Chapter 2 Communication and network technologies
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Q1.(a)Explain
the term bit streaming.
– sequence of digital signals / bits
– over a communication path / Internet
– transfer of data at high speed
– requires fast broadband connection
– requires some form of buffering
– bits
arrive in the same order as sent
(b) A person watches a film streamed from a
website on a tablet computer.
(i)
Give two benefits
of using bit streaming for this purpose.
– no need to wait for a whole file to be downloaded
– no need to store large files on user’s computer
– allows on demand playback
– no
specialist software is required for playback in browser
(ii)
State two potential
problems of using bit streaming for this purpose.
video stops / hangs if very slow Internet / broadband speed low
– video stops / hangs if inadequate buffering capacity
– loss of Internet means can’t access films / files
– may require specific software to run the files / films
–
viruses can be downloaded from the websites
(c)
Explain the terms on-demand bit streaming
and real-time bit streaming.
on-demand:
– digital video tape, analogue video tape, or digital files are
converted to bit streaming –
format for broadcasting on the net; this is known as encoding,
these encoded streaming
video files are then uploaded to a dedicated server
– a link for the encoded video is placed on a web site
– a user clicks on the link to download the encoded streaming
video; the streamed video is
– then broadcast to the user as and when they require it
– can be paused / can go back and re-watch / fast-forward, etc.
real-time:
– an event is captured live with a video camera
– the video camera is connected to a computer
– the video signal is converted to streaming media files (encoded)
on the computer
– the encoded feed is then uploaded from the computer to a
dedicated streaming server
via cable, DSL, or a high-speed internet connection
– the server then sends the live images it to all users requesting
it as real-time video
streaming
– cannot
be paused etc.
2 (a) The table shows four statements about IP
addresses.
Tick (✓)
to show which of the statements are true.
(b) Consider the URL:
http://cie.org.uk/computerscience.html
(i) Give the meaning of the following parts
of the URL.
http
cie.org.uk
computerscience.html
http –
enables browser to know what protocol is being used to access
information in the domain
cie.org.uk –
cie.org.uk is the domain name
computerscience.html –
actual web page / file being viewed
(ii) Sometimes the URL contains the characters
%20 and ?.
Describe the
function of these characters.
%20 – because
<space> not allowed in a URL, %20 is the coding for a space (32 in denary)
? – separates the URL from all parameters or
variables
3 A company operates a chemical plant,
which has a number of processes. Local computers monitor these processes and
collect data.
The computers
transfer these data to a central computer 50 km away. A telecommunications
company (telco) provides cables.
Engineers at the
telco had to decide which type of cable to use. They considered the use of
either copper cable or fibre optic cable.
State two benefits of each
type of cable. Each benefit must be clearly different.
Benefits of
copper cable
Benefits of fibre
optic cable
Benefits of fibre
optic cable
fibre optic cables have greater bandwidth
– fibre optic cables need less signal boosting // can transmit over
longer distances
– fibre optic cables have greater security (more difficult to “tap”
into)
– fibre optic cables are immune to electromagnetic and other
effects
– fibre optic cabling is lighter in weight (easier to install)
– fibre optic cables consume less power
Benefits of
copper cable
– copper cabling is less expensive to install
– copper cable is easier to install because it is more flexible
– it is easier to make terminations using copper cabling
– the expertise in use of copper cabling is more extensive
– has been around for years … so very little is “unknown” about
installations using this type
of cabling
4 (a) (i) Describe what is meant by a client-server
model of networked computers.
(i) – at least one
computer used to “serve” …
– … other computers are referred to as “clients”
– server provides services / applications etc. …
– … which may be requested by clients
(ii) Give two benefits of using
the client-server model.[2]
– files and resources are centralised
– creation of security / manage security
– user needs user name and password to access network
– centralised back-up
– intranet capability
– Internet monitoring
– clients can be less powerful machines, therefore less expensive
to buy
– saving resources on server reduces the burden on the client.
Name the hardware
device labelled X.
Router
(c) A web page offers a link for users to
request another web page. The requested web page contains HTML code and
JavaScript code.
Put each
statement in the correct sequence by writing the numbers 1 to 5 in the
right-hand column.
