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<h1>Overview of Network-Assisted Cell Change (NACC)</h1>

<p>Network Assisted Cell Change (<a href="NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id019376#id019376" onclick="openSmallPopup(event,'NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id019376#id019376');return false" shape="rect" target="_blank">NACC</a>)
reduces service outage time for all <a href="NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id08604#id08604" onclick="openSmallPopup(event,'NED?action=retrieve&amp;identifier=general_glossary&amp;edition=13&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=id08604#id08604');return false" shape="rect" target="_blank">QoS</a> classes
when a GPRS MS in packet transfer mode moves between GSM cells. NACC improves
both autonomous and network-controlled cell change. </p>


<p>When a mobile station (MS) performs an autonomous cell change or is
commanded to perform a cell change, it has to stop data transmission in the
serving cell. The serving cell is the cell containing the serving BTS. After
this the MS has to acquire certain system information from the target cell.
The target cell is the neighbour cell that has been determined by the MS or
the network during the cell change. After this the MS has to restart the data
transmission in the new cell. This leads to a certain delay as the MS has
to synchronise with the system information broadcast cycle, and collect a
consistent set of system information (SI) and packet system information (PSI)
messages from the target cell. NACC reduces this service outage time for the
MSs in packet transfer mode. </p>


<p>Outage time is reduced because the network is allowed to assist MSs
before and during the cell change. The network sends neighbour cell system
information on the packet associated control channel (PACCH) to the MS in
packet transfer mode, while it is still camping on the serving cell, and introduces
the PACKET SI STATUS procedure for the cells that have no packet broadcast
control channel (PBCCH). </p>


<p>Neighbour cell system information messages sent to the MS contain a
set of SI or PSI messages needed in performing packet access in the new cell.
When all required messages are sent to the MS and PACKET SI STATUS is supported
by the PCU (no PBCCH allocated) in the new cell, the MS may perform packet
access and use PACKET SI STATUS procedures for the acquisition of SI messages. </p>


<p>NACC is an application SW product and requires a valid licence in the
BSC. For more information, see <a href="NED?action=retrieve&amp;identifier=dn04170615&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=oct2641456515#oct2641456515" onclick="sync(this);return true" shape="rect">Licensed
application software</a> and <a href="NED?action=retrieve&amp;identifier=dn04149427&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=oct1841615431#oct1841615431" onclick="sync(this);return true" shape="rect">Overview
of BSS licensing</a>. </p>


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<h2>Benefits of the Nokia solution</h2>

<p>Network-Assisted Cell Change (NACC) minimises the service outage in
cell re-selection by sending target cell system information data sets from
the serving cell to the MS, before cell re-selection is started.</p>


<p>For more information, see <em>Network Assisted Cell Change (NACC)</em>
in BSC/TCSM documentation.</p>
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<div class="related-topics">
<h2>Related Topics</h2>

<ul class="related-topics-list">
<li><a href="NED?action=retrieve&amp;identifier=dn04111744&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=jun234141651#jun234141651" onclick="sync(this);return true" shape="rect">System impact of
Network-Assisted Cell Change (NACC)</a></li>
<li><a href="NED?action=retrieve&amp;identifier=dn04111768&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=sep234177387#sep234177387" onclick="sync(this);return true" shape="rect">Overview
of implementing Network-Assisted Cell Change (NACC)</a></li>
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