STEP 1: The cell phone compares received SID from
the BS with its programmed SID in the phone or the
SIM card..
If they match, the phone is in a network owned by carrier.
If SIDs do not match, the phone is roaming.
STEP 2: If the phone is in its carrier network, it
sends a registration request number to the base
station.
The number is for the MTSO use for tracking the cell(s) in
which the phone is located.
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Steps to Receive a Phone Call (3)
If the phone is roaming, the MTSO of the
remote network contacts the MTSO of the
home network,
which confirms that the SID of the phone belongs
to a valid account.
The MTSO of the remote network then tracks the
phone and sends the call information, including
call length, back to the home MTSO.
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Steps to Receive a Phone Call (4)
STEPS 3 and 4: When a phone call comes in, MTSO
locates the phone through the registration request,
i.e., knowing which cell the phone is in, or use
paging process.
Paging is the process in which the MTSO sends query
signals to each cell to find the location of the phone
After knowing the location of the phone, the MTSO
selects a frequency for communication.
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Steps to Receive a Phone Call (5)
STEP 5: The MTSO sends a ringing signal and
the frequency information to the phone over
the control channel.
STEP 6: Both the phone and transmitter switch
to that frequency, allowing the communication
to begin.
Note that the process of making an outgoing
call is similar to the one for receiving a call.