CHAPTER-1 (Application Layer)
1. List the functions of application layer.?
Answer-
2. What is DNS?
Answer-
DNS is a name resolution service that resolves host names to the IP addresses. DNS has a hierarchical and distributed database that contains mappings of host names with the corresponding IP addresses.
3. Explain the working of DNS with an example.
Answer-
DNS is a name resolution service that resolves host names to IP addresses. A DNS server resolves host names to IP addresses for DNS queries sent by the DNS clients. These queries can be in the form of a name resolution query or a resource record. The resolver sends a User Datagram Protocol (UDP) packet to the local DNS server. The DNS server searches its table and returns the IP address, which matches the domain name. DNS has a hierarchical and distributed database that contains mappings of host names with the corresponding IP addresses.
Resource records are stored in a specific portion of the DNS database called the DNS zone. A DNS zone contains resource records along with the owner names.
For example, an application program calls a procedure with its domain name as parameter. The procedure sends an UDP packet to the local DNS server. The DNS server searches its table and returns the IP address which matches the Domain name. The program can now establish a TCP connection or send UDP packets.
4. What is iterative resolution? Give example.
Answer-
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.
5. What are the functions of the user agent in the Email architecture?
Answer-
In the e-mail architecture, the user agent helps users to interact with the e-mail systems. The functions of the user agent in e-mail architecture are:
6. Discuss the sending and receiving process in Email?
Answer-
The prerequisites for sending and receiving an e-mail are:
The following is the sequence of the e-mail sending process:
In the implementations of POP3, the server maintains a collection of text files, one for each e-mail account. When a message arrives, the POP3 server simply appends it to the bottom of the recipient's file.
The following is the sequence of the e-mail receiving process:-
7. Write a brief note on SMTP?
Answer-
SMTP is a protocol that transfers mail reliably and efficiently. SMTP is independent of a particular transmission subsystem and needs only a reliable ordered data stream channel. An important feature of SMTP is its capability to relay mail across transport service environments.
8. Discuss the working of POP3 in an Email system? What are its limitations?
Answer-
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:
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 :-
9. What is www?
Answer-
WWW is a hypertext-based system that provides a uniform and a user-friendly interface for accessing the resources on the Internet. It is an information space in which the items of interest, referred to as resources, are identified by global identifiers called Uniform Resource Identifiers (URI).
10. Discuss the architecture of WWW?
Answer-
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
Request
CLIENT ------------------ > SERVER
<--------------
Response
Two-Tier 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
CLIENT ---------------> SERVER -----------------> DATA BASE
<--------------- <----------------
Response
three-Tier Architecture of WWW
11. Explain the client side and server side events when a user click on a URL?
Answer-
The client side events when a user clicks on a URL are as follows:
When a user clicks on a URL, the server side events are as follows:
12. Explain what is a server farm? Give an example.
Answer-
A server farm is a group of networked servers that are housed in one location. A server farm streamlines internal processes by distributing the workload between the individual components of the farm and expedites computing processes by harnessing the power of multiple servers. The farms rely on load balancing software that accomplishes the following tasks:
When one server in the farm fails, another can step in as a backup.
--------------------
CHAPTER-2 (Routing Protocols)
1. What is Routing? Discuss direct and indirect Routing?
Answer-
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. The differences between direct routing and indirect routing are as follows.
2. Discuss different approaches used to make the routing table more efficient?
Answer-
There are many approaches to make a routing table efficient such as:
3. Name RIP’s various stability features.
Answer-
The stability features of RIP are:
4. What is the purpose of the timeout timer?
Answer-
The purpose of the route timeout timer is to help purge invalid routes from a RIP node. Routes that are not refreshed for a given period of time are likely to be invalid because of some change in the network. Thus, RIP maintains a timeout timer for each known route. When a route's timeout timer expires, the route is marked invalid but is retained in the table until the route-flush timer expires.
5. What two capabilities are supported by RIP 2 but not RIP?
Answer-
Two capabilities, which are supported by RIP2 but not by RIP1, are:
6. What is the maximum network diameter of a RIP network?
Answer-
The maximum network diameter of a RIP network is 15 hops.
