ComputerNetworks_1.docx

COMPUTER NETWORKS

1. Define Computer Networks.Computer Networks is an interconnected collection of autonomous

computer. Here, two or more devices are connected together for the purpose of sharing data and resources. The connection can be via a guided media or can be unguided media.

2. What are the goals of Computer Networks? Resource Sharing Information Sharing Scalability High reliability Saving money Powerful communication media

3. What is Data Communication?Data Communication is the exchange of data between two devices via

some form of transmission medium. Delivery, Accuracy and Timeliness defines the effectiveness of a data communication system. The components of the data communication system are Sender, Receiver, Transmission medium, Protocol and Message.

4. ___________, __________ and __________ are the important criteria of network.Ans: Reliability, Performance, Security

5. What are the issues to be considered in designing a network for better performance?

Minimize the software overhead by reducing the number of packet counts Minimize the operating system overhead by reducing the number of

context switches to occur Minimize the number of copying of data units Make the delay shorter by improving the protocols used, the OS or the

network interface Increase the CPU speed rather than the network speed Avoid congestion rather than recovering from it Have appropriate timeouts for the sending packets

6. What are the security problems that are associated with Computer Networks society?

Security: It deals with keeping the information reaching our of the hands of unauthorized users

Authentication: It deals with determining the authorized person for accessing the sensitive information and the network resources

Non-repudiation: It deals with Digital Signatures validity

Integrity control: It deals with that the received message was in the appropriate form and does not get modified in transmission

7. In what are all the ways, the networks differ?The networks differ in the

Type of Service offered Protocols used Addressing Presence or absence of multicasting Packet size Quality of Service offered Error handling mechanism Flow control Congestion control Security Accounting Parameters such as timeouts, flow specification etc.

8. Explain the major types of networks. Server-based network: They provide centralized control of network

resources and rely on server computers to provide security and network administration.

Peer-to-Peer network: In this network, computers can act as both servers sharing resources and clients using the resources.

9. What are the types of Line Configuration and explain?The two types of line configuration are

Point-to-Point and Multipoint

In Point-to-Point line configuration, a dedicated link is available between any two devices and in multipoint line configuration, a link is shared by more than two devices.

10. Define Topology and what are the types of topology?Topology is the way a network is designed either physically or logically.

Following are the main types of topology: Bus Star Tree Mesh Ring

11. What is a passive topology?

When the computers on the network simply listen and receive the signal, they are referred to as passive topology, because they do not amplify the signal in any way.

E.g. Linear Bus topology

12. Briefly explain the types of topologies. Bus topology: In this topology, many devices are attached to a single link,

which acts as a backbone in the network. Star topology: Here, the hub acts as a central controller to which every

device has a dedicated point-to-point link. Tree topology: In this case, there will be one primary hub into which any

numbers of secondary hubs or devices are attached to it. The secondary hubs in turn consist of many devices attached to it.

Mesh topology: In this topology, every device has a dedicated link to every other device.

Ring topology: In this topology, each device is attached with its either side of the adjacent devices only, which forms like a ring.

13. What are the types of transmission modes and explain? Simplex: The communication is unidirectional between two devices.

E.g. Keyboards Half-duplex: Here, both the devices can transmit or receive the data, but

not at the same time.E.g. Walkie-talkies

Full-duplex: In this mode, both the devices can transmit and receive the data simultaneously.

E.g. Telephones

14. Sketch the layers of OSI (Open Systems Interconnection) model?

Application LayerPresentation Layer

Session Layer

Transport Layer

Network Layer

Data Link Layer

Physical Layer

15. What is Project 802?It is a project started by IEEE to set standards that enable

intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extend the network layer to allow interconnectivity of major LAN protocols.

It consists of the following:

802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.

802.2 Logical Link Control (LLC) is the upper sub layer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.

Media Access Control (MAC) is the lower sub layer of the data link layer that contains some distinct modules carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).

802.6 is Distributed Queue Dual Bus designed to be used in MANs.

16. What is Protocol Data Unit (PDU)?The data unit in the LLC level is called the Protocol Data Unit (PDU).

The PDU contains four fields: a Destination Service Access Point (DSAP), a Source Service Access Point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a Information frame (I-Frame) or a Supervisory frame (S-Frame) or a Unnumbered frame (U-Frame).

17. Name the data unit exchanged in each layer of OSI model?

Layer Data Unit Exchanged

Physical Bit

Data Link Frame

Network Packet

Transport Transport Protocol Data Unit (TPDU)

Session Session Protocol Data Unit (SPDU)

Presentation Presentation Protocol Data Unit (PPDU)

Application Application Protocol Data Unit (APDU)

18. What are the main functions concerned with Physical Layer? Bits representation Bits synchronization Data transmission rate Line configuration Transmission mode Topology Physical characteristics of media

19. What are the main functions of Data Link Layer? Framing

Physical addressing Flow control Error control Access control

20. What are the functions of Network Layer? Logical addressing Routing Congestion control

21. What are the functions of Transport Layer? Service-point addressing Segmentation and reassembling Connection control Flow control Error control

22. What are the functions of Session Layer? Dialog control Synchronization Token management

23. What are the functions of Presentation Layer? Translation of data Authentication Encryption Compression

24. What are the functions of Application Layer? Network Virtual Terminal (NVT) Mail service Directory service File transfer, access and management Network management

25. What is Logical Link Control (LLC) layer?It is one of two sub-layers of the data link layer of OSI reference model, as

defined by the IEEE 802 standard. This sub layer is responsible for maintaining the link between computers when they are sending data across the physical network connection.

