibly ongoing queueing is continued until timer T10 expires.

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Directed Retry in BSC Functionality of Directed Retry

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g The value of the timer max time limit directed retry (MADR) should be smaller than the value of the timer T10. If the MADR value is more than the T10 value, the call is released after the T10 timer has stopped and the MADR is still ticking

Successful queueing during Directed Retry

If queueing is in progress while the BSC is processing measurement reports to make a real-time target cell list for Directed Retry, a suitable busy traffic channel may be released in the BTS. In this case, during the Directed Retry procedure, the creation of the candidate cell list is terminated and the call attempt is successfully handled in the initial BTS.

Queueing time-out during DR procedure

If queueing is in progress while the BSC is processing measurement reports to make a real-time target cell list for Directed Retry, a queueing time-out may occur. In this case, during the Directed Retry procedure, the BSC does not start clearing call attempts immediately, but only after the time allowed for creating a candidate cell list has passed.

Special cases in BSC internal Directed Retry handoverRadio resource allocation in Directed Retry handover

As in the normal BSC internal handover, it is possible to send a maximum of 16 chosen BTSs as target BTSs to be used in the channel allocation algorithm also in a Directed Retry. These BTSs are sent in a single allocation request message to the BSC. This increases the possibility of finding a new cell with available radio resources. For more information, see Radio Channel Allocation.

Queueing possibility of Directed Retry handover in the new cell

No queueing is allowed in the new target BTS after the Directed Retry procedure has been started. The BSC starts a clearing procedure if no TCH can be allocated in the target cell during the BSC internal Directed Retry handover.

Unsuccessful entering of an MS to a new traffic channel

An MS may fail to enter the new traffic channel in the new target cell when the BSC internal Directed Retry procedure is in progress. In this case the MS returns to the old radio resource, that is, to the SDCCH in the initial BTS, and the BSC starts to clear the Directed Retry attempt.

Other examples of unsuccessful Directed Retry

An MS can clear a call during the BSC internal Directed Retry handover attempt. In this case all allocated resources are released and the attempt is cleared.

If the message CONNECTION FAILURE INDICATION arrives from the new channel after the message HANDOVER COMMAND has been received, the BSC starts clearing the Directed Retry attempt.

If the timer T8 expires, the Directed Retry attempt is cleared. This takes place if HANDOVER COMPLETED message has not been received from the MS after the HANDOVER COMMAND message during supervision.

Special cases of BSC external Directed Retry handoverHandover type reselection due to Directed Retry

If all the BSSs in the network do not support Directed Retry, the parameter disable external DR (DEXDR) must be set in the BSC.

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Functionality of Directed Retry

If the parameter disable external DR is set in the serving BSC and the first candi-date cell belongs to another BSC, the BSC searches through the candidate cell list for cells belonging to the serving BSC. This search creates a new candidate cell list, which is then used for attempting a BSC-internal Directed Retry.

For more information on Handover type reselection, see Handover Signalling in BSC.

Radio resource allocation and queueing in DR handover

Radio resource allocation in the BSC is performed in the same way as in the normal BSC external handover. For more information, see Radio Channel Allocation and Handover Signalling in BSC.

If no traffic channel can be allocated in the target cell during the BSC external Directed Retry handover, the MSC starts a clearing procedure.

During the BSC external Directed Retry procedure, queueing is not allowed in the BTS of the target BSC. It is not allowed even if the MSC would allow queueing in the HANDOVER REQUEST message. The queueing information received in the HANDOVER REQUEST message is stored, and after the call set-up phase, the information is used in the subsequent channel allocations for handovers during this call.

Unsuccessful entering of an MS to a new TCH

It is possible that an MS fails to enter the new TCH in a new target cell while the BSC external Directed Retry procedure is in progress. In this case the MS returns to the old radio resource, that is, to the SDCCH in the initial BTS. In this situation the MSC starts to clear the Directed Retry attempt.

Other instances of unsuccessful Directed Retry

An MS can clear a call during a BSC external Directed Retry handover attempt. In this case, all allocated resources are released and the attempt is cleared.

