ATO over FRMCS

Automated driving has its own communication partners

Automatic Train Operation (ATO) automates defined driving tasks. In the ATO-over-ETCS context considered here, ETCS retains its train-protection and supervision responsibilities. FRMCS supplies communication; it does not itself calculate the driving profile or permitted train movement.

ATO-OB denotes the on-board ATO part and ATO-TS the trackside part. They exchange information used for the planned journey, among other things. ATO-OB also interacts with on-board ETCS equipment and the vehicle. These relationships must not all be drawn as a single radio path. ERA lists separate specifications: SUBSET-125 for the system, SUBSET-126 for the ATO-OB/ATO-TS application interface and SUBSET-130 for ATO-OB/ETCS-OB. [S16; S51; S52]

Bound the FRMCS contribution

Open diagram at full size (SVG, new tab) G14

In the teaching case, ATO-OB exchanges data with ATO-TS through the defined FRMCS integration. The selected SRS assigns ATO to Host-to-Host addressing. The previously explained MCData communication helps us follow session and data path. ATO remains responsible for interpreting journey information. [S06, clause 6.5.2.3]

Talbahn therefore records two chains of states. The communication chain asks whether application and service are ready, whether a session exists and whether data arrives. The ATO chain asks whether the information is appropriate and usable for the current journey. A packet may arrive on time but belong to the wrong journey. Conversely, a transport problem may prevent the application from receiving necessary information.

Interruption from the application's perspective

Talbahn specifies which messages the trial expects and how freshness is assessed. It distinguishes absent communication from invalid or stale application data. The course supplies no universal braking or continued-driving rule. Permitted reactions follow the specific application, safety and operating basis.

For a network transition, Talbahn checks both continuation or recovery of the data service and resumption of the application exchange. Successful re-establishment without appropriate application states is not complete recovery. “ATO always needs FRMCS” would also be too broad: this lesson explicitly examines the selected ATO integration over FRMCS.

Check your understanding

After a connection change, FRMCS reports “session active” again. Is this sufficient to claim that ATO is fully operational?

Model answer

No. Correct partners, current journey association and usable application information also require evidence. On-board cooperation between ATO, ETCS and the vehicle remains a separate test subject. Communication readiness is a prerequisite for this exchange, not complete functional approval.

What to remember

ATO has its own application relationships. Its FRMCS communication must be explained separately from ETCS communication and internal vehicle interfaces.

Your Talbahn case file

Alongside the ETCS case, add a separate ATO case with partners, data purpose and two evidence categories: communication function and application processing.