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1. Compare Error Detection and Error Correction:

The correction of errors is more difficult than the detection. In error detection, checks only any error has occurred. In error correction, the exact number of bits that are corrupted and location in the message are known. The number of the errors and the size of the message are important factors.

2. Define Bandwidth and Latency?

Network performance is measured in Bandwidth (throughput) and Latency (Delay). Bandwidth 
of a  network is given by the number of bits that can be transmitted over the network in a certain  period of 
time. Latency corresponds to how long it t5akes a message to travel from one end off a network  to the other. It 
is strictly measured in terms of time.

3. Define Character Stuffing?

In byte stuffing (or character stuffing), a special byte is added to the data section of the frame when there is a character with the same pattern as the flag. The data section is stuffed with an extra byte.  This  byte   is  usually called  the escape character   (ESC),  which has  a predefined bit  pattern. Whenever the receiver encounters the ESC character, it removes it from the data section and treats the next character as data, not a delimiting flag.

4. Define Decoder?

A device or program that translates encoded data into its original format (e.g. it decodes the data). The term is often used in reference to MPEG-2 video and sound data, which must be decoded before it is output.

5. Define Encoder?

A device or program that uses predefined algorithms to encode, or compress audio or video data for storage or transmission use. A circuit that is used to convert between digital video and analog video.

6. Define Network?

A network is a set of devices connected by physical media links. A network is 
recursively is a connection of two or more nodes by a physical link or two or more networks 
connected by one or more nodes.

7. Define Retransmission?

Retransmission is a technique in which the receiver detects the occurrence of an error and asks the sender to resend the message. Resending is repeated until a message arrives that the receiver believes is error-freed.

8. Define Routing?

The process of determining systematically hoe to forward messages toward the destination nodes based on its address is called routing.

9. Define the terms Unicasting, Multiccasting and Broadcasting?

If the message is sent from a source to a single destination node, it is called Unicasting.

If the message is sent to some subset of other nodes, it is called Multicasting.

If the message is sent to all the m nodes in the network it is called Broadcasting.

10. 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 / N) 

  where N is no-of-bits represented by each signal shift.

11. Difference between the communication and transmission.

Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.

Communication  means  the  meaning  full  exchange  of  information  between  two communication media.

12. Expand IDEA.

IDEA stands for International Data Encryption Algorithm.

13. Explain 5-4-3 rule?

In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of  those  five segments only  three of segments can be populated.

14. How Gateway is different from Routers?

A  gateway  operates  at  the  upper  levels  of  the  OSI  model  and  translates  information between two completely different network architectures or data formats.

15. List the layers of OSI

a. Physical Layer

b. Data Link Layer

c. Network Layer

d. Transport Layer

e. Session Layer

f. Presentation Layer

g. Application Layer

16. List the steps involved in creating the checksum.

a. Divide the data into sections

b. Add the sections  together using 1's complement arithmetic

c. Take the complement of the final sum, this is the checksum.

17. Name the categories of Multiplexing?

a. Frequency Division Multiplexing (FDM)

b. Time Division Multiplexing (TDM)

   i. Synchronous TDM

   ii. ASynchronous TDM Or Statistical TDM.

c. Wave Division Multiplexing (WDM)

18. Name the factors that affect the performance of the network?

a. Number of Users

b. Type of transmission medium

c. Hardware

d. Software

19. Name the factors that affect the reliability of the network?

a. Frequency of failure

b. Recovery time of a network after a failure

20. Name the factors that affect the security of the network?

a. Unauthorized Access

b. Viruses

21. What are Code Words?

"r" redundant bits are added to each block to make the length n = k + r. The resulting n-bit blocks are called codewords. 2n - 2k codewords that are not used. These codewords are invalid or illegal.

22. What are Cyclic Codes?

Cyclic codes are special linear block codes with one extra property. In a cyclic code, if a codeword is cyclically shifted (rotated), the result is another codeword.

23. What are Data Words?

In block coding, we divide our message into blocks, each of k bits, called datawords. The block coding process is one-to-one. The same dataword is always encoded as the same codeword.

24. What are Digrams and Trigrams?

The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.

25. What are major types of networks and explain?

Server-based network: provide  centralized  control  of  network  resources  and  rely  on server computers to provide security and network administration
• Peer-to-peer network: computers can act as both servers sharing resources and as clients using the resources. 

