The original paper for payment channels only describes a 2-party payment channel, which enables two people to interact off-chain, while keeping their transactions enforceable on-chain. The problem is that this architecture, although brilliant, does not scale with the number of parties; an N-party channel with the same smart contract requires all N participants to be in consensus for any of them to be able to settle the channel and withdraw their funds. Furthermore all N participants would want to enter, and then settle, the channel at the same time, and still need to monitor the smart contract for fraudulent settlement requests from all other participants. Clearly this architecture needs some help in this regard.