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
Computer network
A computer network consists of communications media, devices, and software needed to connect two or more computer systems or devices
The computers and devices on the networks are called network nodes
Nodes can share data, information, and processing jobs
Personal area network(PAN)
A network that supports the interconnection of information technology within a range of ten metres e.g. at home (e.g. Bluetooth is the industry standard for PANs)
Local area network
A network that connects computer systems and devices within a small area, such as an office, home or several floors in a building, is a LAN
Metropolitan area network
a telecommunications network that connects users and their computers in a geographical area that spans a campus or city, app 100km
Wide area network
a telecommunications network that connects large geographic regions
long-distance networks used around the world.
Mesh networking
A way to route communications among network nodes (computers or other devices) by allowing for continuous connections and reconfiguration around blocked paths by ‘hopping’ from node to node until a connection can be established
Full mesh topology:
each node (workstation or other device) is connected directly to each of the other nodes
Part Mesh topology
some nodes might be connected to all the others, and other nodes are connected only to nodes with which they frequently exchange communications
Mesh networks are very robust: if one node fails, all the other nodes can still communicate with each other, directly or through one or more intermediate nodes
Centralized processing
all processing occurs in a single location or facility. This approach offers the highest degree of control because a single centrally managed computer performs all data processing
Decentralized processing
processing devices are placed at various remote locations. Each computer system is isolated and does not communicate with another system e.g. independent operating divisions
Distributed processing
computers are placed at remote locations but connected to each other via telecommunications devices
managers can allocate data to the locations that can process it most efficiently.
Distributed processing can also minimize the consequences of a catastrophic event at one location and ensure uninterrupted systems availability
Client/server
A client is any computer (often a user’s personal computer) that sends messages requesting services from the servers on the network
1.An application server holds the programs and data files for a particular application.
2.An e-mail server sends and receives e-mails.
3.A web server sends out web pages
Network operating system
The NOS is systems software that controls the computer systems and devices on a network and allows them to communicate with each other
Software defined networking (SDN)
is an emerging approach to networking that allows network administrators to manage a network via a controller that does not require physical access to all the network devices.
Encryption
Encryption is the process of converting an original message into a form that can be understood only by the intended receiver
Wired equivalent privacy (WEP)
used to use encryption based on 64 bit key, which has been upgraded to a 128 bit key.
WEP represents an early attempt at securing wireless communications and is not difficult for hackers to crack
WiFi Protected Access (WPA)
security protocol that offers significantly improved protection over WEP
Virtual private network
a private network that uses a public network (usually the Internet) to connect multiple remote locations.
VPNs support secure, encrypted connections between a company’s employees and remote users through a third party service provider
Internet
The Internet is the world’s largest computer network
Actually, it is a collection of interconnected networks, all freely exchanging information
History
ARPANET (Advanced Research Projects Agency) - 1969
MILNET
ARPANET
Internet2 - University Corporation for Advanced Internet Development (uCAID)
Protocols
Internet Protocol (IP) – the set of conventions to pass packets from one host to another
Transmisison Control Protocol (TCP/IP) most commonly used
Uniform resource locator
Each computer on the Internet has an assigned address for identification – Uniform Resource Allocator (URL) for example: https://www.ufh.ac.za
URL
http: specifies the access method and tells your software to access a file using the Hypertext Transport Protocol
www: part of the address signifies that the files associated with this website reside on the World Wide Web server of ufh.ac.za
ufh.ac.za: the domain name that identifies the Internet host site
Internet service providers
Companies that provide people and organizations with access to the Internet
To use this type of connection, you must have an account with the service provider and software that allows a direct link via TCP/IP
Web broswer
A Web browser is used to access and read Web pages which are usually written in HyperText Markup Language (HTML)
World wide web
The World Wide Web was developed by Tim Berners as an internal document management system
The World Wide Web (web, WWW, or W3) has grown to a collection of tens of thousands of independently owned computers that work together as one in an Internet service
The web
The Web is a menu-based system that uses the client/server model
It organizes Internet resources throughout the world into a series of menu pages, or screens, that appear on your computer
Hypertext markup language
Hypertext allows the linking of certain words to other web pages, so users can click on them to access related material. This feature gives the web its name, as all information is linked together like a spider’s web
Hypertext Markup Language (HTML)
the standard page description language for web pages.HTML file is made up of two things: text and tags.
The text is your message, and the tags are codes that mark the way words will be displayed
HTML Tags
let the browser know how to format the text: as a heading, as a list or as main text, for example users mark up a page by placing HTML tags before and after a word or words
New standards
1.Extensible Markup Language (XML)
XML web documents contain the content of a web page.
