Computer Networks Full(i to IV Unit) Two Marks

Computer Networks Unit wise 2 Marks Q & A

COMPUTER NETWORKSUNIT – I

1. What is mean by data communication?Data communication is the exchange of data (in the form of 1s and 0s) between two devices via some

form of transmission medium (such as a wire cable).

2. Define computer Networks.The Collection of Computers interconnected to perform a job/task is called as Computer Networks

3. What are the three criteria necessary for an effective and efficient network?The most important criteria are performance, reliability and security.Performance of the network depends on number of users, type of transmission medium, and the capabilities of the connected h/w and the efficiency of the s/w. Reliability is measured by frequency of failure, the time it takes a link to recover from the failure and the network’s robustness in a catastrophe.Security issues include protecting data from unauthorized access and viruses.

4. What are the three fundamental characteristics determine the effectivenessof the data communication system?The effectiveness of the data communication system depends on three fundamental characteristics:Delivery: The system must deliver data to the correct destination.Accuracy: The system must deliver data accurately.Timeliness: The system must deliver data in a timely manner.Jitter: Refers to the variation in the packet arrival time. It is the uneven delay in the delivery audio Or video

5. What are the advantages of distributed processing?Advantages of distributed processing include security/encapsulation, distributed databases, faster problem solving, security through redundancy and collaborative processing.

6. Why are protocols needed?In networks, communication occurs between the entities in different systems. Two entities cannot just send bit streams to each other and expect to be understood. For communication, the entities must agree on a protocol. A protocol is a set of rules that govern data communication.

7. Why are standards needed?Co-ordination across the nodes of a network is necessary for an efficient Communication. If there are no standards, difficulties arise. A standard provides a model or basis for development towhich everyone has agreed.

8. For n devices in a network, what is the number of cable links required for a mesh and ring topology?Mesh topology – n (n-1)/2Star topology-nBus topology-(n-1)Ring topology – n

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9. What is the difference between a passive and an active hub?An active hub contains a repeater that regenerates the received bit patterns before sending them out. A passive hub provides a simple physical connection between the attached devices.

10. Distinguish between peer-to-peer relationship and a primary-secondary relationship.Peer-to-peer relationship: All the devices share the link equally.Primary-secondary relationship: One device controls traffic and the others must transmit through it.

11. Assume 6 devices are arranged in a mesh topology. How many cables are needed? How many ports are needed for each device?Number of cables=n (n-1)/2=6(6-1)/2=15Number of ports per device=n-1=6-1=5

12. Uses of Computer Networks Business Application- (Resource Sharing, Client-Sever Model, E-mail, E-Commerce) Home Application (Access to remote information, Person to Person comm., Interactive entertainment, Electronic Commerce) Mobile Users-(Web, Telephone, wireless n/w, fixed wireless n/w) Social Issues

13. List out the Components of Computer Networks. Sender Receiver Medium Message Protocol

14. Give the different Types of Data Representation. Text, Number, Images, Audio, Video

15. Direction of Data Flow. Simplex, Half-Duplex, Full-Duplex

16. Define Simplex Only one of the two devices on a link can transmit the other can only receive Eg: Keyboards, Traditional Monitors

Direction of Data

17. Define Half-Duplex.

Mainframe Monitor

2

Sender Receiver

Rule 1.

Rule n

Rule 1.

Rule n Message

Medium


Each station can transmit and receive but not at the same time. Eg: Walkie-Talkies and CB (Citizens Band) radios Direction of data at time1

18. Define Full-Duplex. In this mode both stations can transmit and receive simultaneously Eg: Telephone Network Direction of data at all direction

19. Define Networks. A network is a set of devices connected by communication links. A node can be computer, printer or any other device capable of sending and/or receiving data generated by other nodes on the network.

20. What is the physical Structure of Network? 1. Types of Connection-(Point – to – Point and Multi Point) 2. Physical Topology-(Mesh, Star, Bus, Ring)

21. Types of Connection. Point – to – Point It provides a dedicated link between two links.Eg: Micro wave or Satellite links

Link

Multi-PointIt is a one in which more than two specific devices share a single link.

Link

Main Frame

22. Types of Multi Point. 1. Time Shared-(User Takes Turns)2. Spatial-(Several devices can use the link simultaneously)

Direction of data at time2

3

Station Station

Station Station

Station Station

Station

Station

Station


23. Define Physical Topology It refers to the way in which a network is laid out physically. Two or more devices connect to a link; two or more links form a topology.

