mansoor2
2008-10-05, 08:31 AM
The GPRS system is used by <a href="http://en.wikipedia.org/wiki/GSM" title="GSM">GSM</a> Mobile phones, the most common mobile phone system in the world (as of 2004), for transmitting <a href="http://en.wikipedia.org/wiki/Internet_protocol" title="Internet protocol" class="mw-redirect">IP</a> packets. The GPRS Core Network is the centralised part of the GPRS system and also provides support for <a href="http://en.wikipedia.org/wiki/WCDMA" title="WCDMA" class="mw-redirect">WCDMA</a> based <a href="http://en.wikipedia.org/wiki/3G" title="3G">3G</a> networks. The GPRS core network is an integrated part of the <a href="http://en.wikipedia.org/wiki/GSM_core_network" title="GSM core network" class="mw-redirect">GSM core network</a>.</font><h2 style="text-decoration: underline;">GPRS Core Network in General</span></h2>The GPRS Core Network (GPRS stands for General Packet Radio Services) provides <a href="http://en.wikipedia.org/wiki/Mobility_management" title="Mobility management">mobility management</a>, <a href="http://en.wikipedia.org/wiki/Session_management" title="Session management">session management</a>
and transport for Internet Protocol packet services in GSM and WCDMA
networks. The core network also provides support for other additional
functions such as <a href="http://en.wikipedia.org/wiki/Billing" title="Billing">billing</a> and <a href="http://en.wikipedia.org/wiki/Lawful_interception" title="Lawful interception">lawful interception</a>. It was also proposed, at one stage, to support packet radio services in the US <a href="http://en.wikipedia.org/wiki/Digital_AMPS" title="Digital AMPS">D-AMPS TDMA</a> system, however, in practice, most of these networks are being converted to GSM so this option is becoming largely irrelevant.</font>
Like GSM in general, GPRS is an open standards driven system and the standardization body is the <a href="http://en.wikipedia.org/wiki/3GPP" title="3GPP">3GPP</a>.</font><a href="http://upload.wikimedia.org/wikipedia/en/a/a1/GPRS_core_structure.png"><img style="width: 305px; height: 211px;" alt="Image:GPRS core structure.png" src="http://upload.wikimedia.org/wikipedia/en/a/a1/GPRS_core_structure.png" border="0"></a><h2 style="text-decoration: underline;">GPRS Tunnelling Protocol (GTP)</span></h2><br><i>GPRS Tunnelling Protocol</i> is the defining <a href="http://en.wikipedia.org/wiki/Internet_Protocol" title="Internet Protocol">IP</a> <a href="http://en.wikipedia.org/wiki/Communications_protocol" title="Communications protocol">protocol</a>
of the GPRS core network. Primarily it is the protocol which allows end
users of a GSM or WCDMA network to move from place to place while
continuing to connect to the internet as if from one location at the <i>Gateway GPRS Support Node</i> (GGSN). It does this by carrying the subscriber's data from the subscriber's current <i>Serving GPRS Support Node</i> (SGSN) to the GGSN which is handling the subscriber's session. Three forms of GTP are used by the GPRS core network.</font>
<ul><li>GTP-U: for transfer of user data in separated tunnels for each <a href="http://en.wikipedia.org/wiki/PDP_context" title="PDP context" class="mw-redirect">PDP context</a></font></li><li>GTP-C: for control reasons including:
</font><ul><li>setup and deletion of <a href="http://en.wikipedia.org/wiki/PDP_context" title="PDP context" class="mw-redirect">PDP contexts</a></font></li><li>verification of GSN reachability</font></li><li>updates, e.g. as subscribers move from one SGSN to another.</font></li></ul>
</li><li><a href="http://en.wikipedia.org/wiki/GTP%27" title="GTP'">GTP'</a> : for transfer of charging data from GSNs to the charging function.</font></li></ul>
GGSNs and SGSNs (collectively known as GSNs) listen for GTP-C messages on <a href="http://en.wikipedia.org/wiki/User_Datagram_Protocol" title="User Datagram Protocol">UDP</a>
port 2123 and for GTP-U messages on port 2152. This communication
happens within a single network or may, in the case of international
roaming, happen internationally, probably across a <a href="http://en.wikipedia.org/w/index.php?title=GPRS_Roaming_Exchange&action=edit&redlink=1" class="new" title="GPRS Roaming Exchange (page does not exist)">GPRS Roaming Exchange</a> (GRX).</font>
The <i>"Charging Gateway Function" (CGF)</i> listens to <a href="http://en.wikipedia.org/wiki/GTP%27" title="GTP'">GTP'</a>
