Micromax Launches Two Budget Windows Phone 8.1 Smartphones in India More than two months after Microsoft announcedMicromax as a Windows Phone partner, the domestic handset manufacturer has announced two budget Windows Phone 8.1 handsets - the Canvas Win W092and Canvas Win W121, priced at Rs. 6,500 and Rs. 9,500 respectively. Both handsets will be available on retail shelves in India from early July, according to the official Windows blog. The Canvas Win W092 and Canvas Win W121 feature dual-SIM support, making them some of the few such Windows Phone devices - the Lumia 630 Dual SIM( announced in Apriland launched in India in May) was the first dual-SIM Windows Phone. The Canvas Win W121 (seen above) is nearly identical with the Canvas Win W092, though it features a larger display and a high-resolution camera. The Canvas Win W121 bears a 5-inch HD (720x1280 pixels) IPS display, and is powered by 1.2GHz quad-core Snapdragon 200 (MSM8212) SoC that is coupled with 1GB of RAM. It once again features 8GB of built-in storage that can be expanded via microSD card (up to 32GB). The Canvas Win W121 bears an 8-megapixel rear autofocus camera with flash, and a 2-megapixel front-facing camera. It also features 2000mAh battery that's rated to deliver up to 8 hours of talk time and 150 hours of standby time. It also has a leather finish on the rear panel. Connectivity options include 3G, GPRS/ EDGE Wi-Fi, Bluetooth, and GPS.

Micromax Launches Two Budget Windows Phone 8.1 Smartphones in India More than two months after Microsoft announcedMicromax as a Windows Phone partner, the domestic handset manufacturer has announced two budget Windows Phone 8.1 handsets - the Canvas Win W092and Canvas Win W121, priced at Rs. 6,500 and Rs. 9,500 respectively. Both handsets will be available on retail shelves in India from early July, according to the official Windows blog. The Canvas Win W092 and Canvas Win W121 feature dual-SIM support, making them some of the few such Windows Phone devices - the Lumia 630 Dual SIM( announced in Apriland launched in India in May) was the first dual-SIM Windows Phone. The Canvas Win W121 (seen above) is nearly identical with the Canvas Win W092, though it features a larger display and a high-resolution camera. The Canvas Win W121 bears a 5-inch HD (720x1280 pixels) IPS display, and is powered by 1.2GHz quad-core Snapdragon 200 (MSM8212) SoC that is coupled with 1GB of RAM. It once again features 8GB of built-in storage that can be expanded via microSD card (up to 32GB). The Canvas Win W121 bears an 8-megapixel rear autofocus camera with flash, and a 2-megapixel front-facing camera. It also features 2000mAh battery that's rated to deliver up to 8 hours of talk time and 150 hours of standby time. It also has a leather finish on the rear panel. Connectivity options include 3G, GPRS/ EDGE Wi-Fi, Bluetooth, and GPS.

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BOLLYWOOD MOVIE JAY HO IS SALMAN KHAN

Salman Khan's film Jai Ho has received mixed reactions at the box-office and the superstar feels that the response at the theatres and the collections garnered are not "matching up". "This time we are also confused because the reactions inside the theatres and the collections are not 

matching up. So it's a very strange thing," the 48-year-old said here Monday at the launch of Gixxer bikes by Suzuki. 

However, Salman believes that their effort at doing something different from their regular stuff might be a reason for people not thronging to the theatres. 

"We have done something different, may be people were expecting something like Dabangg, Ready like time pass film to enjoy. Some must have understood that Jai Ho is not that kind of film, this is a serious film with a social message," Salman said. 

The 48-year-old says that he is the only person to be blamed for any kind of debacle. 

"I will only say that the credit or the blame for my film should come to me and not to anybody else. Perhaps I have failed in bringing in the people," he said. 

Directed by his brother Sohail Khan, Jai Ho has managed to collect around approximately Rs. 61 crore in the opening weekend of it's release.

- See more at: http://www.hindustantimes.com/entertainment/bollywood/salman-confused-by-jai-ho-response-business/article1-1177578.aspx#sthash.mK65Few1.dpuf

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kuvempu university KU 2012 EXAM Question Answer BSIT-63

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 ?

 ANS- GIVEN IN 2013 ANSWERS

  2. List the basic functions that an email system support.

 ANS- GIVEN IN 2013 ANSWERS

 3. What is routing ? What are direct and indirect routing ?

 ANS- GIVEN IN 2013 ANSWERS

4. Explain the need for audio compression.

 ANS- GIVEN IN 2013 ANSWERS

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.

 ANS- GIVEN IN 2013 ANSWERS

 b)Discuss the working of POP3 in a email system. What are its limitations

 ANS- GIVEN IN 2013 ANSWERS

2. a) Explain the client-side and server-side events when a user click on a URL.

 ANS- GIVEN IN 2013 ANSWERS

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..

 ANS- GIVEN IN 2013 ANSWERS

4 a) What is BGP ? Explain external and interior BGP with a neat figure. Explain attributes of BGP. 

 ANS-GIVEN IN 2013 ANSWERS

b) What criteria is used by BGP when it selects a path for a destinations ?

 ANS- GIVEN IN 2013 ANSWERS

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

 FIND YOURSELF

 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.

 GIVEN IN 2013 ANSWERS

8  a)Explain the three dimensions along with cryptographic subsystems are classified.

 GIVEN IN 2013 ANSWERS

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

kuvempu university KU june 2013 EXAM Question Answer BSIT-63

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

c) CSMA/CD mechanism.

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.