24. Define Topology The Topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another.

25. Types of Topology.1. Mesh topology2. Star topology3. Bus topology4. Ring topology

26. Define Hybrid Topology Collection of various Topologies forms Hybrid Topology.

27. Categories of Networks1. LAN(Local Area Network)2. WAN(Wide Area Network)3. MAN(Metropolitan Area Network)

28. Name the seven layers of the OSI Model.1. Physical Layer( 0’s and 1’s)2. Data Link Layer(Frames)3. Network Layer(Packets)4. Transport Layer(Segments)5. Session layer(Sessions)6. Presentation Layer(Conversion)-(Encryption, Translation, Compression)7. Application Layer(Network services to application)

29. TCP/IP Model.

ApplicationSMTP FTP TELNET DNS SNMP NFS TFTP RPCPresentation

Session

Transport TCP UDP

ICMP IGMP Network IP ARP RARPData link Network Interface LayerPhysical

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30. Compare OSI/TCP

OSI TCP7 layers 4 layersModel was first defined before implementation Takes place

It is defined after

OSI model based on three concepts i.e.Service, interface and protocol

Model did not originally clearly distinguish between service, interface and protocol

Reliable delivery of packet No Reliable delivery of packetDoes not support internet working TCP/IPStrict layering Loosely layeredBoth Connection oriented and Connectionless Service Only Connection oriented Service

31. Group the OSI layers by function. The seven layers of the OSI model belonging to three subgroups. Physical, data link and network layers are the network support layers; they deal with the physical aspects of moving data from one device to another. Session, presentation and application layers are the user support layers; they allow interoperability among unrelated software systems. The transport layer ensures end-to-end reliable data transmission.

32. What are header and trailers and how do they get added and removed? Each layer in the sending machine adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it. This information is added in the form of headers or trailers. Headers are added to the message at the layers 6,5,4,3, and 2. A trailer is added at layer2. At the receiving machine, the headers or trailers attached to the data unit at the corresponding sending layers are removed, and actions appropriate to that layer are taken.

33. The transport layer creates a communication between the source and destination. What are the three events involved in a connection?Creating a connection involves three steps: connection establishment, data transfer and connection release.

34. Functions of Physical Layer.1. Physical characteristics of interfaces and media,2.Representation of bits,3.Data rate 4. Synchronization of bits

35. Functoins of Data Link Layer.1. Framing,2.Physical addressing,3.Flow control,4.Error control,5.Access Control2.

36. Functions of Network Layer.1. Logical Addressing ,2.Routing

37. Functions of Transport Layer.1. Port addressing, 2. Segmentation and reassembly, 3.Connection control, 4. Flow control, 5. Error Control

37. Functions of Session Layer.

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1. Dialog Control (Communication between two processes take place in either half or full duplex)2. Synchronization (This Layer adds synchronization points into stream of data)

38. Functions of Presentation Layer. 1. Translation, 2.Encryption, 3.Compression

39. Functions of Application Layer. Network Virtual Terminal, File Transfer,Access & Management (FTAM),Mail Services, Directory Services

40. Define CellCell is an information unit of a fixed size whose source and destination are data link layer entities. Cells are used in switched envin,such as ATM and SMDS networks. It contains header and payload.

41. Types of Multiple Access Protocols

ALOHA RESERVATION FDMA CSMA POLLING TDMA CSMA/CD TOKEN PASSING CDMA CSMA/CA

42. Formula used in ALOHA. Protocol Vulnerable Time Through put Max.Through putPURE ALOHA 2*Tfr S=G*e-2G Smax=0.184 (G=1/2)

Slotted ALOHA

Tfr G*e-G 0.368 (G=1)

43. What are the Persistent methods in CSMA?I-Persistent, Non-Persistent, P-Persistent

44. Define Token Ring. Token ring is a special bit pattern called the token, circulates around the ring whenever all stations are idle. It contains RIU (Ring Interface Unit).45. Define FDDI.Fiber distributed data interface is a local areas. Network protocol standardized by ANSI and ITU-7. It supports data rates of 100 Mbps and provides a high-speed alternative to Ethernet and token

6

cell

Multiple Access Protocols

Random Access Protocol

Controlled Access Protocols

ChannelizationProtocol


ring access method used here is token passing.

46. What are the disadvantages of optical fiber as a transmission medium?• Very expensive.• Installation and maintenance is difficult.• Fragility.

47. Addressing Types1. Physical address2. Logical Addressing3. Port Addressing4. Specific Addressing

48. List the Ethernet Evolution1. Standard Ethernet -10 Mbps2. Fast Ethernet-100 Mbps3. Gigabit Ethernet-1 Gbps4. Ten-Gigabit Ethernet-10 Gbps

49. IEEE Data link Layer Types1. Logical Link Control(LLC)2. Media Access Control (MAC)

50. Standard Ethernet Types1. 10 Base 5 (Bus thick Coaxial)2. 10 Base 2 (Bus, thin Coaxial)3. 10 Base T (Star UTP)4. 10 Base F (Star Fiber)

51. Fast Ethernet Types.1. 100 Base TX (Two wires category 5UTP)2. 100 Base FX (Two wires Fiber)3. 100 Base T4 (Four wires category 3UTP)

52. Gigabit Ethernet Types.1. 1000 Base SX (2 wire short wave fiber)2. 1000 Base LX (2 wire long wave fiber)3. 1000 Base CX (Two wires copper)4. 1000 Base T (Two wires UTP)

53. 10Gigabit Ethernet Types.1. 10GBase-S2. 10GBase-L, 3.10GBase-E

54. Define Random Access

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In Random access or contention methods no station is superior to another station and none is controlled over other station

55. Define Controlled Access In Controlled Access the stations consult one another to find which station has the right to send. A station cannot send unless it has been authorized by other stations.

