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Chapter (1) 2005/2006/2007
1. List the two basic components of a computer network.
Links
Nodes
2. Sate the two primary objectives of a telecommunications operator.
To meet the end-users needs.
To make a profit
3. Name the seven layers of the Open Systems Interconnection (OSI) model and describe the
function of each layer.
Physical layer
Deals with physical attachment to communication lines
Data link layer
Provides transfer and control data over communication lines, error correction, etc.
Network layer
Adds destination switching, routing, and relaying functions and presents them independency of
the network in use.
Transport layer
Provides user-to-user services, including multiplexing to make he most effective use of network
facilities. It enhances the quality of service.
Session layer
Controls the dialogue between uses and supports synchronization of their activity.
Presentation layer Allows for the selection of the representation of data, resolving differences between systems.
Application layer
Provides the interface to user applications and common services, such as file transfer and
terminal support.
4. State which layers of the OSI model a voice network has to comply with.
Layer 1 to 3
5. What is a protocol?
When information is transferred from one computer to another the method of transfer must be
strictly controlled.
A protocol is a set of rules that control this transfer of information.
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6. Why are protocols necessary for communication in networks?
Protocols allow computers form different manufacture and/ or running different software to
communicate with each other.
7. Briefly describe three of the resources that make up a network.
The interconnecting circuits that allow communication over the network.
The equipment that is connected by these circuits.
The people responsible for planning, building, and running the network.
The software running on the network.
Chapter-2 (2005/2006/2007)
1. Compare and contrast two different bearer media, giving examples of its use.
Example- Fiber-optic cable
Transmission occurs at light-wave frequencies that allow a much greater amount of information
to be carried.
They are immune to electrical interference.
Capable of carrying signals over long distances and capable of facilitating high transmission
speeds.
Suitable example - large LAN.
Example- Copper cable
Easy to connect and disconnect which has disadvantages as well as advantages.
Takes the form of coaxial cable or twisted pair.
Big advantage is the relative low cost.
Suitable example Ethernet.
2. Use a diagram to explain the difference between star and interconnected star networks.
3. Describe a situation where an interconnected star network may be used.
Star network are often used to provide interconnectivity in a particular locality.
It would often be uneconomical to provide the same level of interconnectivity to a different
location so trunk or tandem exchanges are used to connect star networks.
4. Explain the term transmission bearer network.
The high order network used to provide the links from which communication channels can be
derived in order to link telephone exchanges, packet switching exchanges, etc.
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5. a) Explain the concept of the carriers carrier.
b) Give an example use for each of the media given in your anser to question a)
A network operator may have spare capacity on their network and in order to fully utilize this
capacity they will rent it out to one of their competitors.
E.g. Fiber-optic cable
Suitable Example: large LAN
E.g. Copper cable
Suitable example: Ethernet.
Chapter-3 (2005/2006/2007)
1. Define analogue transmission.
Analogue transmission involves transmission of a continuously variable signal, either directly, as
a varying voltage on a cable, or indirectly, by using the analogue signal to modulate a carrier
signal.
2. Define digital transmission.
Digital transmission involves transmitting a signal that is encoded as two or more discrete
levels.
3. Briefly describe the following type of distortion that may affect the signal quality in analogue
transmission system.
(i) Amplitude distortion
(ii) Harmonic distortion
(iii) Intermodulation distortion
(iv) Attenuation distortion
Amplitude distortion
The amplitude of the output signal is not directly proportional to the amplitude of the input signal
Harmonic distortion
The output signal contains elements that are not present in the input signal but are harmonics of
the input frequency.
Intermodulation distortion
If the input signal contains several frequencies the output will also contain the sums and
differences of these frequencies.
Attenuation distortion
Attenuation occurs due to energy loss and delay due to the distance traveled.
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4. Define the term of crosstalk.
Sounds hearing in a telephone receiver associated with one channel resulting from the
transmission of a signal in another channel.
5. Describe THREE causes of crosstalk.
The greatest cause of crosstalk in multi-core cables is due to capacitive imbalance between
wires and from each wire in a circuit and earth.
Crosstalk may occur if two wires have a different resistance due to a bad connection.
Crosstalk may occur in frequency division multiplex system due to amplifier non-linearity.
6. Describe the term Multiplexing.
The term multiplexing is used to describe the division of a large bandwidth into a series of
smaller bandwidth channels.
These smaller channels are termed baseband channels.
And the transmission channel from which they are derived is termed the broadband or bearer
channel.
7. Describe the two mains methods of multiplexing.
Frequency Division Multiplexing (FDM) used in analogue systems. In FDM the baseband
channels uses the entire bandwidth of the bearer on a permanent basis.
Time Division Multiplexing (TDM) used in digital systems. In TDM each baseband channel
uses the entire bandwidth, but only on a temporary basis.
8. Describe the different between Dense Wave Division Multiplexing (DWDM) and early WDM
systems.
Advances in optical amplifiers and lasers allow wavelengths to be more closely spaced.
This allows multiple signals to be transmitted at the same time along the same fiber at different
wavelengths.
The effect is that one fiber is transformed into multiple virtual fibers. And the capacity of each fiber is greatly increased.
9. Describe four advantages of DWDM.
It allows the network to carry a greater amount of traffic.
It is protocol and bit-rate independent and can carry different types of traffic at different speeds.
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Creates a lower cost way of meeting customer bandwidth needs and for protocol changes.
Increases distances between network elements.
10. Define the term modulation.
Modulation is a process of making a signal suitable for sending over a transmission medium.
11. Describe each of the following modulation methods.
(i)Amplitude Modulation
(ii)Frequency Modulation
(iii)Pulse Amplitude Modulation
Amplitude Modulation
Amplitude Modulation where the modulator causes the envelope of the carrier frequency to
follow the waveform of the modulating signal.
The demodulator recovers this modulating signal from the envelope.
Frequency Modulation
Frequency Modulation where the modulating signal causes changes to the frequency of the
carrier signal.
This gives a more complex spectrum than AM and as a result occupies more bandwidth.
Pulse Amplitude Modulation
Pulse Amplitude Modulation where carriers are modulated with a train of pulses.
A train of direct current digital signals is converted into a train of carrier frequency samples. These samples are applied to an Analogue-to-Digital Converter (ADC) resulting in a series of
on-off pulses.
12. State three reasons why modulation may be required.
To modulate a radio frequency carrier with an audio frequency signal.
To improve the signal-to-noise ratio.
To divide a bandwidth up into smaller communication channels.
13. Define the term non- linear distortion.
The output signal amplitude is not proportional to the input signal amplitude.
The output signal also contains harmonics that were not present in the input signal.
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14. Draw a simple diagram to illustrate how several muldex units can be used to combine 120 64
Kbits/s channels to form a single 8.448 Mbits/s channel.
15. Describe in detail UDP- based Data Transport (UDT).
UDT is a combination of 2 existing protocols, User Datagram Protocol (UDP) and Transmission
Control Protocol (TCP).
UDP provides a connectionless datagram service that offers best-effort delivery, i.e. delivery is
not guaranteed and sequencing is not verified.
Therefore UDP is fast and efficient but not reliable.
TCP is a connection oriented reliable protocol in that it ensures error free delivery.
TCP corresponds to the transport layer in the OSI 7-layer model.
