Internet Transmissions

Question 1

What is a modem?

Answer 1

The term ‘modem’ has been taken from ‘modulator’ and ‘demodulator’. The task it performs is to communicate digital
data using the telephone system infrastructure.
The conventional telephone network deals with analog signals and computer systems use digital data so the modem is
used to carry out the necessary conversions.

Question 2

What is modulation?

Answer 2

The sending modem converts digital data into analog which is compatible with the
telephone system.

Question 3

What is demodulation?

Answer 3

The receiving modem converts analog data from the telephone into digital data for use
in computer systems.

Question 4

What is the speed of a modem?

Answer 4

56 kilo bits per second

Question 5

What is the file extension for HTML and what is it?

Answer 5

The file extension is .htm

HTML – Hypertext Mark-up Language is a text-based language that is used to create web pages.

Question 6

What is the file extension for JPEG and what is JPEG?

Answer 6

The file extension is .jpg
JPG – Joint Photographic Experts Group. 24 bit colour depth bitmap format with lossy compression that is normally used for high-quality photographs; can be compressed to create acceptable small website images.

Question 7

What is the file extension for GIF and what is a GIF?

Answer 7

The file extension is .gif
GIF – Graphic Interchange Format. A lossless compression bitmap format based on
a colour depth of 256 colours. Mainly used on websites for logos and animated
images.

Question 8

What is the file extension for PNG and what is PNG?

Answer 8

The file extension is .png
PNG – Portable Network Graphic. 24 bit colour depth lossless compression raster
graphic file that is used widely for transferring images on the Internet.

Question 9

What is the file extension for PDF and what is a PDF?

Answer 9

The file extension is .pdf
PDF – Portable Document Format. This de facto standard was developed by Adobe
for exchanging documents where text, formatting and images are presented as an
accurate copy of the original document.

Question 10

What is the file extension for MP3 and what is MP3?

Answer 10

The file extension is .mp3
MP3 – Moving Pictures Expert Group Audio Layer 3. An MP3 audio file is a lossy
compression file format to approximately 10% of normal digital audio file size.
Sounds that are not normally audible to most people are reduced in amplitude to
achieve this compression standard.

Question 11

What is the file extension for MPEG and what is MPEG?

Answer 11

The file extension is .mpg or .mp2
MPG – Moving Pictures Expert Group. MPEG is a lossy compression format used for
audio and video information. Different versions of the standard are available with
MPG files used for short video clips and MP2 files used for high-resolution movies.

Question 12

What is lossless compression?

Answer 12

is used when the compressed file has the option to be
expanded back into exact original format after it has been transmitted or
processed. It is necessary to use lossless formatting in the following situations:
An image might be compressed to low resolution for display on a
website, but may also be needed in a higher resolution in a
publication.
A program may be compressed to be downloaded over the Internet, but it will need to be expanded to an
exact copy of the original file before it runs.
A document might be compressed into a zip file for attachment and transmission using email. Again the
document will need to be expanded to an exact copy of the original to ensure that it can be understood.

Question 13

What is lossy compression?

Answer 13

Is not possible to recreate an exact
copy of the original file using this method. It is used when some data can be
removed from the file to make it smaller, but the final compressed file is still
acceptable for the use for which it was intended.
Lossy formatting can be used in the following situations:
A copy of an image might be compressed to a small file size for
display on a website, but there is no need to expand back to an exact
copy of the original file.
Sound files reduce unnecessary data to compress the files, but overall output quality is acceptable for the
user.

Question 14

What is an IP address?

Answer 14

An IP address is an address which is allocated to a computer system on a network, usually by a DHCP server. Alternatively, you may assign your own IP address if you do not wish to rely on the services of a DHCP server. An example of an IP address is 195.10.213.120.

Question 15

What is an IP address used for?

Answer 15

It is used by the TCP/IP protocol to uniquely identify computer systems on a network, thus allowing communication between them. In routing tables the corresponding IP address of a unique MAC
address is stored and updated as necessary.

Question 16

What is a MAC address?

Answer 16

A MAC address (media access control address), also known as a physical address or a hardware address, is
a unique hexadecimal number given to any communication device, such as a network interface card. An
example of a MAC address is 74:E1:B6:8E:18:77. The address is usually stored in a communication devices’
ROM. Hexadecimal notation is used as it allows for over 281 trillion different combinations of MAC
address.

Question 17

What is packet switching?

Answer 17

Packet switching is the process of delivering packets from
one computer system to another using a designated device, such as a switch or a router. Packets are
provided to a network for delivery to a specified destination. Each packet of data is redirected by a
computer system along the network, until it arrives at its destination. Data may be split up into a number
of packets. These packets are transmitted over a network and may take different routes to its destination.
When all the packets have arrived the data is reassembled. The Internet is an example of a packet-
switching network.

Question 18

What is routing?

Answer 18

Routing is the name given to the method of selecting paths along which packets are sent on a computer
network. Specialist computer systems such as routers, switches, bridges, firewalls and gateways construct
in their memory a routing table, which stores a number of paths along which it is best to send packets to
reach a specific destination. Maintaining accurate routing tables is essential for ensuring that packets are
delivered as quickly as possible.

Question 19

What are the steps in the process of Packet Switching?

Answer 19

The TCP protocol breaks down the - Data packets are normally
email into a series of data packets. - less than 128 KB and
contain details of the
destination computer.

A check code is created based - The check code is sent in the
on the contents of the packet. - data packet and is used to confirm
the accuracy of the data sent at the
destination computer.

Each packet contains the IP - The IP address for the destination
address of the destination - computer contains the host ID and the
computer. - network ID. This ensures that the packet
is only received by the computer
requesting the data.

A series of routers transfer the - The data packets for the individual addressed data packets. - email can travel via different
They use the destination IP address - routes, with the best route
to obtain the best network route. - determined by the routers
based on the destination address.

At the destination computer, - The reassembled message is checked
the TCP protocol reassembles - for accuracy. If any data packet the email from the data - shows an error, it is rejected and
packets. - requested again from sending
computer.