56. Define Channelizations. Channelization is a Multiple-access method in which the available bandwidth of a link shared in time, frequency and code between different stations. 57. Services in WLAN or IEEE 802.11

1. BSS(Basic Service Set)2. ESS(Extended Service Set)

58. Types of BSS (Basic Service Set)1. With Access Point (Infra structure Network)2. Without Access Point (Infra Structureless Network or Adhoc)

59. Station Types in IEEE 802.111. No-transition (Inside one BSS)2. BSS-transition (Between two BSS but within one ESS)3. ESS-transition (ESS to ESS)

60. 802.11 IEEE Types.IEEE Technique Band Modulation Rate (Mpbs)

802.11FHSS 2.4 GHz FSK 1 & 2DSSS 2.4GHz PSK 1 & 2

Infrared PPM 1 & 2802.11a OFDM 5.725 GHz PSK or QAM 6 to 54802.11b DSSS 2.4GHz PSK 5.5 & 11802.11g OFDM 2.4GHz Different 22 & 54

UNIT-II

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DATA LINK LAYER1. What are the responsibilities of data link layer?Specific responsibilities of data link layer include the following.a) Framing, b) Physical addressing, c) Flow control, d) Error control, e) Access control

2. Mention the types of errors.There are 2 types of errorsa) Single-bit error.b) Burst-bit error.

3. Define the following terms.a) Single bit error: The term single bit error means that only one bit of a given data unit (Such as byte character/data unit or packet) is changed from 1 to 0 or from 0 to 1.b) Burst error: Means that 2 or more bits in the data unit have changed from 1 to 0 from 0 to 1.

4. What is redundancy?It is the error detecting mechanism, which means a shorter group of bits or extra bits may be appended at the destination of each unit.

5. List out the available detection methods.There are 4 types of redundancy checks are used in data communication.a) Vertical redundancy checks (VRC).b) Longitudinal redundancy checks (LRC).c) Cyclic redundancy checks (CRC).d) Checksum.

6. Write short notes on VRC.The most common and least expensive mechanism for error detection is the vertical redundancy check (VRC) often called a parity check. In this technique a redundant bit called a parity bit, is appended to every data unit so, that the total number of 0’s in the unit (including the parity bit) becomes even.

7. Write short notes on LRC.In longitudinal redundancy check (LRC), a block of bits is divided into rows and a redundant row of bits is added to the whole block.

8. Write short notes on CRC.The third and most powerful of the redundancy checking techniques is the cyclic redundancy checks (CRC) CRC is based on binary division. Here a sequence of redundant bits, called the CRC remainder is appended to the end of data unit.

9. Write short notes on CRC generator.A CRC generator uses a modulo-2 division.a) In the first step, the 4 bit divisor is subtracted from the first 4 bit of the dividend.b) Each bit of the divisor is subtracted from the corresponding bit of the dividend without disturbing the next higher bit.

10. Write short notes on CRC checker.A CRC checker functions exactly like a generator. After receiving the data appended with

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the CRC it does the same modulo-2 division. If the remainder is all 0’s the CRC is dropped and the data accepted. Otherwise, the received stream of bits is discarded and the dates are resent.

11. Give the essential properties for polynomial.A polynomial should be selected to have at least the following properties.a) It should not beb) It should be divisible by(x+1).

12. Define checksum.The error detection method used by the higher layer protocol is called checksum.Checksum is based on the concept of redundancy.

13. What are the steps followed in checksum generator?The sender follows these stepsa) The units are divided into k sections each of n bits.b) All sections are added together using 2’s complement to get the sum.c) The sum is complemented and become the checksum.d) The checksum is sent with the data.

14. List out the steps followed is checksum checker side.The receiver must follow these stepsa) The unit is divided into k section each of n bits.b) All sections are added together using 1’s complement to get the sum.c) The sum is complemented.d) If the result is zero.

15. Write short notes on error correction.It is the mechanism to correct the errors and it can be handled in 2 ways.a) When an error is discovered, the receiver can have the sender retransmit the entire data unit.b) A receiver can use an error correcting coder, which automatically corrects certain errors.

16. Mention the types of error correcting methods.There are 2 error-correcting methods.a) Single bit error correctionb) Burst error correction.

