VI Semster B. Sc.
(I.T.) Examination,
Nov./Dec. 2012
Distance Education
ADVANCED COMPUTER
NETWORKS
Time : 3 Hours Max.
Marks : 100 Instructions :
1.
What is DNS ?
2. List the
basic functions that an email system support.
3. What is routing ? What are direct and
indirect routing ?
4.
Explain the need for audio compression.
5. List out
the advantages and disadvantagess of WLAN.
WLAN is a
network that uses high-frequency radio waves rather than wires to communicate
between nodes. WLAN
technologies
enable users to establish wireless connections within a local area such as
within a corporate or
campus
building, or in a public space like airport. IEEE approved the 802.11 standard
for WLANs, which specifies a
data
transfer rate of 1-2 Mbps.
The advantages of WLAN are:
Flexibility:
Within radio coverage, nodes can communicate without further restriction. Radio
waves can penetrate
walls,
and senders and receivers can be placed anywhere.
Easy to use:
The wireless networks are easy to set-up and use. Just plug-in a base station
and equip your laptops
with
WLAN cards.
Robustness:
Wireless networks can survive disasters. Networks requiring a wired
infrastructure will break down
completely
some time. If one base station goes down, users may be able to physically move
their PCs to be in range
of
another.
The disadvantages of WLAN are:
Quality of Service (QoS):
WLANs typically offer lower quality than wired networks. The main reasons for
offering
low
quality are lower bandwidth due to limitations in radio transmission, higher
error rates due to interference (10-
4 instead
of 10-10 for fiber optics), and higher delay/delay variation.
Vulnerable to interference: If a powerful transmitter operating in the same band as
the wireless network is nearby,
the
wireless network could be rendered completely useless.
Speed: Data
speeds drop as the user moves further away from the access point.
Operation within limited distance: Devices will only operate at a limited distance from an
access point. Obstacles
between
the access point and the user such as walls, glass, water, trees and leaves can
also determine the distance
of
operation.
6. What are
the three aspects of information security ?
The classification of
security services are classified as follows:
l Confidentiality:
This is the main service offered by the cryptography. This ensures
that the
information in a
computer system and transmitted information are accessible only for reading by
authorized parties.
This type of access includes printing, displaying and other forms of disclosure
including simply revealing
the existence of an object.
l Authentication:
This ensures that the origin of a message or electronic document
is correctly
identified, with an
assurance that the identity is not false.
l Integrity:
Ensures that only authorized parties are able to modify computer
system assets and
transmitted
information. Modification includes writing, changing, changing status,
deleting,
creating, and
delaying or replaying of transmitted messages.
l Non-repudiation:
This requires that neither the sender nor the receiver of a
message be able
to deny the
transmission.
l Access
control: Requires that access to information resources may be controlled by
or for the
target system.
l Availability:
Requires that computer system assets be available to authorized
parties when
needed.
7.
Write a figure showing adtive and passive network security threats.
PART – B
Answer any
FIVE full questions :
1. a) Write a
brief note on SMPTP.
b)Discuss the working of POP3 in a email
system. What are its limitations
2.
a) Explain the client-side and server-side events when a user click on a URL.
b) Discuss the
architecture of WWW.
The
architecture of WWW is two tiered. It consists of the client and the server.
The client (web browser) requests
for
a web page. This page is retrieved from the server. The architecture depends on
three key standards: HTML for
encoding
document content, Uniform Resource Locator (URL) for naming remote information
objects in a global
namespace,
and HTTP for staging the transfer. The following figure shows the two-tiered
architecture of WWW.
If
the web pages are interacting with the database, then the architecture becomes
three-tiered, as shown in the
following
figure.
Request
Response
Two-Tier
Architecture of
WWW
Request
Response
Three-Tier
Architecture of WWW
Client
SERVER
Client
SERVER DATABASE
3. a) Write a
note on routing information protocol.
The Routing
Information Protocol, or RIP, as it is more commonly called, is one of the most
enduring
of all routing
protocols. RIP is also one of the more easily confused protocols because a
variety of RIPlike
routing protocols
proliferated, some of which even used the same name! RIP and the myriad RIPlike
protocols were based
on the same set of algorithms that use distance vectors to mathematically
compare routes to
identify the best path to any given destination address.
Today’s open standard
version of RIP, sometimes referred to as IP RIP, is formally defined in two
documents: Request
For Comments (RFC) 1058 and Internet Standard (STD) 56. As IP-based networks
became both more
numerous and greater in size, it became apparent to the Internet Engineering
Task
Force (IETF) that RIP
needed to be updated. Consequently, the IETF released RFC 1388 in January
1993, which was then
superceded in November 1994 by RFC 1723, which describes RIP 2 (the second
version of RIP).
These RFCs described an extension of RIP’s capabilities but did not attempt to
obsolete
the previous version
of RIP. RIP 2 enabled RIP messages to carry more information, which permitted
the
b)
Give the format of OSPF packet and explain each field of it..
