The GRX is built on a private or public IP backbone and
transports GPRS roaming traffic via the GPRS Tunneling
Protocol between the visited and the home Public Land
Mobile Network (PLMN). A Gp interface is added to support
roaming when a mobile terminal is traveling in a visited
PLMN and its data packets are still handled by a GGSN in its
home PLMN. The Gp interface is similar to the Gn interface
except that an additional security is provided through external
border gateways.
The GRX acts as a hub. There is no need for a GPRS
operator to establish a dedicated connection to each roaming
partner; instead the GPRS operator establishes a connection
with the GRX. This allows a faster implementation of new
roaming relations and a rapid deployment time for new
operators. Furthermore, the services offered by the GRX allow
the GPRS operator for better scalability. The operator may
start with a low capacity connection to the GRX and upgrade
if volumes and types of traffic require more bandwidth and
better quality.