Network Areas
• Cell: radio coverage area of one base station (BTS)
• GSM assigns a cell global identity number to each cell
• Location Area: Group of cells served by one or more
BSCs.
• When there is an incoming call, the mobile is paged
throughout its location area. A unique Location Area
Identity (LAI) is assigned to each LA.
• MSC Service Area: part of network covered by one MSC.
• All mobiles in this area will be registered in the VLR
associated with the MSC.
• PLMN Service Area: public land mobile network area - the
area served by one network operator
• GSM assigns a cell global identity number to each cell
• Location Area: Group of cells served by one or more
BSCs.
• When there is an incoming call, the mobile is paged
throughout its location area. A unique Location Area
Identity (LAI) is assigned to each LA.
• MSC Service Area: part of network covered by one MSC.
• All mobiles in this area will be registered in the VLR
associated with the MSC.
• PLMN Service Area: public land mobile network area - the
area served by one network operator
In order to understand the concepts of mobility management, it is necessary to understand
the structure of network areas used within GSM systems. This is also relevant to the concepts
for call management and paging procedures.
the structure of network areas used within GSM systems. This is also relevant to the concepts
for call management and paging procedures.
7.3.1 GSM SERVICE AREA
A GSM Service Area is defined as the total area served by a combination of all member
countries where a mobile can be serviced.
countries where a mobile can be serviced.
7.3.2 PUBLIC LAND MOBILE NETWORK (PLMN)
The PLMN is defined as a network serving a specific geographical area or a specific operator.
For example, a country could be divided into a number of regions, each covered by a PLMN
or, as is the case in the UK, each of the four major vendors (Cellnet, Vodafone, Orange and
One-to-One) each provide a country-wide PLMN.
The links between PLMNs or a PLMN and PSTNs will be on the level of national or
international transit exchanges. All incoming calls for a GSM PLMN will be routed to a
Gateway MSC which acts as an incoming transit exchange for the GSM PLMN.
For example, a country could be divided into a number of regions, each covered by a PLMN
or, as is the case in the UK, each of the four major vendors (Cellnet, Vodafone, Orange and
One-to-One) each provide a country-wide PLMN.
The links between PLMNs or a PLMN and PSTNs will be on the level of national or
international transit exchanges. All incoming calls for a GSM PLMN will be routed to a
Gateway MSC which acts as an incoming transit exchange for the GSM PLMN.
7.3.3 MSC/VLR SERVICE AREA
A PLMN is divided into a number of MSC/VLR Service Areas, each controlled by a single
MSC. The size of each area is dependant upon the capacity constraints of the MSC and/or the
size of the geographical region. All MSs within and Service Area are registered with the VLR
associated with that MSC. All MS-originated and MS-terminated calls are routed through the
MS’s parent MSC.
MSC. The size of each area is dependant upon the capacity constraints of the MSC and/or the
size of the geographical region. All MSs within and Service Area are registered with the VLR
associated with that MSC. All MS-originated and MS-terminated calls are routed through the
MS’s parent MSC.
7.3.4 LOCATION AREAS (LA)
MSC/VLR Service areas can comprise one or more LAs, each uniquely identified by a
Location Area Identity (LAI). LAs are used to group MSs for paging purposes. When an
MSC needs to locate an affiliated MS, it transmits a broadcast paging request message. To
reduce the load on the signalling channels, rather than broadcasting this message over the
whole MSC Service Area, it is only transmitted in the LA in which the MS is currently
operating.
In order to achieve this, the MSC must retain up-to-date knowledge of the current LA in
which each MS is operating. This is achieved through location update messages transmitted
by all MSs each time an MS moves into a new LA.
Location Area Identity (LAI). LAs are used to group MSs for paging purposes. When an
MSC needs to locate an affiliated MS, it transmits a broadcast paging request message. To
reduce the load on the signalling channels, rather than broadcasting this message over the
whole MSC Service Area, it is only transmitted in the LA in which the MS is currently
operating.
In order to achieve this, the MSC must retain up-to-date knowledge of the current LA in
which each MS is operating. This is achieved through location update messages transmitted
by all MSs each time an MS moves into a new LA.
7.3.5…CELLS
The lowest level of functional area within a GSM Network is the Cell. An LA comprises a
number of cells, each cell serving a number of mobile subscribers. As the MS is moving
between cells, it distinguishes new cell by receiving the Base Station Identity Code (BSIC)
which is transmitted regularly by each Base Transceiver Station (BTS).
number of cells, each cell serving a number of mobile subscribers. As the MS is moving
between cells, it distinguishes new cell by receiving the Base Station Identity Code (BSIC)
which is transmitted regularly by each Base Transceiver Station (BTS).
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