12 IPT - Comm Sys Flashcards
What are the characteristics of a comm sys?
1) Data source
2) Transmitter
3) Transmission medium
4) Receiver
5) Destination
List examples of messaging systems (both traditional and recent) as well as E-Commerce.
Teleconferencing systems: Skype, mobile phones
Traditional: Phone/Fax
Recent: Voicemail / Email
Others:
- E-Commerce, Eftpox, electronic banking
What are protocols?
A set of rules that govern the transfer of data between computers, defines how information is transmitted and how errors are detected
What is “handshaking”?
An agreement about which protocol to use to accomplish the exchange of in-formation, it is a series of signals that flow between devices using during datatransmission.
Methods of handshaking:• Hardware flow control uses a dedicated connection such as a wire RTS / CTS protocol
• Software flow control uses a special code sent with the data, used for long distance communications XON / XOFF, X = transmit
How is speed of transmission measured?
1) Bandwidth - capacity of the channel or transmission medium
2) Bits per second - number of bits that can be transmitted in a second
3) Baud rate - number of distinct symbol changes (signaling events) made to the transmission medium per second. (1 byte per second =
Explain how Parity Checking works
Parity checking - The parity is set by the system (even or odd) and each packet must conform to the system parity. A bit of 0 or 1 can be added as a checkbit to ensure it conforms.
Explain how checksum works
Counts the number of digits in a datum block (total data is divided into smaller groups to create the block) the count of bits is attached to the data packet, if the count matches then it is assumed a complete transmission was received.
e. g. the datum block can be a sentence, paragraph or several paragraphs of data being transmitted.
https: //en.wikipedia.org/wiki/Checksum
What is the difference between parallel and serial transmission?
Parallel - transmission of data simultaneously using separate channels
Serial - transmission of data one after the other, can be synchronous or asynchronous
- —> Asynchronous - non constant rate, specifies each byte with start and stop bits
- —-> Synchronous - constant rate, synchronised be each device using a clock, faster and more efficient then asynchronous
Explain the term “Cyclic Redundancy Check”
CRC:
data is divided into predetermined lengths and divided by a secret divisor, the remainder of the calculation is attached and sent with the data. When the data is received the remainder is recalculated, this can be done with either a 16 or 32 bit key.
Twisted Pair
Explain and list its advantages and disadvantages.
** Please look up image if you don’t know what it looks like **
Thin insulated copper wires twisted into a spiral, twisting reduces the amount of interference from other cabling, the wire can be shielded or unshielded.
Coaxial Cable
Explain and list its advantages and disadvantages.
** Please look up image if you do not know what it looks like **
A type of cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield.
ADVANTAGES
- Sufficient frequency range to support multiple channel, which allows for much greater throughput.
- Lower error rates. because the inner conductor is in a Faraday shield, noise immunity is improved, and coax has a lower error rates and therefore slightly better performance than twisted pair.
greater spacing between amplifiers coax’s cable shielding reduces noise and crosstalk, which means amplifiers can be spaced farther apart than with twisted pair.
DISADVANTAGES
- More expensive to install compare to twisted pair cable.
- The thicker the cable, the more difficult to work with.
SPEED: Up to 1.54 Mbps (mega bits per sec)
USES
Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers with their antennas, computer network (Internet) connections, digital audio (S/PDIF), and distributing cable television signals.
Optic Fibre
Explain and list its advantages and disadvantages.
** Please google image if you do not know what it looks like **
Cable that uses light to transmit data. The optical fiber elements are individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.
Ref: http://services.eng.uts.edu.au/~akadi/ite/major_assignments/barber/advdisad.htm
SPEED: Up to 1 Gigabits per second
ADVANTAGES:
- Bandwidth
- Long transmission distances
- Immune to electromagnetic interference
- 30 times smaller than copper wires but 4.5 times more capacity
- Physical: lighter and bends more easily
- Security: difficult to tap into
DISADVANTAGES:
- Expensive
- Require more protection around the cable compared to copper (to avoid wear and tear)
Data can flow in three different ways, list and explain these methods
- Simplex - one direction only, e.g. radio
- Half duplex - both directions but not at the same time, e.g. walkie talkie
- Full duplex - both directions at the same time e.g. telephone
Microwave Transmission
A microwave is an electromagnetic wave with a very short wavelength, between .039 inches (1 millimeter) and 1 foot (30 centimeters). Within the electromagnetic spectrum, microwaves can be found between radio waves and shorter infrared waves. Their short wavelengths make microwaves ideal for use in radio and television broadcasting. They can transmit along a vast range of frequencies without causing signal interference or overlap.