17. What is the purpose of hamming code?A hamming code can be designed to correct burst errors of certain lengths. So the simple strategy used by the hamming code to correct single bit errors must be redesigned to be applicable for multiple bit correction.

18. How to determine the number of redundant bit in hamming code?

2r=m+r+1 where, r=0, 1, 2, 3…m=Original Length of datar=Number of Redundancy bit

19. Define Burst Length? 5 Bits

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Sender Data: 1 0 1 1 1 1 1 0 Receiver Data: 1 0 1 0 1 1 1 1

Burst Length=5 Bits

20. Define flow control.Flow control refers to a set of procedures used to restrict the amount of data. The sender can send before waiting for acknowledgment.

21. What is a buffer?Each receiving device has a block of memory called a buffer, reserved for storing incoming data until they are processed.

22. Mention the categories of flow control.There are 2 methods have been developed to control flow of data across communication links.a) Stop and wait- send one from at a time.b) Sliding window- send several frames at a time.

23. What is the function of stop and wait flow control?In this method, the sender sends one frame and waits for an acknowledgement before sending.

24. Mention the advantage and disadvantage of stop and wait flow control.Advantage: simplicityDisadvantage: inefficiency.

25. Define ARQ.Error control in the data link layer is based on Automatic repeat request (ARQ), which means retransmission of data in 3 cases.a) Damaged frameb) Lost framec) Lost acknowledgment.

26. Mention the function of go-back N-ARQ.It is the popular mechanism for continuous transmission error control. In the method, if our frame is lost or damaged, all frames sent since the last frame acknowledged are retransmitted.

27. What is selective reject ARQ?In selective reject ARQ only the specific damaged or lost frame is retransmitted. If a frame is corrupted in transit, a NAK is returned and the frame is resent out of sequence.

28. Define 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.

29. List the types of stations is HDLC.HDLC differentiates between 3 types of stations.a) Primary

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b) Secondaryc) Combined

30. Define configuration.The bond configuration refers to the relationship of hardware devices on a link.

31. List the various ways of station configuration.The stations are configured in 3 waysa) Unbalanced configurationb) Symmetrical configurationc) Balanced configuration

32. What are the different communication modes in HDLC?HDLC supports 3 modes of communication between stations.a) Normal response mode (NRM)b) Asynchronous response mode (ARM)c) Asynchronous balanced mode (ABM)

33. Mention the types of frames in HDLC.There are 3 types of HDLC frames.a) Information frames (I-frames)b) Supervisory frames (S-frames)c) Unnumbered frames (U-frames)

34. Give the usage of I, S, U frames.I frames – used to transport user data and control information relating to user data.S frames – used only to transport control information, primarily data link layerand error controls.U frames – reserved for systems management.

35. Write the types of frame fields contained in HDLC.Each frame in HDLC may contain up to 6 fields.

FCS- Frame check sequence

36. What is meant by bit stuffing?Bit stuffing is the process of adding one extra 0 whenever there are 5 consecutivein the data so that the receiver doesn’t mistake the data for a flag. Eg: Before Stuffing: 1111111111, After Stuffing: 111110111110

37. Define LAN.A Local Area Network (LAN) is a data communication system that allows a number of independent devices to communicate directly with each other in a limited geographic area.

38. Mention the various architecture in a LAN.LAN is dominated by 4 architectures.a) Ethernet

flag address control Data FCS flag

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b) Token busc) Token ringd) Fiber distributed data interface (FDDI)

39. Define a standard 802.3IEEE 802.3 supports a LAN standard originally developed by Xerox and laterextended by a joint venture between digital equipment corporations. Intel Corporationand Xerox. This was called ‘Ethernet’.

40. List the most command kinds of Base band 802.3 LAN.a) 10 Base 5,b) 10 Base 2,c) 10 Base T, d) 1 Base 5,e) 100 Base T,

41. Mention the different kinds of Ethernet networks.a) Switched Ethernetb) Fast Ethernetc) Gigabit Ethernet

42. Describe the three HDLC station types?The three HDLC station types are:Primary station: The primary station has the complete control of the link. The Primary station sends commands to the secondary station.Secondary station: The secondary station sends responses.Combined station: Combined station sends both commands and responses.

43. What is piggy backing?Piggy backing means combining data to sent and acknowledgement of the frame received in one single frame. Piggy backing can save bandwidth because the overhead from a dataframe and an ACK frame can be combined into just one frame

44. Name the four types of S-frames?The four types of S-frames are

Code Field Status00011011

Receive ready (RR)Reject (REJ)Receive not ready(RNR)

Selective reject(SREJ)

45. Name the five categories of U-frames?The five categories of U-frames are

1. Mode setting, 2. Unnumbered exchange, 3. Disconnection. 4. Initialization mode,5. Miscellaneous mode

46. Define Bridge.

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A bridge is a device that is attached to two or more LANS to create extended LAN. It divides the large network into segments. It operate in the both the Physical and the Data Link Layer of the OSI model.

