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1. What is a pseudo tty. ->A pseudo tty or false terminal te rminal enables external machines to connect through Telnet or rlogin. Without a pseudo tty, no connection can take place. 2. What is a DNS resource record? ->A resource record is an entry in a name server's database. There are several types of resource records used, including name-to-address resolution information. Resource records are maintained as ASCII files. 3. What protocol is used by DNS name servers? ->DNS uses UDP for communication between servers. I t is a better choice than TCP because of the improved speed a connectionless protocol offers. Of course, transmission reliability suffers with UDP. 4. What is source route? ->It is a sequence of I P addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header. 5. What is RIP (Routing Information Protocol)? ->It is a simple protocol used to e xchange information between the routers. 6. What is SLIP (Serial Line Interface Protocol)? ->It is a very simple protocol used for transmission of IP datagrams across a serial line. 7. What is Proxy ARP? ->It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router. 8. What is Kerberos? ->It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files. 9. What is a Multi-homed Host? ->It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host. 10. What is Gateway-to-Gateway protocol? ->It is a protocol formerly used to exchange routing information between Internet core routers. 11. What is BGP (Border Gateway Protocol)? ->It is a protocol used to advertise adver tise the set of networks that can be reached with in an a utonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol). 12. What is autonomous system? ->It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol. 13. What is Mail Gateway? ->It is a system that performs a protocol translation between different electronic mail delivery protocols.
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14. What is silly window syndrome? ->It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but a n interactive application on the receiving side reads 1 byte at a time. 15. What is multicast routing? ->Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing. 16. What is virtual path? ->Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path. 17. What is virtual channel? ->Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit. 18. Why should you care about the OSI Reference Model? ->It provides a framework for discussing network operations and design. 19. What is MAU? ->In token Ring , hub is called Multistation Access Unit (MAU). 20. What is the range of addresses in the classes of internet addresses? -> Class A 0.0.0.0 - 127.255.255.255 Class B 128.0.0.0 - 191.255.255.255 Class C 192.0.0.0 - 223.255.255.255 Class D 224.0.0.0 - 239.255.255.255 Class E 240.0.0.0 - 247.255.255.255 21. What is the minimum and maximum length of the header in the TCP segment and IP datagram? ->The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes. 22. What is ICMP? ->ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. 23. What is Bandwidth? ->Every line has an upper limit and a l ower limit on the frequency of signals it can carry. This limited range is called the bandwidth. 24. What is Bit Rate? -> Bit rate is the number of bits transmitted during one second.
25. What is Baud Rate? -> Baud rate refers to the number of signal units per second that are required to represent those bits.
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26. Give the relationship between Bit Rate and Baud Rate? -> Baud rate = bit rate / N where N is no-of-bits represented by each signal shift. 27. What is MAC address? ->The address for a device as it is identified at the Media Access Control (MAC) layer in t he network architecture. MAC address is usually stored in ROM on the network adapter card and is unique. 28. What is attenuation? ->The degeneration of a signal over distance on a network cable is called attenuation. 29. What is cladding? ->A layer of a glass surrounding the ce nter fiber of glass inside a fiber-optic cable. 30. What is RAID? ->A method for providing fault tolerance by using multiple hard disk drives. 31. What is terminal emulation, in which layer it comes? ->Telnet is also called as terminal emulation. It belongs to application layer. 32. What is frame relay, in which layer it comes? ->Frame relay is a packet switching technology. It will operate in the data link layer. 33. What is SAP? ->Series of interface points that allow other computers to communicate with the other layers of network protocol stack. 34. What is subnet? ->A generic term for section of a large networks usually separated by a bridge or router. 35. How Gateway is different from Routers? ->A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats. 36. What is Repeater? -> Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the l ink. 37. What are Bridges? -> These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipient and control congestion. 38. What are Routers? -> They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable t hem to determine which of the several possible paths is the best for a particular transmission.