messages sent from the GSNs on TCP or UDP port 3386. The core network
sends charging information to the CGF, typically including PDP context
activation times and the quantity of data which the end user has
transferred. However, this communication which occurs within one
network is less standardised and may, depending on the vendor and
configuration options, use proprietary encoding or even an entirely
proprietary system.</font><br style="text-decoration: underline;"><h2 style="text-decoration: underline;">GPRS Support Nodes (GSN)</span></h2>A GSN is a network node which supports the use of GPRS in the GSM core network. All GSNs should have a <i>Gn</i><a href="http://en.wikipedia.org/wiki/GPRS_Tunnelling_Protocol" title="GPRS Tunnelling Protocol">GPRS Tunnelling Protocol</a>. There are two key variants of the GSN; the GGSN and the SGSN defined below.</font> <br><h3>GGSN - Gateway GPRS Support Node</span></h3>
A gateway GPRS support node (GGSN) acts as an interface between the
GPRS backbone network and the external packet data networks (radio
network and the IP network). It converts the GPRS packets coming from
the SGSN into the appropriate packet data protocol (PDP) format (e.g.
IP or X.25) and sends them out on the corresponding packet data
network. In the other direction, PDP addresses of incoming data packets
are converted to the GSM address of the destination user. The
readdressed packets are sent to the responsible SGSN. For this purpose,
the GGSN stores the current SGSN address of the user and his or her
profile in its location register. The GGSN is responsible for IP
address assignment and is the default router for the connected UE (User
Equipment).The GGSN also performs authentication and charging functions</font><br><h3>SGSN - Serving GPRS Support Node</span></h3>
A Serving GPRS Support Node (SGSN) is responsible for the delivery
of data packets from and to the mobile stations within its geographical
service area. Its tasks include packet routing and transfer, mobility
management (attach/detach and location management), logical link
management, and authentication and charging functions. The location
register of the SGSN stores location information (e.g., current cell,
current VLR) and user profiles (e.g., IMSI, address(es) used in the
packet data network) of all GPRS users registered with this SGSN.</font><br><h3>Common SGSN Functions</span></h3>
<ul><li>Detunnel GTP packets from the GGSN (downlink)</font></li><li>Tunnel IP packets toward the GGSN (uplink)</font></li><li>Carry out mobility management as Standby mode mobile moves from Routing Area to Routing Area.</font></li><li>Billing user data</font></li></ul><br><h3>GSM/<a href="http://en.wikipedia.org/wiki/Enhanced_Data_Rates_for_GSM_Evolution" title="Enhanced Data Rates for GSM Evolution">EDGE</a> Specific SGSN functions</span></h3>
<ul><li>Carry up to about 60 kbit/s (150 kbit/s for Edge) traffic per subscriber</font></li><li>Connect via <a href="http://en.wikipedia.org/wiki/Frame_relay" title="Frame relay">frame relay</a> or <a href="http://en.wikipedia.org/wiki/Internet_protocol" title="Internet protocol" class="mw-redirect">IP</a> to the PCU using the Gb protocol stack</font></li><li>Accept uplink data to form IP packets</font></li><li>Encrypt downlink data, decrypt uplink data</font></li><li>Carry out mobility management to the level of a <a href="http://en.wikipedia.org/wiki/Radio_cell" title="Radio cell" class="mw-redirect">cell</a> for connected mode mobiles;</font></li></ul><br><h3>WCDMA Specific SGSN functions</span></h3>
<ul><li>Carry up to about 300 kbit/s traffic per subscriber (R99)</font></li><li>Carry up to about 7.2 Mbit/s traffic downlink & 2.0 Mbit/s traffic uplink (HSPA)</font></li><li>Tunnel/detunnel downlink/uplink packets toward the RNC</font></li><li>Carry out mobility management to the level of an <a href="http://en.wikipedia.org/wiki/RNC" title="RNC">RNC</a> for connected mode mobiles.</font></li></ul>
These differences in functionality have led some manufacturers to
create specialist SGSNs for each of WCDMA and GSM which do not support
the other networks, whilst other manufacturers have succeeded in
creating both together, but with a performance cost due to the
compromises required.</font><br><br>
and transport for Internet Protocol packet services in GSM and WCDMA