5
(a) Telephone
calls can be made by using:
• conventional telephones (using
the Public Service Telephone Network (PSTN) system)
over a wired network
• a computer, equipped with
speakers and microphone, connected to the Internet
Put a tick (ü) in the correct column
to match each description to the appropriate communication
method.[5]
(b) Distinguish between the Internet and the
World Wide Web (WWW).
Internet
• massive network of networks/interconnected
network of computer devices
• Internet stands for Interconnected Networks
• uses TCP/IP protocol
World Wide Web (www)
• is a collection of (multimedia) web
pages/documents
• ...stored on websites
• http/protocols used to transmit data
• web pages are written in HTML
• URLs specify the location of the web pages
• web documents are accessed using browsers
(c) Name the hardware device that is being
described:
(i) A device that transfers data from one
network to another in an intelligent way. It has the task of forwarding data
packets to their destination by the most efficient route.
(ii) A device used between two dissimilar
LANs. The device is required to convert data packets from one protocol to
another.
(iii) A device or software that provides a
specific function for computers using a network. The most common examples
handle printing, file storage and the delivery of web pages.
(i)Router
(ii)gateway
(iii) server
6 Access to World Wide Web content uses IP
addressing.
(a)
State what IP stands for.
(b) The
following table shows four possible IP addresses.
Indicate for each
IP address whether it is valid or invalid and give a reason.
C)Describe
two differences
between public and private IP addresses.
A] Internet Protocol
B]
C]
Public address can be reached across the Internet.
• Private address can only be reached
internally/through the LAN/Intranet // private address cannot be reached across
the Internet.
• NAT (Network Address Translation) is necessary
for a private IP address to access the Internet directly.
• A private address is more secure than a public
address // A public address is less secure than a private address.
• Public addresses are provided by ISP /
assigned by InterNIC // Private addresses are assigned by the router (of the
network concerned).
• Public addresses are unique (to the Internet)
// Private addresses (are unique within their network, but) can be duplicated
within other (discrete) networks.
• 10.0.0.1 to 10.255.255.254 and 172.16.0.1 to
172.31.255.254 and 192.168.0.1.to 192.168.255.254 form the private address
space // IP addresses from the private address space are never assigned as
public.
Q7)
The design of a
web-based application can require the use of client-side scripting.
(a)
Describe what is meant by client-side scripting.
The user’s
web browser is the client software
The requested web page has program code
/ script embedded within it
• This
code is interpreted by the web browser
(b)
A user requests a web page by keying the
Uniform Resource Locator (URL) into the address bar of their web browser.
The requested page contains a client-side script.
Describe the sequence of steps leading to the display
of the web page on the computer
screen.[4]
The browser parses
the URL to obtain the Domain Name 1
• The
browser software passes the Domain Name to the nearest Domain Name
Server (DNS)
• The DNS
stores a list of Domain Names and matching IP addresses
• The DNS
Name Resolver looks for the Domain Name in its database
• If found
the corresponding IP address is returned to the originator
• If not
found the request is forwarded to another higher level DNS
• The
original DNS adds the returned IP address to its cache
• The
original DNS returns the IP address to the originator
• The
browser uses the IP address to request the required web page from the web
server
• The web
server retrieves the page and delivers it to the originator
• The browser software interprets the
script and displays the web page
(c) A web page used for data capture consists
of:
• two
text boxes for the entry of:• a
product code the number of items to be purchased.
• a button which is
clicked when the user wants to submit this order.
The developer has
used three variables in the JavaScript code. State the identifiers used.
Ans)
Message1, Message2 ,X
(ii) The button has an event whose identifier
is onMouseDown. When the submit
button is
clicked, some
code is executed.
State the line
numbers that contain this code.
From line
.............................. to line ..............................
Ans)
6 – 19
(iii) The JavaScript code uses a selection
statement.
State the line
number that contains the condition.
Line number:
.................................................................
Ans)
11
(iv) Describe the purpose of the validation
check that the code performs.
Ans)Checks
that the product code has not be left blank // presence check on product
code
(v) Name and describe two other types of
validation check that could be appropriate for this
data capture
form.
Validation check:
Description
Validation check:
Description
Ans)
• Range
check
Check the number
entered is (say) between 1 and 100
• Format
check
Checks the product
code is a particular format // Checks the number has digit
characters only // by
example
• Length
check
The number of items
has exactly five characters
• Existence
check
To ensure the product
code has been assigned
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