47. Functions of a Bridge. 1. Frame Filtering and Forwarding

2. Learning the address 3. Routing

48. Types of Bridges.1. Simple Bridge2. Multi port Bridge

3. Transparent Bridge

49. Define Spanning TreeA spanning tree is a graph n which there is no loop. In a bridged LAN, a spanning tree this

means creating a topology in which each LAN can be reached from any other LAN through only one path (no loop).

50. Write down Three Error Control Mechanisms.

Stop and wait ARQ Go-back-n ARQ Selective Reject ARQ

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UNIT IIINETWORK LAYER

1. What are the network support layers and the user support layers?Network support layers:The network support layers are Physical layer, Data link layer and Network layer. These deals with electrical specifications, physical connection, transport timing and reliability.

User support layers:The user support layers are: Session layer, Presentation layer, Application layer. These allow interoperability among unrelated software system.

2. With a neat diagram explain the relationship of IEEE Project to the OSI model?The IEEE has subdivided the data link layer into two sub layers:* Logical link control (LLC)* Medium access control (MAC)LLC is non-architecture specific. The MAC sub layer contains a number of distinct modules ,each carries proprietary information specific to the LAN product being used.

3. What are the functions of LLC?The IEEE project 802 model takes the structure of an HDLC frame and divides it into 2 sets of functions. One set contains the end user portion of the HDLC frame - thelogical address, control information, and data. These functions are handled by the IEEE802.2 logical link control (LLC) protocol.

4. What are the functions of MAC?MAC sub layer resolves the contention for the shared media. It contains synchronization, flag, flow and error control specifications necessary to move information from one place to another, as well as the physical address of the next station to receive and route a packet.

5. What is protocol data unit?The data unit in the LLC level is called Protocol Data Unit (PDU). It contains fourfields.• Destination Service Point Address (DSAP)• Source Service Access Point (Other layers,Network,Data link,Physical Other layers )(Network,Logical Link Control,Media Access Control,Physical,DSAP, SSAP,Control Information)• Control field• Information field

6. What are headers and trailers and how do they get added and removed?The control data added to the beginning of a data is called headers. The control data added to the end of a data is called trailers. At the sending machine, when the message passes through the layers each layer adds the headers or trailers. At the receiving machine, each layer removes the data meant for it and passes the rest to the next layer.

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7. What are the responsibilities of network layer?The network layer is responsible for the source-to-destination delivery of packet across multiple network links. The specific responsibilities of network layer include the following:• Logical addressing.• Routing.

8. What is a virtual circuit?A logical circuit made between the sending and receiving computers. The connection is made after both computers do handshaking. After the connection, all packets follow the same route and arrive in sequence.

9. What are data grams?In datagram approach, each packet is treated independently from all others. Even when one packet represents just a place of a multipacket transmission, the network treatsit although it existed alone. Packets in this technology are referred to as datagram.

10. What are the two types of implementation formats in virtual circuits?Virtual circuit transmission is implemented in 2 formats.• Switched virtual circuit• Permanent virtual circuit.

11. What is meant by switched virtual circuit?Switched virtual circuit format is comparable conceptually to dial-up line in circuit switching. In this method, a virtual circuit is created whenever it is needed and exits only for the duration of specific exchange.

12. What is meant by Permanent virtual circuit?Permanent virtual circuits are comparable to leased lines in circuit switching. In this method, the same virtual circuit is provided between two uses on a continuous basis. The circuit is dedicated to the specific uses.

13. Define Routers.Routers relay packets among multiple interconnected networks. They Route packets from one network to any of a number of potential destination networks on internet routers operate in the physical, data link and network layer of OSI model.

14. What is meant by hop count?The pathway requiring the smallest number of relays, it is called hop-count routing, in which every link is considered to be of equal length and given the value one.

15. How can the routing be classified?The routing can be classified as,• Static Routing or (Non-Adaptive routing)• Dynamic Routing or (Adaptive routing)

16. What is time-to-live or packet lifetime?As the time-to-live field is generated, each packet is marked with a lifetime, usually the number of hops that are allowed before a packet is considered lost and accordingly,

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destroyed. The time-to-live determines the lifetime of a packet.

17. What is meant by brouter?A brouter is a single protocol or multiprotocol router that sometimes act as a router and sometimes act as a bridge.

18. Write the keys for understanding the distance vector routing.In Distance Vector Routing each router periodically shares its knowledge about the entire network with its neighbors.The three keys for understanding the algorithm are• Knowledge about the whole networks• Routing only to neighbors• Information sharing at regular intervals

19. Write the keys for understanding the link state routing.The three keys for understanding the algorithm areIn Link State Routing each Router Shares its knowledge of its neighborhood with every other router in the internet work.• Knowledge about the neighborhood.• Routing to all neighbors.• Information sharing when there is a range.

