The Network and Switching Subsystem
Its main role is to manage the communications between the mobile users and
other users, such as mobile users, ISDN users, fixed telephony users, etc. It
also includes data bases needed in order to store information about the
subscribers and to manage their mobility. The different components of the NSS
are described below.
TheMobile
services Switching Center (MSC)
It is the central component of the NSS. The MSC performs the switching functions of the network. It also provides connection to other networks.
The Gateway Mobile services Switching Center (GMSC)
A gateway is a node interconnecting two networks. The GMSC is the interface
between the mobile cellular network and the PSTN. It is in charge of routing
calls from the fixed network towards a GSM user. The GMSC is often implemented
in the same machines as the MSC.
Home Location Register (HLR)
The HLR is considered as a very important database that stores information
of the subscribers belonging to the covering area of a MSC. It also stores the
current location of these subscribers and the services to which they have
access. The location of the subscriber corresponds to the SS7 address of the
Visitor Location Register (VLR) associated to the terminal.
Visitor Location Register (VLR)
The VLR contains information from a subscriber's HLR necessary in order to provide
the subscribed services to visiting users. When a subscriber enters the
covering area of a new MSC, the VLR associated to this MSC will request
information about the new subscriber to its corresponding HLR. The VLR will
then have enough information in order to assure the subscribed services without
needing to ask the HLR each time a communication is established.
The VLR is always implemented together with a MSC; so the area under control of the MSC is also the area under control of the VLR.
The
The AuC register is used for security purposes. It provides the parameters
needed for authentication and encryption functions. These parameters help to
verify the user's identity.
The Equipment Identity Register (EIR)
The EIR is also used for security purposes. It is a register containing
information about the mobile equipments. More particularly, it contains a list
of all valid terminals. A terminal is identified by its International Mobile
Equipment Identity (IMEI). The EIR allows then to forbid calls from stolen or
unauthorized terminals (e.g., a terminal which does not respect the
specifications concerning the output RF power).
The GSM Inter-working Unit (GIWU)
The GIWU corresponds to an interface to various networks for data communications. During these communications, the transmission of speech and data can be alternated.
The
It is the central component of the NSS. The MSC performs the switching functions of the network. It also provides connection to other networks.
The Gateway Mobile services Switching Center (GMSC)
A gateway is a node interconnecting two networks. The GMSC is the interface
between the mobile cellular network and the PSTN. It is in charge of routing
calls from the fixed network towards a GSM user. The GMSC is often implemented
in the same machines as the MSC.Home Location Register (HLR)
Visitor Location Register (VLR)
The VLR contains information from a subscriber's HLR necessary in order to provide
the subscribed services to visiting users. When a subscriber enters the
covering area of a new MSC, the VLR associated to this MSC will request
information about the new subscriber to its corresponding HLR. The VLR will
then have enough information in order to assure the subscribed services without
needing to ask the HLR each time a communication is established. The VLR is always implemented together with a MSC; so the area under control of the MSC is also the area under control of the VLR.
The Authentication Center
The AuC register is used for security purposes. It provides the parameters
needed for authentication and encryption functions. These parameters help to
verify the user's identity.
The Equipment Identity Register (EIR)
The EIR is also used for security purposes. It is a register containing
information about the mobile equipments. More particularly, it contains a list
of all valid terminals. A terminal is identified by its International Mobile
Equipment Identity (IMEI). The EIR allows then to forbid calls from stolen or
unauthorized terminals (e.g., a terminal which does not respect the
specifications concerning the output RF power).
The GSM Inter-working Unit (GIWU)
The GIWU corresponds to an interface to various networks for data communications. During these communications, the transmission of speech and data can be alternated.
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