Mobile to Mobile Call Flow, Within Same MSC/BSC

Call Flow Mesage Details:-

1. CM Service Request – Message contains Global Cell Identity, Kind of Service required by subscriber e.g Voice, SMS, Fax, USSD. Mobile Identity e.g TMSI/IMSI.
2. CM Service Accept – Message is in reponse of CM Service Request.
3. Set Up - Message contains dailed number from Mobile A (i.e Mob B number) and speech Codec.
4. Send Routing Info-Request (SRI) - After analysis of dialed numbers received from A in set up message, MSC recognises its own MSISDN series and send SRI to HLR to get the Mobile station roaming number(MSRN). This messge contains B MSISDN, Interrogation type e.g Basic Call etc.
5. Assignment Request - Message is to seize a channel for voice call for Mob A between MSC and BSC. Message contains Circuit Identification Code(CIC).
6. Assignment Complete - Acceptance from BSC end that same CIC has been seized.
7. Provide Roaming Number Request - HLR checks in its database to which VLR, Mob B is registered & ask for roaming number from that VLR. Message contains IMSI, MSISDN, VLR ID of Mob B.
8. Provide Roaming Number Response - Message is response of roaming no. request and contains roaming number of Mob B. This message is for HLR. In this VLR checks its database & allocate one free MSRN from its MSRN pool for B number.
9. Send Routing Info-Response - In this HLR forward same roaming number which it receives in above message to MSC.
10. Paging Request - In this VLR checks the MSRN recieved from HLR & search which MSISDN is against that MSRN, now MSC checks the VLR database of that MSISDN to get the LAC & TMSI/IMSI of that MSISDN (Mob B) & initiates the paging request message to that particular LAC on the basis of TMSI/IMSI in that BSC. BSC now page to that LAC on the basis of IMSI/TMSI of Mob B. Message contains LAC, IMSI/TMSI, DPC of BSC.
11. Paging Response - Mob B response to that paging with GCI (Global Cell Identity) to BSC that inturn forwarded to MSC.
12. Assignment Request - Message is to seize a channel for voice call for Mob B between MSC and BSC. Message contains Circuit Identification Code(CIC).
13. Assignment Complete - Acceptance from BSC end that same CIC has been seized.
14. Set Up - It is used to display Mob A number on Mob B handset.
15. Alert - This message indicates Mob A that Mob B is connected & its ringing. The Ring Back Tone is send from MSC to Mob A.
16. Connect - Mob B answers the call & connect message from Mob B is send to MSC, inturn MSC sends connect message to Mob A indiacting that phone has been answered & connects those 2 voice channels which were seized during the assignment complete message.
17. Connect Acknowledge - To acknowledge the connection.