ASSIGNMENT # 1
Data Communication &
Networks
15-11-2018
Submitted by:
ASMA SHABIR
Roll no:
fa15-bscs-269
Class:
6th (b)
Submitted to:
DR ASIF
Q No: 1 Write the difference between the
following
(i)
Amplifier & Repeater:
1: Amplifier is used to magnify a signal, whereas repeater is used to receive and retransmit a
signal with a power gain
2: Repeater has an amplifier as a part of it.
3: Sometimes, amplifiers introduce some noise to the signal, whereas repeaters contain
noise eliminating parts.
(ii) LAN & WAN:
1: LAN has to cowl small geographical area that’s why its data change speeds are extreme. While WAN
has to cowl bigger distance which suggests knowledge has to journey prolonged distance, so there is likely
to be mechanically low change tempo.
2: LAN is usually managed and managed by one particular person or a small dimension group whereas
WANs have collective or distributed possession and administration for each specified area.
3: LAN has low repairs value whereas WAN setup costs are typically bigger on account of hook up with
distant areas
4: It could also be very easy to trace out errors or fault in LAN that could be very onerous in case of
WAN.
(iii) Mesh & Star topologies:
1: The Star topology organizes the node in a star shape where the central hub is
connected to all the other nodes. On the other hand, in the mesh configuration, each node
is connected to the other nodes
2: Easy installation and reconfiguration is possible in the star topology. As against, the
mesh topology requires more transmission media, effort and time for installation and
reconfiguration.
3: Star topology is cost-effective to some extent, while the mesh is expensive.
4: The star topology has a drawback where the inoperative central hub can make the
entire system inoperative. On the contrary, the mesh topology is more robust than the star
topology.
(iv) Physical and logical address:
1: The basic difference between Logical and physical address is that Logical address is
generated by CPU in perspective of a program. On the other hand, the physical address is a
location that exists in the memory unit.
2: The logical address is also called virtual address as the logical address does not exist
physically in the memory unit. The physical address is a location in the memory unit that
can be accessed physically.
3: The logical address is a reference used to access physical address. The user can access
physical address in the memory unit using this logical address.
(v) Hub and Switch:
1: Hub are network devices that operate on physical layer-1 to connect network devices for
communication while switches are forward data at the data link layer (layer 2) of OSI model.
2: Hub is a passive device (without software) while switch is an active device (with software) &
networking device.
3: Hub cannot learn or store MAC address while switch stores MAC addresses in a lookup table.
Q No:2: What is a peer-to-peer process?
Peer-to-peer process:
A layer appears to be communicating directly with the same layer at the other end of the
link (i.e. its peer). What is actually happening is that the data is being passed down to
lower layers for transmission and is passed up again at the other end.
Q No: 3: What are the advantages of layering?
Advantages of layering:
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It prevents changes in one layer from affecting other layers.
It describes what functions occur at each layer of the model that encourages industry standardization.
Dividing network communication process in smaller component makes software development, design,
and troubleshooting easier.
Standardization of network components allows multiple-vendor development.
It allows different types of network hardware and software to communicate.
Dividing network in layers make network administrators life easier. They can troubleshoot issue more
quickly and effectually by looking in layer that is causing issue rather than finding it entire network. It
also makes learning easier.
Q No 4: Is it true that the most upper layer of
OSI Model can enjoy all the services provided
by all lower six layers? if yes, why?
ANS:
The layered model allows for abstraction. In other words, the higher layers do not necessarily have to
know how the lower layers are doing their jobs. In addition, the lower layers do not necessarily have to
know what the upper layers are actually doing with the results of the lower layers’ labors.
Q No: 5 Suppose a computer sends a packet at the network
layer to another computer somewhere in the internet. The
logical destination address of the packet is corrupted. What
happen to the packet? How can the source computer be
informed of the situation?
Ans:
when a packet gets sent out it has both the destination address and the source address. Once the
destination successfully receives the packet it send a response back to the source address to say it was
successful. (With UDP - you just send it and don’t wait for an acknowledgement that it got there OK).
Therefore if the destination address or source address were incorrect, the source machine would not get a
return saying all got through OK. Normally this would result in the packet being resent after a period of
time. So assuming we have an incorrect address, the packet will eventually be delivered to the wrong
destination (that system might send back that it received it OK - so that could be a problem - but
hopefully it would ignore it - a bit like I do with letters I don’t want to receive - depends on firewall
policies). Otherwise it will fail quite quickly when it can’t be routed to a host, in which case you would
get an error message back. (Using the source address).
Q No:6 Draw a hybrid topology with a star
backbone and three ring networks
Q N0:7 Let n be the number of terminal. What is
the number of cables required for each type of
networks:
a. Mesh:
A fully connected mesh network therefore has n(n-1)/2 physical channels to link n devices
b. Star:
In star a central hub is used and cable depend on the number of system need to b connected
c. Bus:
In bus network one main cable is used and n numbers of computers connected side by side as
needed.
d. Ring:
In ring network cable=number of computers need to form a circle or a ring
Q N0 8: What will happen to each of the
following network of five devices if a single
connection (link) is failed:
a. Mesh Topology:
A MESH TOPOLOGY IS ROBUST. IF ONE LINK BECOMES UNUSABLE, IT DOES NOT HALT THE ENTIRE
SYSTEM.
b. Star Topology:
IF ONE LINK FAILS, ONLY THAT LINK IS EFFECTED, ALL OTHER REMAIN ACTIVE.
c. Bus Topology :
A FAULT OR BREAK IN THE BUS CABLE STOP ALL TRANSMISSION.
Ring Topology:
IN A SIMPLE ONE WIRE RING, A BREAK IN THE RING SUCH AS A DISABLE STATION CAN DISABLE THE
ENTIRE NETWORK. BUT THIS WEAKNESS CAN BE SOLVED BY USING A DUAL RING OR A SWITCH CAPABLE
OF CLOSING OFF THE BREAK.
Q No: 9 Explain function and the structure of
OSI model layers?
The OSI (Open Systems Interconnection) Model is a conceptual model that characterizes and
standardizes the communication functions of a telecommunication or computing system without
regard to its underlying internal structure and technology. Its goal is the interoperability of
diverse communication systems with standard protocols.
In the OSI model, control is passed from one layer to the next, starting at the application layer
(Layer 7) in one station, and proceeding to the bottom layer, over the channel to the next station
and back up the hierarchy. The OSI model takes the task of inter-networking and divides that up
into what is referred to as a vertical stack that consists of the following 7 layers.
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Layer 7 - Application
Layer 6 - Presentation
Layer 5 - Session
Layer 4 - Transport
Layer 3 - Network
Layer 2 - Data Link
Layer 1 - Physical