VI Semester
B.Sc.
(I.T.) Examination,
May/June 2013
(Directorate of
Distance Education)
1. What is the
primary function of DNS ? List out different components of resource
record.
Ans- the
primary function of DNS is to map the Domain Names into Resource Records.
n Resource
Records have five components.
%Domain
Name
%Time
to live
%Class
%Type
%Value
I Domain name tell
the domain to which this record applies. It is the primary search key.
II Time to live:
Indicates how stable the record is. Most stable record has 86400 (the number of
seconds in 1 day).
Unstable records have a duration of 60 (1 minute).
III Class: Its value
for internet information, is IN, other codes are used for other application.
IV Type: Tells what
kind of record this is,
SOA Start of Authors
Parameters for this zone
A IP address 32 bit
integer
2. What is
iterative resolution ? Give example.
Ans- Iterative resolution refers
to the name resolution technique in which a server sends back the information
to a
client
or sends the name of the server that has the information. The client then
iterates by sending a request to this
referred
server. This server may return the information itself or send the name of
another server. This process
continues
till the time the client receives the required
information.
Whenever
the DNS server receive a packet, it will check
whether
it is an authority for the same, if so it will send the
answer
to Resolver. If it is not, then it will send the IP address of
another
server, which it thinks can resolve the DNS query. The client then sends DNS
request to the new DNS
server,
if it is an authority, it gives the IP address else. It sends the IP address of
anther DNS server. This process is
called
iterative resolution.
3. OSPF stands
for _______.
4. List the
drawbacks of the current internet to drive the multimedia data. -
Ans- Drawback:- The
Internet has some drawbacks with regard to multimedia data. For example, the
media player does
not
communicate with the streaming server directly. This delay, before play-out
begins, is typically unacceptable
for
audio/video clips of moderate length. For this reason, audio/video streaming
implementations typically have
the
server send the audio/video file directly to the media player process. In other
words, a direct socket connection
is
made between the server process and the media player process.
5. Name RIP's
various stability features.
The
Routing Information Protocol (RIP) is a dynamic routing protocol_ used in local and wide area
networks. As
such
it is classified as an interior
gateway protocol_ (IGP). It uses the distance-vector routing algorithm_. It was first
defined
in RFC 1058_ (1988). The protocol has since been extended several
times, resulting in RIP Version 2 (RFC
2453). Both versions are still in use today, however, they are
considered to have been made technically obsolete by
more
advanced techniques such as Open
Shortest Path First_ (OSPF) and the OSI_ protocol IS-IS_. RIP has also been
adapted
for use in IPv6_ networks, a standard known as RIPng (RIP next generation),
published in RFC 2080_
(1997).
6. What is
streaming ? Explain.
In this class of
applications, clients request on-demand compressed audio or video files that
are stored
on servers. Stored
audio files might contain audio from a professor’s lecture, rock songs,
symphonies,
archives of famous
radio broadcasts, or archived historical recordings. Stored video files might
contain
video of a
professor’s lecture, full-length movies, prerecorded television shows,
documentaries, video
archives of
historical events, cartoons, or music video clips. This class of applications
has three key
distinguishing
features.
7. What is
routing ? What are direct and indirect routing ? Give example.
Routing
is the process of moving information across an internetwork from a source
router to a destination router.
Routing
occurs at the third layer of the Open System Interconnect (OSI) model, known as
the network layer.
Routing
protocols use metrics to evaluate what path will be the best for a packet to
travel.
These
are four forms of routing.
Next hop Routing
Network specific Routing
Host specific Routing
Default routing
In direct routing, packet delivery occurs
when the source and destination of the
packet is located on the same physical
network or if the packet delivery is
between the last router and the
destination host.
In indirect routing, the packet goes from
router to router until it reaches the router
connected to the same physical network
as its final destination.
In direct routing, the address mapping is
between the IP address of the final
destination and the physical address of
the final destination.
PART-B
Answer any
FIVE full questions.
1. a) Explain
briefly SMTP protocol.
SMTP
.The Simple Mail Transfer Protocol
Within the internet,
e-mail is delivered by having the source machine establish a TCP connection to
port 25 of the
destination machine. Listening to this port is an email daemon that speaks SMTP
( Simple
Mail Transfer
Protocol). This daemon accepts incoming connections and copies message from
them into
the appropriate
mailboxes. If a message cannot be delivered, an error report containing the
first part of
the undeliverable
message is returned to the sender. SMTP is a simple ASCII protocol. After
establishing the TCP
connection to port 25, the sending machine, operating as the client, wits for
the
receiving machine,
operating as the client waits for the receiving machine, operating as the
server, to talk
fist.
b) Explain
client side and server side events. When user click on a URL ?
