Mediated transfer of funds between three parties
Your protocol makes sense, but i would modify it as follows


the 1btc sent to trent should also be mutlisig with Alice's signature as the 2nd one, so that if Trent fails to do what he promised he gets no commission. ((the 1btc will stay in limbo, unless Alice and Trent can somehow work this out)
The Tx2 should also be multisig and Carol's signature should be added, that way Trent can't run with the money.