School
of Computer Science
SPOT
ASSIGNMENT (CY-2013/AY 2012-2013)
NOTE : Part A Contains 3 Questions and will
carry 5 Marks each, Part B Contain 1 Question and will carry 10 Marks. Students
are requested to write 150 words and should not exceed 2 pages each in Part A,
300 words and should not exceed 4 pages in Part B. Referring Materials.
Bachelor
of Computer Applications
Second Year
Course
Code : BCA-10
Course
Title : Computer Network
(Total Marks=25)
Part-
A- Short Answer Questions
Answer all questions (3 X 5 = 15 Marks)
1. Explain the types of transmission modes?
Answer:
Transmission Media
modes:
The purpose of the physical layer is to transport a
raw bit stream from one machine to another. Various physical media can be used
for the actual transmission. Each one has its own niche in terms of bandwidth, delay,
cost, and ease of installation and maintenance. Media are roughly grouped into
guided media, such as copper wire and fiber optics, and unguided media, such as
radio and lasers through the air.
Coaxial Cable
Another transmission medium is the coaxial cable. It
has better shielding than twisted pairs, so it can span longer distances at
higher speeds.
Fiber Optics
Wide
area data communication went from 56 kbps (the ARPANET) to 1 Gbps (modern
optical communication), a gain of more than a factor of 125 per decade, while
at the same time the error rate went from 10-5 per bit to almost zero.
Wireless Transmission
Radio
waves are easy to generate,Can travel long distances Can penetrate buildings
easily So
they are widely used for communication, both indoors and outdoors.
Microwave Transmission
the microwaves travel in a straight line, if the
towers are too far apart, the earth will get in the way. Consequently,
repeaters are needed periodically.
Light wave Transmission
Unguided optical signaling has been in use for
centuries. Paul Revere used binary optical signaling from the Old North Church
just prior to his famous ride.
Communication Satellites
Communication satellites and some of their properties,
including altitude above the earth, round-trip delay time, and number of
satellites needed for global coverage.
- Explain the shortest path Routing?
Answer:
The idea is to build a graph of the subnet,with each
node of the graph representing arouter and each arc of the graph representing a
communication line or link. To choose a route between a given pair of routers,
the algorithm just finds the shortest path between them on the graph.
 |
| The first 5 steps used in computing the shortest path from A to D.The arrows indicate the working node. |
Many other metrics besides hops and physical
distance are also possible.
For example, each arc could be labeled with the mean
queuing and transmission delay for some standard test packet as determined by hourly test runs. With this graph labeling, the
shortest path is the fastest path rather than the path with the fewest arcs or
kilometers.
In the general case, the labels on the arcs could be computed as a
function of the distance, bandwidth, average traffic, communication cost, mean
queue length, measured delay, and other factors.By changing the weighting
function, the algorithm would then compute the “shortest”path measured
according to any one of a number of criteria or to a combination of criteria.
- Write note on switches?
Answer:
Switches:
A switch is a
device that incorporates bridge functions as well as point-to-point 'dedicated
connections. They connect devices or networks and filters forward and floods
frames based on the MAC destination address of each frame. Switch operates at
data-link layer of the OS! model. They are technically called bridges. They
move data without contention. Ethernet switches provide combinations of shared/dedicated
10/100/1000 Mbps connections. Some E-net switches support cut-through switching:
frame forwarded immediately to destination without awaiting for assemble of the
entire frame in the switch buffer. They significantly increases throughput. It
provides express lane for traffic.
 |
| Switches |
______________________________________________________________________________
Part-
B- Long Answer Question
Answer the following
question (1 X 10 = 10 Marks)
- Explain the OSI Model in detail?
Answer:
The Open Systems Interconnect
(OSI) model has seven layers. This article describes and explains them,
beginning with the 'lowest' in the hierarchy (the physical) and proceeding to
the 'highest' (the application). The layers are stacked this way:
- Application
- Presentation
- Session
- Transport
- Network
- Data Link
- Physical
PHYSICAL LAYER
The physical layer, the
lowest layer of the OSI model, is concerned with the transmission and reception
of the unstructured raw bit stream over a physical medium. It describes the
electrical/optical, mechanical, and functional interfaces to the physical medium,
and carries the signals for all of the higher layers.
DATA LINK LAYER
The
data link layer provides error-free transfer of data frames from one node to
another over the physical layer, allowing layers above it to assume virtually
error-free transmission over the link. Frame error checking: checks received
frames for integrity.
NETWORK
LAYER
The
network layer controls the operation of the subnet, deciding which physical
path the data should take based on network conditions, priority of service, and
other factors.
TRANSPORT LAYER
The transport layer ensures
that messages are delivered error-free, in sequence, and with no losses or
duplications. It relieves the higher layer protocols from any concern with the
transfer of data between them and their peers.
SESSION LAYER
The
session layer allows session establishment between processes running on
different stations.
PRESENTATION LAYER
The
presentation layer formats the data to be presented to the application layer.
It can be viewed as the translator for the network. This layer may translate data
from a format used by the application layer into a common format at the sending
station, then translate the common format to a format known to the application
layer at the receiving station.
APPLICATION LAYER
The application layer serves as the window for users and application processes to access network services.
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