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39. What are Gateways? -> They relay packets among networks t hat have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatt ed for another protocol before forwarding it. They operate in all seven layers of the OSI model. 40. What is mesh network? ->A network in which there is multiple network links between computers to provide multiple paths for data to travel. 41. What is passive topology? ->When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
42. What is Bus Topology? Give advantages. -> In this each computer is directly connected to primary network cable in a single line. Advantages: Inexpensive, easy to install, simple to understand, e asy to extend. 43. What is Star Topology? Give advantages. -> In this all computers are connected using a central hub. Advantages: Can be inexpensive, easy to install and reconfigure and e asy to trouble shoot physical problems. 44. What is Ring Topology? Give advantages. -> In this all computers are connected in loop. Advantages: All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it. 45. What are major types of networks? -> Server-based network and Peer-to-peer network. 46. What is Protocol Data Unit? -> The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. 47. What are DSAP and SSAP? -> DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the re ceiving and sending machines that are generating and using t he data. 48. What are the possible ways of data exchange? (i) Simplex (ii) Half-duplex (iii) Full-duplex. 49. What are the types of Transmission Media? -> Guided medium and unguided medium.
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50. What is Guided Medium? -> These are those that provide a conduit from one device to another t hat include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of the se media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. O ptical fiber is a glass or plastic cable that accepts and transports signals in the form of light. 51. What is Unguided Medium? -> This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony. 52. What is point-to-point protocol? ->A communications protocol used to connect computers to remote networking services including Internet service providers. 53. What are the two types of transmission technology available? ->(i) Broadcast and (ii) point-to-point. 54. Difference between the communication and transmission. ->Transmission is a physical movement of information and concern issues like bit polarity, synchronization, clock etc. Communication means the meaning full exchange of information between two communication media. 55. What is Region? -> When hierarchical routing is used, the route rs are divided into what we call re gions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions. 56. What is DHCP? -> Dynamic Host Configuration Protocol is responsible for distributing ip id's to it's clients whenever t he system boots. 57. What are the advantages and disadvantages of DHCP? -> Advantage: By automatically assigning the IP address one can reduce the time. Disadvantage: IP name of the client system dose not change so nearby machine can access the client machine. 58. What is the difference between Physical address and Logical address? -> A Physical address is a 48-bit flat address burned into the ROM of the NI C card which is a Layer1 device of the OSI model. This is divided into 24-bit vendor code and 24-bit serial address. This is unique for each system and cannot be changed. A Logical address is a 32- bit address assigned to each system in a network. This works in Layer-3 of OSI Model. This would be generally the IP address. 59. Under what situations a packet can go into i nfinite loop in a network? -> 1.If TTL (time to live) field becomes zero. 2. Invalid destination. 3. If any fragment is lost.
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60. Describe a 3-way TCP/IP Handshake. -> (1) first time check that destination port i s present on network yes or no. (2) Second time check that port i s on or off and it receive request on port. (3) Send message of destination side that sender side is ready for connection. 61. How many IP's we can assign to a particular PC? -> The total number of ip addresses that can be assigned varies depending on the operating system. 62. What is supernetting? Why it is used? -> Supernetting refers to increase host and reduce the subnets. It means reduce the network bits and increase the host bits. We do use supernetting because when the PCs in the network increase where we need the more valid IP's in the same network. 63. Explain 5-4-3 rule. -> In a Ethernet network, between any two points on the network, there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated. 64. What is the default subnet mask for an IPv6 address? -> 255.255.255.255.255.0 65. What is fragmentation of a packet? -> When the MTU (maximum transmission unit) of a network is smaller than the packet size ,the packet is split in to small units from t he router. This spliting is called fragmentation. 66. What is OSPF? -> Open Shortest Path First (OSPF) is a dynamic routing protocol for use in I nternet Protocol (IP) networks. Specifically, it is a link-state routing protocol and falls into the group of interior gateway protocols, operating within an autonomous system (AS). 67. What is packet filter? -> Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped. 68. What is .ost file? -> Select or clear the Prompt me at startup so I may choose to work offline or online check box, and then click OK. If you clear the check box, Outlook will automatically start offline if a connection to the server is not available. 69. What is piggy backing? -> Piggy backing means the combination of data frame and acknowledgment in stop and wait method which is used for flow and error control mechanism. 70. What is POP3? -> POP3 is Email clients download your emails onto your computer. U sing a specialized email program such as Outlook Express or Apple Mail has the advantage of giving you complete control over your email; every email you receive i s placed on your computer and you can keep as many large file attachments as you want.