UDT uses one UDP based channel for data to be sent at high rates.
And another TCP based channel is used to make the protocol reliable.
The TCP channel is also used by the protocol for congestion control and rate control.
16. Define the term bandwidth.
The range of frequencies that may be transmitted without being strongly attenuated.
17. Briefly explain how Wavelength Division Multiplexing (WDM) works in optical fibers.
Wavelength Division Multiplexing allows two or more optical systems to operate over the same
fiber by using light of different wavelengths or colored laser light, thus effectively increasing the
capacity of the fiber. The technique can be likened to Frequency Division Multiplexing in that separating optical
wavelengths (colors) is little different from separating the frequencies of electrical signals. In
order to work filters are used to pass the required wavelength, while blocking others.
By using WDM it is possible to increase the capacity of a pair of fibers (one for transmit, one for
receive) from 140Mbits/s to Gigabits or even Terabits/s.
18. Describe four advantages of DWDM.
It allows the network to carry a greater amount of traffic.
It is protocol and bit-rate independent and can carry different types of traffic at different speeds.
Create a lower cost way of meeting customer bandwidth needs and for protocol changes.
Increases distance between network elements.
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Chapter-4 (2005/2006/2007)
1. Explain the difference between forward signal and backward signals.
Forward signals are from calling to call.
Backward signals are in the opposite direction.
2. Explain the difference between common- channel signaling and channel associated signaling
Channel associated signaling has controlling and routing signals using the same channel as
speech.
In common channel signaling they use the spate signaling channel.
3. Briefly describe seven advantages offered by common channel signaling.
Information can be exchanged between processors more rapidly.
Allows a wider repertoire of signals to be used giving a wider range of services to the customer.
Signals can be added or changed by software modification to provide new services.
Line signaling equipment is not needed at every junction thus reducing costs.
Junctions can be used for calls in both directions thus reducing the number of circuits.
Signals can be sent whilst the call is in progress thus allowing customers to alter connections
after they have been set up.
Signals can be exchanged for other functions, other than call processing such as network
management.
4. Common Channel Signaling System Number 7 (CCS N0.7) can be modeled as a stack of four
protocols in a similar way to the OSI model above. Give a detailed description of each of these
FOUR layers.
Level 1 is the means of sending bit streams over a physical path.
It uses time slot 16 of a 2 Mbit/s PCM system or slot 24 of a 1.5 Mbit/s system
Level 2 performs the function of error control, link initialisation, error-rate monitoring, flow control
and delineation of messages.
Level 3 provides the functions required of a signaling network. Each network has a 14-bit signal
point code address and every message contains the point codes of the originating and
terminating nodes.
Levels 1 to 3 form the message transfer part of the system.
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Level 4 is the user part that consists of the processes responsible for handling the services
being supported by the signaling system.
The message transfer part is capable of supporting many different user parts including
telephone user part, data-user part, mobile-user part and ISDN-user part.
5. Describe the difference between continuous signals and pulse signals in a telephone. Give an
example of each.
A continuous signal remains in place for a length of time.
E.g. when a caller lifts the receiver a direct current path is maintained with the exchange until
the receiver is replaced.
Pulse signals are intermittent and take the form of a single pulse or coded group of pulses,
E.g. the dialed digits transmitted by a telephone.
6. Describe the term continuous signal as applied to a telephone system and give an example of
the use of a continuous signal in a telephone system.
Continuous signal remains in place for a length of time.
E.g. when a caller lifts the receiver direct current path is maintained with the exchange until the
receiver is replaced.
7. Define the term acknowledged signal and describe the operation of acknowledged signals in
a continuous signaling system
An acknowledged signal receives some kind of response.
Typically the continuous signal is sent at least until the acknowledgement is received.
The acknowledgement signal is maintained until the original signal is removed.
8. Describe the term pulse signal as applied to a telephone system and give an example of the
use of pulse signals in a telephone system.
Typically the continuous signal is sent at least until the acknowledgement is received.
The acknowledgement signal is maintained until the original signal is removed.
9. Describe the operation of acknowledged signals in a pulse signaling system.
Typically if an acknowledgement is expected the pulse will be repeated until the
acknowledgement is received.
10. Define inband signaling systems (voice frequency signaling system).
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Signaling systems that use the 300 Hz to 3.4 kHz speech band.
11. Describe the advantage of inband signalling systems.
They will operate over any circuit that provides satisfactory speech transmission.
12. Describe the disadvantage of inband signalling systems.
Signal imitation impossible.
Chapter-5 (2005/2006/2007)
1. Define the term grade of service in telecommunications traffic theory.
The probability of finding all circuits on a route simultaneously occupied.
2. Define the term traffic carried in telecommunications theory.
The mean number of calls in progress simultaneously.
3. State the formula used for calculating traffic carried and explain the meaning of each symbol
in the formula.
A=C * t/T
A=traffic in erlangs.
T= mean call duration or holding time.
C=number of calls.
T= the time taken for those calls.
4. Describe THREE assumptions made in the basic traffic model used as a mathematical model
for telecommunications traffic.
Calls arrive in a random fashion at a constant rate (a Poisson process).
Calls terminate at random regardless of how long they have been in progress (have an
exponential distribution).
The system has operated with same call rate for some time ensuring that there is statistical
equilibrium.
5. A network has 10 erlangs of traffic and a grade of service of 0.07. Calculate the traffic carried.
Traffic carried = A (1-B)
=10(1-0.07)
=9.3erlangs
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6. Calculate traffic carried by 4 circuits in 100 seconds from the following information.
Circuit 1 carries 1 call of duration 65 seconds.
Circuit 2 carries 1 call of duration 35 seconds and 1 call of duration 40 seconds.
Circuit 3 carries 1 call of duration 80 seconds.
Circuit 4 carries 2 calls each of duration 40 seconds.
Show all you are working out as part of the answer.
Traffic =average occupancy = call arrival rate * call holding time
Total occupancy = 65+35+40+80+(2*40)
Total occupancy = 300 seconds
Traffic carried = total occupancy/ time available
Traffic carried = 300/ 100
Traffic carried = 3 erlangs
7. Briefly describe the TWO alternative methods commonly used by telecommunication
companies
In a non-hierarchical network the use of automatic alternative routing increases network
capacity. However, once the traffic increases to a maximum possible level effect of automatic
alternative routing decreases. Therefore measures must be taken to prevent --- an overload
reducing network capacity. One method uses trunk reservation where calls overflowing from a
direct route are blocked when there are fewer than predetermined quantities of circuits free on
the alternative route.
An alternative method of dealing with congestion is known as call gapping and this is achieved
by the Network Management Centre (NMC) only allowing through, say, one call every x
seconds, where x is varied according to the capacity of the destination to receive calls.
Chapter 6 (2005/2006/2007)
1. Describe the THREE basic types of paging service in common use.
Tone paging. The unit vibrates or emits an audible bleep when the wearer is paged. The user
then has to call the service operator to collect any message;
Numeric paging. The unit emits an audible bleep and displays a call-back number;
Message paging. The unit can display a text message of variable length (up to 400 characters in
length, but this figure varies between network operators and as terminals are updated).
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2. Briefly describe THREE major limitations of paging systems.
No voice services are offered.
Data transmitted is only in the form of text or numeric messages.
One-way communication only, from base to mobile.
