Technology Guide 4 Notes.doc

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Department
Administrative Studies
Course
ADMS 2511
Professor
Cristobal Sanchez- Rodriguez
Semester
Fall

Description
Technology Guide 4 Notes The Telecommunications System - a telecommunications system: consist of hardware and software that transmit information from one location to another - these systems can transmit text, data, graphics, voice, documents or full motion video information - they transmit this information with two basic types of signals: analog and digital - Analog signals: are continuous waves that transmit information by altering the characteristics of the waves - analog signals have two parameters: amplitude and frequency - for example, voice and all sounds are all analog, travelling to human ears in the form of waves - the greater the height (or amplitude) of the waves, the louder the sound, the more closely packed the waves, the higher the frequency or pitch - Digital Signals: discrete pulses that are either on or off, representing a series of bits (0s and 1s) - this quality allows them to convey information in a binary form that can be clearly interpreted by computers - major components of telecommunications system include the following devices, communications processors, and communications channels and media - devices include all types of hardware, from smart phones to supercomputers Communications Processors - are hardware devices that support data transmission and reception across a telecommunications system - these devices include, modems, multiplexers and front end processors Modems - the function of modems is to convert digital signals to analog signals (a process called modulation) and analog signals to digital signals (a process called demodulation) - modems are used in pairs - modem at the sending end converts a computers digital information into analog signals for transmission over analog lines - at the receiving end, another modem converts the analog signal back into digital signals for the receiving computer - three types of modems: dial up modem, DSL modems and cable modems - the US public telephone system was originally designed as an analog network to carry voice signals or sounds in an analog wave format - in order for this type of circuit city to carry digital information, that information must be converted into an analog wave pattern by a dial up modem usually have a transmission speeds of up to 56 Kbps - Cable modems: modems that operate over coaxial cable (example cable TV) - offer high speed access to the internet or corporate intranets - cable modems use a shared line, therefore when large numbers of users access the same modem, they can slow down the access speed - DSL (digital subscriber line) modems operate on the same lines as voice telephones and dial up modems, but DSL signals do not interfere with voice service - also DSL modems always maintain a connection, so an internet connection is immediately available Multiplexcer - is an electronic device that allows a single communications channel to carry data transmission simultaneously from many sources - multiplexing can be accomplished by dividing a high speed channel into multiple channels of slower speeds or by assigning each transmission source a very small amount of time for using the high speed channel - multiplexers lower communication costs by allowing devices to share communications channels - therefore makes more efficient use of these channels by merging the transmissions of several computers (for example personal computers) at one end of the channel, while a similar unit separates the individual transmissions at the receiving end (for example a mainframe) Front End Processor - with most mainframes and minicomputers, the central processing unit (CPU) must communicate with multiple computers at the same time - routine communication takss can absorb a large proportion of the CPU;s processing time, keading to degraded performance on more important jobs - in order not to waste valuable CPU time, many computer systems have a small secondary computer dedicated solely to communication this is known as a front – end processor, this specialized computer manages all routing communications with peripheral devices Communications Media And Channels - for data to be communicated from one location to another, some form of pathway or medium must be used these pathways are called communications channels - these are divided into two types of media: cable (twisted pair wire, coaxial cable and fibre optic cable) and broadcast (microwave, satellite, radio and infrared) - Cable or wireline media: use physical wires or cables to transmit data and information - twisted pair wire and coaxial cable are made of copper, and fibre optic cable is made of glass - alternate is communication over broadcast or wireless media - key to mobile communications is data transmissions over electromagnetic media – the ‘airwaves’ Advantages and Disadvantages of Wireline communications channels Channel Advantage Disadvantage Twisted Pair Wire: most prevalent Inexpensive, widely available, easy to Slow (low bandwidth), subject to form of communications wiring, used work with, unobtrusive by running it interference from other electrical for almost all business telephone inside walls, floors and above ceilings sources, easily tapped by unintended wiring receivers for gaining unauthorized - consists of strands of copper wire access to data (low security) twisted in pairs Coaxial Cable: consists of insulated Higher bandwidth than twisted pair, Relatively expensive and inflexible, copper wire, can carry much more less susceptible to electromagnetic easily tapped (low to medium data than twisted pair, commonly used interference security), somewhat difficult to work to carry high speed data traffic as well with as TV signals Fibre optic cable: Very high bandwidth, relatively Difficult to work with (difficult to - consist of thousands of very thin inexpensive splice) filaments of glass fibres that transmit Difficult to tap (good security) -Attenuation, the reduction in the information via light pulses generated strength of the signal by lasers - attenuation occurs for both analog - surrounded b y cladding, a coating and digital signals that prevents the light from leaking out - to resolve these problems, of the fibre manufacturers must install equipment - are smaller and lighter than to receive the weakened or distorted traditional cable media signals, amplify them to their original - can transmit far more data, and they strength, and then send them out to the provide greater security from intended receiver interference and tapping - typically used as the backbone for a network, while twisted pair wire and coxial cable connect the backbone to individual devices on the network - an example is The Ontario Research and Innovation Optical Network (ORION) which added 1500 km of fibre optic cable to connect urban and rural communities in Ontario to its network Transmission Speed Bandwidth: refers to the range of frequencies available in any communications channel - Bandwidth is very important concept in communications because the transmission capacity of any channel is largely dependent on its bandwidth - in general, the greater the bandwidth, the greater the