Chapter 6-Fundamentals Flashcards
Computer networks
Telecommunications
The electronic transmission of signals for communications, by such means as telephone, radio, and television
Telecommunications impacts businesses greatly because it lessens the barriers of time and distance
Sending unit
A sending unit such as a person, a computer system, a terminal, or another device, sends the message signal to a telecommunications device
Telecommunications medium
A telecommunications medium is any material substance that carries an electronic signal to support communications between a sending and receiving device
Synchronous communication
the receiver gets the message almost instantaneously, when it is sent. Examples are a phone call, and instant messaging services such as MSN
Asynchronous communication
there is a measurable delay between the sending and receiving of the message, sometimes hours or even days. Examples are sending a letter through the post office and e-mail
Channel bandwidth
The rate at which data is exchanged, usually measured in bits per second (bps) e.g. Kbps, Mbps, Gbps
The broader the bandwidth, the more info can be exchanged
Broadband communications
Narrowband communications
Transmission media
can be divided into two broad categories: guided transmission media, in which communications signals are guided along a solid medium; and wireless, in which the communications signal is broadcast over airwaves as a form of electromagnetic radiation
Twisted-pair wire
contains two or more twisted pairs of wire, usually copper .Proper twisting of the wire keeps the signal from ‘bleeding’ into the next pair and creating electrical interference. Because the twisted pair wires are insulated, they can be placed close together and packaged in one group. Hundreds of wire pairs can be grouped into one large wire cable.
Coaxial cable
falls in the middle of the guided transmission media in terms of cost and performance. The cable itself is more expensive than twisted pair wire but less so than fibre optic cable. Coaxial cable offers cleaner and crisper data transmission (less noise) than twisted pair wire. It also offers a higher data transmission rate.
Fiber optic cable
Consisting of many extremely thin strands of glass or plastic bound together in a sheathing (a jacket), transmits signals with light beams . These high intensity light beams are generated by lasers and are conducted along the transparent fibers. These fibers have a thin coating, called cladding, which effectively works like a mirror, preventing the light from leaking out of the fiber. The much smaller diameter of fiber optic cable makes it ideal when there is not room for bulky copper wires – for example, in crowded conduits, which can be pipes or spaces carrying both electrical and communications wires. Because fiber optic cables are immune to electrical interference, they can transmit signals over longer distances with fewer expensive repeaters to amplify or rebroadcast the data
Broadband over power lines
Data transmitted over standard high-voltage power lines
can provide internet service to rural areas
Can be expensive
Wireless Transmissions
Microwave: Terrestrial (Earthbound) and satellite
3G and 4G wireless communication
WiFi
Near Field Communication
Bluetooth
Ultra wideband
Infrared
Microwave
microwave stations are placed in a series – one station receives a signal, amplifies it and retransmits it to the next microwave transmission tower
Satellite
The satellite receives the signal from the Earth station, amplifies the relatively weak signal and then rebroadcasts it at a different frequency. The advantage of satellite communications is that it can receive and broadcast over large geographic regions.
Mobile transmissions
4G broadband mobile wireless delivered more advanced versions of enhanced multimedia, smooth streaming video, universal access and portability across all types of devices
5G, is bringing higher data transmission rates, lower power consumption, higher connection reliability with fewer dropped calls, increased geographic coverage and lower infrastructure costs
WIFI
Wifi is a medium range wireless option typically operating up to about 30 metres around a single building
The area covered by one or more interconnected wireless access points is called a ‘hot spot’
NFC
a very shortrange wireless connectivity technology designed for consumer electronics, smartphones and credit cards
Bluetooth
a wireless communications specification that describes how smartphones, computers, printers and other electronic devices can be interconnected over distances of a few metres at a rate of about 2 Mbps
Ultra wideband
a wireless technology for transmitting large amounts of digital data over a wide spectrum of frequency bands with very low power for a short distance
Infrared
infrared light isused in wired and wireless operations. Remote controls use near-infrared light, transmitted with light-emitting diodes (LEDs), to send focused signals to home-entertainment devices, such as televisions
Telecommunications hardware
1.Modems
Allowing analogue and digital devices to commmunicate
2.Multiplexer
encodes data from two or more data sources onto a single communications channel
3.Front end processor
special purpose computers that manage communications to and from a computer system serving hundreds or even thousands of users
4.Private branch exchange (PBX)
telephone switching exchange that serves a single organization
It enables users to share a certain number of outside lines (trunk lines) to make telephone calls to people outside the organization
Modulation/Demodulation
Translating data from digital to analogue is called ‘modulation’, and translating data from analogue to digital is called ‘demodulation’. Thus, these devices are modulation/demodulation devices or modems
Multiplexer
A multiplexer is a device that encodes data from two or more data sources onto a single communications channel, thus reducing the number of communications channels needed and therefore lowering telecommunications costs
Telecommunications hardware
1.Switches
uses the physical device address in each incoming message on the network to determine to which output port it should forward the message to reach another device on the same network
2.Bridges
connects one local area network (LAN) to another LAN that uses the same telecommunications protocol
3.Routers
forwards data packets across two or more distinct networks towards their destinations through a process known as ‘routing’
4.Gateways
is a network device that serves as an entrance to another network, converting comms from one protocol to another
