ECE 271 INTRODUCTION TO TELECOMMUNICATION NETWORKS
ANSWERS TO ECE 271 HOMEWORK
Homework Question 29
Twisted Pair, Coaxial, Microwave, Satellite, Fiber and Free Space Optics
Communication Systems in terms of:
a. Frequency of Operation,
aximum Bit Rate which is possible to transmit,
c. Distance Between Repeaters.
Answer to Homework Question 29
Frequency of Operation
Maximum Bit Rate
Homework Question 30
You have a multimode and a single mode fiber.
a. Write their core diameters, cladding diameters
b. Which one is preferred for long distance communication and for LAN applications?
one is preferred to be used with an LED and with a laser diode?
Answer to Homework Question 30
a. For multimode fibers, core diameters are 50, 62.5 and 100 micrometers, corresponding
cladding diameters are 125, 125 and 140 micrometers. For singlemode fi
diameter is 9 micrometers, cladding diameter is 125 micrometers.
b. Singlemode fibers
are preferred for long distance communication and multi
are preferred for LAN applications.
are preferred to be used with an L
to be used with a laser diode?
Homework Question 31
a. List the disturbances due to the atmosphere which effects Free Space Optical
b. List the disturbances other than atmosphere which
effects Free Space Optical
Answer to Homework Question 31
a. Disturbances due to the atmosphere effecting Free Space Optical communication
Fog: Major effect to FSO.
Rain and Snow: Have relatively little effect.
b. Disturbances other than atmosphere which effects Free Space Optical communication
can temporarily (for a short time) block a single
Building sway/seismic activity: Movement of buildings can disturb receiver and
Safety: Human exposure to laser beams
Homework Question 32
Write the main difference between
the connection oriented networking and the
Answer to Homework Question 32
In the connection oriented networking, connection set up is done before information
transfer occurs, i.e first the connections from the information sou
rce up to the final
destination point are made, then the information flow starts.
However, in the connectionless networking no connection set
up is made before data is
transmitted, i.e no preconceived path exists. Each individual fragment of the overall t
stream (i.e data packet) is individually adressed and individually routed to its destination
based on information contained in the header of the individual data packet
Homework Question 33
Explain the advantages and the disadvantages of connectio
n oriented networking and the
Answer to Homework Question 33
Advantages of connection oriented networking:
Provides service guarantees
Convenient in time
sensitive applications such as voice and video transmission
use network bandwidth by switching transmissions to appropriate connections
as the connections are set up
After the path is determined there is no delay at intermediate nodes.
Can be operated in:
Provisioned mode: Connections are made ahead of time (be
fore the request from
the customer) based on expected traffic. E.g. leased lines in circuit switching or
PVCs (Permanent Virtual Circuits) in packet switching
Switched mode: Connections are made on demand and released after the
communication ends E.g. dial
up in circuit switching or SVCs (Switched Virtual
Circuits) in packet switching
Disadvantage of connection oriented networking
There can be certain delay at the beginning while the connection is being built up.
Advantages of Connectionless Networkin
Flexible networks like the public internet consisting of more than 150,000 separate
subnetworks and around 10,000 ISPs (Internet Service Providers) can be formed.
Disadvantages of Connectionless Networking
Delay in the overall transit time is increase
d because each packet has to be individually
routed at each intermediate node
Not very convenient for time sensitive applications like on
line voice, video transmission
because path is not guaranteed
Difficult to calculate the potential delays or latencies
Homework Question 34
Describe the “packet” used in packet switching networks.
Answer to Homework Question 34
A packet (or frame, block, cell or datagram) is a container carrying control and data bits.
Control and data bits can each be in va
rious sizes, i.e. can contain different number of bits.
Control bits (start, header, destination address, data sequence number, stop, ...etc) are
used by the network nodes to route the packet under certain protocol (available bandwidth,
existing noise, nee
d for retransmission, latency considerations, ... etc).
Homework Question 35
a. Explain how the communication is established in circuit switching.
b. Explain how the communication is established in packet switching
Answer to Homework Question 35
Establishment of communication in circuit switching:
When requested by the end user (for example when the user dials up the phone), a
circuit is formed between the calling and the called party,
A fixed share of the network resources for that connection a
re reserved for this specific
communication during the full duration of
conversation. İ.e no other call can use those
resources until the communication ends. This means that the capacity provisioned on
that specific path can only be used by this call, no one else can share or use the
capacity available on that path,
When the c
onversation is over, connection is released, i.e the circuit is disconnected.
b. Establishment of communication in packet switching:
A packet (or frame, block, cell or datagram) is generated
Packets are stored
forwarded by packet switches up to th
Packets from many different sources are statistically multiplexed and sent to their
destinations over virtual circuits
Packet switches examine packet header and check destination against a routing table
Packets are routed to the specified