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71. What is IMAP? -> IMAP is protocol that is being used in webmail. Checking your email through our webmail is similar to using Hotmail or YAHOO! Mail. You never actually copy your messages to your computer; in fact, you are looking at them through your web browser on somebody else's computer. When you are not online, you are not able to see your email. 72. How Is IP Carried On A Network? -> IP is just a protocol which used to carry data, packets over t he network in the manner which the n/w components can understand. IP is a identity of n/w devices. 73. What is TCP/IP? -> TCP/IP is a name given to the collection (or suite) of netw orking protocols that have been used to construct the global Internet. The protocols are also referred to as the DoD (dee-oh-dee) or Arpanet protocol suite because their early development w as funded by the Advanced Research Projects Agency (ARPA) of the US Department of Defense (DoD). 74. What is the Role of TCP/IP in data transmission from source to destination? -> TCP/IP is a protocol stack used for data transmission from source to destination. In the physical layer all the physical connections like LAN cards, cables etc will b there which will send data in the form of bits. layer 2 operates with frames where the switches comes into picture. 75. What are sockets? -> Socket is the combination of IP addre ss and Port no. in TCP/IP network. 76. DNS uses which protocol? Why? -> DNS uses both TCP or UDP or both. UDP can handle only 512bytes. If data size is withing 512 bytes UDP is used, otherwise, TCP is used. 77. What is IPSec? -> Short for IP Security, a set of protocols developed by the IETF to support secure exchange of packets at the IP layer. IPSec has been deployed widely to implement Virtual Private Networks (VPNs). IPsec supports two encryption modes: Transport and Tunnel. IPsec to w ork, the sending and receiving devices must share a public key. 78. You have one IP: 192.168.10.29. In which layer this IP works? -> Network layer. 79. What is IP? -> It is a network protocol and work for data transfer from one computer to another. 80. What is Flow Control? -> Flow control: adjust and confirm data flow rate for successful transmission. 81. What is Error Control? -> Error Control: a way to recover corrupted data . 82. Mention one real place to use TCP/IP. -> LAN cards, Internet.
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83. Can the TCP keep alive timeouts be configured? -> This varies by operating system. The re is a program that works on many Unices (though not Linux or Solaris), called netconfig, that allows one to do t his and documents many of the variables. 84. What IP addresses should I assign to machines on a private internet? -> For private network one can use private IP addresses which are Class A 10.0.0.0 to 10.255.255.255 Class B 172.16.0.0 to 172.31.255.255 Class C 192.168.0.0 to 192.168.255.255 With overload NAT or PAT both are same. Most of time class A address are used cause it provide lots of room for explanation. 85. You are in home. But you need to access the office server router. How can you do that? -> By using "Telnet" or "SSH". 86. What is the data unit of "Transport layer"? -> The data unit of transport layer is "Segment". 87. What is the port number of Telnet and DNS? -> Telnet = 23 and DNS = 53. 88. What are the responsibilities of Network Layer? -> 1] routing 2] provides logical addressing 3] path determination. 89. How Is IP Carried On A Network? -> An Ip packet or datagram is carried on network in a connection-less manner. Every individual datagram can take its own route and there is no relationship between any two data-grams. IP is the best-effort service. It does not ensure error and flow control and leaves this to the upper layer protocols such as TCP or SCTP. 90. Error control is down in which layer? -> Layer 4 91. How can I measure the performance of an IP link? -> You can get a quick approximation by timing how long it takes to FTP or RCP a large file over the link, but bear in mind that that measurement will be skewed by the time spent in dealing with the local and remote filesystems, not simply with the network itself. And remember to measure the time it takes to receive a file, not the time it takes to send it; the sender can report completion even though large amounts of data are still buffered l ocally by TCP and have not yet bee n delivered to the destination. 92. What is a wide area network? -> Wide Area Network (WAN) is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries 93. What is LAN? -> LAN is a computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves.
