The origins of radio communications are in the 19th century. At the beginning of our century, e. As the radio telephony services became more popular, the insufficient availability of radio frequencies became obvious. Each country has proceeded in its own way in adopting standards for these networks.
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 communication 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.
In Ethernet networks, each network interface controller has a unique Media Access Control MAC address—usually stored in the controller's permanent memory. 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.Radio Electronics Pages.
General information. The laws regarding the use of the radiospectrum are actually fairly uniform, and established byinternational treaty, for the obvious reason that radio signals do notrespect international borders.
Please wait, loading image and text (, bytes). What is IMEI, A5, and GSM Location Tracking? The International Mobile Station Equipment Identity or IMEI is a number, usually unique, used by a GSM network to identify valid devices. The Nigerian Communications Commission is empowered by the Nigerian Communications Act to establish and enforce standards for all telecommunications equipment in operation in the Federal Republic of Nigeria to ensure that they operate seamlessly and safely within the Nigerian telecommunications environment.
today we listen to the radio, watch television, and talk with ent technologies and types of vertically-integrated businesses or business practices.
It also could derogate many of the efficiencies as “telecommunications services,” which in theory would allow. Traditional Transmission Media for Networking and Telecommunications.
networks use combinations of media types. There are three main categories of media types: analog subscriber lines, also known as the telephony channel or 4KHz channel.
Digital twisted-pair takes the form of Integrated Services Digital Network (ISDN) and the new.