3. Define the term Mobile Communication Network.
a. A communications network that allows communication to take place whilst some or all of
the users of the network are moving relative to each other.
4. Describe FOUR advantages of mobile networks.
It is easier to stay in contact.
Access to timely and accurate information is available while away from a home base.
Productivity and efficiency are improved.
Different working patterns can be accommodated, e.g. working from home.
5. Give a detailed description of how mobile data communications are provided via satellite.
Access to satellite communications is via a terrestrial network provider in the home country.
They look after the space segment of the communications path.
Public fixed network providers provide the connection to the base station in the home country.
Satellites provide a relay link to homeland earth station from mobile terminal.
Two-way voice communications are available.
Data is broken into packets for transmission and reassembled at the land earth station or mobile
terminal.
Data rates vary the service but can be moderately high for dedicated channels.
Closed user groups can be formed.
Satellite services are the only option if truly global mobile data communications are requirement
6. Describe FOUR reasons why the quality of voice communications on analogue mobile
networks can be lower than on fixed ones.
Mobile network tend to use lower bandwidth than fixed networks. As radio spectrum is scarce
large chunks cannot be allocated for high quality voice communications.
Higher backgrounds noise as this is more significant on radio channels than fixed channels.
More interference from other users of the radio spectrum.
Some networks use the voice channel for network control signaling and this blank out the voice
when control signals are sent.
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7. Describe the key features of a mobile communication networks.
A communication network that allows communication to take place whilst some of all of
the users of the network are moving relative to each other.
8. Compare the quality of voice communications on digital mobile networks to fixed networks.
The quality levels are similar between digital mobile networks and modern terrestrial voice
networks.
9. Describe FOUR characteristic features of Private Mobile Radio (PMR).
Provide local radio communication on a single channel (e.g. taxi firm).
Communications are half-duplex and require strict operating procedures (e.g. the use of over
at the end of a message).
Requires a license from the relevant government department.
Bandwidth and channel availability is limited.
10. Describe THREE disadvantages of Private Mobile Radio.
Lack of privacy as all communication takes place on a single channel and anyone with a
suitable receiver can listen to the broadcasts.
Communications are limited to a small radius resulting in a mobile unit losing the ability to
communication when it is out of range.
The channel may become congested at peak times making it difficult to access.
11. Briefly describe THREE environmental factors that may affect the operating range of a
wireless LAN within a building.
General building design - the position of walls, ceilings, windows, etc.
Construction materials steel, wood, etc. Room layout the position of furniture and the materials it is made out of electrical interference
from motor, TV, radio, etc.
Chapter 7 (2005/2006/2007)
1. Define a switched network.
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Data is transferred from source to destination through intermediate nodes.
The nodes provide the switching capability from progressing the data towards its destination.
2. Define a packet switched network.
o Data is sent in a series of small chunks called packets.
o Each packet is transferred from node to node towards its final destination.
o At each node the packet is stored briefly and then transmitted to the next node.
3. Describe SEVEN important differences between a switched network and a packet switched
network.
A single user cannot monopolies a transmission line as packets from different users can be
mixed.
Circuit switching has static bandwidth allocated whereas packet switching allows fro dynamic
acquisition and release of bandwidth.
Packet switching allows different packets to travel via different routes.
Packet switching allows more economical use of transmission lines as a result of the previous
two points.
Circuit switching allows a more deterministic flow from source to destination which is important in
some applications.
Circuit switching requires time to set up the circuits, this is not necessary in packet switching.
Charges for circuit switching are usually based upon time of connection and possibly distance
whereas packet switching may charge on quantity of data transmitted.
4. Briefly describe the TWO major functions of a (PAD).
Assemble characters from the Data Terminal Equipment (DTE) into packets for transmission
across the network.
Disassemble the packets into characters that are passed onto the DTE.
5. Briefly describe SEVEN advantages of X.25 packet switching.
Support for the X.25 interface is widespread on host, terminal, LAN and switching systems.
Multiplexing allows connection from a single DTE to many DTEs.
Virtual calls in connection oriented networks enable soft connections to be made between DTEs.
The network connections are balanced.
Emulation of asynchronous protocols by PADS provides opportunities for cheap wide-area
connections between PCs.
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Any number of applications can share the available capacity on a network.
DTE support for X.25 is available on most manufacturers equipment and packets can be routed
without the need to configure a physical circuit.
Can handle relatively large numbers of DTEs sending packets at speeds of 64kbit/s.
6. Give a brief description of the following:
a) Circuit switching
Consists of the establishment of an end-to-end link for the time the connection is being used.
b) Packet switching
Consists of the establishing a connection at intervals between two points in order to transmit a
discrete packet of data.
7. Explain how circuit switching and packet switching methods operate when all possible links
in a connection are occupied.
Circuit switching
The user receives a busy signal and the call attempt is lost.
Networks should be dimensioned so that the incidence of this is small.
Packet switching
The packets are stored in a queue and transmitted when a link becomes available.
In this method the call is delayed but not lost.
8. Describe the key features of a Frame Relay network.
Provides a greatly simplified packet switching protocol.
It is a connection oriented network with no error or flow control.
The customer leases a Permanent Virtual Connection providing connectivity between
locations.
The PVs is created in software by the network provider and configured remotely.
Chapter-8 (2005/2006/2007)
1. Describe video conferencing using ISDN.Remote meetings can take place using dial-up connections and high quality video and audio
monitors.
Allows people to be brought into and taken out the discussion as required.
This will save time and money as staff can be effectively in more than one place at one time.
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2. Describe remote surveillance using ISDN.
Used by organizations with remote sites that requires guarding against intrusion, fire on
other threats.
Does not require neither private connections nor permanent on-site security guards as
all sites can be monitored at a central office.
Allows automatic alarms to be reported automatically.
High data rates allow cameras to have screen refresh times of around second giving improved
security coverage.
3. Briefly describe THREE conversational service applications that may be provided by
broadband ISDN.
Tele-education sound, video and written material can be used for distance learning
and be transferred in both directions.
Video surveillance using cameras to monitor a situation, e.g. CCTV, traffic cameras,
etc.
Video/audio transmissions TV signal transfer and audio transfer.
Multiple sound programme signals several different audio signals can be
transmitted simultaneously, (e.g. multi-lingual commentary).
High speed data transmission has many uses including multi-site interactive
CAD/CAM and real-time metering systems.
4. Define the term integrated services digital networks (ISDN).
ISDN is network, in general evolving from telephony IDN.
It provides end-to-end digital connectivity.
It supports a wide range of services, including voice and non-voice services.
Users have access by a limited set of standard multi-purpose, user-network interfaces.
5.i) Describe how B-channels and D-channels are combined to give the Primary Rate Access
(PRA) ISDN of 2.048 Mbit/s in Europe.
European PRA ISDN is made up of 30 B-channels an 2 D-channels.
Both B-channel and D-channels work at 64 kbit/s.
Thus 32 * 64 Kbits = 2048 kbit/s.
=2.084 Mbit/s.
ii) Explain the function of the B-channels and D-channels within PRA ISDN.
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Each B-channel carries voice or data.
One D-channel is used for signalling.
The other D-channel is used for synchronization and monitoring functions.
6. Briefly describe how analogue signals can be transmitted in digital form.
The analogue signal is sampled at regular intervals.