Server Side Operations
Server
side operations are concerned with the sending of the web page data from the
server to the web page
visitors
browser. In the case of Static Web Pages the data is simply served immediately
upon request for the data
from
the visitors browser. If the requested page is a Dynamic Web Page then any pre
processing of the page is
carried
out and the output is then served to the visitor.
PHP and
ASP(vbscript) are server side
scripting languages that are used
to pre process pages and output HTML
before
the page is sent to the visitor. HTML is the language that the browser
understands that tells it how to display
the
page.
Client Side Operations
Client
side operations are performed on the visitors computer by the users Internet
browser to display the web
page
as the data is received from the server.
HTML
is interpreted as it is read by the browser resulting in the display of the web
page within the browser. Once
the
page has loaded HTML cannot be reprocessed without refreshing the page.
The
visitors experience on the web page can however be enhanced by means of a
client side scripting language,
typically
Javascript used in conjunction with dynamic html and cascading style sheets,
which enable interactive
menu
systems, hi-lighting effects, image effects, data manipulation and many other
actions to be performed on the
page
without reloading or refreshing the page.
2. a) Discuss
the working of Pop 3 in an E-mail system. What are its limitations ?
When users check their e-mail, the e-mail client connects
to the POP3 server by using port 110. The POP3 server
requires an account name and a password.
The POP3 server issues a series of commands to bring
copies of user e-mail messages to user’s local machine.
Generally, it will then delete the messages from the
server (unless the user chooses the not to option in the e-mail
client).
Once the connection has been established, the POP3
protocol goes through three stages in sequence:
Authorization
Transactions
Update
The authorization state deals with the user log in. The
transaction state deals with the user collecting e-mail
messages and marking them for deletion from the mailbox.
The update state causes the e-mail messages to be
deleted.
During the authorization state, at times, when the server is set for three passwords
trials, if you give the
wrong
password thrice, your mail box will get locked.
POP3
servers have certain limitations such as:
There is no folder structure
for sorting e-mail messages that are saved on the POP3 server. The server has
only
one folder for incoming mails, which is the inbox.
No rules can be set at the
POP3 server. All rules are set at the client end only. If a user’s machine
crashes, e-
mail
messages can only be recovered if a copy of them is left on the server.
To check e-mail, users have
to download them first and only then they can view their mails on the e-mail
client
software. User cannot see mails first and then download the required mails. If
there are spam e-mail
messages
in the
inbox that can be dangerous for
the computer, these will also
get downloaded and
the
user
has to delete them.
b) Explain
audio streaming process.
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.
Audio
streaming is the transfer of audio-encoded packets that are decoded and sent to
the client’s soundcard upon
reception.
The host side is responsible for encoding and packetizing the audio stream. The
client side is responsible
for
decoding the packets and sending the decoded audio to the sound card.
There
are delays inherent in the overall system. These delays are contributed by the
encode/decode delay, transfer
delay,
buffer delay, modem delay, sound card delay, and other delays. As long as the
delays are kept constant, then
the
audio will be delivered uninterrupted.
3. a) Discuss
the features of real time protocol.
The
features of Real Time Protocol (RTP) are:
RTP provides end-to-end
delivery services for data with real-time characteristics such as interactive
audio
and
video. However, RTP itself does not provide any mechanism to ensure timely
delivery. It needs support
from
the lower layers of OSI model that actually have control over resources in
switches and routers. RTP
depends
on Resource Reservation Protocol (RSVP) to reserve resources and to provide the
requested
quality
of service.
RTP provides timestamps,
sequence numbers as hooks for adding reliability, flow, and congestion control
for
packet delivery, but implementation is totally left to the application.
RTP is a protocol framework
that is deliberately not complete. It is open to new payload formats and new
multimedia
software. By adding new profile and payload format specifications, one can
tailor RTP to new
data
formats and new applications.
The flow and congestion
control information of RTP is provided by Real-Time Control Protocol (RTCP)
sender
and receiver reports.
RTP/RTCP provides
functionality and control mechanisms necessary for carrying real-time content.
But
RTP/RTCP
itself is not responsible for the higher-level tasks like assembly and
synchronization. These have
to
be done at the application level.
b) Briefly
explain the WLAN architecture.
4. a) What is
an encryption ? Explain any one encryption method with a suitable
example.
In cryptography_, encryption
is the
process of transforming
information_ (referred to as plaintext_) using
an
algorithm
(called cipher_) to make
it unreadable to
anyone except those
possessing special knowledge,
usually
referred to as
a key_. The result
of the process
is encrypted
information (in
cryptography, referred to as
ciphertext). In many contexts, the word encryption
also implicitly refers to the
reverse process, decryption (e.g.
“
software
for encryption” can typically also perform
decryption), to make the encrypted information readable again
(i.e.
to make it unencrypted).
