Chapter9:Communications and Networks

COMMUNICATION CHANNELS

• In telecommunications and computer networking , a communication channel, or channel, refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel.
•  A channel is used to convey an information signal, for example a digital bit stream, from one or several senders (or transmitters) to one or several receivers.
• This medium can be a physical wire or cable, or in can be wireless.                                                                                                                                       (1)

Mobile devices networks :mobile telecommunications

• Global System for Mobile Communications (GSM): divided into three major systems: the switching system, the base station system, and the operation and support system.
• Personal Communications Service (PCS): PCS is a radio band that can be used by mobile phones in North America and South Asia. Sprint happened to be the first service to set up a PCS.
• D-AMPS: Digital Advanced Mobile Phone Service, an upgraded version of AMPS, is being phased out due to advancement in technology.

       1. Microwave

• Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently.
• Practical microwave technique tends to move away from the discrete resistors, capacitors, and inductors used with lower frequency radio waves.
• The boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study.
• Microwave is a good medium for sending data between building in a city or on a large college campus.

   (2)                  (3)           

      2.Satelite

• A satellite is an object which has been placed into orbit by human endeavor.
• Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.
• Common types used  Satellites include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and research satellites.
• Satellites are usually semi-independent computer-controlled systems.
• Types of satelite     >Astronomical satellites    >Biosatellites     >Communications satellites   >Miniaturized satellites      >Navigational satellites      >Reconnaissance satellites  >Reconnaissance satellites     >Space stations     >Tether satellites    >Weather satellites (5)

• Global Positioning System (GPS):

               >A simulation of the original design of the GPS space segment, with 24 GPS satellites (4 satellites in each of 6 orbits), (45ºN) on earth .

                > Global navigation satellite systems (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage.

                >GNSS allows small electronic receivers to determine their location to within a few metres using time signals transmitted along a line-of-sight by radio from satellites.(5)

        

(6)

Citation:

(1)http://www.madasafish.com/broadband/online-gaming/nintendo-wii.shtml

(2) http://www.eetimes.com/design/microwave-rf-design/4019066/The-case-for-using-millimetre-waves-for-solving-the-backhaul-capacity-crunch

(3)http://en.wikipedia.org/wiki/File:Microwave_tower_silhouette.jpg

(4)http://en.wikipedia.org/wiki/Satellite

(5)http://en.wikipedia.org/wiki/Satellite_navigation

(5)http://en.wikipedia.org/wiki/File:ConstellationGPS.gif

CHAPTER 9 - COMMUNICATIONS AND NETWORKS

INTRANETS

• Intranets is a private computer network that uses Internet Protocol technology to securely share any part of an organization's information or network operating system within that organization. 
• It is used in contrast to internet, a network between organization, and instead refers to a network within an organization. 
• An intranet is build from the same concepts and technology used for the internet, such as client-server computing and the Internet Protocol Suite.
• Intranet have also contrasted with extranets. 
• Intranet may provide a gateway to the Internet by means of the network gateway with a firewall, shielding the intranet from unauthorized external access. 
• Intranets are being used to deliver tools and applications. 
• Intranets are also being used as corporate culture-change platforms, example large numbers of employee discussing key issues in an intranet forum application could lead to new ideas in management, productivity, quality, and other corporate issues. 
• Intranet user-experience, editorial, and technology team work together to produce in-house sites. 
• Intranet are managed by the communication, HR or CIO departments of large organizations or some combinations of these.     

Advantages of Intranets      

1. Intranets allow organization to distribute informations to employee on an as-needed basic, employee may link to relevant information at their convenience, rather than being distracted indiscriminately by electronic line.  
2. Intranet promote common corporate culture, so every users has ability to view the same information within the intranet. 
3. Intranets are also being used as a platform for developing and deploying applications to support business operation and decisions across the internetworked enterprise. 
4. Intranets can serve as powerful tools for communication within an organization, vertically and horizontally.    

