Mechanism established for secondary market and underlying price: TRUM field 29 - Procedure applicable, requires that the TSO is obliged to determine which mechanism is used in the Secondary market.
In this respect TSOs that use FCFS would need to fill in TRUM field 34 - Price paid to TSO (Underlying Price).
Do you mean that through TRUM field 34 information about the price that Shipper 1 pays to the TSO in first instance for capacity booking (before the transaction on secondary market takes place) shall be submitted to ARIS? Please clarify.
TRUM field 29 is only applicable in case of secondary market allocations. It is not the responsibility of the TSO to determine the mechanism (field 29), but of the involved market participants.
The same applies for field 34. The underlying price is the price that Shipper 1 pays to the TSO in first instance for capacity booking (before the transaction on secondary market takes place).