TCP vs UDP

TCP and UDP are communication protoclos however there are significant differences between these protocols:

TCP (Transmission Control Protocol)

a. Reliable - when you send a message along a TCP socket, you know it will get there unless the connection fails completely. If it gets lost along the way, the server will re-request the lost part. This means complete integrity, things don't get corrupted.

b. Ordered - if you send two messages along a connection, one after the other, you know the first message will get there first. You don't have to worry about data arriving in the wrong order.

c. Heavyweight - when the low level parts of the TCP "stream" arrive in the wrong order, resend requests have to be sent, and all the out of sequence parts have to be put back together, so requires a bit of work to piece together.

UDP (User Datagram Protocol). 

a. Unreliable - When you send a message, you don't know if it'll get there, it could get lost on the way.

b. Not ordered - If you send two messages out, you don't know what order they'll arrive in.

c. Lightweight - No ordering of messages, no tracking connections, etc. It's just fire and forget! This means it's a lot quicker, and the network card / OS have to do very little work to translate the data back from the packets.