networks. The core network also provides support for other additional
functions such as <a href="http://en.wikipedia.org/wiki/Billing" title="Billing">billing</a> and <a href="http://en.wikipedia.org/wiki/Lawful_interception" title="Lawful interception">lawful interception</a>. It was also proposed, at one stage, to support packet radio services in the US <a href="http://en.wikipedia.org/wiki/Digital_AMPS" title="Digital AMPS">D-AMPS TDMA</a> system, however, in practice, most of these networks are being converted to GSM so this option is becoming largely irrelevant.</font>
Like GSM in general, GPRS is an open standards driven system and the standardization body is the <a href="http://en.wikipedia.org/wiki/3GPP" title="3GPP">3GPP</a>.</font><a href="http://upload.wikimedia.org/wikipedia/en/a/a1/GPRS_core_structure.png"><img style="width: 305px; height: 211px;" alt="Image:GPRS core structure.png" src="http://upload.wikimedia.org/wikipedia/en/a/a1/GPRS_core_structure.png" border="0"></a><h2 style="text-decoration: underline;">GPRS Tunnelling Protocol (GTP)</span></h2><br><i>GPRS Tunnelling Protocol</i> is the defining <a href="http://en.wikipedia.org/wiki/Internet_Protocol" title="Internet Protocol">IP</a> <a href="http://en.wikipedia.org/wiki/Communications_protocol" title="Communications protocol">protocol</a>
of the GPRS core network. Primarily it is the protocol which allows end
users of a GSM or WCDMA network to move from place to place while
continuing to connect to the internet as if from one location at the <i>Gateway GPRS Support Node</i> (GGSN). It does this by carrying the subscriber's data from the subscriber's current <i>Serving GPRS Support Node</i> (SGSN) to the GGSN which is handling the subscriber's session. Three forms of GTP are used by the GPRS core network.</font>
<ul><li>GTP-U: for transfer of user data in separated tunnels for each <a href="http://en.wikipedia.org/wiki/PDP_context" title="PDP context" class="mw-redirect">PDP context</a></font></li><li>GTP-C: for control reasons including:
</font><ul><li>setup and deletion of <a href="http://en.wikipedia.org/wiki/PDP_context" title="PDP context" class="mw-redirect">PDP contexts</a></font></li><li>verification of GSN reachability</font></li><li>updates, e.g. as subscribers move from one SGSN to another.</font></li></ul>
</li><li><a href="http://en.wikipedia.org/wiki/GTP%27" title="GTP'">GTP'</a> : for transfer of charging data from GSNs to the charging function.</font></li></ul>
GGSNs and SGSNs (collectively known as GSNs) listen for GTP-C messages on <a href="http://en.wikipedia.org/wiki/User_Datagram_Protocol" title="User Datagram Protocol">UDP</a>
port 2123 and for GTP-U messages on port 2152. This communication
happens within a single network or may, in the case of international
roaming, happen internationally, probably across a <a href="http://en.wikipedia.org/w/index.php?title=GPRS_Roaming_Exchange&action=edit&redlink=1" class="new" title="GPRS Roaming Exchange (page does not exist)">GPRS Roaming Exchange</a> (GRX).</font>
The <i>"Charging Gateway Function" (CGF)</i> listens to <a href="http://en.wikipedia.org/wiki/GTP%27" title="GTP'">GTP'</a>
messages sent from the GSNs on TCP or UDP port 3386. The core network
sends charging information to the CGF, typically including PDP context
activation times and the quantity of data which the end user has
transferred. However, this communication which occurs within one
network is less standardised and may, depending on the vendor and
configuration options, use proprietary encoding or even an entirely
proprietary system.</font><br style="text-decoration: underline;"><h2 style="text-decoration: underline;">GPRS Support Nodes (GSN)</span></h2>A GSN is a network node which supports the use of GPRS in the GSM core network. All GSNs should have a <i>Gn</i><a href="http://en.wikipedia.org/wiki/GPRS_Tunnelling_Protocol" title="GPRS Tunnelling Protocol">GPRS Tunnelling Protocol</a>. There are two key variants of the GSN; the GGSN and the SGSN defined below.</font> <br><h3>GGSN - Gateway GPRS Support Node</span></h3>
A gateway GPRS support node (GGSN) acts as an interface between the
GPRS backbone network and the external packet data networks (radio
network and the IP network). It converts the GPRS packets coming from
the SGSN into the appropriate packet data protocol (PDP) format (e.g.
