GSM Architecture and

Call FlowPresented by

Mohd Nazir Shakeel

GSM Architecture

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.

Inter MSC call BSC MSC-O MSC-T HLR RNC

During The Call

Sign ResponseBearer Establishment

on the Caller side 1. IAM

2. SAMPAGING

Bearer Establishment on the Callee side

Alerting3. ACMAlertingConnect

4. ANM

ConnectConnect Ack

Connect Ack

Disconnect5. REL

6. RLCBearer Release on

the Caller side Bearer Release on the Caller side

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

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 REPLY22. Connect

23. Connect Ack 23. Connect Ack

25. Bearer release on the caller side

25. Bearer release on the callee side