The sampled signal levels are transmitted as a digital data stream.
7. Describe the TWO principal access structures for ISDN which have been defined by the ITU-T.
Basic Rate Access
Provides the user with two simultaneous user channels (B channels).
Each can carry data to different locations at a rate of 64 Kbit/s.
A third channel (D channel) is primarily used fro signaling.
The D channel is sometimes used to provide the user with a slower 9.6 Kbit/s data channel.
A total data rate of 144 Kbit/s is available.
Primary Rate Access
Provides the user with 30(23 in North America/Japan) independent data/voice use channels (B
channels).
Each can carry data to different locations at a rate of 64 Kbit/s.
One D channel is primarily used for signalling and another for monitoring and synchronization.
A total data rate of 2.048 Mbit/s (1.544 Mbit/s in North America/Japan is available.
Can accommodate higher speed H channels.
Chapter-9 (2005/2006/2007)
1. Briefly describe the SIX key features of the Asynchronous Transfer Mode of data
transmission.
Packets are of fixed length (53 Octets) and known as cells.
Operates in a connection-oriented mode and before information is transmitted a virtual
connection is established and the resources for this reserved. If insufficient resources are
available at the time the call is refused.
There is no error protection or flow control on a link-by-link basis. Error control for the
information in cells (not in their headers) can be omitted because of the very low error rates.
The headers are short because they are limited to identifying the virtual connection and to
ensure correct routing of the cell.
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The information field is short. This also reduces the length of the cell, which reduces the
packetizing delay at the sending terminal. It also reduces the size of internal buffers at switching
nodes and their queuing delays.
A policing function is included to ensure that a user is not sending and receiving digits at a
higher rate than they have chosen to pay for.
2. Explain why copper-based broadband is used when there are advantages to using fiber-
optics.
Much of the worlds telecommunications infrastructure is still based upon copper wires.
Therefore, the cost of replacing all this copper wire with fiber-optic cable is high and would also
require time. This means that there is a need for broadband systems based upon copper wire.
3. Describe in detail the operation of the Asymmetric Digital Subscriber Line (ADSL) technology.
Allows existing wiring into the home to be used for high speed digital communication.
Uses separate transmission frequencies to provide what are effectively a voice channel and a
data channel on a single standard telephone line.
A POTS splitter at the exchange and a signal filter in the ADSL modern keep the voice signals
and data signals apart.
At the exchange the ADSL traffic is handled by a DSLAM which handles a number of ADSL
lines and concentrates them into a single ATM line.
Because ADSL is asymmetric the data does not flow at the same rate in both directions.
Maximum download is at 8 Mbit/s and maximum upload at 784 kbit/s.
4. Describe the difference between cable broadband and ADSL.
Cable broadband generally utilizes coaxial cable and cable modems to provide broadband
services to the home.
Cable not always available to commercial users as often provided by cable TV companies.
5. Describe FIVE delays that are encountered in a n ATM networks.
Packetisation typically a few milliseconds for Pulse Code Modulation.
Transmission for modern networks this is typically around 5 microseconds per kilometer.
Fixed switching the time taken for a cell to traverse a switch. There are 10s of cells per
exchange with a typical delay of around 30 microseconds per exchange.
Queuing delays are necessary to avoid loss of cells and increase with traffic load on a switch.
Typically around half a millisecond for a 53 octet cell.
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Depacketisation cells are buffered at receiving terminals and must accommodate delay
variations in queuing delay but the maximum is specified in the queuing delay.
6. Briefly describe the TWO major functions of a Packet Assembler Disassembler (PAD).
(i) Describe in detail the operation of the Asymmetric Digital Subscriber Line (ADSL)
technology.
ii) Describe the main differences between Rate Adaptive Digital Subscriber Line (RADSL)
technology and ADSL technology.
The TWO major functions of a Packet Assembler Disassembler (PAD).
Assemble characters from the Data Terminal Equipment (DTE) into packets for transmission
across the network.
Disassemble the packets into characters that are passed onto the DTE.
The operation of the Asymmetric Digital Subscriber Line (ADSL) technology.
Allows existing wiring into the home to be used for high speed digital communication.
Uses separate transmission frequencies to provide what are effectively a voice channel and a
data channel on a single standard telephone line.
A POTS splitter at the exchange and a signal filter in the ADSL modem keep the voice signals
and data signals apart.
At the exchange the ADSL traffic is handled by a DSLAM which handles a number of ADSL
lines and concentrates them into a single ATM line.
Because ADSL is asymmetric the data does not flow at the same rate in both directions.
Maximum download is at 8 Mbit/s and maximum upload at 784 Kbit/s (modern xDSL can do 40
Mbit/s).
The main differences between RADSL technology and ADSL technology
RADSL is a variation of ADSL in which software is able to determine the rate at which signals
can be transmitted on a given customer phone line and adjust the delivery rate accordingly.
It delivers the highest possible performance over standard phone lines.
7. Describe the main differences between cable broadband and ADSL.
Cable broadband generally utilizes coaxial cable and cable modems to provide broadbandservices to the home whereas ADSL uses different frequencies to provide data channel on a
standard telephone line.
Cable not always available to commercial users as often provided by cable TV companies
whereas ADSL is supplied by telephony companies and, therefore, usually available to all.
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Chapter 10 (2005/2006/2007)
1) Describe THREE reasons why the initial take-up rate of wireless networking was slow.
The original data rates were too slow for mainstream users on a shared LAN and
wireless speeds were much slower than for wired networks.
Only property, non-standard solutions were available with little interoperability betweendevices and users had little confidence in the market.
The cost was high compared to wired solutions despite the slower speed.
2) Describe the TWO key components of a wireless LAN.
An Access Point acts as a base station transmitting and receiving voice/data via radio
waves. Access Points provide the link between devices and the network.
Each device has a Wireless Adapter that is usually situated in the device itself. These
are capable of transmitting and receiving digital signals and come ion a variety of
formats depending upon the device.
3) Define the term wireless hotspot.
An area defining the range of transmission around an access point.
4) i) In terms of threats to security, describe the main difference for a wireless LAN when
compared to a conventional wired LAN.
The transmission of a wireless network cannot be confined to the building.
RF signal can be easily intercepted outside the premises.
Any unauthorized mobile device can act as a receiver.
Enabling eavesdropping or drive-by hacking from nearby premises.
The hacker may remain undetected as there is no need to physically enter or connect to
the premises.
ii) Name and describe the standard that minimizes the risk of security compromise for
wireless LAN.
IEEE 902.1lb includes a security feature called Wired Equivalent Privacy.
It provides a method for encryption transmissions and authenticating each
computer using the network.
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(5)Detail how Bluetooth wireless networking operates.
Each piconet can support up to 8 devices simultaneously
- Piconets can be bridged to make larger networks.
- The maximum operating range for devices that can extend the range to 100 meters in ideal
conditions.
- Offers stable and reliable performance even in noisy environment.
- Data rates are low with throughput up to 1 M bit/s.
(6)List TWO imitations of Bluetooth
- Short operating range
- Limited data throughput
- Reliance on a crowded spectrum band (2.4 GHz)
(7)Define the term Mobile Communications Network
- A communications network that allows communication to take place whilst some or all of the
users of the network are moving relative to each other.