Encryption
is also used to protect data in transit, for example data being transferred via
networks_ (e.g.
the
Internet, e-commerce_), mobile
telephones_, wireless
microphones_, wireless
intercom_ systems, Bluetooth_
devices
and bank automatic teller machines_. There have been numerous reports of data in transit
being
intercepted
in recent years.[2]_ Encrypting data in transit also helps to secure it as it
is often difficult to physically
secure
all access to networks.
Encryption,
by itself, can protect the confidentiality of messages, but other techniques
are still needed to protect
the
integrity and authenticity of a message; for example, verification of a message authentication code_ (MAC)
or a
digital
signature_. Standards and cryptographic
software_ and hardware to perform encryption are widely
available,
but successfully using encryption to ensure security may be a challenging problem.
A single slip-up in
system
design or execution can allow successful attacks. Sometimes an adversary can
obtain unencrypted
information
without directly undoing the encryption. See, e.g., traffic analysis_, TEMPEST_, or Trojan horse_.
b) Write a figure
showing active and passive network security threats.
Passive
Attack: In this attack the goal of opponent is to obtain information that
is being transmitted.
Their exists 2 types
of passive attacks. They are release of message contents and traffic analysis.
l The release
of message contents is easily understood. A telephone conversation, an
electronic
Passive
Attacks Active Attacks
Release of traffic
analysis Masquerade Replay Modification of messages
Denial of service
Message contents mail
message, and a transferred file may contain sensitive or confidential
information. It is necessary to
prevent the opponent
from learning the contents of the transmissions.
Active
attacks
These attacks involve
some modification of the data stream or the creation of a false stream and it
has
been divided into 4
categories like masquerade, replay, and modification of messages and denial of
service.
Masquerade:
This takes place when on entity pretends to be a different than
other entity. This includes
one of the other form
of active attacks i.e. replay or modification of messages or denial of service.
Replay:
This involves the passive capture of a data unit and its
subsequent retransmission to produce an
unauthorized effect.
Modification
of messages: This means that some portion of the message is altered or that
messages
are delayed or
reordered to produce an unauthorized effect.
Denial
of service: This prevents or inhibits the normal use or management of
communications facilities.
5. a) Give the
format of OSPF packet and explain each field of it.
All OSPF packets begin with a 24-byte header, as
illustrated in Figure 2.6.
The
following descriptions summarize the header fields illustrated in Figure
Version
number—Identifies the OSPF version
used.
Type—Identifies the OSPF packet type as one of the following:
Hello—Establishes
and maintains neighbor relationships.
Database description—Describes the contents of the topological database. These
messages are
exchanged
when an adjacency is initialized.
Link-state request—Requests
pieces of the topological database from neighbor routers. These
messages
are exchanged after a router discovers (by examining database-description
packets)
that
parts of its topological database are outdated.
Link-state update—Responds
to a link-state request packet. These messages also are used for
the
regular dispersal of LSAs. Several LSAs
can be included within a single link- state update
packet.
Link-state
acknowledgment—Acknowledges link-state update packets.
Packet
length—Specifies the packet length,
including the OSPF header, in bytes.
Router
ID—Identifies the source of the
packet.
Area
ID—Identifies the area to which
the packet belongs. All OSPF packets are associated with a single area.
Checksum—Checks the entire packet contents for any damage suffered
in transit.
Authentication
type—Contains the authentication
type. All OSPF protocol exchanges are authenticated. The
authentication
type is configurable on per-area basis.
Authentication—Contains authentication information.
Data—Contains encapsulated upper-layer information.
b) Compare
802.11 a and 802.11b protocol.
6. a) Explain
BGP protocol.
The Border Gateway Protocol (BGP) is an inter-autonomous system routing protocol. An
autonomous system is a
network
or group of networks under a common administration and with common routing
policies. BGP is used to
exchange
routing information for the Internet and is the protocol used between Internet
service providers (ISP).
Customer
networks, such as universities and corporations, usually employ an Interior
Gateway Protocol (IGP) such
as
RIP or OSPF for the exchange of routing information within their networks.
Customers connect to ISPs, and ISPs
use
BGP to exchange customer and ISP routes When BGP is used between autonomous
systems (AS), the protocol
is
referred to as External BGP (EBGP). If a service provider is using BGP to
exchange routes within an AS, then the
protocol
is referred to as Interior BGP (IBGP). Figure 2.7 illustrates this distinction.
BGP
is a very robust and scalable routing protocol, as evidenced by the fact that
BGP is the routing
protocol
employed on the Internet. At the time of this writing, the Internet BGP routing
tables number
more
than 90,000 routes. To achieve scalability at this level, BGP uses many route
parameters, called
attributes,
to define routing policies and maintain a stable routing environment.