channel capacity - Narrowband: channels typically provide low speed transmission speeds up to 64 Kbps but can now reach speeds of up to 2 Mbps - Broadband: channels provide high speed transmission rates ranging from 256 Kbps up to several terabits per second The speeds of particular communications channels are as follows: - twisted pair wire: up to 100 Mbps (megabits or one million bits per second) - Microwave: up to 200 Mbps - Satellite: up to 200 Mbps - Coaxial Cable: up to 200 Mbps - Fibre optic cable: over 25 tbps (terabits or one trillion bits per second) Transmission Technologies - number of telecommunications technologies enable users to transmit high volume data quickly and accurately over any type of network 1. Integrated services digital network - ISDN: an older international telephone standard for network access that uses existing telephone lines and allows users to transfer voice, video, image, and data simultaneously 2. Digital Subscriber Line - DSL provides high speed, digital data transmission from homes and businesses over existing telephone lines - since the existing lines are analog and the transmission is digital you need DSL modems 3. Asynchronous Transfer Mode - ATM networks: allow for almost unlimited bandwidth on demand - offers several advantages, since makes possible large increases in bandwidth - provides support for data, video and voice transmissions on a single communications line - currently requires fibre optic cable but can transmit up to 2.5 gigabytes per second - ATM is more expensive then ISDN and DSL 4. Synchronous Optical Network - SONET: an interface standard for transporting digital signals over fibre optic lines that allows users to integrate transmissions from multiple vendors - SONET defines optical line rates known as optical carrier (OC) signals - base rate is 51.84 Mbps (OC -1), and higher rates are direct multiples of the base rate - for example OC- 3 runs at 155.52 Mbps, or three times the rate of OC-1 5. T-Carrier System - digital transmission system that defines circuits that operate at different rates, all of which are multiples of the basic 64 Kbps used to transport a single voice call - these circuits include T1 (1.544 Mbps, equivalent to 24 channels); T2 (6.312 Mbps, equivalent to 96 channels); T3( 44.736 Mbps, equivalent to 672 channels) and T4 (274.176 Mbps, equivalent to 4032 channels) Types of Networks - a computer network is a system that connects computers via communications media so that data can be transmitted among them - essential to modern organization since networked computer systems enable orgniazations to be more flexible so they can adapt to rapidly changing business conditions - second, networks enable companies to share hardware, computer applications and data across the organization and among organizations - third, networks make it possible for geographically dispersed employees and work groups to share documents, ideas and creative insights, this sharing encourages, teamwork, innovation, and more efficient and effective interactions - lastly, networks are a critical link between businesses and their customers - types of networks include (from smallest to largest), personal area networks (PANs), local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs) and the internet Local Area Networks - LAN connects two or more devices in a limited geographical region, usually within the same building, so that every device on the network can communicate with every other device - for a LAN with 4 computers and a printer connect via a switch, special purpose comuter that allows the devices in LAN to communicate directly with each other - every device in a LAN has a network interface card (NIC) that allows the device to physically connect the the LAN’s communications medium - this medium is typically unshielded twisted pair wire (UTP) - many LAN’s have file server or network server - File Servers: often powerful microcomputers with large, fast access hard drives - the server typically contains various software and data for the network and houses the LAN’s network operating system which manages the server and routes and manages communications on the network - the network gateway connects the LAN to external networks, either public or corporate, so it can exchange information with them - A Gateway: communications processor that connects dissimilar networks by translating from one set of protocols to another - a communications processor that connects two networks of the same type is called a Bridge - Router: communications processor that routes messages through several connected LAN’s or across a wide area network such as the internet - since LAN is restricted to a small area, the nodes can be connected either through cables or via wireless technologies - wireless local area network (WLAN’s) provide LAN connectivity over short distances typically less than 150 metres Wide Area Networks - when businesses have to transmit and receive data beyond the confines of the LAN, they use wide area networks - WAN’s: networks that cover large geographic areas, connect multiple LAN’s - generally provided by common carriers such as telephone companies and the international networks of global communications services providers - WANs have large capacity and they typically combine multiple channels (example, fibre optic cables, microwaves, and satellite) - internet example of WAN - important type of WAN is the value added network (VAN) - these are private, data only networks managed by outside third parties that provide telecommunication and computing services to multiple organizations - many companies use VAN’s to avoid the expenses of creating and managing their own networks Enterprise Networking - organizations have multiple LANs and multiple WANs which are interconnected to form an enterprise network - diagram page 408 example of model of enterprise computing - Corporate Backbone Networks: high speed central networks to which multiple smaller networks (such as LANs and smaller WANs) connect - the LANs are called embedded LANs because they connect to the backbone WAN Network Fundamentals - network protocols and types of network processing, these topics describe how networks actually transmit and process data and information over the basic telecommunications system Network Protocols - computing devices that are connected to the network access and share the network to transmit and receive data - these components are often referred to as ‘nodes’ of the network - they work together by adhering to a common set of rules that enable s them to communicate with one another - this set of rules and procedures that govern transmission across a network is a Protocol Ethernet - common LAN protocol - most large corporations use gigabit Ethernet in which the network provides data transmission speeds of one billion bits per second - however, 10 gigabit Ethernet is becoming the standard (10 billion bits per second) Transmission Control Protocol / Internet Protocol - Transmission Control Protocol / Internet Protocol (TCP/IP): is the protocol of the internet TCP/IP uses a suite of protocols, the main ones being the Transmission Control Protocol (TCP) and the Internet Protocol (IP) - the TCP performs three basic functions: (
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