(8)Describe FOUR advantages of mobile network
- It is easier to stay in contact
- Access to timely and accurate information is available while away from a home base.
- Productivity and efficiency are improved
- Different working patterns can be accommodated. E.g. working form home
Chapter11
2005/2006/2007
(1)Each computer (host) connected to the Internet has a unique IP address. Describe from of this
address and explain what it is used for.
- Addresses have the form of a dotted quad a. b. c. d.
- Where a, b .c, d are 8-bit numbers between 0 and 255.
- These addresses are attached to packets.
- Allowing the target address to be determined.
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(2)Using an example, explain how the Domain Name System (DNS) is used to provide a name for a
website host.
E.g. www.ncceducation.co.uk:
- A textual name is used instead of a numerical IP address
- The name is built up from a number of domains separated by dots, read from left to right.
- The www host belongs to the NCC education domain
- This in turn belongs to the co domain which is reserved for companies
- This in turn belongs to the UK domain which is used UK based organizations.
Ensure that marks are awarded for alternative examples, e.g. biz, .com, .net or domains for other
countries e.g. nccedu.ae
(3) Describe the objectives of the standard Interior Gateway Protocol of Open Shorter Path First
(OSPF).
Dynamic-has to allow the dynamic updating of routing tables.
Load balancing- must balance the load of packets sent over different routes so that capacity is
used effectively.
Hierarchical- impossible to know the entire internet so a hierarchy of knowledge is required.
Security-preventing routers from being subverted by hackers.
(4)Describe the problems faced by exterior routing protocols.
- Must allow for the fact that certain routes may or should not be used
- Data transmission must be paid for so the owners of the data must pay for the necessary links.
- Packets from non-contributing networks should be excluded.
- Must be capable of handling extremely high volumes of data in a secure and robust fashions.
(5)i) Define an internet
An internet is a collection of packet switching networks interconnected by routers, using
protocols that allow them to perform logically as one single network.
(ii)Define the Internet
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The internet is a collection of networks and routers spanning most countries and uses the
TCP/IP protocol to form a single virtual network.
(6)Describe how subnet addressing works
- A part of the HOSTID section of the address is used to indicate which network is intended.
- These subnets are meaningless to any router outside the business.
- Internal routers can use this route packet to the relevant subnet work.
- A subnet mask is used to show which part of the address is used for the host.
(7)Name and briefly describe the EIGHT component parts of an IPng (Internet Protocol version 6)
header.
VERSION- 4-bit Internet Protocol version number=6.
PRIORITY- 4-bit priority value enables the source to identify the desired delivery priority
of its packets, relative to other packets from the same source.
FLOW LABEL- 24-bit label may be used by source to label those packets for special
handling by IPv6 routers
PAYLOAD LENGTH- 16-bit unsigned integer giving the length of payload, i.e. the rest of
the packet following the header, in octets
NEXT HEADER- 8-bit selector identifying the type of header immediately following the
IPng header.
HOP LIMIT- 9-bit unsigned integer decremented by 1 by each node that forwards the
packet. The packet is discarded if this reaches zero.
ADDRESS- 128-bit address of the sender
ADDRESS-128-bit address of the recipient of the packet which may be the ultimate
recipient
(8)Describe the responsibilities of the Internet Corporation for Assigned Names and Numbers (ICANN)
- Responsible for coordinating and managing the Domain Name System (DNS).
- Ensure that every address is unique and that all users can find all addresses.
- It does this by distributing unique addresses and domain names and ensuring that they map
onto each other
- Also responsible for accrediting domain name registrars.
- This means to identify and set minimum standards for registration functions.
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- And recognize entities meeting those standards and enter into accreditation agreements.
(9)Briefly explain the purpose of the Internet Protocol (IP)
IP defines the rules for the transfer of packets from one location to another.
(10)Describe the functions of the Transmission Control Protocol (TCP)
- TCP operates on top of IP to produce reliable delivery of data from one host to another.
- It takes care of breaking down data into packet-sized chunks and reassembling them at their
destination.
- It ensures the transmission is reliable by using a checksum for each packet.
- If a packet is corrupted TCP will detect this and request a retransmission of that packet.
- It will detect missing packets and request their transmission.
(11)(i)Describe how Voice-over IP (VoIP) works
- The voice signal needs to be turned into a digital signal
- Chopped up into packets
- Sent by possible varying routes with different timings
- Assembled back into an audio waveform with no gaps and accurate timing
(ii)Briefly describe FOUR advantages in using Voice-over IP
- Voice and data can be transported over the same lines.
- By using compression technology more calls can be placed on those lines than in the circuit
switched environment.
- Up to 8 times as many calls can be placed on the lines without sacrificing sound quality
network infrastructure.
- Enables different devices to communicate with one another, e.g. PC to phone.
(iii)Briefly describe THREE disadvantages to using Voice-over IP
- In order for an IP network to consistently transmit voice packets it must meet strict performance
criteria.
- The underlying system must be transparent to phone users.
- Basic management procedures such as addressing, security and accounting must be in place.
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(12)Describe in detail UDP-based Data Transport (UDT)
- UDT is a combination of 2 existing protocols. User Datagram Protocol (UDP) and Transmission
Control Protocol (TCP)
- UDP provides a connectionless datagram service that offers best-effort delivery. I.e. delivery is
not guaranteed and sequencing is not verified
- Therefore UDP is fast and efficient but not reliable
- TCP is a connection oriented reliable protocol in that it ensures error free delivery
- TCP corresponds the transport layer in the OSI 7-layer model
- UDT uses one UDP based channel for data to be sent at high rates
- And another TCP based channel is used to make the protocol reliable
- The TCP channel is also used by the protocol for congestion control and rate control.
(13)(i)Describe the role and operation of the Internet Engineering Task Force (IETF) in the developmen
of the Internet
- The IETF is a large, open, international community of network designers, operators,
vendors and researchers concerned with the evolution of the internet architecture and
the smooth operation of the internet.
- Its work is done by working groups which are organized by topic into several areas (e.g.
transport, security, etc.)with much work being handled by mailing lists.
(ii)Describe the role and operation of the Internet Assigned Numbers Authority (IANA) in the
development of the internet.
- The IANA is the central coordinator for the assignment of unique parameter values for internet
protocols
- The IANA is chartered by the Internet Society (ISOC) to act as a clearing house to assign and
coordinate the use of numerous Internet protocol parameters
(14)Describe in detail, the purpose and operation of an Extranet.
- An Extranet is a virtual intranet that is run on a system managed by a third party.
- Corporate information and events can be accessed and updated by authorized employees from
any Internet connected PC.
- It allows all staff to receive up to date corporate information in any Extranet
- Built using a comprehensive system of firewalls to control and manage access and maintain
integrity
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- It is partially private, partially public network.
- Typically a server acts as an intermediary between the companys intranet and the Internet.
- The purpose of this server is to authenticate users and allow access to the companys intranet
and block out unauthorized access.
(15)Describe the reasons for the development of Internet Protocol version 6 (IPv6) which is also known
as Next Generation Internet Protocol (IPng).
There is a limit on the number of addressees available via the dotted quad format of IP version 4 and
this is becoming a problem.
An updated IP was therefore required that was interoperable with the current IP.