BGP Attributes:- Routes
learned via BGP have associated properties that are used to determine the best
route to a
destination
when multiple paths exist to a particular destination. These properties are
referred to as BGP
attributes,
and an understanding of how BGP attributes influence route selection is
required for the design of
robust
networks. This section describes the attributes that BGP uses in the route
selection process:
Weight
Local preference
Multi-exit discriminator
Origin
AS_path
Next hop
Community
b) Explain the
following terms:
i) Modulation
Data rates of a few
bits per minute (bpm), all the way to 100 Mbps, do not have radio
characteristics
that are sufficient
to allow them free movement through the air. To make data move through the air,
it
must be mixed with a
frequency that has good free-air transmission characteristics. The frequency
that
can carry the data is
called the carrier frequency.
In Figure 4.1, we see
a block diagram of a simple transmitter. Note that, as the data enters on the
left
of the figure, it is
mixed with the carrier frequency in a functional box called a modulator. A
generator
produces the carrier
frequency. When the intelligence is mixed with that frequency, it creates an
output
signal that may
resemble the output shown in the antenna.
ii) Carriers
If you tune the radio
in your home to 103.9 FM, you will receive the same station all the time. In
the
US, this is because
the FCC regulates this range of frequencies. However, the frequency band used
for
wireless – both the 2
and 5 GHz ranges – are unregulated. There is no ownership of any one frequency.
Interference could
become a problem if fixed carrier frequencies were used. To overcome this
problem,
carrier frequencies
are consistently changed via several approaches. The major approach used in
wireless
is called spread
spectrum. The height of the carrier is reduced (suppressed carrier), and
the carrier
frequency is
consistently changed within a predefined range and with a pattern known by both
the receiver
and the transmitter.
iii) Signal
strength
When a signal is sent
into space, it mixes with radio noise. Once this happens, it is difficult to
separate
the two. In radio
communications, you may have two units of signal strength, but if one unit is
noise, you
really have one
useable unit of signal. The relationship in proportions of signal to noise is
called signal-tonoise
ratio. The lower the
signal-to-noise ratio, the lower the overall data performance. In Figure 4.4,
we
see a radio signal
and noise for a fixed carrier signal.
iv) Bandwidth.
Bandwidth alone
should not be the deciding factor in equipment purchase and installation. In a
wired
environment, many
devices share the same wires. In a wireless environment, many devices share the
same radio spectrum.
However, with the use of spread-spectrum technology, the resources are reused
many times over.
It is said that
bigger is better, so more bandwidth is better, right? It may not be. In wired
networks,
sometimes the rating
of the wire’s clock speed is confused with traffic throughput. Because Ethernet
uses CSMA/CD with
statistical multiplexing, the general rule is to design networks in which the
throughput
does not exceed 30%
of the rating, so an Ethernet-based 10Mbps link would have an average
throughput
of 3Mbps.
7. a) Describe
the three general types of crypt analytic attacks.
b) Explain the
three dimensions along with cryptographic subsystems are
classified.
8. Write short
notes on
a) DNS system.
It is well known that
the IP addresses are used to identify the devices in the internet such as
Routers,
Servers etc. In the
absence of a domain name for an Email server, we would have ended with a
representation such
as Xyz@144.16.70.2, abc@202.167.72.16 etc. It can been seen that such a
representation is
very difficult to remember that too impossible if there are hundreds of such
email ids. If
the email server is
loaded to a different machine with a different IP address, they above scheme
does not
work.
If this is the case
with Email, then how about the thousands of websites? For example, http://
202.16.70.2/~index.html, is
a URL. We need to remember the entire number to access the page.
b) Multimedia
on internet.
Recall that the IP
protocol deployed in the Internet today provides a best-effort service to all
the
packets it carries.
In other words, the Internet makes its best effort to move each datagram from
sender
to receiver as
quickly as possible, but it does not make any promises whatsoever about the end-to-end
delay for an
individual packet. Nor does the service make any promise about the variation of
packet delay
within a packet
stream. Because TCP and UDP run over IP, it follows that neither of these
transport
protocols makes any
delay guarantees to invoking applications. Due to the lack of any special
effort to
deliver packets in a
timely manner, it is an extremely challenging problem to develop successful
multimedia
networking
application for the Internet.
To date, multimedia
over the Internet has achieved significant but limited success. For example,
streaming stored
audio/video with user-interactivity delays of five to ten seconds is now
commonplace in
The receiver accessed
the medium after waiting for duration of SIFS and, thus, no other station can
access the medium in
the meantime and cause a collision. The other stations have to wait for DIFS
plus
their backoff time.
This acknowledgement ensures the correct reception of the frame on the MAC
layer,
which is especially
important in error-prone environments such as wireless connections. If no ACK
is
returned, the sender
automatically retransmits the frame. But now the sender has to wait again and
compete for the
access right.
