Routers Distribution routers aggregate traffic from multiple access routers.

1. Routers forward data packets across computer networks. A Router checks the data packet for its destination address and protocol format details
2. When multiple routers are used in interconnected networks, the routers exchange information about destination addresses, using a dynamic routing protocol.
3. A router records a routing table listing what route should be used to forward a data packet, and through which physical interface connection. It does this using internal pre-configured addresses, called static routes.
4. The router forwards data packets between incoming and outgoing interface connections. It routes it to the correct network type using information that the packet header contains. It uses data recorded in the routing table control plane.
5. Routers may provide connectivity within enterprises, between enterprises and the Internet, and between internet service providers (ISPs) networks
6. All sizes of routers may be found inside enterprises.The most powerful routers are usually found in ISPs, academic and research facilities.
7. Access routers, including 'small office/home office' (SOHO) models, are located at customer sites such as branch offices that do not need hierarchical routing of their own
8. A core router resides within an Autonomous System as a back bone to carry traffic between edge routers.
9. Distribution routers aggregate traffic from multiple access routers, either at the same site, or to collect the data streams from multiple sites to a major enterprise location.
10. a  core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be optimized for high bandwidth

modem digital information, and alsotransmitted information.

1. A modem (modulator-demodulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information.
2. Modems are generally classified by the amount of data they can send in a given time unit, normally measured in bits per second (bit/s, or bps)
3. They can also be classified by the symbol rate measured in baud, the number of times the modem changes its signal state per second.
4. Modems grew out of the need to connect teletype machines over ordinary phone lines instead of more expensive leased lines which had previously been used for current loop-based teleprinters and automated telegraphs.
5. The next major advance in modems was the Smart modem, introduced in 1981 by Hayes Communications. The Smart modem was an otherwise standard 103A 300-bit/s modem,
6. A Win modem or soft modem is a stripped-down modem that replaces tasks traditionally handled in hardware with software.
7. A standard modem of today contains two functional parts: an analog section for generating the signals and operating the phone, and a digital section for setup and control.
8. The standard digital transmission in modern networks is 64 knit/s but some networks use a part of the bandwidth for remote office signaling
9. Wireless modems come in a variety of types, bandwidths, and speeds. Wireless modems are often referred to as transparent or smart.
10. Smart modems come with a media access controller inside which prevents random data from colliding and resend data that is not correctly received.
11. Voice modems are regular modems that are capable of recording or playing audio over the telephone line. They are used for telephony applications. See Voice modem command set for more details on voice modems.

network interface controller is a computer hardware referred to as a network adapter.

1. A network interface controller is a computer hardware component that connects a computer to a computer network. The controller may also be referred to as a network adapter, or a LAN adapter
2. The NIC allows computers to communicate over a computer network. It is both an OSI layer 1 (physical layer) and layer 2 (data link layer) device
3. Every Ethernet network card has a unique 48-bit serial number called a MAC address, which is stored in ROM carried on the card.
4. The card implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet or token ring
5. A network card typically has a RJ45, BNC, or AUI socket where the network cable is connected, and a few LEDs to inform the user of whether the network is active, and whether or not there is data being transmitted on it
6. The 'controller' may take the form of a network card that is installed inside a computer, or it may refer to an embedded component as part of a computer motherboard, a router, expansion card, printer interface or a USB device.
7. network cards used to be expansion cards that plug into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard.
8. It allows users to connect to each other either by using cables or wirelessly.
9. Programmed I/O is where the microprocessor alerts the designated peripheral by applying its address to the system's address bus.
10. Network cards are typically available in 10/100/1000 Mbit/s varieties. This means they can support a notional maximum transfer rate of 10, 100 or 1000 Megabits per second.