26. What are the advantages of Distributed Processing?

a. Security/Encapsulation

b. Distributed database

c. Faster Problem solving

d. Security through redundancy

e. Collaborative Processing

27. What are the categories of Transmission media?

a. Guided Media

  i. Twisted - Pair cable

    1. Shielded TP

    2. Unshielded TP

  ii. Coaxial Cable

  iii. Fiber-optic cable

b. Unguided Media

  i. Terrestrial microwave

  ii. Satellite Communication

28. What are the concerns of the Physical Layer?

Physical layer coordinates the functions required to transmit a bit stream over a physical medium.

a. Physical characteristics of interfaces and media

b. Representation of bits

c. Data rate

d. Synchronization of bits

e. Line configuration

f. Physical topology

g. Transmission mode

29. What are the criteria necessary for an effective and efficient network?

a. Performance

   It can be measured in many ways, including transmit time and response time.
b. Reliability

   It is measured by frequency of failure, the time it takes a link to recover from a failure, 
and the network's robustness.

c. Security

   Security issues includes protecting data from unauthorized access and virues.

30. What are the Data link protocols?

Data link protocols are sets of specifications used to implement the data link layer. The categories of Data Link protocols are
1. Asynchronous  Protocols

2. Synchronous Protocols

  a. Character Oriented Protocols

  b. Bit Oriented protocols

31. What are the data units at different layers of the TCP / IP protocol suite?

The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created  is called  the datagram, at  the data  link  layer  the datagram  is encapsulated  in  to a  frame and finally transmitted as signals along the transmission media.

32. What are the different link types used to build a computer network?

a. Cables

b. Leased Lines

c. Last-Mile Links

d. Wireless Links

33. What are the different type of networking / internetworking devices?

Repeater: Also called a regenerator,  it  is an electronic device  that operates only at physical layer.  It receives  the  signal  in  the network before  it becomes weak,  regenerates  the original bit pattern and puts the refreshed copy back in to the link.
• Bridges: These  operate  both  in  the  physical  and  data  link  layers  of LANs  of  same  type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
• Routers: They  relay  packets  among  multiple  interconnected  networks  (i.e.  LANs  of different type). They operate in the physical, data link and network layers. They contain software that  enable  them  to  determine which  of  the  several  possible  paths  is  the  best  for  a  particular transmission. 
• Gateways: They  relay  packets  among  networks  that  have  different  protocols  (e.g.  between  a LAN and a WAN). They accept a packet  formatted  for one protocol and convert  it  to a packet formatted for another protocol before  forwarding  it. They operate  in all seven  layers of  the OSI model.

34. What are the important topologies for networks?

BUS topology: In  this each computer  is directly connected  to primary network cable  in a single line.

Advantages: Inexpensive, easy to install, simple to understand, easy to extend.

• STAR topology: In this all computers are connected using a central hub.

Advantages: Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
• RING topology: In this all computers are connected in loop. 
Advantages: All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.

35. What are the key design issues of a computer Network?

a. Connectivity

b. Cost-effective Resource Sharing

c. Support for common Services

d. Performance

36. What are the key elements of protocols?

The key elements of protocols are

a. Syntax

   It refers to the structure or format of the data,  that is the order in which they are presented.

b. Semantics

   It refers to the meaning of each section of bits.

c. Timing

   Timing refers to two characteristics: When data should be sent and how fast they can be sent.

37. What are the possible ways of data exchange?

(i) Simplex  (ii) Half-duplex  (iii) Full-duplex.

38. What are the responsibilities of Application Layer?

The Application Layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as e-mail, shared database management and other types of distributed information services.

a. Network virtual Terminal

b. File transfer, access and Management (FTAM)

c. Mail services

d. Directory Services

39. What are the responsibilities of Data Link Layer?

The Data Link Layer transforms the physical layer, a raw transmission facility, to a reliable link and is responsible for node-node delivery.

a. Framing

b. Physical Addressing

c. Flow Control

d. Error Control

e. Access Control

40. What are the responsibilities of Network Layer?

The Network Layer is responsible for the source-to-destination delivery of packet possibly across multiple networks (links).

a. Logical Addressing

b. Routing

41. What are the responsibilities of Presentation Layer?

The Presentation layer is concerned with the syntax and semantics of the information exchanged between two systems.

a. Translation

b. Encryption

c. Compression

42. What are the responsibilities of Session Layer?

The Session layer is the network dialog Controller. It establishes, maintains and synchronizes the interaction between the communicating systems.

a. Dialog control

b. Synchronization

43. What are the responsibilities of Transport Layer?

The Transport Layer is responsible for source-to-destination delivery of the entire message.

a. Service-point Addressing

b. Segmentation and reassembly

c. Connection Control

d. Flow Control

e. Error Control

44. What are the two classes of hardware building blocks?

Nodes and Links.

