At the human level, some communication rules are formal and others are simply understood based on custom and practice. For devices to successfully communicate, a network protocol suite must describe precise requirements and interactions. Networking protocols define a common format and set of rules for exchanging messages between devices. Some common networking protocols are IP, HTTP, and DHCP.
The figures illustrate networking protocols that describe the following processes:
- How the message is formatted or structured, as shown in Figure 1
- The process by which networking devices share information about pathways with other networks, as shown in Figure 2
- How and when error and system messages are passed between devices, as shown in Figure 3
- The setup and termination of data transfer sessions, as shown in Figure 4
For example, IP defines how a packet of data is delivered within a network or to a remote network. The information in the IPv4 protocol is transmitted in a specific format so that the receiver can interpret it correctly. This is not much different than the protocol used to address an envelope when mailing a letter. The information must adhere to a certain format or the letter cannot be delivered to the destination by the post office.