(16)Describe SIX changes made by Internet Protocol version 6 (IPv6) that improve on Internet Protocol
version 4 (IPv4).
- The address size is increased from 32-bit to 128-bit allowing for more levels of hierarchy and
more addressable nodes.
- The use of any cast addresses allowing a node to specify the path through which a message
flows
- The header has been simplified producing a smaller header even though the addresses are
longer.
- Changes in the way header options are coded allows for more flexibility to introduce more
options in the future- Quality of service capabilities have been introduce allowing the sender to specify non-standard
handling of packets
- Extensions are defined that allow for the handling of authentication, confidentiality and data
integrity.
(17)The following is layout of an IP datagram:
Describe the usage of the following parts of the datagram:
(i)HLEN
- The datagram header length
- This is necessary because the IP OPTIONS and PADDING many vary in length
(ii)TOTAL LENGTH
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- The total length of the datagram
- Measured in octets
(iii)SERVICE TYPE
- How a datagram should be handled by routers and destination host.
- It allows for priorities and preferred transport to be defined
Chapter 12
2005/2006/2007
(1)Briefly describe the primary functions of a network management system.
- To monitor the networks performance to determine whether it is fully operational.
- To take effective remedial actions should any of the networks operating parameters fall outside
the predetermined values.
(2)(i) Describe the FOUR levels of management of a network. Include their levels of responsibility
1. Business level
- Management of the network operating business including sales, marketing,
customer administration, billing, accounting, inventory control and investment
planning
2. Service level
- Management of the user services.
3. Network level
- Asset management including management of the database that records all
assets. The database also includes details of the network, route optimization;
flow control measures contingency pans, etc.
4. Network element level
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- Records the installation of equipment, the prediction, detection and rectification
of faults, plus the management of maintenance.
(ii)Explain which of these levels would be of least interest to a network user.
At the business level the decisions are largely strategic for the business and of less interest to the user.
(3)TWO types of financial cost relating to telecommunications network.
- The capital cost of establishing the network
- The ongoing cost of operation the network
(4)(i)Describe the term redundancy when applied to network design
The inclusion of additional links in a network that can be used in the event of failure thus
increasing network resilience.
(ii)Describe FOUR factors that should be taken into account when designing redundancy in a
network.How important is the traffic, what are the implications to the business, how long to repair the
link and is the downtime acceptable.
- What is the most likely reason for failure, interface hardware or the cable?
- What physical paths do the main and back-up links follow? It is best to have different paths toeliminate one threat breaking both.
- Can load sharing be used to utilize both main and back-up links thus improving network
performance?
(5)Define Network Management
Assessing the likely benefits likely to ensure from all facets of work associated with the operation of a
network
(6)(i) Briefly describe the TWO main characteristics of a network operation that are important to network
management.
- The network should preferably be operational at all times
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- If a network becomes unoperational when it is required it should be restored to an operable
state in the shortest possible time.
(ii) Describe how network management ensures that the characteristics given above are maintained
The network performance is monitored
- Remedial action is taken whenever any of the networks parameters move outside of the
predetermined limits.
(7) Briefly describe the TWO main priorities of network management from the network point of view.
Ensuring the cost of network management is kept as low as possible.
- Ensuring that the systems that manage the network are as reliable as possible
(8)Briefly describe the THREE resources that make up a network
- The interconnecting circuits that allow communication over the network.
- The requirement that is connected by these circuits
- The people responsible for planning, building, running the network.
(9)Briefly describe FOUR functions performed by fault management in respect of network faults.
- Detection- carrying out diagnostic tests and continuity tests- Diagnosis- recognizing fault conditions and planning correction
- Isolation- tracing faults and isolating then from the rest of the network
- Correction of abnormal operation- scheduling immediate and deferred repair work.
- Maintenance work tracking- tracking fault repairs, software code bugs and creating tracking
summaries.
(10)What are the THREE main assets of a telecommunications network?
The interconnecting circuits
- The equipment to which the interconnecting circuits are connected
- The people responsible for planning, building and running the network.
(11)Briefly describe the THREE resources that make up a network.
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- The interconnecting circuits that allow communication over the network
- The equipment that is connected by these circuits
- The people responsible for planning,, building and running the network.
(12)Explain the benefit of domain based networking in managing and supporting a network system.
Most network operate over a large geographical area and network management functions must be
carried out over this area
- To facilitate management of the whole network, the network is divided into domains with
different parts of the management system being responsible for different domains.
Chapter 13
05/06/07
(1)Describe the term Digital Enhanced Cordless Telecommunications (DETC)
- A radio technology suited for voice, data and networking applications.
- Up to a range of a few hundred meters
(2)Briefly describe the following advanced digital radio techniques used in DETC
(i)Time Division Multiple Access (TDMA)
Radio access with low interference characteristics
- Can handle up to 100, 000 users per sq km of office floor space
(ii)Dynamic Channel Selection/Allocation (DCS/DCA)
- Guarantees that the best radio channels available are used
- Ensure the ability to co-exist with other DECT applications and give high quality secure
communication.
(3)Briefly explain the main differences between Key Telephone Systems (KTS) and Private Branch
Exchanges (PBX). Draw a simple diagram of each type of a system to illustrate your answer.
KTS
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In a Key Telephone System the control and switching functions for calls is built into the
telephone handsets themselves.
All KTS station users can be allowed to gain access to and answer nay specific
external lines.
There is no central control unit (switchboard) and no need for a dedicated switchboard
operator to control and manage calls.
PBX
A PBX system uses a central call processor to handle the routing of incoming,
outgoing and interextension calls
PBXs can be either manual, requiring the use of an operator or automatic with no staff
intervention required for the routing of calls
Generally PBXs are suited to larger organizations involving hundreds or even
thousand of telephone extensions.
(4)Describe how Caller Line Identification (CLI) can used to improve the efficiency of call centre agents.
This allows the computer to present the information needed by the agent for that particular caller onto
the agents computer screen, marginally before the agent answers the call. It also allows the agent to
greet the caller in a personalized manner, which enhances the caring impression
To have all the required information on hand to deal with the call in the most affective manner possible
thus increasing productivity.
(5)Describe the SEVEN basic functions of a telephone
- Provide a signal when a call is received so that the user is alerted
- Send a signal to the exchange when a user wants to originate a call
- Allow the user to advise the exchange of the number to be called
- Inform the exchanges when a call is finished so that it knows resources are free.
- Convert voice signals into varying electrical signals to allow their transmission via an electrical
circuit
- Convert electrical signals back into voice and allow the user to listen to there audible signals.
- Give voice signals in preparation for conversion.
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Chapter-14 (2005/2006/2007)
1. Describe the main features of a LAN.
A LAN is a data communications network that provides a data connection between computers
and other digital devices.
Covers a limited geographical are but it is able to connect a larger number of devices Does not use external network services.
High data rates
Low probability of undetected errors.
2. Describe the operation of a Token Ring topology for a LAN includes:
(a) A Description of the token passing process.
(b) The specific IEEE standard.
(c) The problems inherent with a ring topology.
(a) Description of the token passing process
A special pattern of bits (called a token) passes around the ring.
A node can only transmit data when it has the token.
Data only travels in one direction around the ring. This prevents collision.
Resources can be placed at any point on the ring as data will reach them.
(b) The specific IEEE standard.
