GSM Network Signaling 2003. 4. 8. Kim Myung Jo (silveraspen@hanmail)

1. GSM Network Signaling 2003. 4. 8. Kim Myung Jo (silveraspen@hanmail.net) Communication Protocol Engineering Lab.

2. Contents • GSM Protocol Interfaces • GSM MAP protocol Hierarchy • GSM MAP Service Framework • MAP Protocol Machine • MAP Dialogue • MAP Service Primitives

3. GSM Protocol Interfaces(1/2) • Databases • VLR (visitor location register) • HLR (home location register) • AuC (authentication center) • EIR (equipment identity register) • Used to maintain a list of legitimate, fraudulent, or faulty mobile stations • Works with HLR to block calls from illegitimate MS • Switches • MSC (mobile switching center) • GMSC (gateway MSC) • SSP (service switching point) • Radio systems • BSC (base station controller) • BTS (base transceiver station) • MS (mobile station)

4. GSM Protocol Interfaces(2/2)

5. GSM MAP protocol Hierarchy (1/2)

6. GSM MAP protocol Hierarchy (2/2) • The network entities may consist of several application service elements (ASEs) • The SCCP addresses these ASEs with subsystem numbers (SSNs) • Intra-GSM network message delivery • The destination address of the message may be a simple destination point code (DPC) that can be used by the MTP for direct routing • Inter-GSM network message delivery • The origination node does not have enough knowledge to identify the actual address of the destination • In this case, the SCCP translates the actual destination address by GTT(global title translation)

7. GSM MAP Service Framework(1/4) • GSM network entities • communicate with each other through MAP dialogues by invoking MAP service primitives • Service primitive • Initiated by a MAP service user of a network entity called the dialogue initiator • Request, Indication, Response, Confirm • Procedure • The service request is sent to the MAP service provider of the network entity • The service provider delivers the request to the peer network entity • the peer network entity invokes the same service primitive with type Indication to inform the destination MAP service user • The same service primitive with type Response in invoked by the MAP service user of the dialogue responder • After the MAP service provider of the dialogue type Confirm

8. GSM MAP Service Framework(2/4) <GSM MAP service model>

9. GSM MAP Service Framework(3/4) • The parameters of a service primitive type • M (Mandatory) • O (Service Provider Option) • U (Service User Option) • C (Conditional) • Two type of MAP services • Specific MAP service • Mobility services • Operation and maintenance services • Call-handling service • Supplementary service • Short message service management service

10. GSM MAP Service Framework(4/4) • Common MAP services • MAP-OPEN • Used to establish a MAP dialog • MAP-CLOSE • Used to clear a MAP dialogue • MAP-DELIMITER • Used to explicitly request the TCAP to transfer the MAP protocol data units • MAP-U-ABORT • Used by the service user to abort a dialogue • MAP-P-ABORT • Used by the service provider to abort a dialogue • MAP-NOTICE • Used by the service provider to inform the service user of protocol problems such as abnormal event detected by the peer and response rejected by the peer

11. MAP Protocol Machine(1/2) • DSM(dialogue state machine) • Coordinates the service state machines (SSMs) • For every MAP dialogue, an instance of DSM in created to handle the dialogue • RSM(requesting service state machine) • Handles a MAP-specific service requested • PSM(performing service state machine) • Handles a MAP service performed • Load Control • Monitors the traffic generated by the service activities • If overload situation in detected, low-priority MAP operations may be ignored • Handoff, mobility management, short message services, subscriber-controlled inputs

12. MAP Protocol Machine(2/2)

13. MAP Dialogue

14. MAP Dialogue (contd.) • Step 1 • A service user initiates a MAP dialogue by invoking the MAP-OPEN Request servece primitive

15. MAP Dialogue (contd.) • Step 2 • The MAP PM creates an instance of DSM to handle the MAP-OPEN Request primitive • For every one of the following user request primitives, an RSM is created • RSM uses the TC-INVOKE procedure to set the operation code and TCAP parameters for the service request • The DSM continues to process the user request primitives until the MAP-DELIMITER Request primitive is encountered • MAP PM enables the TC-BEGIN primitive

