I am installing a test version of WSUS 3 SP1 as a replica server in my WSUS 2
SP1 environment. When trying to get it to synchronize with the WSUS 2 SP1
master server I get an error: "The upstream server's protocol version is
incompatible with the protocol version required by the downstream server.
Generally, this occurs when the version of Update Services on the upstream
server is too old. Please upgrade..."

What protocol is it referring to? BITS? I thought BITS was a service not a
protocol.