26. Define TCP/IP.

TCP/IP is a set of rules and procedures that governs the exchange of messages in an inter network. It was designed before the OSI model and contains the following five layers.

Application LayerTransport LayerNetwork LayerData link LayerPhysical Layer

27. Define Protocol.A protocol is a set of rules that govern data communication. It represents

an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating.

28. Define IP.Internet Protocol is an unreliable and connectionless datagram protocol.

Packets produced in the IP layer are called Datagrams. A Datagram is a variable length packet of up to 65,536 bytes long with the header length of maximum 60 bytes.

29. What do you mean by a SAP?It is a series of interface points that allow other computers to communicate

with the other layers of network protocol stack.

30. What is MAC address?The address for a device as it is identified at the Media Access Control

layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.

31. How many physical channels and I/O ports are needed to link ‘n’ devices in a Mesh topology?

Physical Channels –> n (n-1)/2I/O Ports –> (n-1)

32. What are the different conversion schemes available to send data from one device to another?

Digital-to-Digital Digital-to-Analog Analog-to-Analog Analog-to-Digital

33. What is meant by bandwidth?

It is the amount of information that can be sent over a given transmission channel. It is usually expressed in terms of the range of frequencies or number of bits per second that can be carried.

34. What is the difference between Bit rate and Baud rate?Bit rate is the number of bits transmitted during one second, whereas Baud

rate refers to the number of signal units per second that are required to represent those bits.

Baud rate = Bit rate/Nwhere, N is number of bits represented by each signal shift.

35. What is a Point-to-Point protocol?This is a communication protocol used to connect computers to remove

networking services including Internet service providers.

36. ____________ and __________ are the two types of data transmission modes.Ans: Parallel and Serial

37. What is a null modem?A null modem is a short cable of 15-meter of maximum length which

allow a data rate up to 20kbps. It can be used to connect two Data Terminal Equipments (DTE) directly without the need of any intermediatory Data Circuit-Terminating Equipments (DCE).

38. What is meant by DTE and DCE? Data Terminal Equipment (DTE): It includes any unit that functions either

as a source of or as a destination for binary digital data.E.g. Computer, Printer

Data Circuit-terminating Equipment (DCE): It includes any functional unit that transmits or receives data in the form of an analog or digital signal through a network.

E.g. Modem

39. What are the types of transmission media? Guided media: It provides a conduit from one device to another that

include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metals that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.

Unguided media: This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcasted through air by radio satellite communication and cellular telephony.

40. ________, _________ and _________ are referred to as guided media and ________, _________ are referred to as unguided media.

Ans: Twisted-pair cable, coaxial cable, Fiber-optic cable, Air, Water

41. What is the difference between Base band and Broadband transmission?In a base band transmission, the entire bandwidth of the cable is consumed

by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.

42. How are the signals transmitted through a link gets affected? Distortion Attenuation Noise

43. What do you mean by attenuation?Attenuation refers to the degeneration of signals when traveling through a

longer distance.

44. _________, _________ and __________ measure the performance of a transmission media.

Ans: Throughput, Transmission speed, Transmission time

45. What are the different framing methods available? Character count Character stuffing or Byte stuffing Bit stuffing Physical layer coding violations

46. What is meant by Bit Stuffing?In Bit stuffing, a bit 0 is stuffed or added in the sending data, when it

encounters five consecutive 1’s. In the receiving end, the added bits are destuffed and processed.

47. What is meant by single bit error and burst error? Single Bit Error: When transmitting data from one end to other end, if

only a single bit changes from 1 to 0 or o to 1, due to noise then it is said to be single bit error.

Burst Error: When more than one bits in a data unit gets changed from 1 to 0 or 0 to 1 when transmitting data, then it is said to be Burst error. The length of the burst is measured from the first affected bit to the last affected bit.

48. _________, __________, __________ and __________ are the types of redundancy check used for error detection in Data Communication.

Ans: Vertical Redundancy Check (VRC), Longitudinal Redundancy Check (LRC), Cyclic Redundancy Check (CRC), Checksum

49. Briefly explain about CRC.In CRC, a sequence of redundant bits is appended to the end of a data unit, so

that the resulting data unit becomes exactly divisible by a second predetermined binary number. At the destination, the incoming data unit is assumed to be intact and is therefore accepted. A remainder indicates that the data unit has been damaged in transmission and therefore must be discarded.

50. Briefly explain about stop-and-wait and sliding window mechanism of flow control.

Stop-and-Wait: In stop-and-wait method, the sender waits for an acknowledgement after every frame it sends. The next frame is sent only when an acknowledgement has been received.

Sliding Window: In sliding window mechanism, several frames are transmitted by the sender, before needing an acknowledgement. The receiver acknowledges only some of the frames, using a single ACK to confirm the receipt of multiple frames.

51. What is meant by Automatic Repeat Request (ARQ)?When transmitting data from one end to another end, if an error is detected

in an exchange, a negative acknowledgement is returned and the specified frames are retransmitted. This process is called as ARQ. Retransmission of frames are happened due to lost frame, damaged frame or lost acknowledgement.

52. Explain Go-Back-n and Selective-Reject ARQ. Go-Back-n ARQ: In this method, when one frame is lost or damaged, all

frames are sent since the last frame acknowledged is retransmitted. Selective-Reject ARQ: In this method, only the damaged or lost frames are

retransmitted.

53. What is meant by Piggybacking?The technique of temporarily delaying the outgoing acknowledgements, so

that they can be hooked onto the next outgoing data frame is known as piggybacking. In other words, the combining process of data to be sent and acknowledgement of the frame received in a single frame is meant by piggybacking.

54. __________, ___________, __________ and __________ are the four important LAN Architectures.