7. When using OSPF, can you have two areas attached to each other where only one AS has an interface in Area 0?
Answer-
Yes, you can. This describes the use of a virtual path. One area has an interface in Area 0 (legal), and the other AS is brought up and attached off an ABR in Area 1, so you can call it Area 2. Area 2 has no interface in Area 0, so it must have a virtual path to Area 0 through Area 1. When this is in place, Area2 looks like it is directly connected to Area 0. When Area 1 wants to send packets to Area 2, it must send them to Area 0, which in turn redirects them back through Area 1 by using the virtual path to Area 2.
8. Area 0 contains five routers (A, B, C, D, and E), and Area 1 contains three routers (R, S, and T). What routers does Router T know exists? Router S is the ABR.
Answer-
Router T knows about routers R and S only. Likewise, Router S only knows about R and T, as well as routers to the ABR in Area 0. The AS’s separate the areas so that router updates contain only information needed for that AS.
9. Can IBGP be used in place of an IGP (RIP, IGRP, EIGRP, OSPF, or ISIS)?
Answer-
Use of IBGP in place of IGP is conditional. The next-hop information from EBGP is carried into IBGP. If IBGP does not have a route to reach the next hop, then the route will be discarded. Typically, an IGP needs to be used to exchange routes to the next hop, but this can be achieved by using static routes on all the routers running IBGP. So, the answer is yes if you want to use and maintain static routes. Otherwise, you can not use IBGP in place of IGP.
10. Assume that a BGP router is learning the same route from two different EBGP peers. The AS_path information from peer 1 is {2345,86,51}, and the AS_path information from peer 2 is {2346,51}. What BGP attributes could be adjusted to force the router to prefer the route advertised by peer 1?
Answer-
Weight and local preference are two BGP attributes that make adjustments to force the router to prefer the route advertised by peer 1. Both have a higher preference than AS_path length.
11. Can BGP be used only by Internet service providers?
Answer-
No. BGP can also be used to scale large enterprise networks. A large network can be divided into segments, with each segment running an IGP. Routing information between segments could then be exchanged by using BGP.
12. If a directly connected interface is redistributed into BGP, what value will the origin attribute have for this route?
Answer-
Any redistributed route will have an incomplete value of origin.
--------------------
CHAPTER-3 (Multimedia Networking)
1. What is multimedia? Give examples of multimedia data.
Answer-
Multimedia defines applications and technologies that manipulate text, data, images, and voice and full motion video objects. Classic example of multimedia is the games available on CDs or songs and music available on sites.
2. What is an audio? What is a video?
Answer-
Audio: It deals with only voice. For example, a song or a lecture on any university site.
Video: It has got both voice and live image, such as a movie, a song, or a clipping of a lecture.
3. What is streaming?
Answer-
Streaming is the process of receiving stored audio/video application from a server where they are placed. A client begins to play either an audio or a video once the media player of the client’s PC begins receiving the audio or video file from the server. During the process, the client will be playing audio/video from one location in the file while it is receiving the remaining parts of the file from the server. In other words, streaming avoids long download times and the need to store the entire file on the user's computer.
4. List the drawbacks of the current internet to drive the multimedia data?
Answer-
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 betwen the server process and the media player process.
5. How the existing internet can be made to port multimedia data?
Answer-
For making the existing Internet portable to multimedia data, the following modifications need to be done:
6. Explain the Why Audio and Video need to be compressed?
Answer-
Compression is required to reduce the size of audio and video so that they can be easily transmitted over the Internet. For example, a single image consisting of 1024 pixel * 1024 pixels, with each pixel encoded into 24 bits requires 3 MB of storage without compression. There are eight bits, three each for the colors red, green, and blue. It would take approximately seven minutes to send the image over a 64 kbps link. If the image is compressed at a modest 10:1 compression ratio, the storage requirement is reduced to 300 Kbytes and the transmission time also drops by a factor of 10.
7. Explain audio streaming process?
Answer-
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.
8. What is a streaming server?
Answer-
Streaming servers are meant for the audio/video streaming applications. Upon client request, a server directs an audio or a video file to the client by sending the file into a socket. Both the TCP and UDP socket connections are used. Before sending the audio/video file to a network, the file is segmented, and the segments are typically encapsulated with special headers appropriate for audio and video traffic. Streaming servers send digital video for news, entertainment, or educational content over the Internet by using RTP/RTSP. A multimedia file gets uploaded on the server and streaming servers encodes content in the latest media formats including MPEG- 4 (Moving Picture Expert Group) and the AAC (Advanced Audio Coder) audio.