45. What are the two types of transmission technology available?

(i) Broadcast   and   (ii) point-to-point

46. What are the types of errors?

a. Single-Bit error

  In a single-bit error, only one bit in the data unit has changed

b. Burst Error

  A Burst error means that two or more bits in the data have changed.

47. What are the types of Transmission media?

Signals are usually  transmitted over some  transmission media  that are broadly classified in to two categories.

a.) Guided Media: These  are  those  that  provide  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 metallic  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.

b.) Unguided Media: This  is  the wireless media  that  transport electromagnetic waves without using  a physical  conductor.  Signals  are  broadcast  either  through  air.  This  is  done  through  radio communication, satellite communication and cellular telephony.

48. What Automatic Repeat Request (ARQ)?

Error control is both error detection and error correction. It allows the receiver to inform the sender of any frames lost or damaged in transmission and coordinates the retransmission of those frames by the sender. In the data link layer, the term error control refers primarily to methods of error detection and retransmission. Error control in the data link layer is often implemented simply: Any time an error is detected in an exchange, specified  frames are retransmitted. This process is called automatic repeat request (ARQ).

49. What do you meant by "triple X" in Networks?

The  function  of  PAD  (Packet  Assembler  Disassembler)  is  described  in  a  document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X".

50. What is a gateway or Router?

A node that is connected to two or more networks is commonly called as router or Gateway. It
generally forwards message from one network to another.

51. What is a Linear Block Code?

A linear block code is a code in which the exclusive OR (addition modulo-2) of two valid codewords creates another valid codeword.

52. What is a Link?

At the lowest level, a network can consist of two or more computers directly connected 
by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as 
Link.

53. What is a Multi-homed Host?

It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.

54. What is a node?

A network can consist of two or more computers directly connected by some physical medium 
such as coaxial cable or optical fiber. Such a physical medium is called as Links and the computer it 
connects is called as Nodes.

55. What is a peer-peer process?

The processes on each machine that communicate at a given layer are called peer-peer process.

56. What is attenuation?

The degeneration of a signal over distance on a network cable is called attenuation.

57. What is autonomous system?

It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.

58. What is Bandwidth?

Every  line has an upper  limit and a  lower  limit  on the frequency of signals  it can carry. This limited range is called the bandwidth.

59. What is Beaconing?

The process  that allows a network to self-repair networks problems. The stations on  the network  notify  the  other  stations  on  the  ring  when  they  are  not  receiving  the  transmissions. Beaconing is used in Token ring and FDDI networks.

60. What is BGP (Border Gateway Protocol)?

It is a protocol used to advertise the set of networks that can be reached with in an autonomous  system. BGP  enables  this  information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).

61. What is Bit Stuffing?

Bit stuffing is the process of adding one extra 0 whenever five consecutive Is follow a 0 in the 
data, so that the receiver does not mistake the pattern 0111110 for a flag.

62. What is Brouter?

Hybrid devices that combine the features of both bridges and routers.

63. What is Checksum?

Checksum is used by the higher layer protocols (TCP/IP) for error detection

64. What is cladding?

A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.

65. What is CRC?

CRC, is the most powerful of the redundancy checking techniques, is based on binary division.

66. What is 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 a ARP query packet that includes the IP address of the receiver. 

The  reverse  address  resolution  protocol  (RARP)  allows  a  host  to  discover  its  Internet 
address when it knows only its physical address.

67. What is difference between baseband and broadband transmission?

In a baseband 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.

68. What is EGP (Exterior Gateway Protocol)?

It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.

69. What is Error Control ?

Error control is both error detection and error correction. It allows the receiver to inform the sender of any frames lost or damaged in transmission and coordinates the retransmission of those frames by the sender. In the data link layer, the term error control refers primarily to methods of error detection and retransmission.

