Public mobile networks and roaming

Public coverage is not yet a railway service

Talbahn's diagnostic application should be able to use public mobile access. A Mobile Network Operator (MNO) operates a mobile network. A public network can provide a transport path without taking over all FRMCS service functions. First establish which service the application needs to reach and through which approved access.

Roaming means a subscriber uses a visited network under the relevant subscriber and operator agreements. A separate public-mobile subscription can instead be used directly in its own home network. Public-network use is therefore not automatically roaming. Changing transport paths is also not automatically a service-domain change. [S08; S13]

Three decisions for the teaching case

Talbahn first determines whether public access is permitted for this application. Second, it checks a protected, reachable path to the service platform. Third, it establishes the treatment and performance actually provided under agreed conditions. The SRS includes permission to use a Non-FRMCS Transport Domain as a configuration aspect. This is not blanket permission to use arbitrary public networks for every application. [S06, clause 19.3]

Use multiple paths deliberately

Multipath means using several transport paths through a function designed for that purpose. Depending on the method, data may be distributed, duplicated or moved to another path. Two modems alone do not implement this behaviour. Shared power, antenna sites and service platforms may also limit independence.

DB reports testing hybrid railway/public access and multipath methods in the Ore Mountains within 5G-RACOM. This is evidence from the described experimental configuration, not a blanket availability guarantee for Talbahn. [S47]

Check your understanding

A public network delivers a high data rate. A supplier claims this also secures the prioritised railway call during overload. What is missing?

Model answer

Missing evidence includes permitted access and service authorisation, the path to the service platform, agreed priority and QoS treatment, and a test under the claimed load. A high rate in one trial demonstrates neither admission under scarcity nor continuity or the appropriate service function.

What to remember

Public access, roaming, multipath and service-domain transition are distinct mechanisms. Their combination must be explained and tested for the particular service.

Your Talbahn case file

Design an approved public access and a failure trial for the diagnostic application. Do not automatically transfer its approval to voice or ETCS.