6.8 Procedures at the MCData gateway

24.2823GPPMission Critical Data (MCData) signalling controlProtocol specificationRelease 18TS

6.8.1 General

As described in clause 5.4, the MCData gateway servers are inserted in the path between MCData functions that reside in MCData systems from different trust domains.

This clause specifies the behavior of an MCData gateway server that acts as an exit point from an MCData system or as an entry point in an MCData system.

Local policies enforcement covers a wide variety of actions that are left to implementation. An example of local policies enforcement is given in clause 6.8.4.

6.8.2 MCData gateway server acting as an exit point from an MCData system

When acting as an exit point from a local MCData system to an interconnected MCData system, the MCData gateway server receives SIP requests and SIP responses intended for the controlling, non-controlling or participating function in the interconnected MCData system.

When receiving an outgoing SIP message, the MCData gateway server acting as an exit point:

1) shall identify the MCData system identity of the interconnected MCData system from information elements in the outgoing SIP message, e.g., the Request-URI;

2) may enforce local policy, and if local policy enforcement results in rejecting a SIP request (e.g., not having a mutual aid relationship), the MCData gateway shall reject the request by sending back a SIP 403 (Forbidden) response including a warning text "1xx service not authorized with the interconnected system", and the MCData gateway server shall not continue with the rest of the steps;

3) may replace in the outgoing SIP message any addressing information linked to the local MCData system topology with its own addressing information; this includes:

a) the P-Asserted-Identity header field may be set to the MCData gateway server’s own URI; and

b) the Request-URI may be set to the public service identity of the targeted function in the interconnected MCData system, or to the URI of the MCData gateway server that acts as an entry point in the interconnected MCData system; and

NOTE: How the MCData gateway server determines the public service identity of the targeted MCData function in the interconnected MCData system or the URI of the MCData gateway server in the interconnected MCData system is out of the scope of the present document.

4) shall forward the outgoing SIP message according to 3GPP TS 24.229 [5].

6.8.3 MCData gateway server acting as an entry point in an MCData system

When acting as an entry point in an MCData system from an interconnected MCData system, the MCData gateway receives SIP requests and SIP responses intended for the controlling, non-controlling or participating function in the local MCData system.

When receiving an incoming SIP message, the MCData gateway server acting as an entry point:

1) shall identify the MCData system identity of the interconnected MCData system from the P-Asserted-Identity header field of the incoming SIP messages;

2) may enforce local policy and. if local policy enforcement results in rejecting a SIP request (e.g., not having a mutual aid relationship), the MCData gateway shall reject the request by sending back a SIP 403 (Forbidden) response including a warning text "180 service not authorized by the interconnected system", and the MCData gateway server shall not continue with the rest of the steps;

3) should replace in the incoming SIP message its own addressing information with the addressing information of the targeted MCData function in the local MCData system:

a) the Request-URI should be set to the public service identity of the targeted MCData function in the local MCData system; and

NOTE: How the MCData gateway server determines the public service identity of the targeted MCData function in the local MCData system is out of the scope of the present document.

4) shall forward the incoming SIP message according to 3GPP TS 24.229 [5].

6.8.4 Local policies enforcement

Below is one example of local policy enforcement that can be handled by an MCData gateway server.

If an MCData gateway server acting as an exit point receives a SIP request or a SIP response that contains sensitive information that cannot be exposed to the targeted interconnected system based on local policies but does not prevent the service from being delivered (e.g. a functional alias), the MCData gateway server can remove that information from the outgoing SIP message before forwarding it.