16. MAP Dialogue (contd.) • Step 3 • The TC-* Request primitives will be delivered by the TCAP and the lower-layer protocols of SS7 to the peer MAP PM • The primitives are now of type Indication

17. MAP Dialogue (contd.) • Step 4 • When the MAP PM of the dialogue responder receives the TC-BEGIN Indication, a DSM is invoked • If the DSM identifies any error from the received TC-BEGIN Indication, a TC-U-ABORT Request in sent back to the dialogue initiator to terminate the dialogue • The DSM checks if the system is overloaded • The DSM issues the MAP-OPEN Indication primitive to its MAP service user • The DSM encounters the TC-INVOKE Indication primitive, it creates a PSM

18. MAP Dialogue (contd.) • Step 4 (contd.) • The PSM sends a MAP-NOTICE to its MAP service user • No error occurs, the PSM issues a MAP-Service1 Indication primitive to be passed to its service user, and the control is passed back to the DSM • After the DSM has processed all received components, it informs its MAP service user by the MAP-DELIMITER Indication primitive

19. MAP Dialogue (contd.) • Step 5 • The MAP service user processes the Indication primitives received from the MAP service provider, and returns the results with the MAP-OPEN and the MAP-Service1 Response primitives, followed by the MAP-DELINITER Request primitive

20. MAP Dialogue (contd.) • Step 6 • When the MAP service provider receives the MAP-OPEN Response primitive, the DSM first checks if the response is negative • If so, it generates a MAP_Refuse_PDU (Protocol Data Unit) to be delivered by the Indication primitive TC-END • The response is positive, a MAP_Accept_PDU is generated • The DSM proceeds to receive the MAP-Servece1 Response primitive and passes the control to the PSM • The PSM checks if any user error in present • PSM issues a TC-RESULT-L Request primitive and passes the control to back to the DSM

21. MAP Dialogue (contd.) • Step 6 (contd.) • The DSM continues to process the specific service primitives until the MAP-DELIMITER Request primitive is encountered • The DSM issues a TC-CONTINUE Request primitive with the MAP_Accept_PDU

22. MAP Dialogue (contd.) • Step 7 • The TC-CONTINUE/ TC-RESULT-L Indication primitives are received by the MAP service provider of the dialogue initiator • When the DSM receives the TC-CONTINUE, it performs tests, as described in step 4 • It accepts the the dialogue and passes the control to the RSM to handle the specific service primitives • The RSM maps the TC-RESULT-L parameters to the MAP-Service1 Confirm primitive and passes the control back to the DSM • After all components have been processed, the DSM informs the MAP service user

23. MAP Dialogue (contd.) • Step 8 • The MAP service user of the dialogue initiator handles the Confirm primitives and, possibly, makes new requests

24. MAP Service Primitives(1/3) <Retrieval of routing information>

25. MAP_SEND_ROUTING_INFORMATION Parameters (1/3)

26. MAP_SEND_ROUTING_INFORMATION Parameters (2/3) • Invoke ID • A unique number generated by the MAP service user to identify the corresponding service primitives in the MAP service user-provider interface • MSISDN • The mobile station ISDN number • CUG(closed user group) Interlock • A group of users (e.g company) with specific network services • possible to limit the incoming/outgoing calls inside the group • CUG Outgoing Access • Represents the outgoing access of a closed user group • Number of Forwarding • Counts the number of times the call has been forwarded

27. MAP_SEND_ROUTING_INFORMATION Parameters (3/3) • Network Signal Info • Provides external signal information • Signaling protocol between the GSM network and the PSTN • IMSI (International Mobile Subscriber Identity) • Used to identify the called MS • MSRN (Mobile Subscriber Roaming Number) • The routing number that identifies the current location of the called MS • Forwarding Data • Used to invoke the call-forwarding service • User Error • Send by the responder when an error is detected

28. MAP_PROVIDE_ROAMING_NUMBER Parameters (1/2)

29. MAP_PROVIDE_ROAMING_NUMBER Parameters (2/2) • MSC Number • The ISDN number of the MSC where the called MS resides • LMSI(Local Mobile Station Identity) • Used by the VLR for internal data management of the called MS • GSM Bearer Capability • Included if the connection is for nonspeech services such as short message services • User Error • Sent when an error is detected