TCP vs UDP

There are two types of Internet Protocol (IP) traffic. They are TCP or Transmission Control Protocol and UDP or User Datagram Protocol. TCP is connection-oriented – once a connection is established, data can be sent bidirectional. UDP is a simpler, connectionless Internet protocol. Multiple messages are sent as packets in chunks using UDP.




TCP

UDP

Acronym for
Transmission Control Protocol
User Datagram Protocol or Universal Datagram Protocol
Connection
TCP is a connection-oriented protocol.
UDP is a connectionless 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 suited for applications that require high reliability, and transmission time is relatively less critical.
UDP is suitable for applications that need a fast, efficient transmission, such as games. UDP's stateless nature is also useful for servers that answer small queries from huge numbers of clients.
Use by other protocols
HTTP, HTTPs, FTP, SMTP, Telnet
DNS, DHCP, TFTP, SNMP, RIP, VOIP.
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 the order 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 an 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, CheckSum.
Source port, Destination port, CheckSum.
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 honoured upon receipt, meaning a read operation at the receiver socket will yield an entire message as it was originally sent.
Weight
TCP is heavy-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. CheckSum, 11. Source port, 12. Destination port
1. Length, 2. Source port, 3. Destination port, 4. CheckSum
Acknowledgement
Acknowledgement segments.
No Acknowledgment.
Handshake
SYN, SYN-ACK, ACK
No handshake (connectionless protocol)


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