TCP/IP

The standard protocols for the Internet are TCP and IP.
TCP stands for Transmission Control Protocol;
 IP stands for Internet Protocol.
IP:
Operates at the Network layer of the OSI stack.
Its basic unit is the datagram.
A datagram contains the source and destination
addresses of the machines that need to pass data.
Inside the payload of a datagram is the data placed
in to it by higher-level protocols, such as TCP or UDP.
TCP:
Operates at the Service level of the OSI stack.
Its job is to reliably get data to and from applications.
It must have sequential numbers on each packet,
checksums to test for corrupted packets, and timers
to detect lost packets.
UDP:
A connectionless protocol that operates at the same layer
as TCP.  It's benefits are: 1) It doesn't have the overhead
of a connection-based protocol, and 2) The code to implement
UDP is very small, compared to TCP, so it can be implemented
in firmware put onto a network card.
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