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Flashcards in 12 IPT - Comm Sys Deck (35):

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

- 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.


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"

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.

- 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.

- 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)

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

- 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

- 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.




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


What is the role of the network administrator in maintaining the network?

1) Ensuring the security of the network
2) Installing and maintaining software (e.g. removals and upgrades)
3) Backing up
4) Enforcing licensing agreements


What features are usually included in a network operating system?

1) Administration of users (adding, removing or editing details including passwords)

2) File management, e.g. different permisisons for dfferent types of users, or different file limits

3) Resource management - handles requests from users to share data and applications


Differentiate between thin and fat clients

Thin clients have most of its applications stored on a server, whilst fat clients have most of its applications stored in the node.


Application Level Protocol

Explain application layer of the TCP/IP protocol model. Give examples.

Page 37 of syllabus

Consists of protocols that focus on process-to-process communication across an IP network.

Examples: HTTP, SMTP, SSL


Explain the function of HTTP protocol

Page 37 of syllabus

The Hypertext Transfer Protocol (HTTP) is an application protocol.

HTTP functions as a request–response protocol in the client–server computing model. A web browser, for example, may be the client and an application running on a computer hosting a web site may be the server. The client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, returns a response message to the client.


Explain the function of SMTP protocol

Page 37 of syllabus

Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (email) transmission.

SMTP is a delivery protocol only. In normal use, mail is "pushed" to a destination mail server as it arrives. Mail is routed based on the destination server, not the individual user(s) to which it is addressed. Other protocols, such as the Post Office Protocol (POP) and the Internet Message Access Protocol (IMAP) are specifically designed for use by individual users retrieving messages and managing mail boxes


Explain the function of SSL protocol

Page 37 of syllabus

The Secure Sockets Layer (SSL) is the most widely deployed security protocol used today. It is essentially a protocol that provides a secure channel between two machines operating over the Internet or an internal network.


Transport and Internet Layer are the communication control and addressing level protocol layers. Explain its function.

Page 37 of syllabus

It provides host-to-host connectivity.
The protocol handles all handshaking and transmission details so that an application does not need to know the particular mechanisms for sending data via a link to another host

Used for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.


Network Access Layer (transmission level protocol)

Ethernet - describe how it works.

Page 37 of syllabus


Ethernet uses the logical bus topology. It is the most popular LAN technology in the world. It is an easy, relatively inexpensive way to provide high-performance networking to all different types of computer equipment.

Carrier Sense Multiple Access with Collision Detection or CSMA/CD)

The CSMA/CD approach is used by any form of Ethernet operating in half-duplex

Each piece of information transmitted on an Ethernet network is sent in something called a packet. A packet is simply a chunk of data enclosed in one or more wrappers that help to identify the chunk of data and route it to the correct destination. Destination in this sense means a particular application or process running on a particular machine. These wrappers consist of headers, or sometimes headers and trailers. Headers are simply bits of data added to the beginning of a packet. Trailers are added to the end of a packet.

Ethernet packets are sometimes called network frames because they add both a header and a trailer to the packets, thus framing the network data being transmitted



Network Access Layer (transmission level protocol)

Token Ring - describe how it works.

Page 37 of syllabus

Token ring networks use the token passing access method, which is based on a small frame called a token that circulates a ring-shaped media in a logical direction when devices are idle. To transmit, the device must seize the token.


A modem is a device that is used for modulation and demodulation of the data that is transmitted or received.
What is an ADSL modem?

An ADSL (Asymmetric Digital Subscriber Line) is one of the types of DSL broadband communication technology. Hence, an ADSL modem is a type of DSL modem. A downstream speed of 1.5 to 9 MBPS is possible and an upstream speed of 16 to 640 KBPS is possible, when an ADSL modem is used.

Read more at Buzzle: http://www.buzzle.com/articles/adsl-vs-dsl-modem.html