IP or X.25) and sends them out on the corresponding packet data
network. In the other direction, PDP addresses of incoming data packets
are converted to the GSM address of the destination user. The
readdressed packets are sent to the responsible SGSN. For this purpose,
the GGSN stores the current SGSN address of the user and his or her
profile in its location register. The GGSN is responsible for IP
address assignment and is the default router for the connected UE (User
Equipment).The GGSN also performs authentication and charging functions</font><br><h3>SGSN - Serving GPRS Support Node</span></h3>
A Serving GPRS Support Node (SGSN) is responsible for the delivery
of data packets from and to the mobile stations within its geographical
service area. Its tasks include packet routing and transfer, mobility
management (attach/detach and location management), logical link
management, and authentication and charging functions. The location
register of the SGSN stores location information (e.g., current cell,
current VLR) and user profiles (e.g., IMSI, address(es) used in the
packet data network) of all GPRS users registered with this SGSN.</font><br><h3>Common SGSN Functions</span></h3>
<ul><li>Detunnel GTP packets from the GGSN (downlink)</font></li><li>Tunnel IP packets toward the GGSN (uplink)</font></li><li>Carry out mobility management as Standby mode mobile moves from Routing Area to Routing Area.</font></li><li>Billing user data</font></li></ul><br><h3>GSM/<a href="http://en.wikipedia.org/wiki/Enhanced_Data_Rates_for_GSM_Evolution" title="Enhanced Data Rates for GSM Evolution">EDGE</a> Specific SGSN functions</span></h3>
<ul><li>Carry up to about 60 kbit/s (150 kbit/s for Edge) traffic per subscriber</font></li><li>Connect via <a href="http://en.wikipedia.org/wiki/Frame_relay" title="Frame relay">frame relay</a> or <a href="http://en.wikipedia.org/wiki/Internet_protocol" title="Internet protocol" class="mw-redirect">IP</a> to the PCU using the Gb protocol stack</font></li><li>Accept uplink data to form IP packets</font></li><li>Encrypt downlink data, decrypt uplink data</font></li><li>Carry out mobility management to the level of a <a href="http://en.wikipedia.org/wiki/Radio_cell" title="Radio cell" class="mw-redirect">cell</a> for connected mode mobiles;</font></li></ul><br><h3>WCDMA Specific SGSN functions</span></h3>
<ul><li>Carry up to about 300 kbit/s traffic per subscriber (R99)</font></li><li>Carry up to about 7.2 Mbit/s traffic downlink & 2.0 Mbit/s traffic uplink (HSPA)</font></li><li>Tunnel/detunnel downlink/uplink packets toward the RNC</font></li><li>Carry out mobility management to the level of an <a href="http://en.wikipedia.org/wiki/RNC" title="RNC">RNC</a> for connected mode mobiles.</font></li></ul>
These differences in functionality have led some manufacturers to
create specialist SGSNs for each of WCDMA and GSM which do not support
the other networks, whilst other manufacturers have succeeded in
creating both together, but with a performance cost due to the
compromises required.</font><br><br>