TCP vs UDP
Both TCP :rfc:`793` and UDP :rfc:`768` provide data transfer between processes through ports. Those process ports can be on the same computer or separate computers connected by a network. TCP provides the following: reliability, flow control, and connections. (UDP does not) This means TCP will be sending more header data, more packets between ports and doing more processing to provide its capabilities. UDP requires less header data in the individual packets and requires less packets on the network to do its work. However, because UDP does not guarantee reliability, UDP allows for packets not getting communicated end to end after leaving the sender. The choice of protocols to use is often based on whether the risk of losing packets in real-time without immediate alerting is acceptable. In some cases UDP may be acceptable, such as video or audio streaming where programs can interpolate over missing packets. However, TCP will be required because of its guarantees in systems that support banking or healthcare.
An example of the difference between the two protocols that will help us understand the tradeoffs is a comparison of what it takes to send the first data byte. TCP requires an initial "three way handshake" in order to begin sending data. That amounts to one initial packet sent between ports from initiator of the communication to the receiver, then another packet sent back, and then a final packet sent from the initiator to the receiver again. All that happens before sending the first byte of data. In UDP the first packet sent contains the first byte of data.
Another example of the difference between the protocols is the size of the headers of the two protocols. The TCP header is 20 bytes and the UDP header 8 bytes.
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