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<div class="div">
<h1>Overview of System Level Trace</h1>

<p>System Level Trace is an operating software, which extends
the current GSM tracing facility to the GPRS service. Currently tracing is
available in the network elements of the GSM network to trace circuit switched
calls.</p>


<p>The trace facility enables customer administration and
network management to trace activities of various entities (IMSIs and IMEIs),
which result in events occurring in the PLMN. Trace facility is a useful maintenance
aid and development tool, which can be used during the system testing. In
particular, it may be used in conjunction with test-MSs to ascertain the digital
cell 'footprint', the network integrity, and also the network quality of service
as perceived by the PLMN. The GSM specification specifies the Trace facility
for GSM where it refers to (the figure below):</p>


<ul>
<li><p>Subscriber tracing (tracing of IMSI)</p>
</li>
<li><p>Equipment tracing (tracing of IMEI).</p>
</li>
</ul>


<a name="apr15419351313" shape="rect"></a>
<div>
<img alt="urn:mars:dn0469311:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0469311&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Trace activation/deactivation and report generation</p>
</div>


<p>The subscriber tracing can be defined for a certain subscriber
in the HLR or in a specific SGSN. Equipment tracing can be defined in the
SGSN.</p>


<p>The trace is already implemented in the GSM network, but
introduction of GPRS-service adds new network elements to the GSM network
(GGSN, SGSN) and changes old principles: existing trace features will be updated.</p>


<p>The network management can use the facility for subscriber
trace, for example, in connection with a customer complaint or if an equipment
malfunction is suspected.</p>


<p>The figure below presents the architecture of the GPRS
network and related network elements. All network elements that can send trace
reports to NetAct are darker in this figure.</p>


<a name="apr1541936414" shape="rect"></a>
<div>
<img alt="urn:mars:dn0469347:1:en:global:tiff:data:data" border="0" src="NED?action=retrieve&amp;identifier=dn0469347&amp;edition=1&amp;language=en&amp;coverage=global&amp;encoding=gif&amp;component=data&amp;item=data" /><p class="figure-caption">Figure: Architecture of the GPRS network and related network elements</p>
</div>


<p>In the figure above, the overall picture of the GPRS trace
can be seen. The trace is activated by OSS. The HLR, SGSN, GGSN, and BSS send
trace records to OSS when an invoking event occurs.</p>


<p>In the SGSN trace three different scenarios can be identified
from an operators' viewpoint:</p>


<ul>
<li><p>HPLMN operator traces its own IMSI
within the HPLMN</p>
</li>
<li><p>HPLMN operator wants to trace foreign
roaming subscriber (IMSI) within its own HPLMN</p>
</li>
<li><p>HPLMN operator wants to trace equipment
(IMEI).</p>
</li>
</ul>


<p>When an operator wishes to trace a GPRS subscriber in its
own (home) network, the trace is first activated in the HLR. If a subscriber
is not roaming outside the HPLMN and he/she is a register in the HLR, the
HLR activates the trace in a specified SGSN. Otherwise, the HLR waits until
the subscriber becomes active in HPLMN before it activates a trace in the
SGSN.</p>


<p>When an operator wants to trace a foreign subscriber, the
trace is activated directly via MMI commands to all SGSNs in an operator's
network. The trace of a subscriber is in a state of active pending until an
invoking event occurs. The amount of active trace cases can be limited.</p>


<p>When an operator wants to trace equipment, the trace is
activated directly via MMI commands to all SGSNs in operator's network. The
trace of equipment is in a state of active pending until an invoking event
occurs. The amount of active trace cases can be limited.</p>


<p>The tracing of roaming IMSIs and the exchange of data is
subject to bilateral agreements, and the request to trace a particular IMSI
comes through administrative channels. The HPLMN operator can use the HLR
parameters to define whether the trace settings are sent to the VPLMN.</p>


<a name="mar941359152" shape="rect"></a>
<div class="topic">
<h2>NE's
involved </h2>

<p>The trace is a system level feature, and in order to get
a full advantage of trace, it must be implemented in all main network elements
of the GPRS network: the SGSN, GGSN, BSC, MSC/HLR, and OSS.</p>
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