Read more: http://www.scienceclarified.com/Ma-Mu/Microwave-Communication.html#ixzz4EkyFJmvb
Satellite Transmisison
In satellite communication, signal transferring between the sender and receiver is done with the help of satellite. In this process, the signal which is basically a beam of modulated microwaves is sent towards the satellite. Then the satellite amplifies the signal and sent it back to the receiver’s antenna present on the earth’s surface.
Radio Transmisison
For the propagation and interception of radio waves, a transmitter and receiver are employed. A radio wave acts as a carrier of information-bearing signals; the information may be encoded directly on the wave by periodically interrupting its transmission (as in dot-and-dash telegraphy) or impressed on it by a process called modulation. The actual information in a modulated signal is contained in its sidebands, or frequencies added to the carrier wave, rather than in the carrier wave itself
Ref: http://www.infoplease.com/encyclopedia/science/radio-transmission-reception-radio-waves.html
Infrared (IR) Transmission
Infrared (IR) is a wireless mobile technology used for device communication over short ranges. IR communication has major limitations because it requires line-of-sight, has a short transmission range and is unable to penetrate walls. IR transceivers are quite cheap and serve as short-range communication solutions.
Because of IR’s limitations, communication interception is difficult. In fact, Infrared Data Association (IrDA) device communication is usually exchanged on a one-to-one basis. Thus, data transmitted between IrDA devices is normally unencrypted.
https://www.techopedia.com/definition/630/infrared-ir
Servers
Define the term.
List the different types and explain their roles
Server - a computer that provides services to other computers on a network
• File server - controlling computer in a network that stores the programs and data to be printed
• Print server - computer on a network that controls one or more printers and stores data to be printed
• Web server - provides a connection to the internet and/or stores and serves files on the internet or intranet
• Mail server - computer that provides e-mail facilities and stores incoming mail for distribution to users and forwards outgoing mail
Explain the function of a switch in transmitting data
A switch is more intelligent than a hub. Like a hub, a switch is the connection point for the computers (and other devices) in a network. However, a switch is more efficient at passing along traffic. It records the addresses of the computers connected to it in a table. When traffic comes through, the switch reads the destination address and sends that traffic to the appropriate computer rather than sending it to all the connected computers. If the destination address is not in the table, the switch sends the traffic to all the connected computers.
Ref: http://eccitsolutions.com/differences-hubs-switches-routers/
Explain the role of a router in comm sys transmisison.
A router is the most intelligent of the three hardware devices. It is typically a small computing device designed specifically to understand, manipulate, and direct traffic. Routers include a user interface so that you can tell them where to direct the traffic.
The primary function of a traditional router is to connect two or more networks (or network segments in a very large network) and direct traffic between them. For instance, a business might use a router to manage the connection between its local network and the Internet. To distribute the traffic to the computers in the local network, the business could connect the router to a switch or hub.
While traditional routers are still available, most small business and home office routers today combine the functionality of a router and the functionality of a switch or hub in a single unit.
Ref: http://eccitsolutions.com/differences-hubs-switches-routers/
Explain the role of hubs in transmitting data
A hub is the least intelligent of the three hardware devices (hubs, routers, switches). It serves as a connection point for the computers (and other devices such as printers) in a network. A hub simply passes along the traffic it receives to the computers connected to it. Any traffic that goes in one port comes out the other ports. As a result, all the computers receive the traffic, even if it is not for them. For that reason, they have been rendered obsolete by switches.
Ref: http://eccitsolutions.com/differences-hubs-switches-routers/
Explain the term ‘bridge’ in transmitting data
- combination of hardware and software that links two similar networks,e.g. connects LANs that use the same protocol
Explain the term ‘gateways’ in transmitting data
A combination of hardware and software that links two different types of networks. e.g. LANs and WANs
Explain the role of ‘repeaters’ in transmitting data.
Used to rebuild a fading signal to its original strength