9. What are the limitations of the best effort service? Explain.
Answer-
Limitations of the best effort service are:
10. Discuss the features of Real Time Protocol?
Answer-
The features of Real Time Protocol (RTP) are:
11. Explain how does the helper application get the data from a streaming server?
Answer-
Getting data from streaming server to helper application like the media player requires at least two servers where data is placed. One server is the HTTP server, and the second server is the streaming server. For example, when a user visits any songs/news web site, the web browser communicates with the web server where the user chooses the file that has music or news. The moment the user clicks any media file; media player requests for the media file to the streaming server and user receives the media file on the media player.
12. Explain RTSP?
Answer-
RTSP is a protocol that enables a media player to control the transmission of a media stream. RTSP messages use the port number 544 from the media stream. The RTSP specification, RFC 2326, permits RTSP messages to be sent over TCP or UDP. RTSP server keeps a track of the state of the client for each ongoing RTSP session. For example, the server keeps track of whether the client is in an initialization state, a play state, or a pause state. The session and sequence numbers, which are part of each RTSP request and response, help the server to keep track of the session state. The session number is fixed throughout the entire session; the client increments the sequence number each time it sends a new message; the server echoes back the session number, and the current sequence number.
--------------------
CHAPTER-4 (Wireless Local Area Network (WLAN))
1. What are WLANs?
Answer-
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.
2. What is modulation?
Answer-
Modulation is the addition of information or the signal to an electronic or optical signal carrier. There are several reasons to modulate a signal before transmitting signal in a medium. This includes the ability of various users sharing a medium and making the signal properties physically compatible with the propagation medium.
3. What is a carrier signal?
Answer-
A carrier signal is a specific frequency in an analog communication channel that is modulated with an information-carrying signal. Carrier signals are commonly used in Amplitude Modulation (AM), Frequency Modulation (FM), and other radio transmissions to differentiate among channels. You turn a radio dial to select a carrier frequency. The radio then amplifies the signal carried on the selected frequency. In AM, modulation changes the strength or amplitude of the carrier signal. In FM, the frequency of the carrier signal is modulated.
4. Define SNR?
Answer-
SNR stands for Signal-to-Noise Ratio. It is the ratio between the typical signal level and the softest signal that can be produced accurately.
5. What is BW?
Answer-
BW stands for bandwidth, which is the range within a band of frequencies or wavelengths. BW can also be defined as the amount of data that can be transmitted in a fixed amount of time. For digital devices, bandwidth is usually expressed in bits per second or bytes per second (bps). For analog devices, bandwidth is expressed in cycles per second or Hertz (Hz).
6. Compare 802.11a, 802.11b, 802.11g and blue tooth.
Answer-
Feature -- 802.11a -- 802.11b -- 802.11g -- Bluetooth
Data rate -- 54-72Mbps-- 11Mbps 54Mbps-- 721Kbps--56 Kbps
Frequency --5Ghz -- 2.4Ghz-- 2.4Ghz-- 2.4Ghz
Modulation-- OFDM-- DSSS/CCK -- DSSS/PBCC-- FHSS
Channels -- 12/8 -- 11/3 -- 11/3-- 79 ( 1Mhz wide)
Bandwidth Available--300--83.5-- 83.5(22MHz per channel)--83.5
Power -- 40-800mW -- 100mW -- 100mW -- 100mW
7. List out the advantages and disadvantages of WLAN?
Answer-
The advantages of WLAN are:
The disadvantages of WLAN are:
8. Compare Infrared and Radio transmission?
Answer-
Comparision of Infrared and Radio transmission
9. Discuss the architecture of WLAN?
Answer-
WLAN architecture consists of three components:
The wireless end station can be any device that can communicate using the 802.11 standard. These devices include laptops, workstations, and PDAs, as well as printers and scanners.
The access point (AP) is a device. It acts as a network platform for connections between WLANs or to a wired LAN and as a relay between stations attached to the same AP.
BSS is the logical component of wireless architecture. In general, it is a set of wireless stations controlled by a single management function and has two configuration options that is, Infrastructure BSS (IBSS) and Extended Service Set (ESS).
