The over all procedure of the calling from one Mobile station to another with respect to channel mapping and call setup.

1. CALL PROCEDURE IN GSM
& CHANNEL MAPPING

2.  OVERVIEW OF GSM CHANNELING
 CHANNEL MAPPING
 Functions and applications of different channels
before the call initialization.
 CALL FLOW
 From the caller side
 At the receiver side
TABLE OF CONTENTS
2

3. 3
 GSM Network works in a way that, multiple processes
and techniques are going on behind the
communication of the calls or the messages using
mobile station.
 There are multiple channels in the GSM application
which are different entities, and each channel is used
for a specific functions.
 We are going to discuss that when we call on the
GSM network, how those channels are being
arranged or mapped and what is the sequence behind
when we call the other GSM subscriber.
GSM OVERVIEW

4. 4
CHANNEL MAPPING
When the cell phone is turned on and
the sim is inserted, the MS initializes the
linking with the FCCH channel to be able
to sync itself with a carrier frequency, in
order to establish a link with BTS make a
call any moment.
In next step, the MS links to SCH
synchronization channel, this channel
gives the information about the sync
available in time slots or TDMA frame
structure and assign us the temporary
channel.
BCCH broadcast channel gets active,
basically this channel looks for the
information about other cells which are
outside BTS, our location areas, ranges of
the frequencies that can we use, and
output power channel can hold.
Then the PCH paging channel
continuously links with our MS to check
the incoming dial. If MS detects the
incoming message its request the RACH
channel to gran the access to that link
to acknowledge the call.

5. 5
CHANNEL MAPPING ..2
The MS will be provided the access
through the AGCH, which also tells the
MS which SDCCH is to use for call. Along
with grant access to call, the SACCH is
also activated which tracks the call and
tells information about call timing, delay
and output power etc.
Then the MS in linked to the TCH
transmission control channel by the
same SDCCH, the TCH tsk is to figure
the whether the half rate is available or
the full rate, it tunes MS accordingly,
and the rate tuning can be altered
during the call for efficiency.

6. CALLING FLOW at caller
6
This process starts with the Mobile
Station MS communicating through
electromagnetic signal with nearest BTS
and request a random-access channel
RACH to enter the cellular network
MS - BTS
Once the channel is eing granted, The
BSC allocates the traffic channel which
allows the MS to send the recipiets,
mobile number stored in call message
through BSC to main hub MSC at the
caller side.
BTS - BSC
On arrival, the call is put on hold as the
subscribers' details are validated using
few departments that posse's different
information about the caller and the
recipient.
SC - MSC
The VLR Visitor Location Register,
checks the subscriber information like
Balance credit and the services user
have access to by using IMSI
International Mobile Subscriber Identity.
VLR - HLR
Then MSC verifies the device details
related to security purpose in EIR
Equipment Identity Register, those
parameters contains, whether the device
is Blacklisted, Whitelisted or Gray listed.
HLR - EIR EIR - AUC
After the device is verified, now the
Authentication Centre AUC is used to
verify each sim card through IMEI that
tries to make call on the GSM through
IMEI

7. CALLING FLOW at receiver
7
The MSC caller will send all the gathered
information about the subscriber to the
MSC receiver.
After sharing subscriber information,
both the MSCs ebstablish uplink and
downlink channel for call.
Now the Reciever is identified by his or
her unique Caller ID or MSN Mobile
Subscriber Number.
The connection or communication is
established between the MSCr and
MSCc
Then the same protocol is being
followed by MSC receiver for the
verification of the user who is being
called. VLR > HLR > EIR > AUC.
The MSC receiver at the same time is
linked with the BSC receiver to BTS
Receiver and the Mobile Station at the
end.

8. CALLING FLOW cont…
8
This whole process happens every time,
whether the recipient phone is off, not in
range or in busy at another call.
In the best-case scenario, the user’s phone
rings and the acknlowledgement is being
sent to the MS caller and phone continoues
to go live until call disconnection
acknowledge message receives.
After the call ended, the allocated channel
goes idle again and ready for the next call or
another user calling.

9. THANK
YOU
Noor Nabi Khan
d-19-te-28@students.duet.edu.pk