N - O
A networked device that has a single purpose or role. For example, a server can perform multiple tasks at the same time. It could be both a proxy server and a web server. However the purpose of a network appliance is to focus or specialize in one role only.
The infrastructure or physical layout of a computer network. This includes the network hardware (such as hubs, switches, and routers) as well as the type of cabling used (coaxial, Ethernet, or fiber optic) and the protocols used (TCP/IP, IPX/SPX, etc.)
Network Operating System (NOS)
An operating system that is specifically designed to run a network. This is usually the operating system that is installed on a server(s) and helps manage the hosts of the network. Antivirus software suites are often available in a network version that would work in tandem with the NOS to distribute new virus definitions and software updates to all of the host computers on the network.
As the name implies, a network tap is a device that “taps" into a network. Its purpose is to record network traffic for a other network devices such as LAN analyzers or routers.
OSI (Open Systems Interconnection) Model
The primary communications standard for how information should be transmitted over a TCP/IP network. There are seven layers to the OSI model that define how information is packaged, sent, received, unpackaged, and eventually computed. The idea is to use a universal communications process for the purpose of compatibility as new devices, protocols, and applications are designed for network use. Listed below are these seven layers:
- Layer 1: Physical Layer (hardware specifications like timing/voltage)
- Layer 2: Data Link Layer (MAC addressing and data framing)
- Layer 3: Network Layer (plans route data will take to destination)
- Layer 4: Transport Layer (oversees the data transmission)
- Layer 5: Session Layer (establishes connection with data recipient)
- Layer 6: Presentation Layer (data conversion and “unpacking")
- Layer 7: Application Layer (provides application(s) with data that can be understood and displayed to the user)
Understanding the OSI model is important for troubleshooting security issues with networked devices (hardware) and applications (software).