In an IBSS, the stations communicate directly to one another without the need for an access point. An ESS is a set of infrastructure BSSs that appear as a single BSS. This is important for connection redundancy but has some security issues that need to be addressed.
10. Briefly explain the WLAN protocol architecture?
Answer-
In a typical WLAN setup, the IEEE 802.11 standard WLAN (Access Point) gets connected to an IEEE 802.3 standard Ethernet (Switch/HUB) via a bridge. The higher layers (application, TCP, IP) look the same for the wireless node as for the wired node. The IEEE 802.11 standard only covers the physical layer (PHY) and medium access layer (MAC) like the other 802.x LANs do. The physical layer is sub divided into the Physical Layer Convergence Protocol (PLCP) and the Physical Medium Dependent Sub Layer. The basic tasks of the MAC layer comprise medium access, fragmentation of user data, and encryption. The PLCP sublayer provides a carrier sense signal called Clear Channel Assessment (CCA), and provides a common PHY interface for the MAC, which is independent of the transmission technology.
11. Write a note on DSSS?
Answer-
Direct Sequence Spread Spectrum (DSSS) is the alternative spread spectrum method, in which the signal is spread over a wide range of frequencies using a chipping code. In the case of IEEE 802.11 DSSS, spreading is achieved by using the 11-chip sequence (+1,-1,+1,+1,-1,+1,+1,+1,-1,-1,-1), which is also called the Barker code.
12. Discuss MAC layer of WLAN.
Answer-
MAC layer controls medium access, and also offers support for roaming, authentication, and power conservation. The services offered by MAC are mandatory asynchronous data service and an optional time-bounded service.
--------------------
CHAPTER-5 (Crytography and Network Security)
1. What is cryptography?
Answer-
Cryptography is the science of using mathematics to encrypt and decrypt data. Cryptography enables us to store or transmit sensitive information across insecure networks (like the Internet) so that unauthorized users except the intended recipient cannot read it.
2. Explain cryptographic algorithms.
Answer- A cryptographic algorithm, also referred to as cipher, is a mathematical function used in the encryption and decryption process. A cryptographic algorithm works in combination with a key. The key may be a word, number, or phrase used to encrypt the plain text, also called a message. The plain text encrypts to cipher text with different keys. The security of encrypted data is entirely dependent on the strength of the cryptographic algorithm and the secrecy of the key.
3. Explain different types of attacks.
Answer-
Attacks are of two types. The types are:
1.Passive attack: In this attack, the goal of the unauthorized user is to obtain information that is being transmitted. Passive attacks have two subtypes, release of message contents and traffic analysis.
Passive attacks are very difficult to detect because they do not involve any alteration of the data. The emphasis in dealing with passive attacks is to prevent the attack rather than to detect it.
2.Active attacks: These attacks involve some modification of the data stream or the creation of a false stream. These attacks are divided into four categories such as masquerade, replay, modification of messages, and denial of service (DoS).
Active attacks posses opposite characteristics than that of passive attacks. Active attacks are difficult to prevent because physical protection of all communications facilities and paths at all times is required. Instead, the goal is to detect active attacks and to restore the network from any disruption or delays caused by them.
4. Explain briefly on security mechanisms.
Answer-
Mechanisms that ensure security of an organization are known as security mechanisms. Encryption or encryption like transformations of information is the most common means of providing security.
There are certain common information integrity functions to secure network/data like identification, validation, authorization, time of occurrence, signature, authenticity, concurrence, ownership, receipts, registration, endorsement, privacy, access, and endorsement.
5. Explain conventional encryption model?
Answer-
Before the development of public key encryption, the conventional encryption (single-key encryption) was available to secure the networks.
There are two types of encryption, classical encryption and modern encryption techniques. These are key based algorithms known as symmetric and public key algorithms.
In conventional algorithms, the encryption key can be calculated from the decryption key. Alternatively, the decryption key can be calculated from the encryption key. In these algorithms, the encryption key and the decryption key are same. These algorithms are also called secret key algorithms, or the one key algorithm. In this encryption technique, the sender and receiver agree to use a key before they communicate securely. The security of the symmetric algorithm rests in the key. The key allows users to encrypt and decrypt messages by using any encryption and decryption algorithms.
6. What is STEGANOGRAPHY?
Answer-
Steganography is a technique that is used to hide the secret message in other messages.