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94. What is PING utility? -> PING stands Packet Internet G opher. This is a utility for ensuring connectivity between computers . ICMP protocol works behind this utility. Under it , sending node sends packets to destination node and reply is received if there is proper communication between two. 95. What is a metropolitan area network? -> A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by m any individuals and organizations. 96. Name the 2 sublayers of data link layer. -> MAC sublayer and LLC sublayer 97. What is Subnet Mask? -> A subnet mask is used to determine the number of networks and the number of host computers. Every class of the IP address uses the different range of the subnet mask. Subnet masks allow the IP based networks to be divided into the sub networks for performance and security purposes. 98. What is Wifi? -> Wi Fi or wireless fidelity is a base band network technology that is used for the wireless data communication. 99. What is WiMax? -> Wi Fi is a next form of the Wi fi. Wi max is a very high speed broadband network technology that is designed for the corporate offices, roaming and home users. 100. Define VOIP. -> VOIP or voice over internet protocol is a technology that uses IP based networks such as internet or private networks to transmit the voice communication. 101. Give any three principles that were applied to arrive at the seven layers of OSI model. -> 1. A layer should be created where a different abstraction is needed. 2. Each layer should perform a well de fined function. 3. The function of each layer should be chosen wit h an eye toward defining internationally standardized protocols. 102. The layer boundaries should be chosen to minimize the information flow across the interfaces. 103. Describe the routing mechanism in the first three layers of the OSI model. -> In the first three layers, a Host A sends the bits/frames/packets to the communication subnet boundary through Host Router Protocol to the respective routers. These routers communicate through Internal Subnet protocol and then to t he Host B through Host Router Protocol. 104. What are various services offered by sessions in the Session Layer. -> 1. Digital Control (Keeping track of whose turn it is to transmit). 2. Token Management (preventing two parties from attempting the same critical operation at the same time).
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3. Synchronization (check pointing long tr ansmissions).
105. What are the different layers present in TCP/IP model and what are the protocols and networks in each layer of OSI model. -> Layers: Host to network layer, Internet layer, transport layer, application layer. Protocols and Networks: 1. Physical + DLL(networks) -ARPANET, SATNET, Packet Radio, LAN. 2. Network layer- IP(protocol) 3. Transport layer - TCP, UDP(protocol) 4. Application layer - TELNET, FTP, SMTP, DNS(protocol) 106. What are the central concepts to OSI model? -> Services, Interfaces and Protocols. 107. Give any two differences between Networks and Protocols? -> A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources. Networks may be classified according to a wide variety of characteristics. A protocol is a set of guidelines or rules. 108. Define Bluetooth Technology? -> Bluetooth is a short range wireless technology that uses radio waves for communication. Many mobile phones, laptops, MP3 players have built in features of the Bluetooth. 109. What’s a Frame Relay? -> Frame relay is high speed data communication technology that operates at the physical and data link layers of the OSI model. Frame relay uses frames for data transmission in a network. 110. What is Firewall? -> A firewall is usually a software program that is installed on the network server or gateway. The purpose of the firewall is to prote ct the network resources from the intruders and unauthorized persons. 111. What is Virtual Private Network (VPN) and how does it work? -> VPN or virtual private network is used to connect two networks by me ans internet. VPN uses PPTP (point to point tunneling protocol) and other security procedures to make a secure tunnel on internet. 112. What tool have you used to create and analyze packet captures? -> Network Monitor in Win2K / Win2K3, Ethereal in Linux, OptiView Series II (by Fluke Networks). 113. Define Shanon Capacity? -> It is the theoretical highest data rate foe a noise channel. Capacity= Bandwidth * log2 (1+SNR)
114. What is Nyquist bit rate formula? -> For a noiseless channel, the Nyquist bit ra te formula defines the theoretical maximum bit r ate.
