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<div class="div">
<h1>Overview of Gb over IP</h1>

<p>The Gb interface has a protocol stack consisting of three layers: the
physical layer, the Network Service (NS) layer, and Base Station System GPRS
Protocol. Gb over IP offers an alternative way to configure the subnetwork
of the Gb interface: the subnetwork is IP-based and the physical layer is
Ethernet.</p>


<p>Gb over IP is an application software product and requires a valid licence
in the BSC. The licencing is based on the number of PCUs to which IP Network
Service Entities can be configured. </p>


<p>Gb over IP requires support from both BSC and SGSN. For more details,
see <a href="NED?action=retrieve&amp;identifier=dn04111802&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="sync(this);return true" shape="rect">System impact of Gb over IP</a>.</p>


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<h2>Benefits of Gb over IP</h2>

<p>As a result of the convergence of mobile communications and the Internet,
the amount of data usage in mobile networks is rapidly growing compared to
traditional voice traffic. The increased demand for packet switched traffic
transmission cost efficiency can be met by deploying IP in the transmission
network. The introduction of IP enables operators to build an efficient transport
network for IP-based multimedia services and helps to reduce the transmission
costs.</p>


<p>The first BSC to SGSN transmission implementation uses Frame Relay (FR)
on Gb interface. When Gb over IP is taken into use, packet switched traffic
goes via the IP network instead of a circuit switched Pulse Code Modulation
(PCM) network. Gb over IP brings an alternative to traditional Frame Relay
based connectivity of Gb interface and thus enables operator to save in CAPEX
by using possible unused IP capacity in site instead of building up new FR
capacity. Both IPv4 and IPv6 are supported in the Nokia implementation of
Gb over IP.</p>
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<div class="topic">
<h2>Implementation of Gb over IP</h2>

<p>In the BSC, the Gb interface protocol software is implemented in the
PCU plug-in unit, located in each Base Station Controller Signalling Unit
(BCSU). The IP transport can be used in parallel with FR under the same BCSU.
One NSE and each PCU always uses either one, IP or FR. Inside one BCSU, separate
PCUs can use different transmission media. </p>


<p>The Gb interface uses communication paths called Network Service Virtual
Channels (NS-VC) to transmit the user data. In Gb over IP, a NS-VC is composed
of IP endpoint addresses (UDP/IP addresses), that is, of one IP endpoint address
in the BSS and another IP endpoint address in the 2G-SGSN. </p>


<p>In the BSC there is always one local IP endpoint per PCU. Similarly,
in a Nokia 2G-SGSN, there is only one local IP endpoint per NSE. There can
be four IP endpoint pairs per NSEI in the Nokia BSS or 2G-SGSN.</p>


<p>Gb over IP supports both dynamic and static configuration:</p>


<ul>
<li><p>In a dynamic configuration only one IP address and UDP port pair
of remote end SGSN, called a preconfigured SGSN IP endpoint, is needed to
establish NS-VC configuration on Gb. The preconfigured IP endpoint is used
to transfer the configuration parameters automatically over the Gb interface
during the initialisation phase.</p>
</li>
<li><p>In a static configuration the NS-VC parameters are configured
manually to both the BSS and the SGSN: they are not transferred over the Gb
interface.</p>
</li>
</ul>


<p>Static configuration can be used, if it is seen feasible to have a fixed
configuration between BSCs and SGSNs, for example, when operator uses a direct
cable connection between the BSC and SGSN.</p>
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<div class="topic">
<h2>Related topics</h2>

<ul>
<li><p>System impact of Gb over IP</p>
</li>
<li><p>Overview of implementing Gb over IP</p>
</li>
</ul>


<p>In BSC/TCSM Product Documentation Set, see</p>


<ul>
<li><p>GPRS Handling in BSC</p>
</li>
<li><p>98 Gb over IP Measurement</p>
</li>
</ul>


<p>In 2G SGSN Product Documentation Set, see</p>


<ul>
<li><p>Feature SG1048: Gb Over IP in Nokia 2G SGSN</p>
</li>
<li><p>IPv6</p>
</li>
<li><p>Nokia 2G SGSN - BSS Interface Description, Network Service Protocol
(NS)</p>
</li>
<li><p>Nokia 2G SGSN Gb Interface Handling</p>
</li>
</ul>
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