Let's say Alice and Bob want a bidirectional lightning channel with common 2-2 multisig address C.
Alice is the only one putting funds in, say 100BTC. They agree on nLock of these funds to be 30 days (channel will be open for 30 days). This requires Bob to sign and give Alice a refund transaction with nLock 30.
Now during next 15 days Alice pays Bob 10 BTC three times, each time giving him a signed transaction with respective outputs 90Alice-10Bob (on day 5) 80Alice-20Bob (on day 10) and 70Alice-30Bob (on day 15).
If Bob wants to close the channel he needs to sign 70Alice-30Bob transaction and broadcast it. And these 3 transactions don't need to have nLock. (unidirectional channel)
But instead Bob wants to pay Alice 10 BTC (on day 20). So he makes and signs a new transaction 80Alice-20Bob and gives it to Alice. They leave the channel open for more transactions.
Which of the above transactions need to have nLock and with what value?