20. How the packet cost referred in distance vector and link state routing?In distance vector routing, cost refer to hop count while in case of link state routing, cost is a weighted value based on a variety of factors such as security levels, traffic or the stateof the link.

21. How the routers get the information about neighbor?A router gets its information about its neighbors by periodically sending them a shortgreeting packets. If the neighborhood responds to the greeting as expected, it isassumed to be alive and functioning. If it dose not, a change is assumed to have occurredand the sending router then alerts the rest of the network in its next LSP(Link State Packet).

22. What are the four internetworking devices?The four internetworking devices are,1. Repeaters, 2.Bridges, 3. Routers, 4. Gateway

23. Define IP address.IP address is the 3-bit number for representing a host or system in the network. One portion of the IP address indicates a networking and the other represents the host in a network.

24. What is Token Bus?Token Bus is a physical bus that operates as a logical ring using tokens. Here stations are logically organized into a ring. A token is passed among stations. If a station wants to send data, it must wait and capture the token. Like Ethernet, station communicates via a common bus.

Network Id Cost Next Hop

…………. ……. ……….

Adviser Network Id Cost Next Hop

……… …………. …… ……….

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25. What is token passing?Stations may attempt to send data multiple times before a transmission makes it onto a link. This redundancy may create delays of indeterminable length if the traffic is heavy. Token ring resolves this uncertainty by requiring that stations take turns sending data. Each station may transmit only during its turn and may send only one frame during each turn. The mechanism that coordinates this rotation is called token passing.

26. Define Masking?Masking is the process that extracts the address of the physical network from an IP address.Types: Boundary-Level Masking and Non Boundary-Level Masking.

27. What are the rules of boundary-level masking?The rules of boundary-level masking• The bytes in the IP address that corresponds to 255 in the mask will be repeated in the subnetwork address• The bytes in the IP address that corresponds to 0 in the mask will change to 0 in the subnetwork address

28. What are the rules of nonboundary-level masking?• The bytes in the IP address that corresponds to 255 in the mask will be repeated in the subnetwork address• The bytes in the IP address that corresponds to 0 in the mask will change to 0 in the subnetwork address• For other bytes, use the bit-wise AND operator

29. Define Gateway.A device used to connect two separate networks that we different communication protocols.

30. What is LSP?In link state routing, a small packet containing routing information sent by a router to all other router by a packet called Link State Packet.

31.Types of Routing Algorithms: 1.Shortest path Algorithm, 2.Flooding,3.Flow based routing,4.Distance vector routing,5.Link state routing, 6.Hierarchical routing.

32. Define Shortest Path Routing.In Shortest Path Routing the path length between each node is measured as a function of distance , bandwidth, average traffic, communication cost ,mean queue length, measured delay.Two algorithms used. (1. Dijkstra’s Algorithm,2. Bellman-Ford Algorithm)

33. Define Flooding.This technique requires no network information. A packet is sent by a source node to all its adjacent nodes. At each node, every incoming packet is retransmitted on every outgoing links, except the link that it arrived from. Flooding generates large number of duplicate packets.

34. Flow Based Routing

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Flow Based Routing Algorithm is used to support Multimedia Streaming for Multicasting Application.Example:RSVP(Resource reSerVation Protocol)-Receiver Reserves the Resource.

35. Define Distance Vector Routing It Works as follows.1. Knowledge about the entire autonomous system2. Routing only to the neighbors3. Information sharing at the regular intervals.

36. Define Link State Routing It Works as follows.

1. Knowledge about the neighborhood2. Sharing with every other routers3. Information sharing when there

is a change.

37. Draw Routing Table For DVR and LSR.Every router keeps a routing table that has one entry for each destination network of which the route is aware.Example:

Distance Vector Routing (DVR) Link State Routing (LSR)

38. Disadvantages of Distance Vector Routing.1. Split Horizon, 2. Count to infinity Problem

39. Hierarchical Routing In Hierarchical Routing the Routers are divided into regions. It contains all the details about how to route packets to destinations within its own region. In two-level Hierarchy maybe insufficient. It is necessary to group the regions into clusters, clusters into zones and zones into groups and so on.

40. Compare Router and Bridge. Router Bridge

Operates in Network Layer Operates on Data Link Layer Expansive Less ExpansiveDifficult to setup and configure Easy to setup and configureAccommodate Multi Paths Accommodate Single PathUses Protocol Address Uses MAC Address

UNIT IV


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TRANSPORT LAYER1. What is function of transport layer?The protocol in the transport layer takes care in the delivery of data fromone application program on one device to an application program on anotherdevice. They act as a link between the upper layer protocols and the servicesprovided by the lower layer.

