CCNA (200-301) - 1.5 - Compare TCP to UDP (TCP vs. UDP)

TCP I like to think of as certified mail. The data is sent, and you receive a receipt confirming that it was received.

• Connection Oriented Protocol
• TCP requires a three way handshake to establish a conversation with the receiving end. 
• The Three Way Handshake Looks like This.
1. The Sender will send a SYN (Sync)
2. The Receiver will respond with a SYN-ACK (Sync-Acknowledgement)
3. The Sender will respond with an ACK (Acknowledgement) 
• Now the connection will be established and traffic can be sent.
• Error Checking
• A checksum field is included within each segment of data which is used to validate the data. 
• Error Recovery
• The receiver will request you resend data  if the data received fails a checksum and is determined to be corrupt.
• Data Sequencing
• The packets of the transmission are numbered in order
• The receiver will request you resend data if its not received
• The receiver knows how to put the data back together thanks to the sequencing
• Because of the above features delivery is guaranteed.
• Also because of the above features it is slower than UDP.
• Best used browsing websites, Emails, downloading files; really anything where a single corrupt packet will make a file unusable, like a word document.

UDP is more like traditional mail where you send it and hope it arrives.

• Connectionless Protocol
• UDP doesn't have a handshake, and does not require an established connection
• Error Checking
• A checksum field is used here as well
• If the checksum fails then UDP will simply discard the packet
• Data Sequencing
• There is no sequencing used. The application layer will have to be the brains if sequencing is required.
• Delivery of all data is not guaranteed
• Because so much of the "fixing" of the data is skipped, UDP is much faster than TCP.
• Best used for DNS, DHCP, Voice and Video.