<?xml version="1.0" encoding="utf-8" standalone="yes"?><html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Flow Control</title>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
<meta content="text/css" http-equiv="Content-Style-Type" />
<script src="NED?action=retrieve&amp;identifier=dn00188761&amp;edition=1&amp;language=none&amp;coverage=global&amp;encoding=javascript&amp;component=data&amp;item=data" type="text/javascript" xml:space="preserve">
</script>
<?conversion name="Pub2XHTML" version="2.0" source="urn:mars:dn0446179:1:en:global:publishing_online_1_0:data:data:*:*:*" date="2005-02-21T16:13:47Z"?>
<link href="NED?action=retrieve&amp;identifier=dn01158124&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=css&amp;component=data&amp;item=data" rel="stylesheet" title="Nokia Networks default online style" type="text/css" />
<meta content="draft" name="status" />
<?conversion name="SplitHTML" version="1.9" source="urn:mars:dn0446179:1:en:global:publishing_online_1_0:data:data:37:*:*" date="2005-02-21T16:13:47Z"?>
</head>
<body lang="en" xml:lang="en">
<p><a name="ned_top" shape="rect"></a>
<a name="ned_1" shape="rect"></a></p>

<a name="jan18510173826" shape="rect"></a>
<a name="p2xhtm-repid-1" shape="rect"></a>
<table width="100%">
<tr>
<td align="center" colspan="1" rowspan="1" width="20%"><?NED5 annotation?>
<br clear="none" /><?NED5 printview?>
</td>
<td align="center" colspan="1" rowspan="1" width="20%"></td>
<td align="center" colspan="1" rowspan="1" width="20%"></td>
<td align="center" colspan="1" rowspan="1" width="20%"></td>
<td align="center" colspan="1" rowspan="1" width="20%"><a href="NED?action=retrieve&amp;identifier=dn0446179_about&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top" onclick="openSmallPopup(event,'NED?action=retrieve&amp;identifier=dn0446179_about&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=xhtml_1_0&amp;component=data&amp;item=data&amp;pointer=ned_top#ned_top');return false" shape="rect" target="_blank"><img alt="Document information" border="0" class="Metainfo" src="NED?action=retrieve&amp;identifier=dn01158003&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /></a></td>
</tr>
</table>


<div class="div">
<h1>Flow Control</h1>

<a name="mar1141617102" shape="rect"></a>
<div class="topic">
<h2>Overload
at MSC</h2>

<p>This feature reduces the traffic in congested signalling
cases.</p>


<p>When the BSC receives an overload message from the MSC,
traffic is reduced by one step. This step reduction involves barring of one
mobile access class, which is performed by sending a new system information
message via the Abis Interface Program Block (ABIPRB) to the MSs. Timers T17
and T18 are started. Overload messages incoming from the MSC are ignored until
the T17 expires. The reception of an overload message after the expiry of
the T17, T18 still being set further, reduces the traffic by one step. The
timers T17 and T18 are both restarted. This reduction of traffic is continued
as long as there are incoming overload messages, and steps to reduce traffic.</p>


<p>The same step-by-step mechanism is also used to increase
traffic if no overload messages are received during T18.</p>
</div>


<a name="mar1141618113" shape="rect"></a>
<div class="topic">
<h2>MTP
Congestion</h2>

<p>The step-by-step method described above is used in a congested
signalling system.</p>
</div>


<a name="mar1141619134" shape="rect"></a>
<div class="topic">
<h2>Message
Overflow at BTS</h2>

<p>The BSC receives messages from the BTS on a regular basis.
The messages indicate the load situation in paging and random access channels.
Paging message overload is transferred to the MSC in order to reduce paging
in this particular cell. Because the BSC does not have the means to reduce
the paging traffic in any sophisticated way, the BTS handles the discarding
of the paging commands that it cannot send.</p>


<p>An access grant channel message overflow is indicated by
the reception of a delete indication message from the BTS. In this case, the
BSC will skip sending the next reject message to an MS but will send all immediate
assignment messages. This guarantees the maximum use of allocated radio resources.</p>
</div>


<a name="mar114162075" shape="rect"></a>
<div class="topic">
<h2>LAPD
Overload</h2>

<p>LAPD overload occurs only in the uplink direction because
radio measurement reports are transferred from the BTS (and MS) to the BSC.
The control of this overload is a matter of network configuration and the
BTS.</p>
</div>


<a name="mar1141620356" shape="rect"></a>
<div class="topic">
<h2>Internal
processor Overload Control</h2>

<p><em>Centralised Unit Overload</em></p>


<p>The main loading sources are the random accesses coming
from the MSs through random access channels. In addition, there are handover
requests. Both of these are handled by the Radio Resource Management. In order
to maintain service for established connections, random accesses are addressed
with a low priority to the Radio Resource Management; handover requests and
TCH requests are addressed with a higher priority to the Radio Resource Management.</p>


<p>In high load situations, therefore, fewer new call attempts
than usual are handled, and fewer new connections established. Handover requests,
however, receive faster service.</p>


<p><em>Distributed Unit Overload</em></p>


<p>Most of the messages received are radio measurement reports
coming from the BTS and the MS. These messages come from the LAPD link. Before
message distribution, the processor load state is checked. If the load exceeds
a certain predefined limit, the message is discarded. The message buffer and
processing capacity demand is thus decreased.</p>


<p>The loss of the radio measurement report does not affect
the service quality significantly; some reports are lost anyway owing to the
load on the LAPD link. The method of discarding messages is random as well
so the loss of messages for one particular connection stays within reasonable
limits.</p>
</div>
</div>
</body>
</html>