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Bitrate=2* Bandwidth*log2L
115. What are the factors on which data rate depends? -> Data rate i.e., how fast we can send data depends upon i) Bandwidth available ii) The levels of signals we can use iii) The quality of the channel (level of noise)
116. How data is transmitted over a medium? -> Data is transmitted in the form of electromagnetic signals. 117. Define internet? -> It is a network of networks. 118. What is a protocol? -> It is a set of rules that governs data communication. A protocol defines what is communicated, how it is communicated, and when it is communicated. The key eleme nts of protocol are syntax, semantics and timing. 119. What is multiplexing? -> Multiplexing is the process of dividing a link, the physical medium, into logical channels for better efficiency. Here medium is not changed but it has several channels instead of one. 120. Define bandwidth? -> The range of frequencies that a medium can pass is called bandwidth. It is the difference between the highest and lowest frequencies that the medium can satisfactorily pass. 121. What is SNR? -> SNR is the signal to noise ratio, it is the statistical ratio of the power of the signal to the power of the noise. Capacity is the capacity of the channel in bits per second 122. Define pulse amplitude modulation? -> It is an analog to digital conversion method which takes analog signals, samples it and generates a series of pulse based on the results of the sampling. It is not used in data communication because the series of pulses generated still of any amplitude. To modify it we use pulse code modulation. 123. Define pulse code modulation? -> Pulse code Modulation modifies pulses created by PAM to create a completely digital signal. 124. What is Asynchronous mode of data transmission? -> It is a serial mode of transmission. In this mode of transmission, each byte i s framed with a start bit and a stop bit. There may be a variable length gap between each byte.
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125. What is Synchronous mode of data transmission? -> It is a serial mode of transmission. In this mode of transmission, bits are sent in a continuous stream without start and stop bit and without gaps between bytes. Regrouping the bits into meaningful bytes is the responsibility of the receiver. 126. What are the duties of data link layer? -> Data link layer is responsible for carrying packets from one hop (computer or router) to t he next. The duties of data link layer include packetizing, addressing, error control, flow control, medium access control. 127. What are the types of errors? -> Errors can be categorized as a single-bit error or burst error. A single bit error has one bit error per data unit. A burst error has two or more bits errors per data unit. 128. What do you mean by redundancy? -> Redundancy is the concept of sending extra bits for use in error detection. Three common redundancy methods are parity check, cyclic redundancy check (CRC), and checksum. 129. Define parity check. -> In parity check, a parity bit is added to every data unit so t hat the total number of 1s is even (or odd for odd parity).Simple parity check can detect all single bit errors. It can detect burst errors only if the total number of errors in each data unit is odd. In two dimensional parity checks, a block of bits is divided into rows and a redundant row of bits is added to the whole block. 130. Define cyclic redundancy check (CRC). -> CRC appends a sequence of r edundant bits derived from binary division to the data unit. The divisor in the CRC generator is often represented as an algebraic polynomial. 131. What is hamming code? ->The hamming code is an error corre ction method using redundant bits. The number of bits is a function of the length of the data bits. In hamming code for a data unit of m bits, we use the formula 2r >= m+r+1 to determine the number of redundant bits needed. By rearranging the order of bit transmission of the data units, the hamming code can correct burst errors. 132. What do you mean by flow control? -> It is the regulation of sender’s data rate so that the receiver buffer doesn’t become overwhelmed i.e., flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgement. 133. What do you mean by error control? ->Error control refers primarily to methods of error detection and retransmission. Anytime an error is detected in an exchange, specified frames are retransmitted. This process is called automatic repeat request (ARQ). 134. Define stop and wait ARQ. -> In stop and wait ARQ, the sender sends a frame and waits for an acknowledgement from the receiver before sending the next frame.