Ans: Ethernet, Token Bus, Token Ring, Fiber Distributed Data Interface

55. What are 10Base2, 10Base5 and 10BaseT Ethernet LAN’s? 10Base2: It refers to a cable with a maximum transfer rate of 10 Megabits

per second that uses base band signaling with a contiguous cable segment of length of 100 meters and a maximum of 2 segments.

10Base5: It refers to a cable with a maximum transfer rate of 10 Megabits per second that uses base band signaling, with 5 continuous segments not exceeding 100 meters per segment.

10BaseT: It refers to a cable with a maximum transfer rate of 10 Megabits per second that uses base band signaling and twisted pair cabling.

56. What do 10Base5, 100Base-T, 10Broad36 and 100Base-FX signify?The first number (i.e.10, 100) indicates the data rate in Megabits/second

(Mbps). The word Base indicates a digital signal and the word Broad indicates an Analog signal. The last number (i.e. 5, 36) indicates the maximum cable length in meters (5 means 500 meters). The letters indicates the type of cable used (T-Twisted pair, FX-Optical fibers).

57. Explain Carrier Sense Multiple Access with Collision Detection (CSMA/CD).In CSMA/CD, a station wishing to transmit its data frame first listens to

the link, to make sure that it is free. If it is free, it transmits its data and then listens again. During the transmission, the station checks the line for any collisions and if it is detected, it stops sending frame and waits for a predetermined amount of time for the line to become free, then sends its data again.

58. 10Base5 is known as _________ and 10Base2 is known as __________.Ans: Thick Ethernet, Thin Ethernet

59. Briefly explain about Token Ring mechanismIn Token Ring mechanism, a simple three-byte token is generated and

being passed along the ring when the network is un-occupied. If any station has data to send, then it waits for the token to reach its Network Interface Card (NIC). When the token enters the station and the token is free, then it keeps the token and then send a data frame. This data frame proceeds around the ring and the intended recipient receives the frame and sets the address recognized bits. This frame is then circulated through the ring. When the sender receives the frame, it checks the appropriate bits. If it is set, then it discards the used data frame and releases the token back to the ring..

60. What is MAU?In Token Ring network, a hub is called as a Multi-station Access Unit.

61. ________, _________ and ______ are the three types of frames that are supported by Token Ring protocol.

Ans: Data/Command, Token, Abort.

62. What are the important types of switching methods and explain? Circuit switching: In this method, a direct physical connection is

established between two devices. E.g. Telephone.

Packet switching: In this method, data that are to be transmitted are divided into small discrete units of potentially variable length packets and then transmitted.

Message switching: In this mechanism, the message from the source gets stored and forwarded by the intermediatory nodes to the destination. The intermediate nodes receive stores and then send the message until the appropriate route becomes free.

63. What are the two types of Packet Switching networks and explain. Datagram approach: In this approach, each packet of a single message is

treated as a different, distinct packet from other packets. When it is transmitted, each packet may take a different route to reach its destination.

Virtual Circuit approach: In this case, the relationship between all packets of a single message gets preserved. When the packets are transmitted, all they belong to a single route one after another, to reach their destination.

64. What is a Virtual circuit?Virtual circuit is a logical transmission path through an X.25 Public

Switched Data Network (PSDN) established by exchange of setup messages between source and destination terminals. There is no physical end-to-end path reserved for a call.

65. What is a 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 a virtual path.

66. What is a 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. Those failing the test are dropped.

67. What are the two types of Virtual Circuit implementation methods? Explain. Switched Virtual Circuit (SVC): In this method, whenever needed a virtual

circuit is created and exists only for the duration of the specific exchange. Permanent Virtual Circuit (PVC): Here, a permanent circuit is assigned to

the specific users and the circuit cannot be shared by any other users.

68. What is the difference between Circuit-Switched and Virtual-Circuit connection?

Circuit-Switched connection Virtual-Circuit connection A Circuit-Switched connection creates

a path between the source and destination by making a physical contact between switches.

The links that make a path are dedicated and cannot be shared by other connections.

A Virtual-Circuit connection creates a route between the connecting devices by making an entry in the routing table of the router.

The links that make a route can be shared by other connections.

69. What is meant by Switching?Switching is a method in which multiple communication devices are

connected to one another efficiently by making use of intermediatory hardware or software switches that links the devices together temporarily.

70. What is meant by Authentication?The mechanism of validating the identity of an user who wants to have the

access to a set of resources is known as Authentication. PPP has created two protocols for authentication. They are:

Password Authentication Protocol (PAP) Challenge Handshake Authentication Protocol (CHAP)

71. Briefly explain the types of Authentication protocols. PAP: The two steps involved in PAP are as follows:

o Step 1: The user who wants to access a system sends authentication identification and a password.

o Step 2: The system checks the validity of the identification and password and either accepts or rejects the connection.

CHAP: It is a three-way hand shaking authentication protocol. In this method the password is kept secret and it is never send online. The three steps involved in CHAP are as follows:

o Step 1: The system sends to the user a challenge packet containing a challenge value.

o Step 2: The user applies a predefined function that takes the challenge value and the users own password and creates a result. The user sends the result in the response packet to the system.

o Step 3: The system does the same. It applies the same function to the password of the user and the challenge value to create a result. If the result generated is same as that of the response packet, then access is granted else it is denied.

72. What do you mean by Kerberos?It is an authentication service developed at the Massachusetts Institute of

Technology (MIT). Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.

73. What is frame relay and in which layer does it come?Frame relay is a packet switching technology and it operates in the data

link layer.

74. What is terminal emulation and in which layer does it operate?Terminal Emulation is called as Telnet and it belongs to application layer.

