Network components of the Switching Subsystem
The switching Subsystem comprises the following subsystems.
MSC (Mobile Switching Centre)
HLR (Home location Register)
VLR (Visitor Location Register)
AU (Authentification Centre)
EIR (Equipment Identification Register)
Network Components of MSC
GSM/DCS has digital exchanges called Mobile Services switching Centre
MSC are responsible for establishing traffic channel connections to
- to the BSS
- to other MSC
- and to other networks
The database of MSC contains the information for the routing traffic channelsconnections and handles the basic and supplementary services
In addition MSC performs the administration of cells and location areas
Unlike the PSTN the mobile subscriber current location determines the MSCresponsible for it at that particular moment.
GSM/DCS contains a central component called the Home location Registerwhich Administers the subscriber data.
Network Components of MSC
Network Components of MSC
The HLR is a database where the mobile subscribers are created, barred ordeleted by the operator
The HLR contains all the permanent subscriber identities as well as theservices (and corresponding restrictions) a mobile subscriber is authorized touse
Network Components of MSC
A great part of the HLR subscriber data is required for the connectionsetup and clear down
For immediate availability of the data for a call the information istemporarily stored in a further database called visitor location Register.
HLR is associated with the MSC, during the location update thesubscriber data is passed from HLR to current VLR.
Network Components of MSC
VLR provides the data whenever it is needed for call handling.
VLR also verifies whether the sim card is approved i.e performs theauthentication
VLR uses the authentication parameters called tripples, which are generatedcontinuously by authentication centre. and on request provided to AC
The Network component AC is associated with the HLR.
Network Components of MSC
Triple
A triple is a set of three parameters which are generated subscriber individually.
Network Components of MSC
The MSc also verifies whether the mobile equipment is approved or nottherefore requests the (IMEI) from the MS and then sends it to the
Equipment identification register.
International Mobile Equipment identity
Represents an internationally uniquely defined code which is assigned to theevery mobile equipment by the manufacturer.
The IMEI consists of
Network Components of MSC
Network Components of MSC
In Equipment identification register, the IMEI of the whole mobile
equipment used are categorized into three lists
White List: contains the mobile equipment approved withoutrestrictions.
Grey List: contains the equipment to be observed
Black list: contains the unapproved equipment.
The EIR checks whether the IMEI fits into one of three list and passes the
results to MSC.
Network Components of Radio subsystem
The radio subsystem consists of
Mobile Equipment
Base station
Radio interface
The Radio Interface
The Radio interface
The GSM/DCS frequency bands
The Radio interface
Both sub-bands uplink and down link are divided into carriers orradio frequency channels (RFC) with a bandwidth of 200khz
The carrier access procedure in the frequency range is calledfrequency division multiple access (FDMA)
The Radio interface
The difference between the GSM and DCS
radio channels relate to
The operating frequency
The bandwidth of sub-bands
The duplex spacing (the spacing between associated channels inuplink and the downlink respectively)
The number of carriers provided
Radio frequency channels in GSM/DCS
Depending upon the traffic volume every radio cell uses one or more RFC
As the network capacity is limited the RFC has to be used several times
To avoid the co-channel interference, it must be observed during the networkplanning that adjacent cells use different RFC
Therefore a safe distance is required between the BTS using the same RFC,called reuse distance
Radio frequency channels in GSM/DCS
In densely populated areas, thetransmission power is kept low andaccordingly the cell radius is small
With a short safe distance amultiple use of the same RFC ispossible.
Similar to PCM 30 system(1 linkwith 32 channels)
1 RFC consists of 8 channels,several mobile subscribers canaccess one RFC at the same time.
Radio frequency channels in GSM/DCS
Physical Channels
A physical channel is defined by a specific carrier pair (i.e., by anRFC) and by the time slot no in the TDMA frame.
Physical Channels
A physical channel can function as
traffic channel for the transmission of speech and data information
Control Channel for the transmission of signaling and controlinformation
The generic term for traffic and control channel respectively is logicalchannel