IEEE 802.5
(c) The problems inherent with a ring topology.
They are dependent on all nodes and cable segments working. If a device is to be added the ring must be broken and remade.
3. Describe the difference between a Fiber Distributed Data Interface (FDDI) LAN and a simple
token ring LAN.
FDDI uses tow counter-rotating rings in the same network.
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Have the same characteristics as a standard ring but with extra resilience due to duplicate
node-to-node connections.
Data is transmitted simultaneously in both directions.
Receiving node can compare 2 versions to ensure no corruption.
Break in one ring can be overcome by using the other as a standard ring.
4. Explain the meaning of non-contention techniques in terms of network access and give ONE
example of such a method.
Designs that prevent conflict of nodes wishing to transmit a message over the network at the
same time.
Usually a node is given exclusive rights to transmit preventing a clash of messages.
Suitable example (e.g. Token Passing)
5. Describe a logical structure of a Bus Topology used for a LAN.
A single data highway connects all the nodes.
Network nodes are tapped onto the highway via T-connection.
6. Explain the operation of the Carrier Sense Multiple Access Collision Detection (CSMACD)
connection technique used by Ethernet.
Each node listens until no other nodes are transmitting
The node then transmits its data
If collision is detected the transmission is stopped
The node then waits for a specified period of time and retransmits.
7. Describe the characteristics of CSMA/CD in terms of:
(a) Order of transmission
(b) Length of wait time before transmission takes place
(c) Network saturation
(d) Capture effect
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(a) Order of transmission
There is no order of transmission.
(b) Length of wait time before transmission takes place
There is no guarantee of the length of time that must be waited before transmission.
(c) Network saturation
As data rates increase the probability of collisions increases.
This means a network can saturate at levels below the theoretical maximum.
(d) Capture effect
If a node transmits frames at a high rate it may have almost exclusive access to the network.
As other nodes are forced to back off a random time whilst transmission is in progress.
This means there is a strong probability that it will have uncontested access to its nest time
frame.
8. Describe the method used to prevent the reflection of signals at the end of bus.
A terminator (or head end) is located at the ends of each bus.
This device may be a resistor or complex electronic device that absorbs dissipates the signa
energy.
9. Describe the advantages of 10Base2 (thin Ethernet) cable when compared to 10Base5 (thick
Ethernet) cable.
It is very easy to disconnect part of a bus thus making communication along the whole bus and
all nodes impossible.
The maximum length of cable (185m) and number of connections (30) that can be made are
significantly lower than 10Base5 (500m, 100).
10. Explain the key differences between contention techniques and non-contention techniques
for allowing network access.
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(ii)Name ONE common non-contention technique for network access and state which network
topology it may be used in.
Contention techniques do not have a predetermined order of access and any node may transmit
at any time.
Contention techniques anticipate conflicts and collisions and use them as part of the design fo
network access.
Non-contention techniques are designed so that there is no conflict between nodes that wish to
transmit over a network.
(ii)Name ONE common non-contention technique for network access and state which network topology
it may be used in.
For Example, token passing is used in ring topology.
11. Explain the operation of the Carrier Sense Multiple Access/ Collision Detection (CSMA/CD)
contention technique used by Ethernet.
Each node listens until no other nodes are transmitting.
The node then transmits its data.
If collision is detected the transmission is stopped.
The node then waits for a specified period of time and retransmits.
Chapter-15 (2005/2006/5007)
1. State and briefly describe the three things that a network must offer if it is to be considered
as secure.
Privacy: The network should offer a reasonable level of assurance to its users that only those
users that are authorized to use its services are able to do so.
Integrity: The network should offer a reasonable level of assurance that the information
transmitted by a user of its services is to not modified, lost or corrupted in transit across the
network to its intended recipients(s).
Availability: The network should offer a reasonable level of assurance that it will be available
for use as and when its users require to use it.
2. Describe the difference between a physical attack and a n electronic attack on a network
Give TWO Examples of each.
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A physical attack is the result of a malicious human act, an accidental human act or an accident of
nature.
Typical examples are fire and theft.
An electronic attack is one that exploits the network itself to make an attack.
Typical examples are eavesdropping or Trojan horses.
. Describe how passwords are used as security measure in network. Give an example to
illustrate your answer.
The system checks that the password and username math.
If they match access to the system is granted.
The username will have rights and privileges attached to it.
The level of access granted will be in accordance with those access rights.
Suitable example: e.g. administrators will have access to parts of the network that are not
available to normal users.
4. Briefly describe what is meant by encryption as a security countermeasure.
Involves translating information from its original clear form by applying an encryption algorithm
ot the information.
It is intended to make it difficult for unauthorized people to read or decode the information.
5. Briefly describe the purpose of a firewall.
A security device that separates two or more networks having differing levels of security
policies.
Aim to prevent unauthorized external users from having access to an internal network.
Allow internal users to have access to external resources.
Can be implemented as software or hardware.
Can operate at different levels of the TCP/IP stack.
6. State TWO reasons why a document should be digitally signed before transmission.
Proves document really does originate from the person claiming to have sent it
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Ensures contents of the document have not been modified after sending.
7. Explain how authentication works as a security measure.
Allow the network to identify a person
It does this by challenging the user for some information and checking if this matches the stored
record.
It also grants particular rights and privileges to the user.
8. Briefly describe FIVE methods that may be used to authenticate the identify of a system user.
. Password: Allocating individual passwords to each user, which are regularly updated.
Personal identification Number (PIN): Each user has an identification number.
Fingerprint recognition: The fingerprint of each user is recorded and scanned on login to the
system.
Smartcard: Users have a card with a magnetic strip containing ID details the card is unique to
the user.
Voice recognition: The voice of each user is stored using special software and the users voice
is compared for authentication.
Handwriting recognition: A sample of handwriting (e.g. Signature) is stored and the user has
to sign again for authentication upon login.
Retinal Scan: The retina of the human eye has a pattern more unique than a fingerprint. This
can be stored and the users retina scanned for comparison.
9. Define the term computer virus and explain how computer viruses are propagated.
A virus is a malicious program that is in a executable from and may carry a payload that causes
damage to the host computer system or network.
Viruses are typically propagated by e-mail attachments but may be carried by any corrupted fileon floppy disk or CD-ROM.
10. Describe TWO ways in which firewalls specifically help prevent virus infection on a network.
Perform virus check on incoming e-mail attachments.
Prevent users from transferring files into the protected network.
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11. Define the term Trojan horse and explain how Trojan Horses are propagated.
Trojan Horses appear as apparently innocuous programs running on the host computer.
Its purpose is to allow an attacker to have access to the host computer via an attached network.
They are propagated in the same way as viruses.
12. State THREE properties required of a secure network.
Privacy
Integrity
Availability
13. Excluding use of a firewall, describe THREE countermeasures used to prevent virus and
Trojan Houser attacks.
Installing virus checking software on all networked machines and keeping the virus definitions
up to date.
Ensuring that all software that can connect to a network is updated so that any holes in their
security are fixed.
Educating all users of the network in the safe use of the technology.
14. Briefly describe what is meant by encryption as a security countermeasure.
Involves translating information from its original clear form by applying an encryption algorithm
to the information.
It is intended to make it difficult for unauthorized people to read or decode the information.
