This document summarizes GSM architecture and call flows, including inter-MSC and intra-MSC call flows. Inter-MSC call flow occurs between two different MSCs, while intra-MSC call flow is between two BSCs within the same MSC. The inter-MSC call flow involves signaling between the BSC, MSC-O, MSC-T, HLR, and RNC to set up and release the call bearers. The intra-MSC call flow involves signaling between the MS-O, BSC-O, MSC/VLR, MGW, HLR, BSC-T, and MS-T to authenticate, set up, and release call bearers within a single MSC

1. GSM Architecture and
Call Flow
Presented by
Mohd Nazir Shakeel

2. GSM Architecture

3. Call Flow in Core Network
 Inter MSC Call Flow
 Intra MSC Call Flow
Inter:-
 Between two different MSC.
 Intra:-
 Between two BSC within same MSC.

4. Inter MSC call
BSC MSC-O MSC-T HLR RNC
During The Call
Sign ResponseBearer Establishment
on the Caller side 1. IAM
2. SAM
PAGING
Bearer Establishment on the Callee side
Alerting3. ACMAlerting
Connect
4. ANM
Connect
Connect Ack
Connect Ack
Disconnect
5. REL
6. RLC
Bearer Release on
the Caller side Bearer Release on the Caller side

5. Intra MSC Call Flow
MS-O BSC-O MSC/VLR MGW HLR BSC-T MS-T
1. CM service request
2. Auth. & security
3. CM service accept
4. Call proceeding
5. Routing info req
6. Provide roam no
7. Provide roam no rsp
8. Routing info conf
9. Paging
10. Bearer establishment on the caller Side
11. Paging response
12.Authentication and security

6. Cont.
MS-O BSC-O MSC/VLR MGW HLR BSC-T MS-T
24. During the Call
13. Setup
14. Call Confirmed
15. Bearer establishment on callee side
16. AlertingAlerting
17. MOD REQ
18. MOD REPLY 19. Connect
20. MOD REQ
21. MOD REPLY
22. Connect
23. Connect Ack 23. Connect Ack
25. Bearer release on the caller side
25. Bearer release on the callee side