• ZeroMQ isn't interested in packaging your data. Bring your own serialization format.
• Frames are the length of data followed by the data.
• More than one frame can be packed in to a message; this is typically used for routing.

Sockets

• Request-reply (REP) socket: SEND a request and wait to RECV the answer.
• Publish-subscribe (SUB) socket: SUB to a number of topics; the server PUBs messages to one or more topics.
• Push-pull socket: PUSH messages to one or more PULL workers or have them all PUSH back to a single PULL worker. Basically, this is the fork-join socket type.
• XPUB and XSUB: used when sticking a proxy or message broker in between a pub-sub relationship. PUB -> XSUB -> proxy -> XPUB -> SUB.
• DEALER and ROUTER: a dealer connects to multiple request sockets, a router connects to multiple reply sockets. It is basically xsub/xpub but for request-reply instead.