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<h3>Inter-System handover penalties and timers</h3>

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<h4>Connection-specific
penalty timers after unsuccessful inter-system handover attempt from GSM to
WCDMA RAN</h4>

<p>The BSC controls connection-specific inter-system handover
requests and attempts in the serving GSM cell with the handover control parameters <span class="parameter-sem">Min Int Between HO Req</span>  and <span class="parameter-sem">Min
Int Between Unsucc HO Attempt</span>. </p>


<p>Also when the BSC initiates the inter-system handover attempt
to a WCDMA RAN cell but fails, the connection-specific penalty timer for the
target WCDMA RAN cell is applied. That is, the connection in question is not
allowed to initiate an inter-system handover attempt to a penalised WCDMA
RAN cell during a penalty. Duration of penalty can be set with the parameter <span class="parameter-sem">Min Interval Between Unsucc ISHO Attempt</span>.</p>
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<h4>Cell-based
penalty timer after unsuccessful handovers from GSM to WCDMA RAN</h4>

<p>Cell-based penalties are used in order to avoid unnecessary
handover attempts from GSM to WCDMA RAN on a serving GSM cell level. Unsuccessful
handover attempts from the serving GSM cell to WCDMA RAN cell indicate that
the WCDMA RAN cell in question is loaded. Thus, it is not sensible to initiate
handovers from serving GSM cell to the loaded WCDMA RAN cell.</p>


<p>When a certain ratio of unsuccessful inter-system handover
attempts in predefined time gap is exceeded in the serving GSM cell, the BSC
gives a cell-based penalty for the target WCDMA RAN cell. That is, none of
the connections in that GSM cell are allowed to initiate an inter-system handover
attempt towards the penalised WCDMA RAN cell. Inter-system handover attempts
from other GSM cells towards the penalised WCDMA RAN cell are allowed.</p>


<p>The ratio of unsuccessful inter-system handover attempts
is defined with the parameter <span class="parameter-sem">Triggering Ratio For WCDMA
RAN Cell Penalty</span>. The time gap from where the unsuccessful inter-system
handover attempts are calculated is defined with the parameter <span class="parameter-sem">Penalty
Trigger Measurement Period</span>. The penalty time is defined with the parameter <span class="parameter-sem">WCDMA RAN Cell Penalty Time</span>.</p>


<p>The maximum number of simultaneous cell-based penalties
is 16. Cell-based penalties can be disabled in the BSC by setting the parameter <span class="parameter-sem">Penalty Trigger Measurement Period</span> to 0.</p>
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<h4>Connection-specific
penalty timer after successful Inter-system handover from WCDMA RAN to GSM</h4>

<p>An inter-system handover from WCDMA RAN to GSM indicates
high load in the WCDMA RAN. When a handover from WCDMA RAN to GSM is detected,
the BSC is not allowed to initiate a handover back to WCDMA RAN for the same
connection during the 30-second penalty time.</p>
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<h4>Service-area-based
penalty timer after successful handovers from WCDMA RAN to GSM </h4>

<p>Service-area-based penalties are used to avoid unnecessary
handover attempts from GSM to WCDMA RAN on the BSC level. Handovers from WCDMA
RAN to GSM indicate that the WCDMA RAN service area where the handover is
coming from is loaded. Thus, it is not sensible to initiate handovers from
GSM to the loaded WCDMA RAN service area.</p>


<p>When a certain number of successful inter-system handovers
in predefined time gap is exceeded in the BSC, the BSC gives a service-area-based
penalty for the source WCDMA RAN service area. That is, none of the connections
in that BSC are allowed to initiate inter-system handover attempt towards
the penalised WCDMA RAN service area.</p>


<p>The number of successful inter-system handovers is defined
with the parameter <span class="parameter-sem">Triggering Threshold For Service
Area Penalty</span>. The time gap from where the number of successful inter-system
handovers are calculated, is defined with the parameter <span class="parameter-sem">Penalty
Trigger Measurement Period</span>. The penalty time is defined with the parameter <span class="parameter-sem">Service Area Penalty Time</span>.</p>


<p>The maximum number of simultaneous service area based penalties
is 16. Service area based penalties can be disabled in the BSC by setting
the parameter <span class="parameter-sem">Penalty Trigger Measurement Period</span>
to 0.</p>
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<h4>Supervision
of an inter-system handover attempt procedure</h4>

<p>GSM timer T3121 parameter defines the maximum supervision
time for an inter-system handover procedure from GSM to WCDMA RAN in the source
BSC. Sending an INTER SYSTEM TO UTRAN HANDOVER COMMAND message to mobile starts
this connection specific T3121 timer. It is normally stopped when the mobile
has correctly seized the WCDMA RAN channel(s). The purpose of the timer is
to keep the old channels for a sufficiently long time in order to enable the
mobile to return to the old channels, and to release the channels if the mobile
is lost. </p>
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