75. What do you mean by a NVT (Network Virtual Terminal)?It is a set of rules defining a very simple virtual terminal interaction. The

NVT is used in the starting of a Telnet session.

76. What does the mount protocol do?The mount protocol returns a file handle and the name of the file system in

which a requested file resides. The message is sent to the client from the server after receiving a client’s request.

77. What do you mean by Beaconing?Beaconing is a process that allows Token-Ring/FDDI networks to self-

repair. The stations on the network notify the other stations on the ring when they are not receiving the transmissions.

78. What do you mean by redirector?Redirector is a software that intercepts file or prints I/O requests and

translates them into network requests. This comes under presentation layer.

79. What are NETBIOS and NETBEUI? NETBIOS: It is a programming interface that allows I/O requests to be

sent to and received from a remote computer and it hides the networking hardware from applications.

NETBEUI: It is NETBIOS extended user interface. It is a transport protocol designed by Microsoft and IBM for the use on small subnets.

80. What is RAID method?It is a method for providing fault tolerance by using multiple hard disk

drives.

81. What are the advantages and disadvantages of Frame Relay technology? Advantages:

o Frame relay operates at a higher speed at 44.376 Mbps.o Frame relay is less expensive than other WAN technologies.o Since it operates only at physical and data link layers, it can be easily

used as a backbone network to provide services to protocols that already have a network layer protocol.

o It allows bursty data.o It allows a frame size of 9000 bytes which can accommodate all LAN

frames.

Disadvantages: o Even though they operate at 44.376 Mbps, still this is not adequate for

protocols with even higher data rates.o Since it allows variable-length frames, it may create varying delays for

different users.

82. What is meant by Congestion and what are the consequences of this congestion in a network?

Congestion in a network may occur, if the data being transmitted in the network at a rate greater than that allowed by the resources of the network. When congestion occurs in a network, it can increase the delay of data transmission and decreases the throughput. Hence it should be avoided in order to attain the high throughput and low delay.

83. What is FRAD?Frame Relay Assembler/Disassembler (FRAD) is a device which

assembles and disassembles frames coming from other protocols such as X.25, ATM etc, to allow them to be carried by Frame Relay frames.

84. What are the goals of ATM? The usage of high data rate transmission media. A system that can interface with existing systems and to provide wide area

interconnectivity between them without lowering their effectiveness or requiring their replacement.

A cost effective solution The new system must be able to support the existing telecommunications

hierarchies. The system must be connection-oriented to ensure accurate and

predictable delivery. The final goal is to move as many as functions to the hardware level to

ensure high speed.

85. Define Cell.A Cell is defined as a small data unit of fixed size. It is of 53 bytes long

with 5 bytes are used for header and the remaining 48 bytes are used for carrying data or pay load. The cell network uses the cell as a basic unit of data exchange.

86. Explain the advantages of using cells in a network. Since the size of the cell is fixed, it doesn’t suffer from a long delay. It can be used to send real-time data’s. The network operation is now more efficient and cheaper because now the

basic unit is cell and not bit. The software implementation of switching and multiplexing can now be

move to hardware level resulting in less expensive devices.

87. Define ATM. Asynchronous Transfer Mode (ATM) is a cell-switched network. It uses the

cells as the basic unit of data exchange. It uses asynchronous time-division multiplexing to multiplex cells coming from different channels. The ATM standard defines three layers and they are Application Adaptation Layer (AAL), the ATM Layer and the Physical layer from top to bottom.

88. What are the functions of ATM layers? AAL: This layer is responsible for allowing the other networks to connect

to ATM network and the facilities of ATM are made available to the networks.

ATM Layer: This layer helps for routing, traffic management, switching and multiplexing services.

Physical Layer: This layer defines the transmission medium, bit transmission, encoding and electrical to optical transformation.

89. Define Quality of Service (QoS).The QoS defines a set of attributes related to the performance of the

connection. For each connection, the user can request a particular attribute. Each service class is associated with a set of the attributes and these attributes can be related to the user-oriented or network-oriented.

E.g. Sustained Cell Rate (SCR), Cell Loss Ratio (CLR).

90. What is meant by Traffic Descriptors?The mechanisms by which the service classes and QoS attributes are

implemented are called the traffic descriptors. A traffic descriptor defines how the system enforces and polices traffic. The algorithm to implement traffic descriptors is called the Generalized Cell Rate Algorithm (GCRA).

91. Define Unicasting, Multicasting and Broadcasting. Unicasting: It is a type of communication between one sender to one

receiver (i.e.) it is a one-to-one means of communication. Multicasting: It is a type of communication of sending packets from one

sender to a subset of receivers in a network. It can be considered as a one-to-many means of communication.

Broadcasting: It is a communication technique in which the sender sends the packets to all of the machines present in a network. It can be considered as one-to-all means of communication.

92. Explain the difference between the Connection-oriented service and Connectionless Service.

Connection-oriented Service Connectionless Service A connection must be established

between both the ends of a transmission before either may transmit data

Data that are received are in the same order that is sending by the sender

Ensures accurate and predictable delivery

A connection need not be established to send data

Data that are received need not be in the same order as that of the sender

Not accurate and doesn’t ensure predictable delivery

93. What is a Repeater and explain its function?

A Repeater is an electronic device that operates only on the physical layer. When signals get transmitted from one end to another end over a long distance, they will become weaker and weaker because of the resistance offered by the medium. This will result in corrupted signals at the receiving end. But the installation of a repeater on a link receives the signal before it becomes weak or corrupted and then regenerates the original bit pattern. These regenerated signals are then put back on to the link. Thus it allows us to extend the physical length of a network, which it can actually handle.

