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<div class="div">
<h1>Trunk Reservation</h1>

<p>The Trunk Reservation is a feature designed to allow the
shared use of the resources of the radio network for different types of subscribers
(GSM, MCN, and PRIORITY).</p>


<p>The coverage area of a cellular network system can be divided
into different service areas, each cell of the network belonging to at least
one of them. For instance, the network system can be composed of the GSM network
with the MCN as a subservice area.</p>


<p>The decision whether a subscriber is served in a cell is
based on the service areas that the cell represents, as well as on subscriber-specific
restrictions. The trunk reservation procedure is used for discriminating the
grade of the different services of a cell joined to several service areas.</p>


<p>On the basis of a cell shared by several services, different
kinds of traffic types (for example, type 1 = GSM, 2 = MCN, etc.) are defined
for a cell. A decision threshold is defined as a function of the number of
currently free radio resources, that is, idle traffic channels and service
types.</p>


<p>When the trunk reservation algorithm is applied, a random
variable R is tested against the applicable threshold to find out whether
a free traffic channel is available for the specific traffic type.</p>


<p>The random value R is uniformly distributed between 0 and
the maximum value M and regenerated for each request. Possible values (Xij)
of the threshold can be presented as a table:</p>


<a name="mar1841154311" shape="rect"></a>
<div>
<p>Table: Possible values (Xij) of the threshold</p>


<table border="1">
<thead>
<tr align="left" char="" charoff="50" valign="bottom">
<th colspan="1" rowspan="1" valign="top"><p>Idle TCHs</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Traffic type 1</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Traffic type 2</p>
</th>
<th align="center" colspan="1" rowspan="1" valign="top"><p>. .</p>


<p>.</p>
</th>
<th colspan="1" rowspan="1" valign="top"><p>Traffic type j</p>
</th>
</tr>
</thead>
<tbody>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="menupath-sem">1</span></p>
</td>
<td colspan="1" rowspan="1"><p>X11</p>
</td>
<td colspan="1" rowspan="1"><p>X12</p>
</td>
<td align="center" colspan="1" rowspan="1"><p>..</p>


<p>.</p>
</td>
<td colspan="1" rowspan="1"><p>X1j</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="menupath-sem">2</span></p>
</td>
<td colspan="1" rowspan="1"><p>X21</p>
</td>
<td colspan="1" rowspan="1"><p>X22</p>
</td>
<td align="center" colspan="1" rowspan="1"><p>..</p>


<p>.</p>
</td>
<td colspan="1" rowspan="1"><p>X2j</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="menupath-sem">3</span></p>
</td>
<td colspan="1" rowspan="1"><p>X31</p>
</td>
<td colspan="1" rowspan="1"><p>X32</p>
</td>
<td align="center" colspan="1" rowspan="1"><p>..</p>


<p>.</p>
</td>
<td colspan="1" rowspan="1"><p>X3j</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="menupath-sem">...</span></p>
</td>
<td colspan="1" rowspan="1"><p>...</p>
</td>
<td colspan="1" rowspan="1"><p>...</p>
</td>
<td align="center" colspan="1" rowspan="1"><p>..</p>


<p>.</p>
</td>
<td colspan="1" rowspan="1"><p>...</p>
</td>
</tr>
<tr align="left" char="" charoff="50" valign="top">
<td colspan="1" rowspan="1"><p><span class="menupath-sem">I</span></p>
</td>
<td colspan="1" rowspan="1"><p>Xi1</p>
</td>
<td colspan="1" rowspan="1"><p>Xi2</p>
</td>
<td align="center" colspan="1" rowspan="1"><p>..</p>


<p>.</p>
</td>
<td colspan="1" rowspan="1"><p>Xij</p>
</td>
</tr>
</tbody>
</table>
</div>


<p>Access is granted only if R &lt; Xij, with i and j corresponding
to the number of free channels and traffic type respectively.  Access can
therefore be rejected even though there are idle channels left. If more than
j channels are free, all access attempts are granted.</p>


<p>Two alternative reservation methods are available for PRIORITY
subscribers: static and dynamic reservation of channels. In static reservation,
once the priority channels have been allocated to priority subscriber type
users, the remaining spare channels will be available to any users. Thus,
in static reservation the parameter value L tells the number of simultaneous
priority calls, which the BTS has to be able to transmit. In dynamic reservation,
the parameter value L tells the number of the channel that has to be left
available to the priority subscriber type subscribers only, no matter how
many ongoing priority calls there are in the BTS. The selection between static
and dynamic reservation of channels is made on a per cell basis.</p>
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