Page 116 - From GMS to LTE

102 From GSM to LTE-Advanced Pro and 5G

Gp
GTP
Home network UDP Visited network
IP
Ethernet, STM-1
GPRS network GPRS network
in country A in country B
GGSN SGSN

BG BG
IP network, Border gateway (BG) to
e.g. Internet ensure security. Not
standardized, IPsec
recommended

Figure 2.26 The Gp interface.

operator and still use GPRS to connect to the Internet. The user’s data will be tunneled
via the Gp interface similarly to the Gn interface from the SGSN in the foreign network
to the GGSN in the subscriber’s home network and from there to the Internet or a
company intranet. From an end‐user’s perspective, using a GGSN in the home network
has the big advantage that no settings in the device need to be changed.
The ability to be able to simply connect to the Internet while roaming abroad without
any configuration changes is an invaluable improvement over previous methods. Before
GPRS and mobile networks, travelers could use only fixed‐line modems. Using fixed‐
line modems abroad was often difficult or even impossible because of the lack of a
fixed‐line connection where required and because of connectors that differed from
country to country. If an adapter was available, the next problem was which dial‐in
service provider could be called to establish a connection to the Internet. A provider in
the visited country was usually not an option. Establishing a modem connection with a
provider in the home country was often also difficult because of their use of special
numbers that could not be reached from abroad.
Note that the Gp interface is for GTP traffic only. For signaling with the HLR, the two
networks also need an SS7 interconnection so that the visited SGSN can communicate
with the HLR in the home network.
It should be noted at this point that it is also possible to use a GGSN in the visited
network. This option is referred to as ‘local breakout’ and can, for example, be used
by network operators in Europe to offer cheaper data roaming. The downside of
‘local breakout’ for data roaming is that the user has to manually change the configuration
of their device, that is, they have to manually change the APN. For details see
Section 2.8.2.

The Gs Interface
3GPP TS 29.018 [6] describes this interface, which is also optional. It connects the
SGSN and the MSC/VLR. The functionality and benefits of this interface in conjunction
with GPRS NOM I are discussed in Section 2.3.6.