History[ edit ] Midcontinent Media was founded in Minneapolis, Minnesota in as the Welworth Theater Company, an operator of movie theaters. The company remained in that business until the s, when it sold its theaters to various chains, including Carmike. Midcontinent purchased several other radio and television stations, but began exiting broadcasting in the s with KELO-TV and its satellites sold off to Young Broadcastingcurrently owned by Media Generaland later Nexstarselling off the last of their radio holdings in Midco diversified and extended its reach into other areas of the Upper Midwestproviding telephone and cable TV in rural parts of its service area, starting in the s.
Terrestrial microwaves are in the low gigahertz range, which limits all communications to line-of-sight. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals. Cellular and PCS systems use several radio communications technologies.
The systems divide the region covered into multiple geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area. Wireless LANs use spread spectrum technology to enable Network and communications between multiple devices in a limited area.
Free-space optical communication uses visible or invisible light for communications. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices. Exotic technologies[ edit ] There have been various attempts at transporting data over exotic media: It was implemented in real life in Node networking Apart from any physical transmission media there may be, networks comprise additional basic system building blocks, such as network interface controllers NICsrepeatershubsbridgesswitchesroutersmodemsand firewalls.
Any particular piece of equipment will frequently contain multiple building blocks and perform multiple functions. Network interfaces[ edit ] An ATM network interface in the form of an accessory card.
A lot of network interfaces are built-in. A network interface controller NIC is computer hardware that provides a computer with the ability to access the transmission media, and has the ability to process low-level network information.
For example, the NIC may have a connector for accepting a cable, or an aerial for wireless transmission and reception, and the associated circuitry.
The size of an Ethernet MAC address is six octets.
The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce.
Repeaters and hubs[ edit ] A repeater is an electronic device that receives a network signalcleans it of unnecessary noise and regenerates it.
The signal is retransmitted at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than meters.
With fiber optics, repeaters can be tens or even hundreds of kilometers apart. A repeater with multiple ports is known as an Ethernet hub. Repeaters work on the physical layer of the OSI model.
Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters that can be used in a row, e.
Hubs and repeaters in LANs have been mostly obsoleted by modern switches. Bridges[ edit ] A network bridge connects and filters traffic between two network segments at the data link layer layer 2 of the OSI model to form a single network.
Network segmentation breaks down a large, congested network into an aggregation of smaller, more efficient networks. Bridges come in three basic types: Directly connect LANs Remote bridges: Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
Switches[ edit ] A network switch is a device that forwards and filters OSI layer 2 datagrams frames between ports based on the destination MAC address in each frame. It can be thought of as a multi-port bridge.Over 2, IT teams trust us to build and manage robust infrastructure Networks, secure Cloud environments and critical Voice services.
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