Page 239 - From GMS to LTE

Long Term Evolution (LTE) and LTE-Advanced Pro 225

PDN-GW SGi Internet
HSS
S8
S6a CP UP
Home Network

IPX

Visited Network
MME S11 S-GW

S1
CP UP

eNode-B
Mobile device

Figure 4.4 LTE international roaming with home routing.

DIAMETER is used to exchange information with the database. It is standardized in
RFC 3588 [10] and referred to as S6a. Further, the name of the database has been
changed to HSS. In practice, however, the HLR and the HSS are physically combined to
enable seamless roaming between the different radio access networks. Each subscriber
has a record in the HLR/HSS and most properties are applicable for communicating
over all radio access networks. The most important user parameters in the HSS are:
the user’s International Mobile Subscriber Identity (IMSI), which uniquely identifies
●
a subscriber. The IMSI implicitly includes the Mobile Country Code (MCC) and
Mobile Network Code (MNC) and is thus used when the user is roaming abroad to
find the home network of the user to contact the HSS. A copy of the IMSI is stored on
the subscriber identity module (SIM) card of the subscriber;
authentication information that is used to authenticate the subscriber and to generate
●
encryption keys on a session basis;
circuit‐switched service properties such as the user’s telephone number, referred to
●
as the Mobile Subscriber Integrated Services Digital Network (MSISDN) number,
and the services the user is allowed to use, such as SMS, call forwarding, and so on.
While the MSISDN is used for some purposes in LTE, the other values are mainly of
interest while the user is connected to GSM or UMTS;
packet‐switched service properties such as the Access Point Names (APNs) the sub-
●
scriber is allowed to use, which in turn references the properties of a connection to
the Internet or other external packet data network, such as the maximum throughput;
IMS‐specific information (see Chapter 5);
●