Identities, service registration and functional aliases

Familiar device, authorised user, current role

In 1.2 Lea and Amir each had their own reachable device; the call to the function still reached Lea’s device. Now we perform this change in the pilot setup. Three assignments must be kept separate.

An identity identifies a participant or function in the relevant system context. The network subscriber identity enables assignment to mobile-network access. The service user identity identifies the user in the communication service. The functional identity describes the operational role under which the user is to be reachable. None of these details answers all the other questions on its own.

A Functional Alias is a functional designation in the MC/FRMCS context. It enables a communication partner to be addressed through an operational function rather than only a permanently person-specific destination identifier. Assignment to the authorised user must be active and valid. [S05, S06, sections 11.6 and 21.3]

The SIM or associated subscriber profile supports identification for network access. It contains the intended subscriber and security information, not automatically the current operational role. It therefore does not automatically establish that Amir has taken over the current driver role. Device handover and role handover are different processes. The subscriber profile describes network access; it is not the physical device. In this lesson we follow the assignment between network access, service user and function.

The life cycle of an assignment

Here, a life cycle describes the states from creating to ending an assignment. For Talbahn, consider four teaching states:

This table is not a prescribed protocol. It makes evidence needs visible. Behaviour under duplicate registration, connection loss or delayed confirmation must be specified.

Keep function and location separate

“Driver of train 1234” describes a function. “Responsible office for this section” additionally involves geographical responsibility. Location information must be mapped to a destination according to rules; it does not itself decide operational responsibility.

In interworking with GSM-R, the intended identities must be mapped across the system boundary. A correct name display does not prove a correct callback or group join. Behaviour is therefore tested in both directions. [S11]

Service registration before the role-based call

Mobile-network registration, SIP registration and MC service authorisation are separate procedures. Service sign-in involves identity verification, an appropriate profile and authorisation for permitted MC services. An access token is a technical authorisation credential with a limited scope; it is neither a train number nor an operational role. The service specification describes preparation and service-specific authorisation. [S09, clause 6.1]

An expired credential may prevent new service use while a device remains registered on the radio network. Talbahn therefore records time, identity and responsible function for each state. The role “driver of train 1234” is then assigned to the intended service user on this basis. A role handover cannot replace the independent service-permission check.

Check your understanding

After Amir's role takeover, calls still reach Lea. What information do you need before identifying a cause? Formulate a positive test case and a conflict-related test case.

Model answer

You need the requested and confirmed assignment states with their timing, the destination resolution actually used, and the agreed conflict rules. Positive case: after the confirmed change, Niko reaches Amir through the function. Conflict case: a second simultaneous takeover is handled according to the defined rule and clearly indicated to the user. Without that rule, no specific expected behaviour can be invented.

Additional application

The device remains network-registered but service access is rejected. Which additional state needs checking?

Model answer

Check service identity, profile and MC service authorisation separately from network registration. An expired credential is also a hypothesis to investigate.

What to remember

• Network, service and functional identities are different.
• Role takeover needs confirmed states and conflict rules.
• Displayed names do not replace behavioural testing.

Your Talbahn case file

Extend the role-change case from 1.3 with states and evidence needs. Preserve the unresolved conflict behaviour.