A few examples of steganography are:-
----------------(END)---------------
1. List the functions of application layer.?
Answer-
2. What is DNS?
Answer-
DNS is a name resolution service that resolves host names to the IP addresses. DNS has a hierarchical and distributed database that contains mappings of host names with the corresponding IP addresses.
3. Explain the working of DNS with an example.
Answer-
DNS is a name resolution service that resolves host names to IP addresses. A DNS server resolves host names to IP addresses for DNS queries sent by the DNS clients. These queries can be in the form of a name resolution query or a resource record. The resolver sends a User Datagram Protocol (UDP) packet to the local DNS server. The DNS server searches its table and returns the IP address, which matches the domain name. DNS has a hierarchical and distributed database that contains mappings of host names with the corresponding IP addresses.
Resource records are stored in a specific portion of the DNS database called the DNS zone. A DNS zone contains resource records along with the owner names.
For example, an application program calls a procedure with its domain name as parameter. The procedure sends an UDP packet to the local DNS server. The DNS server searches its table and returns the IP address which matches the Domain name. The program can now establish a TCP connection or send UDP packets.
4. What is iterative resolution? Give example.
Answer-
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.
5. What are the functions of the user agent in the Email architecture?
Answer-
In the e-mail architecture, the user agent helps users to interact with the e-mail systems. The functions of the user agent in e-mail architecture are:
6. Discuss the sending and receiving process in Email?
Answer-
The prerequisites for sending and receiving an e-mail are:
The following is the sequence of the e-mail sending process:
In the implementations of POP3, the server maintains a collection of text files, one for each e-mail account. When a message arrives, the POP3 server simply appends it to the bottom of the recipient's file.
The following is the sequence of the e-mail receiving process:-
7. Write a brief note on SMTP?
Answer-
SMTP is a protocol that transfers mail reliably and efficiently. SMTP is independent of a particular transmission subsystem and needs only a reliable ordered data stream channel. An important feature of SMTP is its capability to relay mail across transport service environments.
8. Discuss the working of POP3 in an Email system? What are its limitations?
Answer-
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:
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 :-
9. What is www?
Answer-
WWW is a hypertext-based system that provides a uniform and a user-friendly interface for accessing the resources on the Internet. It is an information space in which the items of interest, referred to as resources, are identified by global identifiers called Uniform Resource Identifiers (URI).
10. Discuss the architecture of WWW?
Answer-
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
Request
CLIENT ------------------ > SERVER
<--------------
Response
Two-Tier 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
CLIENT ---------------> SERVER -----------------> DATA BASE
<--------------- <----------------
Response
three-Tier Architecture of WWW
11. Explain the client side and server side events when a user click on a URL?
Answer-
The client side events when a user clicks on a URL are as follows:
When a user clicks on a URL, the server side events are as follows:
12. Explain what is a server farm? Give an example.
Answer-
A server farm is a group of networked servers that are housed in one location. A server farm streamlines internal processes by distributing the workload between the individual components of the farm and expedites computing processes by harnessing the power of multiple servers. The farms rely on load balancing software that accomplishes the following tasks:
When one server in the farm fails, another can step in as a backup.
--------------------
CHAPTER-2 (Routing Protocols)
1. What is Routing? Discuss direct and indirect Routing?
Answer-
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. The differences between direct routing and indirect routing are as follows.
2. Discuss different approaches used to make the routing table more efficient?
Answer-
There are many approaches to make a routing table efficient such as:
3. Name RIP’s various stability features.
Answer-
The stability features of RIP are:
4. What is the purpose of the timeout timer?
Answer-
The purpose of the route timeout timer is to help purge invalid routes from a RIP node. Routes that are not refreshed for a given period of time are likely to be invalid because of some change in the network. Thus, RIP maintains a timeout timer for each known route. When a route's timeout timer expires, the route is marked invalid but is retained in the table until the route-flush timer expires.
5. What two capabilities are supported by RIP 2 but not RIP?
Answer-
Two capabilities, which are supported by RIP2 but not by RIP1, are:
6. What is the maximum network diameter of a RIP network?
Answer-
The maximum network diameter of a RIP network is 15 hops.
