What is a message boundary?

Question

What is \"message bonudaries\" in the following context?

One difference between TCP and UDP is that UDP preserves message boundarie

Answer 1

No, message boundaries have nothing to do with destinations or ports. A "message boundary" is the separation between two messages being sent over a protocol. UDP preserves message boundaries. If you send "FOO" and then "BAR" over UDP, the other end will receive two datagrams, one containing "FOO" and the other containing "BAR".

If you send "FOO" and then "BAR" over TCP, no message boundary is preserved. The other end might get "FOO" and then "BAR". Or it might get "FOOBAR". Or it might get "F" and then "OOB" and then "AR". TCP does not make any attempt to preserve application message boundaries -- it's just a stream of bytes in each direction.