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OSI Model

Application - Creates data that will work its way down the OSI model and be put on the wire
Presentation - Formats the data for the application layer.
Session - manages communications between applications on nodes of the network
Transport - Legitimacy of data between hosts is maintained. Adds socket information to the data packet
Network - Adds network and routing data to frame creating a packet of data
Data link - Groups data into frames. Adds source and destination addresses to the data
Physical - The physical layer physically transmits the data across the wires, airwaves, or whatever medium chosen.

Network Hardware

Network Interface Card (NIC) - Device in a computer to allow connectivity to the network
Hub - used to connect network devices on an Ethernet network. Passive hubs simply take data from a port and pass it through the other ports. Active hubs have built in repeaters. Hybrid hubs have connections for different types of network media. Wireless access points also act as hubs
Switch - used to connect network devices on an Ethernet network. Passive hubs simply take data from a port and pass it through the other ports. Active hubs have built in repeaters. Hybrid hubs have connections for different types of network media. Wireless access points also act as hubs
Router - Used to connect multiple networks. Routers act at the network layer.
Brouter - Combination of a router and a bridge
Repeater - Repeaters are used to boost the electrical signals of the medium used to carry data to extend the distance of the networks. Repeaters operate at the physical layer
Bridge - Like a repeater a bridge is used to connect a network. Unlike a repeater a bridge only passes the data to the other side of the network if that is the data's destination. Bridges operate at the data link layer
Multistation Access Unit (MAU) - Acts as a hub for token ring networks.
Gateway - Interconnects different network environments. Gateways operate at all layers of the OSI model.
Modem - Converts digital information to an analog format for transmission over telephone lines.
ISDN Modem - older technology used to transmit data over telephone lines. Requires special equipment.
Proxy - Proxy servers pass data between clients on a LAN and internet hosts. They process requests for information and pass the data to the requesting client, at the same time the proxy is caching that data for other users. This conserves bandwidth to the internet.
CSU/DSU (Channel Service Unit/Data Service Unit) - connects a leased line from a service provider to the LANs routing equipment. This device is usually considered the point of demarcation. The point of demarcation is where on an internet connection the connectivity responsibility switches from the service provider to the client.
Firewall - Firewalls protect networks by determining which data may pass through it and which data to deny access
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