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135. Define Go-Back-N ARQ? -> In Go-Back-N ARQ, multiple frames can be in transit at the same time. If there is an error, retransmission begins with the last unacknowledged frame even if subsequent frames arrived correctly. Duplicate frames are discarded. 136. Define Selective Repeat ARQ? -> In Selective Repeat ARQ, multiple frames can be in transit at the same time. If there is an error, only unacknowledged frame is retransmitted. 137. What do you mean by pipelining, is there any pipelining in error control? -> The process in which a task is often begun before the previous task has ended is called pipelining. There is no pipelining in stop and wait ARQ however it does apply in Go-Back-N. 138. What is HDLC? -> It is a bit oriented data link protocol designed to support both half duplex and full duplex communication over point to point and multi point links. HDLC is characterized by their station type, configuration and their response modes. 139. What do you mean by point to point protocol? -> The point to point protocol was designed to provide a dedicated line for users who need i nternet access via a telephone line or a cable TV connection. Its connection goes through three phases: idle, establishing, authenticating, networking and terminating. At data link layer it employs a version of HDLC. 140. What do you mean by point to point protocol stack? -> Point to point protocol uses a stack of othe r protocol to use the link, t o authenticate the parties involved, and to carry the network layer data. Three sets of protocols are defined: link control protocol, Authentication protocol, and network control protocol. 141. What do you mean by line control protocol? -> It is responsible for establishing, maintaining, configuring, and terminating links. 142. What do you mean by Authentication protocol? -> Authentication means validating the identity of a user who needs to access a set of resources. It is of two types i)Password Authentication Protocol(PAP) ii)Challenge Handshake Authentication Protocol(CHAP) PAP is a two step process. The user sends a authentication identification and a password. The system determines the validity of the I nformation sent.CHAP is a three step process. The system sends a value to the user. The user manipulates the value and sends the result. The system Verifies the result. 143. What do you mean by network control protocol? -> Network control protocol is a set of protocols to allow the encapsulation of data coming from network layer protocol that requires the services of PPP. 144. What do you mean by CSMA? -> To reduce the possibility of collision CSMA method was developed. I n CSMA each station first listen to the medium (Or check the state of the medium) before sending. It can’t eliminate collision.
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145. What do you mean by Bluetooth? -> It is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers, cameras, printers and so on. Bluetooth LAN Is an adhoc network that i s the network is formed spontaneously? It is t he implementation of protocol defined by the IEEE 802.15 standard. 146. What do you mean by subnetting? -> Subnetting divides one large network into several smaller ones. It adds an intermediate 147. What are the advantages of fiber optics cable? -> The advantages of fiber optics cable over twisted pair cable are Noise resistance-As they use light so external noise is not a factor. Less signal attenuation-fiber optics transmission distance is significantly greater than that of other guided media. Higher bandwidth-It can support higher bandwidth. 148. What are the disadvantages of fiber optics cable? -> The disadvantages of fiber optics cable over twisted pair cable are Cost-It is expensive Installation/maintenance-Any roughness or cracking defuses light and alters t he signal Fragility-It is more fragile.
149. What are the propagation types of radio wave? -> Radio wave propagation is dependent upon frequency. There are five propagation type. i)surface propagation ii)Tropospheric propagation iii)Ionospheric propagation iv)Line of sight propagation v)space propagation. 150. What do you mean by Geosynchronous Satellites? -> Satellite communication uses a satellite in geosynchronous orbit to r elay signals.The Satellite must move at the same speed as the earth so that it seems to remain fixed above a certain spot..Only one orbit can be geosynchronous. This orbit occurs at the equatorial plane and is approximately 22,000 miles from the surface of earth. 151. What are the factors for evaluating the suitability of the media? -> The factors are cost, throughput, attenuation, Electromagnetic interference (EMI),security. 152. What do you mean by medium access control (MAC) sub layer? The protocols used to determine who g oes next on a multi-access channel belong to a sub l ayer of the data link layer is called the multi-access channel (MAC) sublayer.It is the bottom part of data link layer. 153. What do you mean by ALOHA? -> It is the method used to solve the channel allocation problem .It is use d for: i) Ground based radio broadcasting ii) In a network in which uncoordinated users ar e competing for the use of single channel. It is of two types: 1. Pure aloha
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2. Slotted aloha