94. Explain the function of a Bridge.Bridge is a store and forward electronic device which operates on both data

link layer and physical layer. It helps to divide a large network into smaller segments. It also helps for controlling congestion and security. A bridge has access to the physical addresses of all the stations connected to it and gets stored in a table. Hence, when a frame enters the bridge the signals get regenerated and then it reads the address contained in it and compares that address with its table. When it finds the match, the frame will be redirected to the appropriate segment.

95. ________, _________ and _________ are the important types of Bridges.Ans: Simple, Multiport, Transparent Bridge.

96. Explain Simple, Multiport and Transparent Bridges. Simple: A simple bridge is the one in which two segments of a network

can be attached to it and the addresses of each station in a segment should be entered manually before it can be used.

Multiport: It can be used to connect more than two segments. Transparent: It is an intelligent bridge because it builds the table of

physical addresses of each station in a segment dynamically, when it encounters the bridge operation. It has also self-updating feature.

97. What is meant by Router and explain its functions?Router is an internetworking device that operates on physical, data link and

network layer. The main function of router is to forward packets through a set of networks. They have access to the network layer addresses and it contains the software that enables them to determine the shortest path among the possible paths for a particular transmission.

98. Explain about the classifications of Routing. Non-adaptive routing: In this type of routing, once a route is selected

between the source point and destination point, only that route will be used for its entire transmission of the session.

Adaptive routing: In this case, even if the packets belonging to the same session, the router may choose different route for each packet depending on the conditions of the route such as traffic, topology, failure of a link etc.

99. What are the types of routing tables? Fixed: This table must be manually modified every time there is a change. Dynamic: This kind of table changes its information based on network

traffic, thus reducing the amount of manual maintenance. Fixed central: It allows a manager modify only one table, which is then

read by other devices.

100. What is the HELLO protocol used for?The HELLO protocol uses time instead of distance to determine optimal

routing. It is an alternative to the Routing Information Protocol (RIP).

101. What is meant by multicast routing?Sending a message to a group is called multicasting, and its routing algorithm

is called multicast routing.

102. What is called Packet lifetime?In order to avoid bouncing and looping of packets caused due to wrong

routing conditions, a solution is added to the packet field and this is called packet lifetime or Time To Live (TTL). Each packet is associated with a lifetime, usually the number of hops that are allowed to travel before a packet is considered to be lost or destroyed. When each router encounters the packet, the total lifetime will be reduced by 1, and when it attains 0, before reaching the destination it will be destroyed.

103. What is a Gateway and explain its function.Gateway is generally a software installed within a router which helps to acts

as a protocol converter. It potentially operates in all the seven layers of the OSI model. It can accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it.

104. What is the difference between interior and exterior gateways?Interior gateways connect LAN of one organization, whereas exterior

gateways connect the organization to the outside world.

105. How Router is different from Gateway?A router can be able to transfer, accept and relay the packets only across the

networks using similar protocols, whereas the gateway can do the same job across the networks using different protocols.

106. What is meant by Multi-protocol Routers?A multi-protocol router is a type of router in which it can recognize more than

one type of protocol. If the multi-protocol router is connected between two different types of protocol networks, then it can send and receive packets of either type of network protocols, but not for other types of protocol.

107. What is meant by multihomed host?A multihomed host is a host having multiple network interfaces and that

requires multiple IP addresses.

108. What is meant by Brouter?A Brouter (Bridge/Router) is a single protocol or multi-protocol router that

sometimes acts as a bridge and sometimes acts as a router.

109. __________ and ___________ are the commonly used routing algorithms that are used to find out the shortest path between two routers.

Ans: Distance Vector Routing, Link State Routing.

110. What is OSPF?It stands for Open Shortest Path First. It is an Internet routing protocol that

scales well, can route traffic along multiple paths, and uses knowledge of an Internet’s topology to make accurate routing decisions.

111. What is called Flooding?Flooding is a process of sending the information of one router to its neighbor

routers to share its knowledge.

112. ________, ________, _________ and __________ are the four important aspects of reliable delivery.

Ans: Error control, Duplication control, Loss control, Sequence control.

113. What are the stages involved in Connection-oriented transmission? Connection establishment Data transfer and Connection termination

114. Explain Three-way Handshake of connection establishment mechanism.In three-way handshake mechanism, a connection establishment requires three

actions and they are as follows: The computer requesting the connection sends a connection request packet

to the intended receiver. The responding computer returns a confirmation packet to the requesting

computer. The requesting computer returns a packet acknowledging the

confirmation.

115. Explain Three-way Handshake mechanism of connection termination.All these following steps happen, once all of the data have been transferred.

The requesting computer sends a disconnection request packet. The responding computer confirms the disconnection request. The requesting computer acknowledges the confirmation.

116. What is meant by Synchronization points?To control the flow of information and allow recovery from software or

operator errors, the session layer allows reference points to be introduced into the data and this is known as Synchronization point.

117. Explain the types of Synchronization points. Major Synchronization point: It divides an exchange into a series of

dialogs. Generally, each major synchronization point requires acknowledgement before the session can continue. If an error occurs, data can be recovered only up to the last major point.

Minor Synchronization point: These are inserted into the middle of dialogs and may or may not require confirmation, depending on the application. If an error occurs, the control can go back one or more minor synchronization points within a dialog to recover data.

118. What is the need for Translation function in Presentation Layer?In a typical network of computers, the internal representation of a piece of

information might vary from one machine to other. For example, one may use ASCII code and another may use EBCDIC code. So, if the computer that uses ASCII code send an information to the other that supports EBCDIC code, then the result will be a garbage one. Hence in order to avoid this problem, a translation function is introduced into the presentation layer that translates the senders information to a known format that can be recognized by the receiving end.