    
                                                        

                                              http://www.anacominc.com/Kromos-www/index.html

     

 
                                    http://www.eguidelines.co.uk/user/login_newsys.php?%C2%A0
Citation:

• http://en.wikipedia.org/wiki/Intranet   
• http://compnetworking.about.com/cs/intranets/g/bldef_intranet.htm    

DATA TRANSMISSION

The factors that will affect the data tansmission :
  ( 1 )  Bandwidth
  ( 2 )  Protocols

Bandwidth

~Measurement of the width or capacity of the communication channel.

~The amount of information that can be sent through a connection between two computers in a given amount of time.

~Computers may be connected by telephone wires, by coaxial cable, or through radio waves or microwaves.

~A connection that can be transmit more data in a shorter period of time is said to have more bandwidth than another, slower connection.

~To get more information about brandwidth, please refer to http://wiki.answers.com/Q/What_is_the_definition_of_bandwidth_in_data_transmission

 

~There have 4 types of brandwidth :

   1)  Voiceband

        -- also know as low bandwidth.

        -- used for standard telephone communication. Microcomputers with telephone modems & dail-up service use this bandwidth.

        -- Transmission of text documents it is too slow for many types of transmission, including high-quality audio & video.

 

   2)  Medium band 

        -- connect microcomputers and mainframes to tansmit data over long distances.

        -- capable for high-speed data transfer.

        -- for more informations please refer to http://en.wikipedia.org/wiki/Medium_wave

   

   3)  Broadband

        -- widely used for DSL, cable, & satallite connect to internet.

        -- use single broadband connection to high-speed data transfer.

        -- used consistently with different types of internet connections.

        -- For more informations, please refer to http://en.wikipedia.org/wiki/Broadband , 

http://www.tech-faq.com/broadband.html

 

 

                                                         http://blog.irwan.name/?p=209

 

   4)  Baseband

        -- weidely use by those individual computers are located close to one another.

        -- able to suppoert to high-speed transmission.

        -- only can carry a single signal at one time.

        -- the information could also be carried in analog form.

        -- For more informations, please refer to http://www.tech-faq.com/baseband.html

 

 

Protocols

~Data transmission to be sucessful, sending and receiving devices must follow the set of communication rules for exchange of informations.

~Standard protocol for the Internet is TCP/IP (transmission control protocol/Internet protocol)

~Protocols may include signaling, authentication and error detection and correction capabilities.

~A protocol describes the syntax, semantics, and synchronization of communication and may be implemented in hardware or software, or both.

~For more informations, please refer to http://en.wikipedia.org/wiki/Communications_protocol

~The 2 features of protocol is :

  1) Identification

      -- Each computer have unique numeric address called an IP address(Internet Protocol address)

      -- Numerical addresses are difficult to use & remember, a system are automatically convert text-based addresses to numeric IP addresses.This system are call domain name server(DNS).

 

  2)  Packetization

      -- Informations there are transmitted across internet through numerous interconnected networks.

      -- Before the information are sent, it is reformatted or broken down into small parts called packets.

      -- Each information will sent separately.

      -- At the receiving end, the packets are reassembled into the correct order. 

 

 

http://www.maximumpc.com/article/news/border_gateway_protocol_a_gaping_security_hole_internet

 

 

 

Citations :

- More of the information are from Computing Essentials Complete 2010

- http://wiki.answers.com/Q/What_is_the_definition_of_bandwidth_in_data_transmission

- http://en.wikipedia.org/wiki/Medium_wave

- http://en.wikipedia.org/wiki/Broadband 

- http://www.tech-faq.com/broadband.html

- http://www.tech-faq.com/baseband.html

- http://en.wikipedia.org/wiki/Communications_protocol 

 

 

CHAPTER 10 PRIVACY AND SECURITY

COMPUTER CRIME

Computer crime, or cybercrime, refers to any crime that involves a computer and a network. The computer may have been used in the commission of a crime, or it may be the target.

