[1] In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. Within an IP network, UDP doesn't need prior communication to set up communication channels or data paths. It also runs on Internet protocol.
UDP vs. TCP (transmission control protocol) [2] TCP is a connection-based and reliable, but slow transport layer protocol. Connection-based refers to that it uses 3-way handshake to establish connection for safeties before data is sent between clients and servers.
[2] It's reliable because TCP ensures all datas arrive in order/sequences without duplicates or minimum errors. If errors do occur, they're resent via checksums. This is best used for applications/sites that requires accuracies, thus being used by websites, file transfers, remote access (SSH), or emails.
[2] Whereas, UDP is connectioneless and doesn't do any handshakes prior data is sent between the client and server, making it fast but less secure. It's less reliable as it doesn't resend data in case of failures. Thus it's used in applications requiring speed, such as gaming, live calls, and video conferencing. UDP being orderless doesn't necessarily mean that orders don't matter in videos.
Videos often seen glitch, where pixels are out of places as things move onscreen and this is fine because it's better to keep the video going than wait for missing frames. TCP header is also 20 bytes, being larger than UDP header, that's 8-bytes. It offers no flow control unlike TCP.
[2.2]
[2.2] A UDP header is only 8-bits (1-byte) in size and has 4 parts: source port, destination port, length, and checksum, all being 16-bits (or 2-bytes) in sizes.
The source port identifies the destination of the receiving application's port number.
The destination port specifies the port number of the receiving application.
The length field indicates the UDP datagraph's total length, including the header and data.
The checksum field checks the data's integrity and checks errors.
A UDP header being only 8-byte in size makes it more lightweight than TCP's 20-byte header, thus contributing to its speed and efficiency compared to TCP.
[2.2]
Connectionless:
Fast but less reliable:
No gurrantee delivery:
No packet ordering:
Basic error-checking only:
[2.2]