2. What are the duties of the transport layer?The services provided by the transport layerEnd-to- end deliveryAddressingReliable deliveryFlow controlMultiplexing

3. What is the difference between network layer delivery and the transportlayer delivery?Network layer delivery Transport layer deliveryThe network layer is responsible forthe the source-to-destinationdelivery of packetacross multiple network links.The transport layer is responsible forsource-to-destination delivery of theentire message.

4. What are the four aspects related to the reliable delivery of data?The four aspects are,Error controlSequence controlLoss controlDuplication control

5. What is meant by segment?At the sending and receiving end of the transmission, TCP divides long transmissionsinto smaller data units and packages each into a frame called a segment.

6. What is meant by segmentation?When the size of the data unit received from the upper layer is too long for the networklayer datagram or data link layer frame to handle, the transport protocol divides it intosmaller usable blocks. The dividing process is called segmentation.

7. What is meant by Concatenation?The size of the data unit belonging to a single session are so small that several can fittogether into a single datagram or frame, the transport protocol combines them into asingle data unit. The combining process is called concatenation.

8. What are the types of multiplexing?The types of multiplexing are,

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Upward multiplexingDownward multiplexing

9. What are the two possible transport services?Two basic types of transport services are,Connection serviceConnectionless services

10. The transport layer creates the connection between source and destination.What are the three events involved in the connection?For security , the transport layer may create a connection between the twoend ports. A connection is a single logical path between the source anddestination that is associated with all packets in a message. Creating a connectioninvolves three steps:• Connection establishment• Data transfer & Connection release.

11. What are the techniques used in multiplexing?The three basic techniques of multiplexing are,Frequency-division multiplexingTime-division multiplexingWave-division multiplexing

12. What is meant by congestion?Congestion in a network occur if user send data into the network at a rate greater thanthat allowed by network resources.

13. Why the congestion occur in network?Congestion occur because the switches in a network have a limited buffer size to storearrived packets.

14. How will the congestion be avoided?The congestion may be avoided by two bitsBECN - Backward Explicit Congestion NotificationFECN - Forward Explicit Congestion Notification

15. What is the function of BECN BIT?The BECN bit warns the sender of congestion in network. The sender can respond tothis warning by simply reducing the data rate.

16. What is the function of FECN?The FECN bit is used to warn the receiver of congestion in the network. The senderand receiver are communicating with each other and are using some types of flow controlat a higher level.

17. What is meant by quality of service?The quality of service defines a set of attributes related to the performance of theconnection. For each connection, the user can request a particular attribute each serviceclass is associated with a set of attributes.

18. What are the two categories of QoS attributes?The two main categories are

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User OrientedNetwork Oriented

19. List out the user related attributes?User related attributes areSCR – Sustainable Cell RatePCR – Peak Cell RateMCR- Minimum Cell RateCVDT – Cell Variation Delay Tolerance

20. What are the networks related attributes?The network related attributes are,Cell loss ratio (CLR)Cell transfer delay (CTD)Cell delay variation (CDV)Cell error ratio (CER)

21. What is frame?A frame consists of one complete cycle of time slots, including one or more slot dedicatedto each sending device.

22. What is interleaving?The switch moves from device to device at a constant rate and fixed order. This process iscalled interleaving.

23. What is framing bits?One or more synchronization bits are usually added to the beginning of each frame. Thesebits are called framing bits.

24. What is the difference between service point address, logical address andphysical address?Service point addressing Logical addressing Physical addressingThe transport layer header includes a type of address called a service point address or port address, If a packet passes the network boundary we need another addressing to differentiate the source and If the frames are to be distributed to different systems on the network, thedata link layer adds the which makes a data delivery from a specific process on computer to a specific process on another computer. destination systems. The network layer adds a header, which indicate the logical address of the sender and receiver. header, which definesthe source machine’s address and the destination machine’s address.

25. What is UDP.UDP is a connectionless, unreliable protocol that has no flow and error control. It uses portnumbers to Multiplex data from the application layer. The Packet Produced the UDP is called a user datagram.

26.List out Some UDP Port numbers.Port protocol79

EchoDiscard

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111353111123161

UsersDaytimeDNSRPCNTPSNMP

27. User Datagram Format.

Header

Source port number16 bits

Destination port number16 bits

Total length16 bits

Check sum16 bits

28. Define TCP.Transmission control protocol is defined as it is a connection oriented, reliable, stream transport layer protocol in the internet model.

29.List out Some TCP Port numbers.