7. When using OSPF, can you have two areas attached to each other where only one AS has an interface in Area 0?
Answer-
Yes, you can. This describes the use of a virtual path. One area has an interface in Area 0 (legal), and the other AS is brought up and attached off an ABR in Area 1, so you can call it Area 2. Area 2 has no interface in Area 0, so it must have a virtual path to Area 0 through Area 1. When this is in place, Area2 looks like it is directly connected to Area 0. When Area 1 wants to send packets to Area 2, it must send them to Area 0, which in turn redirects them back through Area 1 by using the virtual path to Area 2.
8. Area 0 contains five routers (A, B, C, D, and E), and Area 1 contains three routers (R, S, and T). What routers does Router T know exists? Router S is the ABR.
Answer-
Router T knows about routers R and S only. Likewise, Router S only knows about R and T, as well as routers to the ABR in Area 0. The AS’s separate the areas so that router updates contain only information needed for that AS.
9. Can IBGP be used in place of an IGP (RIP, IGRP, EIGRP, OSPF, or ISIS)?
Answer-
Use of IBGP in place of IGP is conditional. The next-hop information from EBGP is carried into IBGP. If IBGP does not have a route to reach the next hop, then the route will be discarded. Typically, an IGP needs to be used to exchange routes to the next hop, but this can be achieved by using static routes on all the routers running IBGP. So, the answer is yes if you want to use and maintain static routes. Otherwise, you can not use IBGP in place of IGP.
10. Assume that a BGP router is learning the same route from two different EBGP peers. The AS_path information from peer 1 is {2345,86,51}, and the AS_path information from peer 2 is {2346,51}. What BGP attributes could be adjusted to force the router to prefer the route advertised by peer 1?
Answer-
Weight and local preference are two BGP attributes that make adjustments to force the router to prefer the route advertised by peer 1. Both have a higher preference than AS_path length.
11. Can BGP be used only by Internet service providers?
Answer-
No. BGP can also be used to scale large enterprise networks. A large network can be divided into segments, with each segment running an IGP. Routing information between segments could then be exchanged by using BGP.
12. If a directly connected interface is redistributed into BGP, what value will the origin attribute have for this route?
Answer-
Any redistributed route will have an incomplete value of origin.
--------------------
CHAPTER-3 (Multimedia Networking)
1. What is multimedia? Give examples of multimedia data.
Answer-
Multimedia defines applications and technologies that manipulate text, data, images, and voice and full motion video objects. Classic example of multimedia is the games available on CDs or songs and music available on sites.
2. What is an audio? What is a video?
Answer-
Audio: It deals with only voice. For example, a song or a lecture on any university site.
Video: It has got both voice and live image, such as a movie, a song, or a clipping of a lecture.
3. What is streaming?
Answer-
Streaming is the process of receiving stored audio/video application from a server where they are placed. A client begins to play either an audio or a video once the media player of the client’s PC begins receiving the audio or video file from the server. During the process, the client will be playing audio/video from one location in the file while it is receiving the remaining parts of the file from the server. In other words, streaming avoids long download times and the need to store the entire file on the user's computer.
4. List the drawbacks of the current internet to drive the multimedia data?
Answer-
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 betwen the server process and the media player process.
5. How the existing internet can be made to port multimedia data?
Answer-
For making the existing Internet portable to multimedia data, the following modifications need to be done:
6. Explain the Why Audio and Video need to be compressed?
Answer-
Compression is required to reduce the size of audio and video so that they can be easily transmitted over the Internet. For example, a single image consisting of 1024 pixel * 1024 pixels, with each pixel encoded into 24 bits requires 3 MB of storage without compression. There are eight bits, three each for the colors red, green, and blue. It would take approximately seven minutes to send the image over a 64 kbps link. If the image is compressed at a modest 10:1 compression ratio, the storage requirement is reduced to 300 Kbytes and the transmission time also drops by a factor of 10.
7. Explain audio streaming process?
Answer-
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.
8. What is a streaming server?
Answer-
Streaming servers are meant for the audio/video streaming applications. Upon client request, a server directs an audio or a video file to the client by sending the file into a socket. Both the TCP and UDP socket connections are used. Before sending the audio/video file to a network, the file is segmented, and the segments are typically encapsulated with special headers appropriate for audio and video traffic. Streaming servers send digital video for news, entertainment, or educational content over the Internet by using RTP/RTSP. A multimedia file gets uploaded on the server and streaming servers encodes content in the latest media formats including MPEG- 4 (Moving Picture Expert Group) and the AAC (Advanced Audio Coder) audio.