119. Explain Direct and Indirect method of Translation. Direct Translation: In this method, the sender’s information is directly

translated to the format that can be recognized by the receiving end. The translation takes place at the receiving end.

Indirect Translation: Here, the sender’s information is first translated to a standard format at the sender. This standard format is then translated to the receiving end, where the standard format is converted to the format that is recognized by the receiving end.

120. What is external data representation?External data representation is a method of encoding data within an RPC

message to ensure that the data is not system dependent.

121. Define Encryption/Decryption. Encryption: It is the process of converting the original message into an

unrecognizable form at the sender side and then this message is sent out over the network. The resulted message is known as Encrypted message or Cipher text.

Decryption: It is the reverse process of converting back the encrypted message into its original form at the receiver side.

122. Explain the conventional and public key methods of Encryption/Decryption methods.

Conventional method: In this method, the encryption key and decryption key are the same and secret (i.e.) the decryption algorithm is always the inverse of the encryption algorithm and uses the same key.

Public key method: In this case, the decryption algorithm is not the inverse of encryption algorithm. Every user has the same encryption algorithm and key, however the decryption algorithm and key are kept secret.

123. Explain RSA (Rivest Shamir, Adleman) method of public key encryption technique.

In this technique, one party uses a public key Kp, and the other party uses a private key Ks. Both use a number N.

The steps involved in encryption algorithm are as follows: Encode the data to be encrypted as a number to create the plaintext P. Calculate the cipher text C as C = P Kp mod N Send C as the cipher text.

The decryption algorithm follows these steps: Receive C, the cipher text. Calculate plaintext P = C Ks mod N.90 Decode P to the original data.

124. How to choose the public key (Kp), private key (Ks) and the Number (N) values in the RSA encryption method?

First, choose two prime numbers, p and q Calculate N = p x q Select Kp such that it is not a factor of (p-1) x (q-1) Select Ks such that (Kp x Ks) mod (p-1) (q-1) = 1

125. What is meant by Digital Signature and explain the significance of using Digital Signature?

Digital Signature is a form of authentication and secrecy methods used for the transactions of many legal, financial and other important documents over the network.

The receiver can verify the claimed identity of the sender. The sender cannot later refuse to accept the contents of the message. The receiver cannot possibly have mixed up something else to the original

message by himself.

126. Explain the working mechanism of Digital Signature.The customer encrypts the plaintext (p) using a secret key Ks-1 and creates

the first level of cipher text (C1). The first cipher text is encrypted again using the public key, Kp-1, to create the second cipher text (C2). C2 is sent through

the network and received by the bank. The bank uses the secret key (Ks-2) to decipher C2 into C1. It then uses the public key (kp-2) to decipher C1 into the original plaintext. Before it does so, however it copies C1 and stores it in a separate file.

127. Explain the methods of Data Compression. Lossless Compression method: In this method, no data will be lost when

the compressed message gets decompressed again and it will be exact copy of the original message.

Lossy Compression method: This is the method, where some of the data will be lost after decompressing the compressed message. This method is ideal for sending audio and video data over the network.

128. Name the data unit exchanged in each layer of TCP/IP protocol.

Layer Data Unit Exchanged

Physical Bit

Data Link Frame

Network Datagram

Transport Segment or User datagram

Application Message

129. Explain the differences between TCP and UDP.

TCP UDP Connection-oriented protocol The size of the header length is of

maximum 60 bytes It provides sequencing and re-ordering

functions It is slower with more reliability It is complex The packets produced here are referred

to as segments

Connectionless protocol The size of the header length is 8 bytes Doesn’t provide sequencing and re-

ordering functions It is faster but has not reliability It is simple Here it is referred to as user datagram

130. What is called Subnetting?With the use of normal 32 bits long IP address, only two level of hierarchy of

representing the host can be done with the help of host id and net id. With this scheme, the hosts cannot be organized into any groups and all the hosts in the network are the same level. To overcome this problem, the networks are further divided into smaller networks called sub-networks and this process is called subnetting. After subnetting the IP address defines three levels of hierarchy to represent a host and they are net id, subnet id and host id.

131. What is called Masking?Masking is a process of extracting the address of the physical network from an

IP address.

132. Sketch the TCP segment header format.

Source Port (16 bits) Destination Port (16 bits)Sequence Number (32 bits)

Acknowledgement Number (32 bits)TCP

HLEN (4 bits)

Reserved(6 bits)

URG

ACK

PSH

RST

SYN

FIN

Window Size(16 bits)

Checksum (16 bits) Urgent Pointer (16 bits)Options (0 or more 32-bit words)

Data (optional)

where,HLEN - TCP Header LengthURG - Urgent PointerACK - Acknowledgement NumberPSH - Indicates pushed dataRST - Reset bit (Reset a connection)SYN - Synchronization bit (Establish connection)FIN - Finished bit (Release a connection)

133. Sketch the UDP datagram header format.

Source Port Address (16 bits) Destination Port Address (16 bits)UPD length (16 bits) UDP Checksum (16 bits)

134. Sketch the IP datagram header format.

Version (4 bits)

HLEN(4 bits)

Type of Service(8 bits)

Total length(16 bits)

Identification(16 bits)

DF

MF

Fragment offset(13 bits)

Time to Live(8 bits)

Protocol(8 bits)

Header Checksum(16 bits)

Source IP Address (32 bits)Destination IP Address (32 bits)

Options (0 or more words)

where,HLEN - Header LengthDF - Don’t FragmentMF - More Fragments

135. Explain the class ranges of Internet Addresses.

Class Range of Internet AddressesA 0.0.0.0 127.255.255.255B 128.0.0.0 191.255.255.255C 192.0.0.0 223.255.255.255D 224.0.0.0 239.255.255.255E 240.0.0.0 247.255.255.255

136. Define BOOTP.Bootstrap Protocol (BOOTP) is a client-server protocol designed to provide

the following information Its IP address Its subnet mask The IP address of a router The IP address of a name server,for a diskless workstation or a computer that is booted for the first time that

is attached to a TCP/IP internet.