Netcrime refers, more precisely, to criminal exploitation of the Internet. Issues surrounding this type of crime have become high-profile, particularly those surrounding hacking, copyright infringement, child pornography, and child grooming. There are also problems of privacy and confidential information is lost or intercepted, lawfully or otherwise.

TYPES OF COMPUTER CRIMES

Distributed denial of service attacks rank among the most widely reported cyber-crimes. They first appeared in mid-1999 and are relatively easy to perpetrate. Many of the tools required to carry them off are freely available online. Often, DDS attack networks consist of hundreds of compromised systems. The attacker inaugurates the attack sequence from one or more consoles, and it can affect thousands of systems worldwide.

Virus programs infect computer files by inserting copies of themselves into those files; they are spread from host to host when users transmit infected files by e-mail, over the Internet, across a company's network, or by disk. Related problems include worms, which can travel within a computer or network without a user transmitting files; trojan horses, which are disguised as innocuous files but which, once activated, can steal users' login names and passwords, thus facilitating identity theft; and logic bombs, programs activated by a specific event.

Other widely publicized computer crimes involved online fraud, such as stock scams and securities fraud via the Internet. The Securities and Exchange Commission (SEC), which receives about 300 complaints a day concerning online scams, devotes one-fourth of its enforcement staff to computer-related offenses. Theft of online content also is common. A Software & Information Industry Association study maintained that one-third of all business software applications in use in 1999 were pirated copies. And the Internet has made the distribution of information obtained in identity thefts, such as a person's name or social security number, much quicker and easier. The dissemination of child pornography online also has garnered widespread public and law-enforcement attention. Other offenses, such as stalking victims via the Internet, have only recently begun to be addressed.

Sources from 

http://ecommerce.hostip.info/pages/238/Computer-Crime-TYPES-COMPUTER-CRIMES.html

CHAPTER 9 COMMUNICATIONS AND NETWORKS

WHAT IS A MODEM???

The word modem is short for modulator-demodulator. A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decode to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from driven diodes to radio.

Modems are generally classified by the amount of data they can send in a given time unit, normally measured in bits per second (bit/s, or bps). They can also be classified by the symbol rate measured in baud, the number of times the modem changes its signal state per second.

The most familiar example is a voice band modem that turns the digital data of a personal computer into modulated electrics signals in the voice frequency range of a telephone channel. These signals can be transmitted over telephone lines and demodulated by another modem at the receiver side to recover the digital data.

Modems which use a mobile telephone system (GPRS, UMTS, HSPA, EVDO, WiMax, etc) are known as wireless modems (sometimes also called cellular modems). Wireless modems can be embedded inside a laptop or appliance or external to it. External wireless modems are connect cards, usb modems for mobile broadband and cellular routers. A connect card is a PC card or ExpressCard which slides into a PCMCIA/PC card/ExpressCard slot on a computer.

T-Mobile universal mobile
Telecommunications system PC card modem

ADSL modems, a more recent development, are not limited to the telephone’s voice band audio frequencies. Some ADSL modems use coded orthogonal frequency division modulation (DMT, for Discrete MultiTone; also called COFDM, for digital TV in much of the world.

DSL modem

Cable modems use a range of frequencies originally intended to carry RF television channels. Multiple cable modems attached to a single cable can use the same frequency band, using a low-level media access protocol to allow them to work together within the same channel.

New types of broadband modems are beginning to appear, such as doubleway satellite and power line modems. Broadband modems still be classed as modems, since they use complex wave forms to carry digital data. They are more advanced devices than traditional dial-up modems as they are capable of modulating/demodulating hundreds of channels simultaneously. Most broadband modems include the functions of a router (with Ethernet and WiFi ports) and other features such as DHCP, NAT and firewall features.
                                                                            
                          
sources from http://en.wikipedia.org/wiki/Modem