The SANE network protocol is a client/server-style remote procedure call (RPC) protocol. This means that all activity is initiated by the client side (the network backend)--a server is restricted to answering requests sent by the client.
The data transferred from the client to the server is comprised of the RPC code (as a SANE_WORD), followed by arguments defined in the request column below. The format of the server's answer is given in the reply column.