154. What do you mean by persistent CSMA (carrier sense multiple access)? -> When a station has data to send, it first listens to the channel to see if anyone else i s transmitting at that moment. If channel is busy it wait s until the station becomes idle. When collision occurs it waits and then sends. It sends frame with probability 1 when channel is idle. 155. What do you mean by non persistent CSMA (carrier sense multiple access)? -> Here if no one else is sending the station begins doing so itself. Howev er if the channel is already in use, the station doesn’t continuously sense it rather it waits for a random period of time and then repeats. It leads better channel utilization but longer delay. 156. What do you mean by p persistent CSMA (carrier sense multiple access)? -> It applies to slotted channels. When a station becomes ready to send, it senses the channel. If it is idle it transmits with a probability P, with a probability Q=P-1 It defers until the next slot. If that slot is also idle, it either transmits or defers again with probability P and Q. The process is repeated until either the frame has been transmitted or another station begins transmitting. 157. What is FDDI? -> It is high performance fiber optic token ring LAN running at 100Mbps over distance up 1000 stations. FDDI access is limited by time. A FDDI cabling consists of two fiber rings. i) One transmitting clockwise ii) One transmitting counterclockwise 158. What is Firewalls? -> It is an electronic down bridge which is used to enhance the security of a network. Its configuration has two components. i) Two routers II) Application gateway The packets traveling through the LAN are inspected here and packets meeting certain criteria are forwarded and others are dropped. 159. What do you mean by Data Terminal Equipment (DTE)? -> It is any device that is source of or destination for binary digital data. At physical layer it can be a terminal computer. They generate or consume information. 160. What do you mean by Data Terminating Equipment (DCE) ? -> Data circuit terminating equipment includes any functional unit that transmits or receives data in the form of an analog or digital signal through a network.DTE generates digital data and passes them to a DCE, the DCE converts the data to a form acceptable to the transmission media and sends the converted signal to another DCE on the network. 161. What do you mean by protocol stack? -> The list of protocols used by certain system, one protocol per layer is called protocol stack. 162. What do you mean by peer? -> Entities comprising the corresponding layers on different machines are called pee rs. It may be
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Hardware device, Processes, human being, peers communicates by using protocol.
163. What do you mean by broadcasting? -> Broadcast system allows addressing a packet to all destinations by using a special code in address field. When packet is transmitted it i s received and processed by every machine on the network. 164. What is TELNET? -> TELNET is a client –server application that allows a user t o log on to a remote machine, giving the user access to the remote system. TELNET is an abbreviation of terminal Network. 165. What do you mean by Simple Mail Transfer Protocol (SMTP)? -> The TCP/IP protocol that supports electronic mail on t he internet is called Simple Mail Transfer Protocol. SMTP provides for mail exchange between users on the same or different computer and supports Sending a single message to one or more recipient Sending message that include text, voice, video, or graphics. Sending message t o users on network outside the inter net. 166. What is Hypertext Transfer Protocol (HTTP)? -> It is the main protocol used to access data on the World Wide Web. The protocol transfers data in the form of plain text, hypertext, audio, video, and so on. It is so called because its efficiency allows its use in a hypertext environment where there are rapid jumps from one document to another. 167. What is URL? -> It is a standard for specifying any kind of information on the World Wide Web. 168. What is World Wide Web? -> World Wide Web is a repository of information spread all over the world and linked together. It is a unique combination of flexibility, portability, and user-friendly features .The World Wide Web t oday is a distributed client-server service, in which a client using a browser can access a service using a server. The service provided is distributed over many locations called web sites.
169. What is HTML? -> Hypertext Markup Language (HTML) is a language for creating static web pages. 170. Briefly describe Encryption in Cryptography process. -> The messages to be encrypted, PLAINTEXT; are transformed by a function that is paramete rized by a KEY. The output of the encryption process, known as the CIPHERTEXT, is then transmitted. 171. What is Cryptanalysis? -> The art of breaking ciphers is Cryptanalysis. 172. What is Cryptology? -> The art of devising cryptography is known as Cryptology. 173. What is Kirchhoff’s Principle? -> All algorithms must be public; only the keys are secret. 174. What is monoalphabetic Substitution? -> The general system of symbol for symbol substitution is called Monoalphabetic Substitution.
