7TH QUIZ 2ND part

7. Explain the purpose of communications 

software.

Communication software is used to provide

 remote access to systems and exchange files 

and messages in text, audio and/or video 

formats between different computers or user 

IDs. This includes terminal emulators, file

 transfer programs, chat and instant messaging programs, as well as similar functionality integrated within MUDs.

8. Describe various types of lines for communications 

over the telephone network.

       
   The word telephone comes from the Greek words

tele, meaning “far,” and phone, meaning "sound," and

refers to a telecommunications device that allows the

1. human voice to travel across great distances. There are different types of telephones and corresponding types oftelephone systems. The three main types of telephone systems are Plain Old TelephoneService, cellular wireless phones, and Internet Protocol phones.

    Land-line telephone systems are part of the Plain Old

Telephone Service (POTS), the analog service with copper 

wiring that is the direct great-grand-baby of the original

 telephone system courtesy of Alexander Graham Bell. 

The advantages include standardized equipment, predictable 

sound quality, and — due to direct connections to the central 

office of the company — no need to share the system’s 

capacity with others. Because switches are in place, creating 

a private circuit for each phone call, it is also called the Public

Switched Telephone Network (PSTN). A new-fangled term, 

given the recent alternatives, is “landlines.”

  Internet Protocol (IP) telephone systems, also called Voice

 over Internet Protocol (VoIP), are another group of the

 telephone systems that are in use in the 21st century. This

 type oftelephone service piggy-backs on existing Internet 

service, either cable service or DSLbroadband. A device 

called an Analog Telephone Adaptor is the go between that

 connects whatever phone you happen to have with either

 your broadband modem—or your router, if you have one.

9. Describe commonly used communications devices.

Automated Voice Answering Systems 

Automated voice answering systems are used to take messages and to provide  automated information retrieval requests.

GPS Instruments and Modules

Global positioning system (GPS) instruments and GPS modules are radio-navigational devices that provide accurate position information about objects on Earth,  based on information from orbiting satellites.

Intercoms 

Intercoms are an electronic communications system generally composed of fixed microphone/speaker units connected to a central control device.

Magnetic Receivers 

Magnetic receivers use the electromagnetic principle to receive and analyze signals.  The simplest of these devices is the telephone.

Navigational Instruments 

Navigational instruments include products such as distance meters, range finders and mapping systems.

 

Pagers

Pagers are electronic communications devices that are used to notify or alert a user about an event. They beep, vibrate, flash, display text, and use other alerts or methods of notification.  Phone Switchboards

Phone switchboards are used for routing telephone calls and adding advanced features to telephone systems.

Radar Systems and Products 

Radar systems and radar products have synchronized transmitters and receivers that send radio waves and detect their reflections from objects, surfaces or sub-surface structures.

Radios 

Radios are communication systems that send and/or receive electromagnetic waves. Devices such as citizens’ band (CB) radios, walkie-talkies, and handie-talkies are two-way radios that can be used for interpersonal communications.

Telephone Components and Accessories  

Telephone components and telephone accessories are used in telephone systems.

Telephones and Cellular Phones 

Telephones and cellular phones convert voice or other sound signals into a form that can be transmitted to another device that receives and reconverts the waves back into sound.

10. Discuss different ways to set up a home network.

A home network is a must-have in the modern household. However, it's never as simple as merely connecting device A to device B.

What do you need from your network?

Before whipping out your credit card and buying up gear, figure out what you're trying to accomplish with your home network.

Are you just looking to connect a couple of laptops and maybe a Wi-Fi-equipped mobile phone to the internet for web access?

•      You might be able to get by with a single 802.11n access point (802.11n is the current fastest Wi-Fi standard, offering throughput up to 300Mb per second). Do you work at home frequently, and require access to a corporate network through VPN (virtual private network) technology? You'll need a good router that can handle VPN passthrough.
• Are you a serious online gamer? Do you connect to massively multiplayer online games or through services like PlayStation Network or Xbox Live frequently? You'll need not only to buy a good router but also to steep yourself in key router capabilities such as port forwarding.
• Do you watch TV through the internet, using services like Hulu or the networks' own websites? If you're streaming video from the internet to multiple locations in your home, you'll want a reliable networking infrastructure - probably a wired network.
• Determining the answers to such questions will go a long way toward ensuring that you build a network suitable for your home without spending too much in the process.

11. Identify various physical and wireless transmission media.

  

Wireless Media

Transmission of waves take place in the electromagnetic (EM) spectrum. The carrier frequency of the data is expressed in cycles per second called hertz(Hz). Low frequency signals can travel for long distances through many obstacles but can not carry a high bandwidth of date while high frequency signals can travel for shorter distances through few obstacles and carry a narrow bandwidth. Also the noise effect on the signal is inversely proportional to the power of the radio transmitter. The three broad categories of wireless media are:

1. Radio - 10 Khz to 1 Ghz. It is broken into many bands including AM, FM, and VHF bands. The Federal communications Commission (FCC) regulates the assignment of these frequencies. Frequencies for unregulated use are:
   • 902-928Mhz - Cordless phones, remote controls.
   • 2.4 Ghz
   • 5.72-5.85 Ghz
2. Microwave
   • Terrestrial - Used to link networks over long distances but the two microwave towers must have a line of sight between them. The frequency is usually 4-6GHz or 21-23GHz. Speed is often 1-10Mbps. The signal is normally encrypted for privacy. Two nodes may exist.
   • Satellite - A satellite orbits at 22,300 miles above the earth which is an altitude that will cause it to stay in a fixed position relative to the rotation of the earth. This is called a geosynchronous orbit. A station on the ground will send and receive signals from the satellite. The signal can have propagation delays between 0.5 to 5 seconds due to the distances involved. The transmission frequency is normally 11-14GHz with a transmission speed in the range of 1-10Mbps.
3. Infared - Infared is just below the visible range of light between 100Ghz and 1000Thz. A light emitting diode (LED) or laser is used to transmit the signal. The signal cannot travel through objects. Light may interfere with the signal. The types of infared are
   • Point to point - Transmission frequencies are 100GHz-1,000THz . Transmission is between two points and is limited to line of sight range. It is difficult to eavesdrop on the transmission. The speed is 100Kbps to 16Mbps
   • broadcast - The signal is dispersed so several units may receive the signal. The unit used to disperse the signal may be reflective material or a transmitter that amplifies and retransmits the signal. Normally the speed is limited to 1Mbps. The transmission frequency is normally 100GHz-1,000THz with transmission distance in 10's of meters. Installation is easy and cost is relatively inexpensive for wireless.

Terms:

• wireless bridge - Microwave or infared is used between two line of site points where it is difficult to run wire.
• CDPD - Cellular Digital Packet Data will allow network connections for mobile users using satellites.

Physical Media Twisted pair - Wire twisted to avoid crosstalk interference. It may be shielded or unshielded. UTP-Unshielded Twisted Pair. Normally UTP contains 8 wires or 4 pair. 100 meter maximum length. 4-100 Mbps speed. STP-Shielded twisted pair. 100 meter maximum length. 16-155 Mbps speed. Lower electrical interference than UTP. Coaxial - Two conductors separated by insulation such as TV 75 ohm cable. Maximum length of 185 to 500 meters. Thinnet - Thinnet uses a British Naval Connector (BNC) on each end. Thinnet is part of the RG-58 family of cable*. Maximum cable length is 185 meters. Transmission speed is 10Mbps. Thinnet cable should have 50 ohms impedance and its terminator has 50 ohms impedance. A T or barrel connector will have no impedance. Maximum thinnet nodes are 30 on a segment. One end of each cable is grounded. Thicknet - Half inch rigid cable. Maximum cable length is 500 meters. Transmission speed is 10Mbps. Expensive and is not commonly used. (RG-11 or RG-8). A vampire tap or piercing tap is used with a transceiver attached to connect computers to the cable. 100 connections may be made. The computer has an attachment unit interface (AUI) on its network card which is a 15 pin DB-15 connector. The computer is connected to the transceiver at the cable from its AUI on its network card using a drop cable. Maximum thicknet nodes are 100 on a segment. One end of each cable is grounded. The RG value for cable types refers to its size. Coax cable types: RG-58 /U - 50 ohm, with a solid copper wire core for thin ethernet. RG-58 A/U* - 50 ohm, with a stranded wire core. RG-58 C/U* - Military version of RG-58 A/U. RG-59 - 75 ohm, for broadband transmission such as cable TV. RG-62 - 93 ohm, primarily used for ArcNet. RG-6 - Used for satellite cable (if you want to run a cable to a satellite!). RG-8 - 50 ohm thick ethernet. RG-11 - 75 ohm thick ethernet. *Only these are part of the IEEE specification for ethernet networks. Fiber-optic - Data is transmitted using light rather than electrons. Usually there are two fibers, one for each direction. Cable length of 2 Kilometers. Speed from 100Mbps to 2Gbps. This is the most expensive and most difficult to install, but is not subject to interference. Two types of cables are: Single mode cables for use with lasers has greater bandwidth and costs more. Injection laser diodes (ILD) work with single mode cable. Multimode cables for use with Light Emitting Diode (LED) drivers. All signals appear to arrive at the same time. P intrinsic N diodes or photodiodes are used to convert light to electric signals when using multimode.

Cable Standards

The Electronic Industries Association and Telecommunications Industries Association (EIA/TIA) defined a standard called EIA/TIA 568 which is a commercial building wiring standard. It defines transmission speed and twists per foot.

Category	Speed	Notes
1	None	Used for old telephone systems
2	4Mps
3	10Mps	The minimum category for data networks
4	16Mps
5	100Mps	Cat 5 network cable, used by most networks today
6		Data patch, Two pair with foil and braided shield
7		Undefined
8		Flat cable for under carpets with two twisted pair
9		Plenum cable with two twisted pair. It is safe if you're having a fire.

The maximum transmission length is 100 meters. This cable is susceptible to interference.

STP

Shielded twisted pair has a maximum cable length of 100 meters (328 feet). Data rate from 16 to 155 Mbps. Cables require special connectors for grounding. Resists interference. Costs more than UTP or Thinnet, but not as much as Thicknet or Fiber-optic

Terms

• Attenuation - Signal loss due to impedance.
• Bandwidth - Indicates the amount of data that can be sent in a time period. Measured in Mbps which is one million bits per second.
• Impedance - The amount of resistance to the transmission device.
• (ILD) - Injection laser diodes work with single mode cable.
• Interference - Electromagnetic Interference (EMI). Crosstalk - When wires pick up electromagnetic signals from nearby wires also carrying signals.
• Plenum - Space above a false ceiling in an office area where heat ducts and cables may be run. Plenum cabling is special fire resistant cabling required for use in these areas due to fire hazards.
• Shielding - Used to minimize interference.