The GSM EDGE network architecture needed to be updated from the basic GSM network, although it was basically the same as that needed for GPRS.
The large advantage of using GSM EDGE was that it required little upgrade from GPRS and it was also on the evolutionary path from 2G GSM to 3G UMTS. In this way, any upgrades for the GSM EDGE network, would be applicable to the 3G network.
As both GPRS and now EDGE carried packet data, it was necessary for the packet data to be handled by entities that were not present on the basic 2G GSM network. Accordingly the introduction of GPRS and EDGE technology saw the addition of some new entities within the over network architecture.
The two main elements that are required by the GSM EDGE network architecture are the GGSN and SGSN. These enable the network to be able to cater for the packet data that is passed over the network. A network entity called a PCU was also required in the base station controller to route packet and circuit switched data to the required main network entities.
GSM EDGE network architecture upgrades
Although in practice a variety of elements are required within the network architecture, the main new network architecture entities that are needed for the EDGE upgrade are:
- SGSN: GPRS Support Node - this forms a gateway to the services within the network.
- GGSN: Gateway GPRS Support Node which forms the gateway to the outside world.
- PCU: Packet Control Unit which differentiates whether data is to be routed to the packet switched or circuit switched networks.
A simplified view of the GSM EDGE network architecture can be seen in the diagram below. From this it can be seen that it is very similar to the more basic GSM network architecture, but with additional elements.
SGSN network entity
The SGSN or Serving GPRS Support Node element of the GPRS network provides a number of takes focussed on the IP elements of the overall system. It provides a variety of services to the mobiles:
- Packet routing and transfer
- Mobility management
- Logical link management
- Charging data
There is a location register within the SGSN and this stores location information (e.g., current cell, current VLR). It also stores the user profiles (e.g., IMSI, packet addresses used) for all the GPRS users registered with the particular SGSN.
GGSN network entity
The GGSN, Gateway GPRS Support Node is one of the most important entities within the GSM EDGE network architecture.
The GGSN organises the inter-working between the GPRS / EDGE network and external packet switched networks to which the mobiles may be connected. These may include both Internet and X.25 networks.
The GGSN can be considered to be a combination of a gateway, router and firewall as it hides the internal network to the outside. In operation, when the GGSN receives data addressed to a specific user, it checks if the user is active, then forwarding the data. In the opposite direction, packet data from the mobile is routed to the right destination network by the GGSN.
The PCU or Packet Control Unit is a hardware router that is added to the BSC. It differentiates data destined for the standard GSM network (circuit switched data) and data destined for the EDGE network (Packet Switched Data). The PCU itself may be a separate physical entity, or more often these days it is incorporated into the base station controller, BSC, thereby saving additional hardware costs.
GSM EDGE network upgrade
One of the advantages of the migration to GSM EDGE was that the network required little upgrade from what was used for GPRS and what would be used for the future 3G UMTS networks.
This presented a particularly attractive option for network operators who would need little capital expenditure investment to provide the additional capability. Additionally it would be required for the future 3G networks and therefore any investment would be required later anyway.
The EDGE network adds to the existing GSM network. The main new entities required within the network are the SGSN and GGSN, and these are required as the starting point.
The base station subsystems require some updates. The main one is the addition of the PCU described above. Some modifications may be required to the BTS, but often only a software upgrade is required, and this may often be achieved remotely. In this way costs are kept to a minimum.
The GSM EDGE network was steadily upgraded to enable it to handle the required packet data and to ready the network for the future 3G UMTS system that was about to be launched.
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