70. What is Error Detection? What are its methods?

Data can be corrupted during transmission. For reliable communication errors must be deducted and Corrected. Error Detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination. The common Error Detection methods are 

  a. Vertical Redundancy Check (VRC)

  b. Longitudinal Redundancy Check (VRC)

  c. Cyclic Redundancy Check (VRC)

  d. Checksum

71. What is FDM?

FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.

72. What is Fixed Size Framing?

In fixed-size framing, there is no need for defining the boundaries of the frames. The size itself can be used as a delimiter.

73. What is Flow Control?

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

74. What is Forward Error Correction?

Forward error correction is the process in which the receiver tries to guess the message by using redundant bits.

75. What is frame relay, in which layer it comes?

Frame relay is a packet switching technology. It will operate in the data link layer.

76. What is Framing?

Framing in the data link layer separates a message from one source to a destination, or from other messages to other destinations, by adding a sender address and a destination address. The destination address defines where the packet has to go and the sender address helps the recipient acknowledge the receipt.

77. What is Gateway-to-Gateway protocol?

It is a protocol formerly used to exchange routing information between Internet core routers.

78. 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.

79. What is IGP (Interior Gateway Protocol)?

It is any routing protocol used within an autonomous system.

80. What is Kerberos?

It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.

81. What is logical link control?

One  of  two  sublayers  of  the  data  link  layer  of OSI reference model, as defined by  the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.

82. What is LRC?

In LRC, a block of bits is divided into rows and a redundant row of bits is added to the whole block. It can detect burst errors. If two bits in one data unit are damaged and bits in exactly the same positions in another data unit are also damaged, the LRC checker will not detect an error. In LRC a redundant data unit follows n data units.

83. What is MAC address?

The address  for a device as  it  is  identified at  the Media Access Control (MAC)  layer  in the network architecture. MAC address  is usually  stored  in ROM on  the  network adapter card and is unique.

84. What is Mail Gateway?

It is a system that performs a protocol translation between different electronic mail delivery protocols.

85. What is mesh network?

A  network  in  which  there  are  multiple  network  links  between  computers  to  provide multiple paths for data to travel.

86. What is multicast routing?

Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.

87. What is Multiple Access?

If the physical links are shared by more than two nodes, it is said to be Multiple Access.

88. What is Multiplexing?

Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

89. What is NETBIOS and NETBEUI?

NETBIOS 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  is  NetBIOS  extended  user  interface.  A  transport  protocol  designed  by 
microsoft and IBM for the use on small subnets.

90. What is NVT (Network Virtual Terminal)?

It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.

91. What is OSPF?

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.

92. What is packet filter?

Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every  incoming or outgoing packet  to be  inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.

93. What is passive topology?

When the computers on the network simply listen and receive the signal, they are referred to as passive because  they don't amplify  the signal  in any way. Example  for passive  topology -linear bus.

94. What is Piggy Backing?

A  technique   called   piggybacking   is   used   to   improve   the   efficiency   of   the   bidirectional protocols.  When a frame is carrying data from A to B,  it  can also carry control  information about arrived (or lost) frames from B; when a frame is carrying data from B to A, it can also carry control information about the arrived (or lost) frames from A.

95. What is Pipelining ?

In networking and in other areas, a task is often begun before the previous task has ended. This is known as pipelining.

96. What is point-point link?

If the physical links are limited to a pair of nodes it is said to be point-point link.

97. What is point-to-point protocol?

A  communications  protocol  used  to  connect  computers  to  remote  networking  services including Internet service providers.

98. What is Project 802?

It  is  a  project  started  by  IEEE  to  set  standards  to  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 extent  the network  layer  to allow  for 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 sublayer 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 sublayer of  the data  link  layer  that contains some distinct modules  each  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 (DQDB) designed to be used in MANs.

99. What is Protocol Data Unit?

The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an  information  field. 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).

100. What is Protocol?

A protocol is a set of rules that govern all aspects of information communication.

101. What is Proxy ARP?

It is using a router to answer ARP requests. This will be done when  the originating host believes that a destination is local, when in fact is lies beyond router.

102. What is RAID?

A method for providing fault tolerance by using multiple hard disk drives.

103. What is redirector?

Redirector  is software  that  intercepts  file or prints  I/O  requests and  translates  them  into network requests. This comes under presentation layer.

104. What is Redundancy?

The concept of including extra information in the transmission solely for the purpose of comparison. This technique is called redundancy.

105. What is region?

When hierarchical routing  is used, the routers are divided  into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.

