Explain the difference between TCP and UDP

tl;dr

TCP is connection based. UDP is connection-less.

TCP (Transmission Control Protocol)

1. TCP is handshake based. a. There must be an established connection between sender and receiver before data can be sent b. 3 way handshake c. TCP is slower to connect because of this handshake
2. TCP can handle and recover from packet loss
3. TCP is more reliable than UDP
4. TCP can increase latency because it will back off if it knows the network is busy
5. TCP segments are numbered. You can reliably count on the order of packets received is correct a. You won't get a chunk of a PDF in the middle that should have been at the end

UDP (User Datagram Protocol)

1. UDP is a connection-less protocol
2. UDP is less "reliable" since it doesn't require an ack(nowledgement) of each segment
3. UDP is commonly used for applications that can handle some loss of packets. like streaming audio or video. Use UDP where it's worse if a packet arives late than if it doesn't arrive at all.
4. UDP is more concerned with getting the data to you immediately than getting it to you complete. a. e.g. A FPS game you need to know the location of the player is right now, not 2 seconds ago when you lost a packet.
5. UDP is also used in DNS queries