Page 31 - From GMS to LTE

Global System for Mobile Communications (GSM) 17

Figure 1.12 Mobile Switching Center (MSC) Switching center
with integrated Visitor Location
Register (VLR). MSC VLR
‘application’ ‘application’
with SSN = 8 with SSN = 7

SCCP
MTP 1–3
Incoming signaling messages
for VLR and MSC

When a subscriber leaves the coverage area of an MSC, their record is copied from
the HLR to the VLR of the new MSC, and is then removed from the VLR of the previ-
ous MSC. The communication with the HLR is standardized in the D interface speci-
fication, which is shown together with other MSC interfaces in Figure 1.9 and
Figure 1.10.

1.6.3 The Home Location Register (HLR)
The HLR is the subscriber database of a GSM network. It contains a record for each
subscriber, with information about the individually available services.
The International Mobile Subscriber Identity (IMSI) is an internationally unique
number that identifies a subscriber and is used for most subscriber‐related signaling in
the network (Figure 1.13). The IMSI is stored in the subscriber’s subscriber identity
module (SIM) card and in the HLR and is thus the key to all information about the
subscriber. The IMSI consists of the following parts:

The Mobile Country Code (MCC). The MCC identifies the subscriber’s home
●
country. Table 1.2 shows a number of MCC examples.
The Mobile Network Code (MNC). This part of the IMSI is the national part of a
●
subscriber’s home network identification. A national identification is necessary
because there are usually several independent mobile networks in a single country. In
the United Kingdom, for example, the following MNCs are used: 10 for O2, 15 for
Vodafone, 30 for T‐Mobile, 33 for Orange, 20 for Hutchison 3G, etc.
The Mobile Subscriber Identification Number (MSIN). The remaining digits of
●
the IMSI form the MSIN, which uniquely identifies a subscriber within the home
network.

IMSI: max. 15 Digits Figure 1.13 The International Mobile
Subscriber Identity (IMSI).
2–3 Digits

MCC MNC MSIN

3 Digits