4
a) What is BGP ? Explain external and interior BGP with a neat figure. Explain attributes of BGP.
b)
What criteria is used by BGP when it selects a path for a destinations ?
5 a) What are
the functions perfomed by media player ? Elaborate your answer.
The media player has
a graphical user interface with control knobs. This is the actual interface
that
the user interacts
with. It typically includes volume controls, pause/resume buttons, sliders for
making
temporal jumps in the
audio/video stream, and so on.
Plug-ins may be used
to embed the user interface of the media player within the window of the Web
browser. For such
embeddings, the browser reserves screen space on the current Web page, and it
is up
to the media player
to manage the screen space.
b) Discuss the
architecture for audio-video streaming along with a neat diagram.
In
recent years, audio/video streaming has become a popular application and a
significant consumer of network
bandwidth. This trend is likely to continue for several
reasons. First, the cost of disk storage
continues to decrease
rapidly,
making room for storage-hungry multimedia files. Today, terabyte storage facilities
are available, capable
of holding
thousand of MPEG 2 videos.
Second, improvements in
Internet infrastructure, such
as high-speed
residential access
(that is, cable
modems and ADSL,
content distribution techniques
such as caching
and CDNs
greatly
facilitate the distribution of stored audio and video. And third, there is an enormous pent-up
demand for
high-quality video
on demand, an
application that combines
two existing killer
communication technologies
television
and the on-demand Web.
6 a) Explain
the following terms :.
Modulatin,
Carriers, Singal strength and Bandwidth
b) Describe IEEE 802.11 architecture.
The IEEE standard 802.11
specifies the most famous family of WLANs in which many products are
already available.
The standards number indicates this standard belongs to the group of 802.x LAN
standards, e.g. 802.3
Ethernet or 802.5 Token ring. This means that the standard specifies the
physical
and the medium access
layer adapted to the special requirements of wireless LANs. The primary goal of
the standard was the
specification of a simple and robust WLAN which offers time bound and
asynchronous
services.
Furthermore, the MAC layer should be able to operate with multiple physical
layers, each of
which exhibits a
different medium sense and transmission characteristic. Candidates for physical
layers
were infrared and
spread spectrum radio transmission techniques. Additional features of the WLAN
should include the
support of power management to save battery power, the handling of hidden
nodes, and
the ability to
operate worldwide.
7 a) Explain
the security attacks.
Attacks on the
security of a computer system or network are best characterized by viewing the
function of the
computer system as providing information. There are four general types of
cryptanalytic(also
referred as security
attacks) attacks. Each of them assumes that the cryptanalyst has complete
knowledge of the
encryption algorithms used. The four general categories of attacks are as
shown in the diagram
5.1.
(b) Interruption
Source Destination
(a) Normal Flow
(c) Interception
(d) Modification
Chapter 5 -
Crytography and Network Security
b) Describe the model of network security.
8 a)Explain the three dimensions along with
cryptographic subsystems are classified.
b) Describe
the four general types of cryptanalytic attacks.
The whole point of
cryptography is to keep the plaintext (or the key, or both) secrete from the
opponents
(also called
adversaries, attackers, interceptors, interlopers, intruders, opponents, or
simply the enemy).
The process of
attempting to discover X (Message or key) or both is known as cryptanalysis.
There are
four general types of
cryptanalytic attacks.
1. Cipher
text-only attack: The cryptanalyst has the cipher text of several messages,
all of
which have been
encrypted using the same encryption algorithm. The cryptanalyst’s job is to
recover the plaintext
or key of any messages used to encrypt the messages, in order to decrypt
other messages
encrypted with the same key.
Given: C1=Dm(P1),C2=Ek(p2)……ci
=Ek(Pi)
Deduce: Either P1, P2,….Pi,k; or
an algorithm to infer Pi+1 from Ci+1 = Ek (Pi+1)
2. Known –
plaintext attack: The cryptanalyst has the access to the cipher text as
well as
plaintext of the
messages. Cryptanalysts job is to deduce the key (or keys) used to encrypt the
messages or an
algorithm to decrypt any new messages encrypted with the same key (or keys).
Given: P1,C1 =Ek(P1),P2,C2=Ek(P2),…..Pi,Ci=Ek(Pi)
Deduce: Either k, or
an algorithm to infer Pi+1 from Ci+1=(Pi+1)
3.
Chosen plaintext attack: The cryptanalyst not only has access to
the cipher text and associated
plaintext for several
messages, but also chooses the plaintext that gets encrypted. This is more
powerful than a
plaintext attack, because the cryptanalyst can choose specific plaintext blocks
to encrypt, which might
yield more information about the key.
Given: P1,C1 =Ek(P1),P2,C2=Ek(P2),…..Pi,Ci=Ek(Pi),
Where the
cryptanalyst gets to choose P1,P2…Pi
Go for Enterteinment
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