In practice, what is the most appropriate term for the communications transmitted over a network in higher level protocols (those above TCP/IP, for example)? Specifically, I am referring to small, binary units of data.
I have seen both "message" and "packet" referred to in various client/server libraries, but I was interested in the community's consensus.
These are definitely messages. A "packet" is a layer-3 protocol unit, such as an IP packet; and a "datagram" is a layer-1 or layer-2 unit, such as the several Ethernet datagrams that might make up the fragments of an IP packet.
So a message might be split across several packets, particularly if you're using a streaming protocol such as TCP, and a packet might be split across several datagrams.
Just my take. It probably depends on what level you are working at. When I think of the entire transmission (all headers, data, etc) I would call that a Message. A packet, especially in TCP/IP, is just a part of a message. Multiple packets are pushed across the network comprising an entire message.
I think packet refers to the chunks of data transferred on a lower layer like Ethernet and message is used for higher level information exchange.
imo they basically mean the same...
edit:
There's also another terminology called frame, which is defined in RFC 1122 as "the unit of transmission in a link layer protocol, and consists of a link-layer header followed by a packet." [wikipedia]