TCP vs UDP

	TCP	UDP
Acronym for:	Transmission Control Protocol	User Datagram Protocol or Universal Datagram Protocol
Function:	As a message makes its way across the internet from one computer to another. This is connection based.	UDP is also a protocol used in message transport or transfer. This is not connection based which means that one program can send a load of packets to another and that would be the end of the relationship.
Usage:	TCP is used in case of non-time critical applications.	UDP is used for games or applications that require fast transmission of data. UDP's stateless nature is also useful for servers that answer small queries from huge numbers of clients.
Examples:	HTTP, HTTPs, FTP, SMTP Telnet etc...	DNS, DHCP, TFTP, SNMP, RIP, VOIP etc...
Ordering of data packets:	TCP rearranges data packets in the order specified.	UDP has no inherent order as all packets are independent of each other. If ordering is required, it has to be managed by the application layer.
Speed of transfer:	The speed for TCP is slower than UDP.	UDP is faster because there is no error-checking for packets.
Reliability:	There is absolute guarantee that the data transferred remains intact and arrives in the same order in which it was sent.	There is no guarantee that the messages or packets sent would reach at all.
Header Size:	TCP header size is 20 bytes	UDP Header size is 8 bytes.
Common Header Fields:	Source port, Destination port, Check Sum	Source port, Destination port, Check Sum
Streaming of data:	Data is read as a byte stream, no distinguishing indications are transmitted to signal message (segment) boundaries.	Packets are sent individually and are checked for integrity only if they arrive. Packets have definite boundaries which are honored upon receipt, meaning a read operation at the receiver socket will yield an entire message as it was originally sent.
Weight:	TCP requires three packets to set up a socket connection, before any user data can be sent. TCP handles reliability and congestion control.	UDP is lightweight. There is no ordering of messages, no tracking connections, etc. It is a small transport layer designed on top of IP.
Data Flow Control:	TCP does Flow Control. TCP requires three packets to set up a socket connection, before any user data can be sent. TCP handles reliability and congestion control.	UDP does not have an option for flow control
Error Checking:	TCP does error checking	UDP does error checking, but no recovery options.
Fields:	1. Sequence Number, 2. AcK number, 3. Data offset, 4. Reserved, 5. Control bit, 6. Window, 7. Urgent Pointer 8. Options, 9. Padding, 10. Check Sum, 11. Source port, 12. Destination port	1. Length, 2. Source port, 3. Destination port, 4. Check Sum
Acknowledgement:	Acknowledgement segments	No Acknowledgment