Bitcoind

External (p2p network):

• discovers and connects to other nodes
• send and receive messages to and from other nodes

Internal:

• exposes RPC to pool software and to mAPI
• optional REST Interface can be enabled

Pool Software

External (stratum protocol):

• exposed API for ASIC Miners to connect and start mining block headers
• send jobs to ASIC Miners
• receive valid shares or valid block headers

Internal (MinerID):

• request coinbase document from MinerID in order to include it in coinbase transaction
• receive signed coinbase document (or coinbase2) from MinerID

mAPI

External (mAPI public interface):

• expose mAPI calls to the public to advertise fee quote as well as receive transactions
• accept callback registrations for event notifications
• respond with fee quote and transaction responses (and Merkle Proofs)

Internal (Bitcoind RPC):

• connect to Bitcoind RPC to submit transactions
• receive transaction response (eg. txid)
• provide event notifications for double spends and Merkle Proofs.