137. What is the limitation of BOOTP and explain its alternative?The main limitation of BOOTP is that it is a static configuration protocol.

When a client requests its IP address, it searches the table for the corresponding entry of physical address that matches with the IP address of the machine. This means that binding between the physical address and the IP address should already exist. This solution is not ideal for all situations and hence the other alternative Dynamic Host Configuration Protocol (DHCP) was devised. DHCP is an extension to BOOTP and it provides the dynamic configuration of hosts.

138. Define DNS.Domain Naming System is a client-server application protocol which is used

to identify each host on the Internet by an alternative unique user-friendly name, instead of numeric IP addresses. In the internet, the domain name space is divided into three different sections: Generic domains, Country domains and Inverse domain.

139. What protocol is used by DNS name servers?DNS uses UDP for communication between servers. It is a better choice than

TCP because of the improved speed a connectionless protocol offers. On the other hand, transmission reliability suffers with UDP.

140. What do you mean by DNS resource record?

A DNS 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.

141. What is Network Time Protocol (NTP)?NTP is designed specifically to ensure that all internal timers are synchronized

and have similar settings.

142. Explain the structure of URL.The Uniform Resource Locator is a standard for specifying any kind of

information on the Internet. Its structure is as follows:Method:// Host:Port/Path

Method ->Type of protocol used to retrieve the document Host ->Name of the host, where the information is locatedPort ->Port number of the server and is optionalPath ->Pathname of the file, where the information is stored

143. Compare and contrast Circuit-switched networks with Packet-switched networks.

Circuit-switched network Packet-switched network Connection should be established

between the two ends to transfer information

Each packet in the network follows the same route to reach the destination

Congestion can occur only during the setup time

It doesn’t makes use of any store-and-forward transmission

No connection is needed

Each packet in the network may take different route to reach the destination

Congestion may occur on each and every packet

It makes use of the store-and-forward transmission

144. What is RIP (Routing Information Protocol)?It is a simple protocol used to exchange information between the routers.

145. What is SLIP (Serial Line Internet Protocol)?It is a very simple protocol used for transmission of IP datagrams across a

serial line.

146. What do you mean by a source route?It is a sequence of IP addresses identifying the route a datagram must follow.

A source route may optionally be included in an IP datagram header.

147. W hat are the disadvantages of SLIP (Serial Line IP)? It does not do any error detection or correction It does not provide any authentication mechanism It supports only IP

The senders and receivers address cannot be dynamically assigned during setup and hence each side must know the others IP address in advance

It is not an approved Internet standard and hence many different versions exist, which leads to complication issues

148. What is meant by Contention System?Systems in which multiple users share a common channel in a way that can

lead to conflicts are widely known as contention systems.

149. What is meant by ALOHA System?ALOHA systems are used as a channel allocation system in which

uncoordinated, multiple users are competing for a single shared channel. Here, all the frames are of uniform length to achieve the property of maximum throughput.

150. What are the types of ALOHA System? Pure ALOHA: In pure ALOHA, the users can send the data, whenever

they wanted, and there was no restriction. If collision occurs, the station waits for a random period of time and sends the data again. The maximum throughput achieved was 18 percent.

Slotted ALOHA: In slotted ALOHA, the time is divided into discrete intervals, each interval corresponding to one frame. Hence the user can send the data only when his time slot gets allocated. The maximum throughput achieved was 37 percent.

151. What are called Carrier-sense protocols?The protocols in which stations listen for a carrier and act accordingly are

called carrier sense protocols.

152. What is called 1-persistent CSMA (Carrier Sense Multiple Access)?In a network of computers, when a station has data to send, it first checks the

channel to see that whether it is busy or not. If it is busy, then the station waits until it becomes idle. As soon as it detects an idle channel, it transmits a frame. It transmits the data with a probability of 1 and hence this is called 1-Persistent CSMA protocol.

153. What is called Non-persistent CSMA?In any network, when a station has data to send, it first checks the channel and

if it is free, then it starts sending a frame. If it is busy, then the station does not continually sense the channel till it becomes idle, instead it waits for a random period of time and repeats the procedure. This leads to better utilization of the channel. This protocol is said to be Non-persistent CSMA protocol.

154. What are called Reservation protocols?

Protocols in which the stations reserve its slot for its data to be transmitted and get broadcast, before any actual transmission of data are called Reservation protocols.

155. Which protocols are referred to as Collision-free protocols? A Bit-Map protocol Binary countdown protocol

156. What are called limited contention protocols?Protocols that use the contention technique at low load to reduce the delay, but

use the collision-free technique at high load for good channel utilization are called limited contention protocols.

157. What is called Flow-based routing?A static algorithm which uses both topology and the load for routing of

packets is called flow-based routing. In order to use this technique, the type of topology, the traffic matrix and the line capacity matrix in bits/sec must be known in advance.

158. What are the techniques available to control congestion? A tight flow control Spreading the traffic over all the lines (i.e.) Traffic shaping Having appropriate packet lifetime Admission control (i.e.) no more virtual circuits setup, if congestion

occurs

159. What is called Tunneling?Tunneling is the technique, which is used to carry the information from source

to destination which is on the same type of network, but the intermediate network is of different type.

