Data Transport

There are two basic types of communication

• Streams (TCP): Computers establish a connection with each other and read/write data in a continuous stream of bytes---like a file. This is the most common.
• Datagrams (UDP): Computers send discrete packets (or messages) to each other. Each packet contains a collection of bytes, but each packet is separate and self-contained.

The socket type

• STREAM (TCP)
• DATAGRAM (UDP)
• RAW (Used for raw access to the wire)

The data transmission determines your layer 4 protocol.

If your message is "fire and forget", you do not need error handling, or the whole communication is a small request with a small response (e.g. DNS lookup), you will use UDP.

If you are transferring a large amount of data, you require error handling and correction, or you don't know what to choose, use TCP.

In python, the socket module defines the constants as SOCK_DGRAM and SOCK_STREAM respectively. They handle layers 1-4 for you. If you need to control lower the layers, you will use RAW sockets.