Port protocol7911132021235311180

EchoDiscardUsersDaytimeFTP, DataFTP, CtrlTELNETDNSRPCHTTP

30.Services of TCP1.Stream Delivery Service2.Full Duplex Services3.Connection Oriented Service

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31. TCP Segment Format

HEADERSource port address16 bits

Destination port address16 bits

Sequence number(32 bits)

ACK number(32 bits)

HLEN4 bits

Rsvd6bits

URG

ACK

PSH

RST

SYN

FIN

Window size16 bits

Check Sum(16 bits) Urgent Pointer(16 bits)

Options & Padding

32. TCP TimersTypes:1. Retransmission, 2.Presistence, 3.Keep-alive, 4.Time waited

33. Define SocketSocket is defined as an endpoint. Two processes need a socket at each end to communicatewith each other.

34. Types of Sockets. Stream Socket Datagram Socket Raw Socket

35. Congestion Control Techniques.1. Leaky bucket algorithm2. Token bucket algorithm

36. Congestion prevention Policies.1. Traffic shaping, 2.Choke packets, 3.Load Shedding, 4. Jitter Control

37. List out some protocol in Application Layer protocol.1. DNS, 2.SMTP, 3.FTP, 4.HTTP

38. Define Congestion.Congestion in a network may occur if the load on the network the number of packets sent to the network is greater than the capacity of the network the number of packets a network can handle.

39. Congestion Control Categories Open loop Congestion Control (Prevention) Closed loop congestion Control (Removal)

40. Define Congestion Control.Congestion control refers to the mechanisms and techniques to control the congestion and

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to keep the load below the capacity.

41.List of polices that can prevent congestion using Open loop Congestion Control.1.Retransmission Policy,2.Window Policy,3.ACK Policy,4.Discarding Policy,5.Admission policy.

42. List of polices that can prevent congestion using Closed loop Congestion Control.1. Back Pressure, 2.Choke Point, 3.Implict Signaling, 4.Explict Signaling5. Backward Signaling, 6.Forward Signaling

43. What is the purpose of Domain Name System?Domain Name System can map a name to an address and conversely an address to name.

44. Discuss the three main division of the domain name space.Domain name space is divided into three different sections: generic domains, country domains & inverse domain.Generic domain: Define registered hosts according to their generic behavior, uses generic suffixes.Country domain: Uses two characters to identify a country as the last suffix.Inverse domain: Finds the domain name given the IP address.

45. Discuss the TCP connections needed in FTP.FTP establishes two connections between the hosts. One connection is used for data transfer, the other for control information. The control connection uses very simple rules of communication. The data connection needs more complex rules due to the variety of data types transferred.

46. Discuss the basic model of FTP.The client has three components: the user interface, the client control process, and the client data transfer process. The server has two components: the server control process and the server data transfer process. The control connection is made between the control processes. The data connection is made between the data transfer processes.

47. What is the function of SMTP?The TCP/IP protocol supports electronic mail on the Internet is called Simple Mail Transfer (SMTP). It is a system for sending messages to other computer users based on e-mail addresses. SMTP provides mail exchange between users on the same or different computers.

48. What is the difference between a user agent (UA) and a mail transfer agent(MTA)?The UA prepares the message, creates the envelope, and puts the message in the envelope. The MTA transfers the mail across the Internet.

49. How does MIME enhance SMTP?MIME is a supplementary protocol that allows non-ASCII data to be sent through SMTP. MIME transforms non-ASCII data at the sender site to NVT ASCII data and deliverers

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it to the client SMTP to be sent through the Internet. The server SMTP at the receiving side receives the NVT ASCII data and delivers it to MIME to be transformed back to the original data.

50. Why is an application such as POP needed for electronic messaging?Workstations interact with the SMTP host which receives the mail on behalf of every host in the organization, to retrieve messages by using a client-server protocol such as Post Office Protocol , version 3(POP3). Although POP3 is used to download messages from the server, the SMTP client still needed on the desktop to forward messages from the workstation user to its SMTP mail server.

51. Give the format of HTTP request message.& Give the format of HTTP response message.Status Line, Headers,A Blank Line Body (present only in some messages),Request LineHeaders,A Blank Line,Body,(present only in some messages)

52. Write down the three types of WWW documents.The documents in the WWW can be grouped into three broad categories: static,dynamic and active.Static: Fixed-content documents that are created and stored in a server.Dynamic: Created by web server whenever a browser requests the document.Active: A program to be run at the client side.

53. What is the purpose of HTML?HTML is a computer language for specifying the contents and format of a web document. It allows additional text to include codes that define fonts, layouts, and embedded graphics and hypertext links.

54. Define CGI.CGI is a standard for communication between HTTP servers and executable programs. It is used in crating dynamic documents.

55. Name four factors needed for a secure network.Privacy: The sender and the receiver expect confidentiality.Authentication: The receiver is sure of the sender’s identity and that an imposter has not sent the message.Integrity: The data must arrive at the receiver exactly as it was sent.Non-Reputation: The receiver must able to prove that a received message came froma specific sender.

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Documents

Computer Networks Full(i to IV Unit) Two Marks