The timer T7 supervises the responses to the HANDOVER REQUIRED message from the MSC. If this timer expires, the message is not repeated during the Directed Retry pro-cedure. The BSC starts a clearing procedure.

If the message CONNECTION FAILURE INDICATION arrives from the old channel before the message HANDOVER COMMAND, or if it arrives from the new BTS, the BSC starts to clear the Directed Retry attempt.

If the timer T8 expires, the Directed Retry attempt is cleared. This takes place if the message HANDOVER COMMAND has been sent, but neither HANDOVER FAILURE message from the MS nor CLEAR COMMAND message from the MSC is received during supervision.

Message definitions in DR complying with 3GPP TS 48.008Cause values, elements

• HANDOVER REQUEST: cause, Directed Retry • HANDOVER REQUIRED: cause, Directed Retry • ASSIGNMENT FAILURE: in an unsuccessful internal Directed Retry attempt in the

BSC the cause 'no radio resource available' is used. • ASSIGNMENT COMPLETE: new cell identity is included if the BSC internal Directed

Retry has been performed successfully.

Functional message changes

• In a successful BSC internal Directed Retry the message ASSIGNMENT COMPLETE is used and the HANDOVER PERFORMED message is neither required nor used.

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Directed Retry in BSC Functionality of Directed Retry

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• In BSC external Directed Retry on the source side, only the message HANDOVER REQUIRED is used (the message ASSIGNMENT FAILURE is not used).

• The QUEUEING INDICATION message is used in the Directed Retry procedure only if queueing is allowed and if it is started in the initial BTS while the candidate cell list is created.

For more information, see 3GPP TS 48.008: Mobile Switching Centre - Base Station system (MSC-BSS) interface; Layer 3 specification.


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User Interface of Directed Retry

4 User Interface of Directed Retry ParametersThe use of the Directed Retry procedure in the BSC is controlled and can be changed with parameter definitions in a system parameter file. The man-machine language (MML) commands that use the man-machine interface (MMI) of the BSC start and stop the Directed Retry procedure on a cell-by-cell basis.

When the Directed Retry procedure is initiated, the following two timers control the creation procedure for a handover candidate cell list.

• It is possible to determine the period, starting from the assignment request, during which the Directed Retry is not allowed. The BSC can start the target cell evaluation for the DR handover after the time supervision has expired. This period is allowed for the mobile station to decode the base station identity code (BSIC) of the adjacent cells before the target cell evaluation. The time supervision is controlled on a cell-by-cell basis with the parameter min time limit directed retry (MIDR).

• The BSC can continue the target cell evaluation for the DR handover until the maximum time allowed for the start of the DR handover expires. The time supervi-sion is controlled on a cell-by-cell basis with the parameter max time limit directed retry (MADR).

When the Directed Retry procedure is initiated, the Directed Retry threshold method can be implemented. The following two parameters control the Directed Retry threshold method.

• The Directed Retry threshold method makes it possible to use the RX signal level of the adjacent cell in creating candidate cell lists. The Directed Retry threshold method is controlled on a cell-by-cell basis with the parameter directed retry method (DRM).

• Determining the Directed Retry threshold method is based on the predefined minimum threshold value of the RX signal level. The Directed Retry threshold is con-trolled on a cell-by-cell basis with the parameter Directed Retry threshold (DRT).

The BSC internal Directed Retry handover procedure is always possible if allowed in the BSC and in the initial Base Transceiver Station (BTS) parameterisation. With the help of the MMI, the user can either switch ON the BSC external Directed Retry handover or switch it OFF. This is done separately in every BSC. The reason for this implementation is that the BSC external Directed Retry handover requires special functionality in the MSC as well. If the MSC does not support Directed Retry, the external Directed Retry handover must be denied.

The external Directed Retry attempt is controlled on a BSC basis with the parameter disable external DR (DEXDR)

CountersStatistical counters and observation reports have been modified because of the 'stand-alone dedicated control channel (SDCCH) phase handover' function. For more informa-tion, see 4 Handover Measurement.


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Directed Retry

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