106. What is RIP (Routing Information Protocol)?

It is a simple protocol used to exchange information between the routers.

107. What is Round Trip Time?

The duration of time it takes to send a message from one end of a network to the other and back, is called RTT.

108. What is SAP?

Series  of  interface  points  that  allow  other  computers  to  communicate  with  the  other 
layers of network protocol stack.

109. What is semantic gap?

Defining a useful channel involves both understanding the applications requirements and recognizing the limitations of the underlying technology. The gap between what applications expects and what the underlying technology can provide is called semantic gap.

110. What is silly window syndrome?

It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive  application on the receiving side reads 1 byte at a time.

111. What is Sliding Window?

The sliding window is an abstract concept that defines the range of sequence numbers that is the concern of the sender and receiver. In other words, he sender and receiver need to deal with only part of the possible sequence numbers.

112. What is SLIP (Serial Line Interface Protocol)?

It is a very simple protocol used for transmission of IP datagrams across a serial line.

113. What is 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.

114. What is Stop-and-Wait Automatic Repeat Request?

Error correction in Stop-and-Wait ARQ is done by keeping a copy of the sent frame and retransmitting of the frame when the timer expires.

115. What is Stop-and-Wait Protocol?

In Stop and wait protocol, sender sends one frame, waits until it receives confirmation from the receiver (okay to go ahead), and then sends the next frame.

116. What is subnet?

A generic term for section of a large networks usually separated by a bridge or router.

117. What is Synchronous TDM?

In STDM, the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

118. What is TDM?

TDM is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices.

119. What is terminal emulation, in which layer it comes?

Telnet is also called as terminal emulation. It belongs to application layer.

120. What is the difference between routable and non- routable protocols?

Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local  networks and cannot be used with a router.

121. What is the difference between TFTP and FTP application layer protocols?

The  Trivial  File  Transfer  Protocol  (TFTP)  allows  a  local  host  to  obtain  files  from  a remote host but does not provide reliability or security. It uses  the  fundamental packet delivery services offered by UDP. 

The File Transfer Protocol  (FTP)  is  the  standard mechanism  provided  by TCP / IP  for copying a  file  from one host to another. It uses the services offer 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.

122. What is the minimum and maximum length of the header in the TCP segment and IP datagram?

The header should have a minimum  length of 20 bytes and can have a maximum length of 60 bytes.

123. What is the range of addresses in the classes of internet addresses?

Class A   -       0.0.0.0   -   127.255.255.255

Class B   -   128.0.0.0   -   191.255.255.255

Class C   -   192.0.0.0   -   223.255.255.255

Class D   -   224.0.0.0   -   239.255.255.255

Class E   -   240.0.0.0   -   247.255.255.255

124. What is traffic shaping?

One of the main causes of congestion  is that traffic  is often busy. If hosts could be made to transmit at a uniform  rate, congestion would be  less common. Another open  loop method  to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.

125. What is usage of Sequence Number in Relaible Transmission?

The  protocol   specifies   that   frames  need  to be numbered.  This   is  done by using  sequence numbers. A field is added to the data frame to hold the sequence number of that frame. Since we want to minimize the frame size, the smallest range that provides unambiguous communication. The sequence numbers  can wrap around.

126. What is virtual channel?

Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.

127. What is virtual path?

Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.

128. What is VRC?

It is the most common and least expensive mechanism for Error Detection. In VRC, a parity bit is added to every data unit so that the total number of 1s becomes even for even parity. It can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.

129. What is WDM?

WDM is conceptually the same as FDM, except that the multiplexing and demultiplexing involve light signals transmitted through fiber optics channel.

130. What is wide-mouth frog?

Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.

131. What MAU?

In token Ring , hub is called Multistation Access Unit(MAU).

132. When a switch is said to be congested?

It is possible that a switch receives packets faster than the shared link can accommodate and stores in its memory, for an extended period of time, then  the switch will eventually run out of buffer space, and some packets will have to be dropped and in this state is said to congested state.

133. Which layer links the network support layers and user support layers?

The Transport layer links the network support layers and user support layers.

134. Which layers are network support layers?

a. Physical Layer

b. Data link Layer and 

c. Network Layers

135. Which layers are user support layers?

a. Session Layer

b. Presentation Layer and 

c. Application Layer

136. Why should you care about the OSI Reference Model?

It provides a framework for discussing network operations and design.