Network Protocols and Security
Network protocols are formal standards and policies which define rules and conventions for the communication between devices over a network. By the end of the 20th century, protocol development started to be driven by the awareness of network security increasing importance.

Network Models and Layers

TCP/IP and ISO OSI are hierarchical models to define how network devices and their applications should follow protocols in order to communicate with each other.
The Transmission Control Protocol/Internet Protocol (TCP/IP) Model was created by US Department of Defense (DOD) and the Open Systems Interconnect (OSI) Model was created by the International Standards Organization (ISO) in 1983.
The two models are different in several respects, but both partition a communication system into abstraction layers.

OSI Model

The table below displays the ISO OSI model layering and lists the most important network protocols developed from about 1968 to 2000.
Network traffic on any layer can be controlled by firewalls.

Layer Function Protocols
7. Application Layer High-level interface (i.e. resource sharing, remote file access,virtual terminals...) Telnet, Gopher, SMTP, POP, IMAP, FTP, SSH, HTTP(S)
6. Presentation Layer Translation of data between a networking service and an application (including Asymmetric/Symmetric encryption services) HTML, CSS
5. Session Layer Manages connection terms of a session SSL
4. Transport Layer Reliable transmission between points on a network TCP, UDP
3. Network Layer Data addressing and delivery between networks (including Routing) IP
2. Data Link Layer Error detection and packet framing across a physical network (including Packet Switching) IEEE_802.11
1. Physical Layer Network Hardware, Transmission and reception of raw bit streams over a physical medium Ethernet

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