160. What is called Fragmentation?The breaking process of a large packet into number of small packets before

gets transmitted from one type of network to another type of network is called fragmentation.

161. __________, ___________, ___________, and _________ are referred to as control protocols.

Ans: ICMP, ARP, RARP, BOOTP

162. What is meant by Symmetric release and Asymmetric release connection? Asymmetric: In this type of connection, if either sending or receiving

machine releases its connection, the connection gets released. Symmetric: Here, both the sending and receiving machine should release

its connection, for the connection to get released.

163. What are the basic functions that are supported by the E-Mail systems? Composition Transfer Reporting Displaying Disposition

164. What is meant by MIME (Multipurpose Internet Mail Extensions).In the early days, the E-Mails can be used to send messages which are written

in English and expressed in ASCII. Later in order to support the messages which are written in languages with accents, messages in non-Latin alphabets, messages in languages without alphabets, audio and video messages MIME was developed and it was integrated with the already existed E-Mail system.

165. Define PGP (Pretty Good Privacy).PGP is a complete E-Mail security package that provides privacy,

authentication, digital signatures and compression all in easy-to use form.

166. 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. It uses the echo test/reply to test whether a destination is reachable and responding. It also handles both control and error messages.

167. What is the difference between ARP and RARP?The Address Resolution Protocol (ARP) is used to associate the 32 bit IP

address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending an ARP query packet that includes the IP address of the receiver.

The Reverse Address Resolution Protocol (RARP) allows a host to discover its IP address when it knows only its physical address.

168. What is anonymous FTP and why it is used?Anonymous FTP enables users to connect to a host without using a valid

login and password. Usually, anonymous FTP uses a login called anonymous or guest, with the password usually requesting the user’s ID for tracking purposes only. Anonymous FTP is used to enable a large number of users to access files on the host without having the trouble of setting up logins for all of them. Anonymous FTP systems usually have strict controls over the areas an anonymous user can access.

169. What is the difference between TFTP and FTP application layer protocols?The Trivial File Transfer Protocol allows a local host to obtain files fro a

remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.

The File Transfer Protocol is the standard mechanism provided by TCP/IP for copying a file from one host to another. It uses the services offered by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.

Exercises:

1. What are the advantages and disadvantages of different types of topologies?2. What is meant by peer-to peer processes?3. Which are referred to as user support layers?4. Is there a need for network layer, if any two systems are connected to a same

link?5. What is the difference between of having flow control and error control presented

in Data Link layer and Transport layer?6. How TCP/IP protocol model is different from that of OSI model?7. Which layers are referred to as Network support layers?8. How data’s get transformed from one device to another device in a network?9. Which one is the best framing method available?10. What is meant by flow control and error control?11. Explain the important of line discipline.12. What are the advantages and disadvantages of stop-and-wait and sliding window

flow control mechanism?13. Why Go-Back-n method is implemented mostly, even though the selective-reject

method gives better performance?14. What is meant by Data transparency?15. What is called collision?16. What is meant by NIC and explain its role?17. How the situation is handled in the Token Ring mechanism, when the token gets

destroyed?18. What are the disadvantages involved in message switching technique?19. What is the difference between path and route?20. What are the disadvantages of having variable size packet networks?21. Explain LAN, WAN, MAN and internet?22. What is the difference between Wireless networking and Mobile computing?23. Give some of the scenarios that are best suited for Connection-oriented service

and Connectionless service.24. What is meant by request-reply service and where does it employ?25. What are the major applications of Internet?26. Briefly explain about SONET (Synchronous Optical Network).27. How internet is different from Internet?28. What is called symbolic length of the link?29. How the bouncing and looping of packets gets generated in a network?30. Give examples of Transport layer protocols.31. Which one is the best translation method, either direct or indirect?32. Among the conventional method and public key method which one is considered

more secure and why?

33. Give some of the techniques used for the Lossless compression.34. Why the size of the .jpg photo format is very less compared to that of the .bmp

format and which type of compression technique is used here?35. What are the applications that suits best for TCP and UDP?36. Define generic domain, country domain and inverse domain.37. What is meant by TELNET and explain its uses?38. Explain the structure of E-Mail address.39. What is difference between hypertext and hypermedia?40. Compare and contrast optic fiber networks with copper wire networks.41. What is meant by Hierarchial routing?42. What is called Congestion and explain the factors that lead to congestion?43. Explain Leakey Bucket algorithm and for what purpose is it used?44. Is there any difference between fragmentation and segmentation?45. What is a firewall and explain its usage?46. What is the specialty of the IP addresses of the form 127.xx.yy.zz?47. List out the principal control messages that are supported under ICMP protocol.48. What is the use of sending packets that contains no data in it?49. Define the following:a. SMTP (Simple Mail Transfer Protocol)b. POP (Post Office Protocol)c. SNMP (Simple Network Management Protocol)d. HTTP (Hyper Text Transfer Protocol)e. WWW (World Wide Web)f. CGI (Common Gateway Interface)g. USENETh. DFS (Distributed File System)i. NFS (Network File System)j. PING (Packet Internet Gopher)k. PI (Protocol Interpreter)l. RFC (Request For Comments)m. TCB (Transmission Control Block)n. IS-IS (Intermediate System to Intermediate System Protocol)o. ISDN (Integrated Service Digital Network)p. Burst Modeq. Daemonr. Emulations. Enterprise Networkt. Proxyu. Round Trip Timev. Switched Connectionw. Terminal Serverx. X.400