call flow in gsm

Question Posted / sourabhjhamb

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call flow in gsm..

Answer / dhaval

when we dial a number and press send/call key the RACH ask
for a signalling channel,using AGCH.
after this process some steps are taken that is:

1) The MSC receives the message of a call request
2) The MSC from VLR checks if the mobile station is
authorized to access the network.if so,the mobile station
is activated.if the mobiloe station is not
authorized ,service wiil be denied.
3)The MSC from VLR analyzes the number and intiate a call
setup with the PSTN.
4)MSC asks the corresponding BSC to allocate a traffic
channel(a radio ch. and a time slot)
5)The BSC alloctes the traffic channeland passes the
information to the mobile station & BTS.The MS and BTS tune
to that channel
6)The MSC forward the call called number to the local
exchange in the PSTN,vis GMSC which is establishs a
connection to the subscriber.
7)The called party answer vis GMSC & MSC to MS the call and
the conversation takes place.
8)The mobile station keeps on taking measurment of a radio
channels in the present cell and neighboring cells and
passes the information to the BSC.
and the BSC decides if handover is required , if so , a new
traffic channel is allocated to the mobile station and the
handover is performed. if handover is not required,the
mobile stations continues to transmit in the same frequency.

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