The formatting of the content is contained in a separate style sheet. A few typical instructions in XML follow
2.Extensible Hypertext Markup Language (XHTML),
3.Cascading Style Sheets (CSS),
4.Dynamic HTML (DHTML)
5.Wireless Markup Language (WML)
for display of web pages on small screens, such as smartphones and PDAs
XML
XML does not have a predefined tag set.
With XML, web documents contain the content of a web page. The formatting of the content is contained in a separate style sheet.XML is used within a web page to describe and transfer data between web service applications.XML is easy to read and has wide industry support
Web browsers
A web browser translates HTML so you can read it.
It provides a graphical interface to the web.
The menu consists of graphics, titles and text with hypertext links
Clicking with a mouse on a highlighted word or graphic whisks you effortlessly to computers halfway around the world
Popular browsers
Internet Explorer (now Edge), Google Chrome, Mozilla, Firefox, Safari (For AppleMac)
Web programming languages
1.Java an OO language allowing for Applets to be embedded in HTML documents
2.Hardware independent / cross-platform programming language
3.VBScript and ActiveX (used with IE)
4.PHP (Open Source)
Run on different Operating Systems and DBMSs
You can create a web page using one of the following approaches:
(a) write your copy with a word processor and then use an HTML converter to convert the page into HTML format;
(b) use an HTML editor to write text (it will add HTML tags at the same time);
(c) edit an existing HTML template (with all the tags ready to use) to meet your needs; or
(d) use an ordinary text editor such as Notepad and type the start and end tags for each item
Publishing web content
After you develop web content, your next step is to place or publish the content on a web server so others can access it.
Popular publishing options include using ISPs, free sites and web hosting.
Free sites offer limited space for a website
Web hosting services provide space on their websites for people and businesses that don’t have the financial resources, time or skills to host their own website
Some web hosting sites include domain name registration, web authoring software, and activity reporting and monitoring of the website
Microsoft .NET
Microsoft’s .NET platform allows developers to use different programming languages to create and run programs, including those for the web. The .NET platform also includes a rich library of programming code to help build XML web applications
SOAP
SOAP (Simple Object Access Protocol) - SOAP allows businesses, their suppliers and their customers to communicate with each other
WSDL
WSDL (Web Services Description Language) - used to describe a web service. This description is required,so that client applications are able to understand what the web service actually does
UDDI
UDDI (Universal Discovery Description and Integration) - used to register web service applications with an Internet directory so that potential users can easily find them and carry out transactions over the web
Developing Web Content and Applications
Popular Tools:
Adobe Dreamweaver
Microsoft Expression Web
Nvu (Open Source)
Web application frameworks simplifies web development by providing the foundational code, and/or a standard way of developing and deploying a professional interactive website
The down-side of email
Information overload - Productivity
Security - a vehicle to launch social engineering attacks
Telnet
enables you to log on to other computers on the Internet to gain access to their publicly available files. Telnetenables a user to manage an account or device remotely.
FTP
FTP is a standard internet protocol provided by TCP/IP used for transmitting files from one host to another. It is mainly used for transferring the web page files from their creator to the computer that acts as a server for other computers on the internet
Cloud computing
A computing environment in which software and storage are provided as an Internet service and accessed by users through their web browser.
Examples:
Google, Yahoo, Facebook, etc
Benefits
organizations can avoid large, upfront investments in hardware as well as the ongoing investment in the resources that would be required to manage that hardware
Public cloud computing
deployments in which service providers offer their cloud-based services to the general public, e.g. an individual using Google Calendar or a firm
3 Types:
IaaS (H/W) e.g. servers, storage devices, network components
SaaS (S/W), apps are hosted in the cloud
PaaS (OS, DBMS, Programm Dev, Web server,etc)
Benefits: Costs, scalability, speed
Risks: Security, Hidden costs, Legal, Locked-in
Private cloud computing
Single Tenant Cloud - Used within the confines of a private network
Addresses the security concerns of a public cloud
2 Options: Build or Buy
Choice influenced by costs, skills availability to configure and manage
Intranets
an internal company network built using Internet and World Wide Web standards and products. Employees of an organization use it to gain access to company information inexpensive yet powerful alternative to other forms of internal communication
Extranets
When selected externals (such as supplies) are given access to the intranet (or part thereof), it becomes an extranet
a network that links selected resources of the intranet of a company with its customers, suppliers or other business partners e.g. insurance firms, medical aid, etc. Security concerns, performance e.g. speed, availability
The internet of things
A network of physical objects or ‘things’ embedded with sensors, processors, software and network connectivity to enable them to exchange data with the manufacturer of the device, device operators and other connected devices.
sensor detects an event or changes in quantity and produces a corresponding output, usually an electrical or optical signal
Common Applications:
Asset Monitoring (food drug storage)
Agriculture (moisture sensors)
Security monnitoring
Traffic (monitoring, driverless cars
Manufacturing (production lines
Communications protocol
set of rules that governs the exchange of information over a communications channel
