mcmc

There is some difference:

Marking to market is periodically revaluing an OTC contract (swap, forward, etc.) to fair value (current price) and making the necessary payments, in effect resetting the contract to 0 value. Has to do with accounting concepts but its also a type of netting.

Payment netting is just that - you actually pay only the net amount without exchanging the full amounts between two parties. Actually the settlement risk is reduced here.