9. What are the limitations of the best effort service? Explain.
Answer-
Limitations of the best effort service are:
10. Discuss the features of Real Time Protocol?
Answer-
The features of Real Time Protocol (RTP) are:
11. Explain how does the helper application get the data from a streaming server?
Answer-
Getting data from streaming server to helper application like the media player requires at least two servers where data is placed. One server is the HTTP server, and the second server is the streaming server. For example, when a user visits any songs/news web site, the web browser communicates with the web server where the user chooses the file that has music or news. The moment the user clicks any media file; media player requests for the media file to the streaming server and user receives the media file on the media player.
12. Explain RTSP?
Answer-
RTSP is a protocol that enables a media player to control the transmission of a media stream. RTSP messages use the port number 544 from the media stream. The RTSP specification, RFC 2326, permits RTSP messages to be sent over TCP or UDP. RTSP server keeps a track of the state of the client for each ongoing RTSP session. For example, the server keeps track of whether the client is in an initialization state, a play state, or a pause state. The session and sequence numbers, which are part of each RTSP request and response, help the server to keep track of the session state. The session number is fixed throughout the entire session; the client increments the sequence number each time it sends a new message; the server echoes back the session number, and the current sequence number.
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CHAPTER-4 (Wireless Local Area Network (WLAN))
1. What are WLANs?
Answer-
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.
2. What is modulation?
Answer-
Modulation is the addition of information or the signal to an electronic or optical signal carrier. There are several reasons to modulate a signal before transmitting signal in a medium. This includes the ability of various users sharing a medium and making the signal properties physically compatible with the propagation medium.
3. What is a carrier signal?
Answer-
A carrier signal is a specific frequency in an analog communication channel that is modulated with an information-carrying signal. Carrier signals are commonly used in Amplitude Modulation (AM), Frequency Modulation (FM), and other radio transmissions to differentiate among channels. You turn a radio dial to select a carrier frequency. The radio then amplifies the signal carried on the selected frequency. In AM, modulation changes the strength or amplitude of the carrier signal. In FM, the frequency of the carrier signal is modulated.
4. Define SNR?
Answer-
SNR stands for Signal-to-Noise Ratio. It is the ratio between the typical signal level and the softest signal that can be produced accurately.
5. What is BW?
Answer-
BW stands for bandwidth, which is the range within a band of frequencies or wavelengths. BW can also be defined as the amount of data that can be transmitted in a fixed amount of time. For digital devices, bandwidth is usually expressed in bits per second or bytes per second (bps). For analog devices, bandwidth is expressed in cycles per second or Hertz (Hz).
6. Compare 802.11a, 802.11b, 802.11g and blue tooth.
Answer-
Feature -- 802.11a -- 802.11b -- 802.11g -- Bluetooth
Data rate -- 54-72Mbps-- 11Mbps 54Mbps-- 721Kbps--56 Kbps
Frequency --5Ghz -- 2.4Ghz-- 2.4Ghz-- 2.4Ghz
Modulation-- OFDM-- DSSS/CCK -- DSSS/PBCC-- FHSS
Channels -- 12/8 -- 11/3 -- 11/3-- 79 ( 1Mhz wide)
Bandwidth Available--300--83.5-- 83.5(22MHz per channel)--83.5
Power -- 40-800mW -- 100mW -- 100mW -- 100mW
7. List out the advantages and disadvantages of WLAN?
Answer-
The advantages of WLAN are:
The disadvantages of WLAN are:
8. Compare Infrared and Radio transmission?
Answer-
Comparision of Infrared and Radio transmission
9. Discuss the architecture of WLAN?
Answer-
WLAN architecture consists of three components:
The wireless end station can be any device that can communicate using the 802.11 standard. These devices include laptops, workstations, and PDAs, as well as printers and scanners.
The access point (AP) is a device. It acts as a network platform for connections between WLANs or to a wired LAN and as a relay between stations attached to the same AP.
BSS is the logical component of wireless architecture. In general, it is a set of wireless stations controlled by a single management function and has two configuration options that is, Infrastructure BSS (IBSS) and Extended Service Set (ESS).