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175. What is Transposition Substitution? -> Reordering the letters but not to disguise them. 176. What are Qubits? -> Bits sent one photon at a time are called Qubits. 177. What is Privacy Amplification? -> The transformation from original one time pad to a different one that reduces Intruder's knowledge. 178. What are the Cryptographic Principles? -> 1. Messages must contain some redundancy. 2. Some method is needed to foil replay attacks. 179. Give some famous Symmetric Key Algorithms. -> DES, Triple DES, AES, Cipher Modes, Cryptanalysis etc. 180. What are S Boxes? -> The substitution in Symmetric key algorithms is performed by S-Boxes. 181. Briefly explain DES. -> DES is the archetypal block cipher — an algorithm that takes a fixed-length string of plaintext bits and transforms it through a series of complicated operations into another cipher text bit string of t he same length. In the case of DES, the block size is 64 bits. DES also uses a key to customize the transformation, so that decryption can supposedly only be performed by t hose who know the particular key used to encrypt. The key ostensibly consists of 64 bits; however, only 56 of these are actually used by the algorithm. Eight bits are used solely for checking parity, and are thereafter discarded. Hence the effective key length is 56 bits, and it is usually quoted as such. Every 8th bit of the selected key is discarded, i.e. positions 8, 16, 24, 32, 40, 48, 56, 64 are removed from the 64 bit key leaving behind only the 56 bit key. 182. Disadvantages of DES? -> Brute force attack and minor cryptanalytic properties are few methods which proved DES is not suitable for various applications. 183. Give the formulae used in TDES. -> Encryption: ciphertext = EK3 (DK2 (EK1 (plaintext))) Decryption: plaintext = DK1(EK2(DK3(ciphertext))) 184. What are the high level descriptions of the AES algorithm? -> 1. KeyExpansion—round keys are derived from t he cipher key using Rijndael's key schedule 2. Initial Round AddRoundKey—each byte of the state is combined with the round key using bitwise x or 3. Rounds SubBytes—a non-linear substitution step where each byte is replaced with another according to a lookup table. ShiftRows—a transposition step where each row of the state is shifted cyclically a certain number of steps.
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MixColumns—a mixing operation which operates on the columns of the state, combining the four bytes in each column. AddRoundKey 4. Final Round (no MixColumns) SubBytes ShiftRows AddRoundKey.
185. Which is the Symmetric key algorithm which performs encryption before and after decryption? -> Triple Data Encryption Standard. 186. What are the various Cipher Modes? -> Electronic Code Book Mode, Cipher Block Chaining Mode, Cipher Feedback Mode, Stream Cipher Mode, Counter Mode. 187. What are the requirements of Public Key Algorithms? -> 1. D(E(P))=P 2. It is exceedingly difficult to deduce D from E. 3. E cannot be broken by a chosen plaintext attack. 188. What are the various conditions needed in Digital Signatures to send a signed message to another party? -> 1. The receiver can verify the claimed identity of the sender. 2. The sender cannot later repudiate the contents of the message. 3. The receiver cannot possibly have concocted the message himself. 189. Name any few attacks. -> Birthday Attack, Replay attack, 190. Give one security authentication protocol for e-mails. -> Pretty Good Privacy Protocol. 191. What are the fundamental services of Secure DNS. -> 1. Proof of where the data originated. 2. Public Key distribution. 3. Transaction and request authentication. 192. What is ActiveX? -> ActiveX controls are Pentium binary programs that can be embedded in Web pages. 193. What is Authenticode? -> The Microsoft system for verifying ActiveX control is called Authenticode. 194. What is Stenganography? -> The science of hiding messages. 195. What are the various layers in ATM Reference Model? -> Physical layer, ATM layer, ATM adaptation layer. 196. What are the functions of Physical Layer in ATM reference model? -> It deals with the physical medium like voltages, bit timing etc.
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197. Functions of ATM layer? -> It deals with cells and cell tr ansport. 198. What is AAL? What are the various sub layers of AAL? -> ATM Adaptation Layer. Sub Layers are Segmentation, Reassembly and Convergence Sub layer. 199. What is Handshake mechanism in TCP? -> To establish a connection, the three-way (or 3-step) handshake occurs: SYN: The active open is performed by the client sending a SYN to the server. It sets the segment's sequence number to a random value A. SYN-ACK: In response, the server replies with a SYN-ACK. The acknowledgment number is set to one more than the received sequence number (A + 1), and the sequence number that the server chooses for the packet is another random number, B. ACK: Finally, the client sends an ACK back to the server. The sequence number is set to the received acknowledgement value i.e. A + 1, and the acknowledgement number is set to one more than the received sequence number i.e. B + 1. 200. Abbreviate IPC and RPC. Give the various methods provided by API library in Socket Programming? -> Inter Process Communication and Remote Procedure C all. socket(), bind(), listen(), connect(), accept(), send(), recv(), sendto(), recvfrom(), write(), read(), close().
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