15. Briefly describe the TWO encryption modes supported by Secure IP (IPSEC).
Transport mode which only encrypts the payload of each packet and not the header.
Tunnel mode which is more secure and encrypt both header and payload.
16. Briefly describe the role of Point-to-Point Tunneling Protocol (PPTP) in network security.
It encapsulated data and overhead in an IP packet and encrypts data prior to transmission.
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It provides a secure bridge between networks and computers and can be used to construct a
Virtual Private Network.
17. Define the term Denial of Service (DoS) attack
An attack on a network that significantly slow or completely interrupts normal networks traffic.
18. Briefly describe how a DoS attack may harm an organization.
An organization may lose time and money as the result of an attack.
19. Describe EIGHT methods an organization may use to minimize the risk being affected by a
DoS attack.
Install route filters as this will session exposure. It will also aid in preventing users on the
network from launching DoS attacks.
Install patches to guard against TCP SYN flooding where TCP request re sent aster than a
machine can process them. This does not totally eliminate the risk.
Disable any unused or unneeded network services. This prevents an intruder from using those
services.
Enable quota systems on the operating system where available
Observe system performance and establish baselines for ordinary activity. Use the baseline togauge unusual levels of activity.
Routinely examine the physical security of the system.
Invest in redundant and fault-tolerant network configurations.
Establish and maintain regular backup schedules and policies, particularly for importan
configuration information.
Establish and maintain appropriate password policies, especially for highly privileged accounts
20. Define the term Zombie in relation to network security.
A system that has been hacked by an intruder in such a way that they can control it without the
rightful user of the system being aware of anything untoward.
21. Describe the TWO ways in which Zombies are commonly used
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To launch DoS attacks.
To provide a gateway into other parts of the network.
22. Define the term computer virus.
A virus is a malicious program that can be attached to an executable program or can be in other
executable forms such as macros.
The program can carry a payload that can caused damage to the infected host system
23. Briefly describe how data should be protected from physical attacks.
Have good fire prevention and detection equipment
Keep wiring and equipment closets locked.
Prevent unauthorized access to buildings
Keep back-up copies of data and have recover procedures.
24. Describe the steps taken to construct a digital signature and to check it at the receiving end.
The sender uses a hashing function to create a mathematical summary of the document.
The hashing function is one-way: the document cannot be recreated form it.
The sender uses a private key to encrypt the summary. This encrypted summary is the
signature of the document.
The signature will be different each time a new document is used and if a different key is used.
The document and signature are transmitted to the recipient. The same hashing function is used
to calculate the summary.
The senders public key is used to decrypt the signature.
The summary calculated by the recipient should match the summary extracted by deciphering
the signature.
This confirms the sender of the message and that it was not modified in transit.
25. Briefly describe the security benefits provided by Virtual Private Network. (VPNs)
Encryption and encapsulation technology allows a business to securely use the Internet as a
channel for private data communication.
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This greatly reduces cost and simplifies communications as it removes the need to build a
private network.
26. Describe the following threats to network security AND give examples of how they may be
used:
(i) Eavesdropping
(ii) Replay
(iii) Trojan House
Eavesdropping
Snooping on information carried by the network.
This may take the form of borrowing a terminal whilst the user is away.
Or tapping into the cables that carry the signals.
Replay
The attacker snoops on the network and records a series of messages.
The record messages are later replayed to achieve a particular result.
A simple method is to record usernames and passwords to allow the attacker to log into the
network in his/her own right.
Trojan Hosrse
Trojan Horses appear as apparently innocuous programs running on the host computer.
Its purpose is to allow an attacker to have access to the host computer via an attached network
They are propagated in the same way as viruses.
Chapter-16 (2005/2006/2007)
1. You are required to devise a routing plan for a national public telephone network. Assuming
that the country is already divided into local exchange areas. Briefly describe FOUR different
factors that should be covered by the plan.
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Which local exchanges should have direct connections and which should be conneted via
tandem exchanges.
The quantity and location of tandem exchanges
The maximum number of levels of tandem switching to b used.
Whether automatic alternative routing should be used and n what circumstances.
2. Briefly describe the FIVE main areas involved in network planning.
Traffic analysis: An understanding of the capacity logical information flow and types o
information between each point.
Choice of bearers: Choice of cabling is linked to the traffic and requirements to combine data
and voice cabling as well as the networking technology employed.
Choice of Technology: This interacts with the previous two points-traffic analysis and choice of
bearers.
Network Security: Network security is concerned with ensuring that threats to security are
countered.
Implementation: Implementation means how, when and where to carry out the work.
3. Describe the TWO ways in which networks using automatic alternative routing restrict
overflow.
The final route may be split into two with one route reserved for high-level, first-choice final
traffic. And the other route is a common route for all overflowing traffic.
The other method is to use SPC exchanges to implement a truck reservation system
Here overflowing calls from a high usage route are blocked whenever a final route has few free
circuits.
4. i) Draw a Diagram showing a process of a typical planning cycle for a network.
ii) Describe the processes you have shown in your diagram above. (9 Marks)
5. Briefly describe FOUR main areas involved in network planning.
Traffic analysis: An understanding of the capacity logical information flow and types o
information between each point.
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Choice of bearers: Choice of cabling is linked to the traffic and requirements to combine data
and voice cabling as well as the networking technology employed.
Choice of Technology: This interacts with the previous two points-traffic analysis and choice of
bearers.
Network Security: Network security is concerned with ensuring that threats to security are
countered.
Implementation: Implementation means how, when and where to carry out the work.
6. i) Defined the term redundancy when applied to network design.
ii) Describe FOUR factors that should consider when designing redundancy in a network.
The term redundancy when applied to network design.
The inclusion of additional links in a network that can be used in the event of failure, thus
increasing network resilience.
FOUR factors that should considered when designing redundancy in a network
How important is the traffic, what are the implications to the business, how long to repair tha link
and is the downtime acceptable.
What is the most likely reason for failure, interface hardware or the cable?
What physical paths do the main and back-up links follow? It is best to have different paths to
eliminate one threat breaking both.
Can load sharing be used to utilize both main and back-up links thus imporving network
performance?
7. Briefly describe FIVE main areas involved in network planning.
Traffic analysis: An understanding of the capacity logical information flow and types o
information between each point.
Choice of bearers: Choice of cabling is linked to the traffic and requirements to combine data
and voice cabling as well as the networking technology employed.
Choice of Technology: This interacts with the previous two points-traffic analysis and choice of
bearers.
Network Security: Network security is concerned with ensuring that threats to security are
countered.
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Implementation: Implementation means how, when and where to carry out the work.
8. State the THREE main assets of a telecommunications network.
The interconnection circuits
The equipment to which the interconnecting circuits are connected.
The people responsible for planning, building and running the network.
9. i) State the TWO types of financial costs associated with setting up and running a
telecommunications network.
ii) Provide TWO example of EACH type of cost.
TWO types of financial costs associated with setting up and running a telecommunications network
The capital cost of establishing the network.
The ongoing cost of operating the network.
TWO example of EACH type of cost.
Example of capital costs include:
Line Plant
Switching, transmission and singalling equipment
Accommodation including real estate
Exmples of ongoing costs include:
Network employee costs
Equipment and line maintenance costs
Cost of energy
10. List the TWO main sources of revenue for a telecommunications system.
Line or service rental
Call income