In an IBSS, the stations communicate directly to one another without the need for an access point. An ESS is a set of infrastructure BSSs that appear as a single BSS. This is important for connection redundancy but has some security issues that need to be addressed.
10. Briefly explain the WLAN protocol architecture?
Answer-
In a typical WLAN setup, the IEEE 802.11 standard WLAN (Access Point) gets connected to an IEEE 802.3 standard Ethernet (Switch/HUB) via a bridge. The higher layers (application, TCP, IP) look the same for the wireless node as for the wired node. The IEEE 802.11 standard only covers the physical layer (PHY) and medium access layer (MAC) like the other 802.x LANs do. The physical layer is sub divided into the Physical Layer Convergence Protocol (PLCP) and the Physical Medium Dependent Sub Layer. The basic tasks of the MAC layer comprise medium access, fragmentation of user data, and encryption. The PLCP sublayer provides a carrier sense signal called Clear Channel Assessment (CCA), and provides a common PHY interface for the MAC, which is independent of the transmission technology.
11. Write a note on DSSS?
Answer-
Direct Sequence Spread Spectrum (DSSS) is the alternative spread spectrum method, in which the signal is spread over a wide range of frequencies using a chipping code. In the case of IEEE 802.11 DSSS, spreading is achieved by using the 11-chip sequence (+1,-1,+1,+1,-1,+1,+1,+1,-1,-1,-1), which is also called the Barker code.
12. Discuss MAC layer of WLAN.
Answer-
MAC layer controls medium access, and also offers support for roaming, authentication, and power conservation. The services offered by MAC are mandatory asynchronous data service and an optional time-bounded service.
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CHAPTER-5 (Crytography and Network Security)
1. What is cryptography?
Answer-
Cryptography is the science of using mathematics to encrypt and decrypt data. Cryptography enables us to store or transmit sensitive information across insecure networks (like the Internet) so that unauthorized users except the intended recipient cannot read it.
2. Explain cryptographic algorithms.
Answer- A cryptographic algorithm, also referred to as cipher, is a mathematical function used in the encryption and decryption process. A cryptographic algorithm works in combination with a key. The key may be a word, number, or phrase used to encrypt the plain text, also called a message. The plain text encrypts to cipher text with different keys. The security of encrypted data is entirely dependent on the strength of the cryptographic algorithm and the secrecy of the key.
3. Explain different types of attacks.
Answer-
Attacks are of two types. The types are:
1.Passive attack: In this attack, the goal of the unauthorized user is to obtain information that is being transmitted. Passive attacks have two subtypes, release of message contents and traffic analysis.
Passive attacks are very difficult to detect because they do not involve any alteration of the data. The emphasis in dealing with passive attacks is to prevent the attack rather than to detect it.
2.Active attacks: These attacks involve some modification of the data stream or the creation of a false stream. These attacks are divided into four categories such as masquerade, replay, modification of messages, and denial of service (DoS).
Active attacks posses opposite characteristics than that of passive attacks. Active attacks are difficult to prevent because physical protection of all communications facilities and paths at all times is required. Instead, the goal is to detect active attacks and to restore the network from any disruption or delays caused by them.
4. Explain briefly on security mechanisms.
Answer-
Mechanisms that ensure security of an organization are known as security mechanisms. Encryption or encryption like transformations of information is the most common means of providing security.
There are certain common information integrity functions to secure network/data like identification, validation, authorization, time of occurrence, signature, authenticity, concurrence, ownership, receipts, registration, endorsement, privacy, access, and endorsement.
5. Explain conventional encryption model?
Answer-
Before the development of public key encryption, the conventional encryption (single-key encryption) was available to secure the networks.
There are two types of encryption, classical encryption and modern encryption techniques. These are key based algorithms known as symmetric and public key algorithms.
In conventional algorithms, the encryption key can be calculated from the decryption key. Alternatively, the decryption key can be calculated from the encryption key. In these algorithms, the encryption key and the decryption key are same. These algorithms are also called secret key algorithms, or the one key algorithm. In this encryption technique, the sender and receiver agree to use a key before they communicate securely. The security of the symmetric algorithm rests in the key. The key allows users to encrypt and decrypt messages by using any encryption and decryption algorithms.
6. What is STEGANOGRAPHY?
Answer-
Steganography is a technique that is used to hide the secret message in other messages.
A few examples of steganography are:-
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