how call flow happening
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Answer Posted / srinivas padamata
2.Call from PSTN to MS:
The main difference between a call to an MS and a call from
an MS is that, the exact location of MS is unknown in the
call to MS case. Hence, the MS must be located using paging
before a connection can be established.
1. The PSTN subscriber dials the MS’s telephone number
(MSISDN), the MSISDN is analyzed in the PSTN, which
identifies that this is a call to a mobile network
subscriber. A connection is established to the MS’s home GMSC.
2. The GMSC analyzes the MSISDN to find out which HLR, the
MS is registered in, and queries the HLR for information
about how to route the call to the serving MSC/VLR.
3. the HLR translates MSISDN into IMSI, and determines which
MSC/VLR is currently serving the MA. The HLR also checks if
the service, “call forwarding to C-number” is activated, if
so, the call is rerouted by the GMSC to that number.
4. The HLR requests an MSRN from the serving MSC/VLR.
5. The MSC/VLR returns an MSRN via HLR to the GMSC.
6. The GMSC analyses the MSRN and routes the call to the
MSC/VLR.
7. The MSC/VLR knows which LA the Ms is located in. A
paging message is sent to the BSC’s controlling the LA.
8. When the MS detects the paging message to the BTS’s in
the desired LA. The BTS’s transmit the message over the air
interface using PCH. To page the MS, the network uses an
IMSI or TMSI valid only in the current MSC/VLR service area.
9. When the MS detects the paging message, it sends a
request on RACH for a SDCCH.
10. The BSC provides a SDCCH, using AGCH.
11. SDCCH is used for the call set-up procedures. Over SDCCH
all signaling preceding a call takes place. This includes:
Marking the MS as “active” in the VLR
The authentication procedure
Start ciphering
Equipment identification
12. The MSC/VLR instructs the BSC/TRC to allocate an idle
TCH. The BTS and MS are told to tune to the TCH. The mobile
phone rings. If the subscriber answers, the connection is
established.
| Is This Answer Correct ? | 48 Yes | 7 No |
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