Interworking between mobile railway networks and GSM networks

1. An apparatus comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:

receiving a call request for a mission critical, push to talk (MCPTT) call;

accessing, in response to receiving the call request, a mapping of an MCPTT identifier of a user equipment with an interworking identifier that is formed according to an address format implemented in Global System for Mobile communications (GSM) for Railways (GSM-R); and

forwarding the call request based on the mapping.

2. The apparatus of claim 1 , wherein the MCPTT identifier is a uniform resource identifier (URI) and the interworking identifier is represented in an e164 format.

3. The apparatus of claim 1 , wherein the mapping is stored in a user profile that includes a binding between the MCPTT identifier, the interworking identifier, and an identifier of the apparatus.

4. The apparatus of claim 3 , wherein the at least one memory and computer program code is further configured, with the processor, to cause the apparatus to perform:

storing the user profile in a routing table, and wherein the processor is configured to access the mapping from the memory.

5. The apparatus of claim 3 , wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the apparatus at least to perform accessing the mapping from a database that is implemented external to the apparatus.

6. The apparatus of claim 3 , wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the apparatus at least to perform receiving the call request including the MCPTT identifier in response to the user equipment initiating the MCPTT call, and wherein the processor is configured to add the interworking identifier to the call request prior to forwarding the call request to an interworking function associated with a GSM-R system.

7. The apparatus of claim 6 , wherein the interworking identifier is displayed to a GSM-R client or used to initiate another call to the user equipment by the GSM-R client.

8. The apparatus of claim 3 , wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the apparatus at least to perform receiving the call request including an identifier in the address format implemented in GSM-R in response to a GSM-R client initiating a call.

9. The apparatus of claim 8 , wherein the at least one memory and the computer program code is further configured to, with the at least one processor, cause the apparatus at least to perform resolving the identifier into the MCPTT identifier of the user equipment, and wherein the call request is forwarded to the user equipment based on the MCPTT identifier.

10. A method comprising:

receiving, at a server, a call request for a mission critical, push to talk (MCPTT) call;

accessing, from the server and in response to receiving the call request, a mapping of an MCPTT identifier of a user equipment with an interworking identifier that is formed according to an address format implemented in Global System for Mobile communications (GSM) for Railways (GSM-R); and

forwarding the call request from the server based on the mapping.

11. The method of claim 10 , wherein the MCPTT identifier is a uniform resource identifier (URI) and the interworking identifier is represented in an e164 format.

12. The method of claim 10 , further comprising:

storing the mapping in a user profile that includes a binding between the MCPTT identifier, the interworking identifier, and an identifier of the server.

13. The method of claim 12 , wherein storing the mapping in the user profile comprises storing the user profile in a routing table implemented in the server, and wherein accessing the mapping comprises accessing the mapping from the user profile.

14. The method of claim 12 , wherein accessing the mapping comprises accessing the mapping from a database that is implemented external to the server.

15. The method of claim 12 , further comprising

receiving, at the server, the call request including the MCPTT identifier in response to the user equipment initiating the MCPTT call;

adding, at the server, the interworking identifier to the call request; and

forwarding, from the server, the call request to an interworking function associated with a GSM-R system.

16. The method of claim 15 , further comprising:

displaying the interworking identifier to a GSM-R client.

17. The method of claim 15 , further comprising:

receiving, at the server, an other call request from a GSM-R client to initiate another call to the user equipment, wherein the other call request includes the interworking identifier.

18. The method of claim 10 , further comprising:

receiving, at the server, the call request including an identifier in the address format implemented in GSM-R in response to a GSM-R client initiating a call.

19. The method of claim 18 , further comprising:

resolving, at the server, the identifier into the MCPTT identifier of the user equipment; and

forwarding, from the server, the call request to the user equipment based on the MCPTT identifier.

20. A non-transitory computer readable storage medium comprising software with instructions that, when executed by one or more processors, manipulate the one or more processors to cause an apparatus to perform

receiving a call request for a mission critical, push to talk (MCPTT) call;

accessing, in response to receiving the call request, a mapping of an MCPTT identifier of a user equipment with an interworking identifier that is formed according to an address format implemented in Global System for Mobile communications (GSM) for Railways (GSM-R); and

forwarding the call request based on the mapping.