Does filecoin share the same storage network with ipfs?

I know filecoin uses ipfs as decentralized storage, but I am confused of something.
There are two understandings below, which one is right?

  1. Filecoin only uses ipfs protocol, and is a seperated storage network.
    If this, how does filecoin incentivize users to use ipfs? It would incentivize uses migrate from ipfs to filecoin.
  2. Filecoin shares the same storage network with ipfs.
    Filecoin is only an application of ipfs, only an incentive layer. If a file was added to ipfs, it could be retrieved from filecoin, and vice vesa. If this, how is it done? There exists storage and retrieve fee in filecoin while not in ipfs.