computer netwirk 2 marks 1

8/3/2019 Computer Netwirk 2 Marks 1

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(200 TWO MARKS)

COMPUTER NETWORKS

1)DEFINE PROTOCAL:

A protocol defines the format and the order of messages exchanged

between two or more communicating entities, as well as actions taken on the

transmission and/or receipt of a message or other event.

2)DEFINE END SYSTEMS:

The computers connected on the internet are often referred to as end

systems. They are referred to as end systems because they sit at the edge of the

internet. End systems are referred to as hosts because they host application

programs such as a web browser program, a web server program, e-mail reader

program etc.

3)DEFINE CLIENT PROGRAM AND SERVER PROGRAM:

A client program is a program running on one end system that

requests and receives a service from server program running on another end

system.

4)WHY THE TERMINOLOGY CONNECTION-ORIENTED SERVICE AND NOT JUST

CONNECTION SERVICE?

Its due to the fact that the end systems are connected in a very loosemanner. In particular only the end systems themselves are aware of this

connection; the packet switches within the internet are completely oblivious to

the connection. So its called connection-oriented service and not connection

service.



5)WHAT IS STORE-AND-FORWARD TRANSMISSION ?

Store-and-forward transmission means that the switch must receive the

entire packet before it can begin to transmit the first bit of the packet onto the

outbound link.they thus introduce a store and forward delay.

6)WHAT IS ACCESS NETWORKS?

The access networks are defined as the physical link(s) that

connect an end system to its edge router,which is the first router on a path from

the end system to any other distant end system.

7) WHAT ARE THE CLASSIFICATIONS OF ACCESS NETWORKS?

Theyare classified into 3 categories:

Residential access: connecting home end systems into the network.

Company access: connecting end systems in a business or educational

institution into the network.

Wireless access: connecting end systems(that are often mobile) into the

network.

8)WHAT IS A PHYSICAL MEDIA?

The physical medium can take many shapes and forms and

does not have to be of the same type for each transmitter-receiver pair along the

path. Examples of physical media include twisted-pair copper wire,coaxial

cable,multimode fiber-optic cable etc.

9)WHAT ARE THE CLASSIFICATIONS OF PHYSICAL MEDIA?

The physical media is classified into 2 types,they are

Guided media: fiber-optic cable,twisted-pair copper wire,coaxial cable.

Unguided media:wireless LAN,digital satellite channel.



10)WHAT IS POP?

They are expanded as Points of Presence.It is simply a group of one

or more routers in the ISP’s network at which routers in the other ISPs or in the

networksbeloging to the ISP’s customers can connect.Tier1 typically has manyPOPs.

11)WHAT IS NAPs?

The NAPs is expanded as Network Access Points,each of which can be

owned and operated by either some third-party telecommunications company or

by an internet backbone provider.They exchange huge quantities of traffic among

many ISPs.

12)WHAT ARE THE DIFFERENT TYPES OF DELAYS?

Processing delay

Queuing delay

Transmission delay

Propagation delay

13)WHAT IS THE CAUSE FOR PROCESSING DELAY?

The time required to examine the packet’s header and determine where

to direct the packet is a part of processing delay.It also includes the time required

to check for bit-level errors in the packet that occurred during transmission.

14)QUEUING DELAY:

At the queue,the packet experiences a queuing delay as it waits to

be transmitted onto the link.The length of the queuing delay of a specific packet

will depend on the number of earlier-arriving packets that are queued and waiting

for transmission across the link.

15)WHAT IS TRANSMISSION DELAY?



The transmission delay is the amount of time required for the

router to push out the packet;it is a function of packet’s length and the

transmission rate of the link.

16)WHAT IS PROPAGATION DELAY?

The propagation delay is defined as the time it takes a bit to

propagate from one router to the next;it is a function of the distance between the

two routers .

17)List the FUNCTIONS OF APPLICATION LAYER?

It is a layer where network applications and their application layer

protocols reside.The protocols they include are HTTP protocol(web document

request and transfer),SMTP(transfer of e-mail messages) and FTP(transfer of files

between two end systems).

18)TRANSPORT LAYER?

This layer transports application-layer messages between the client andserver sides of an application.The two important transport layer protocols are

TCP(connection oriented protocol,reliable data transfer) UDP(connectionless

protocol,unreliable data transfer).Packet is referred as segment in this layer.

19)FUNCTIONS OF NETWORK LAYER?

The network layer is responsible for moving network layer packets

known as datagrams from one host to another.the transport layer protocol in a

source host passes a transport-layer segment and a destination address to the

network layer.The network layer then provides the service of delivering the

segment to the transport layer in te destination host.

20)FUNCTIONS OF LINK LAYER?



To move a packet from one node to the next node in the route,the

network layer relies on the services of the link layer.At each node the network

layer passes the datagram down to the link layer,which delivers the datagram to

the next node along the route.At this next node the link layer passes the

datagram up to the network layer.

21)FUNCTIONS OF PHYSICAL LAYER?

The function of the link layer is to move entire frame from one

network element to an adjacent network element, the function of the physical

layer is to move the individual bits within the frame from one node to the next.

22)WHAT IS DEMULTIPLEXING?

The job of delivering the data in a transport layer segment to a

correct socket is called demultiplexing.

23)WHAT IS MULTIPLEXING?

The job of gathering data chunks at the source host from different

sockets,encapsulating each data chunk with header information to create

segments, and passing the segments to the network layer is called multiplexing.

24)WHY UDP IS BETTER THAN TCP?

UDP is better than TCP because of

finer application –level control over what data is sent and when

no connection establishment

no connection state

small packet header overhead

25)WHAT IS UDP CHECKSUM?



The UDPchecksum provides for error detection.It is used to find if any bits within

the segment has been altered as it moved from source to destination.At the

sender side 1’s complement of all the 16 bit sum is done and stored in the UDO

checksum segment.if no error is detected in the receiver side then the sum wil be

1111111111111111,if not then error has occurred during transmission.

26)WHAT IS GBN?

It is called Go-Back-N protocol.Here the sender is allowed to transmit

multiple packets without waiting for an acknowledgement.But it is constrained to

have no more than some maximum allowable number N,of unacknowledged

packets in the pipeline.

27)WHAT ARE TE EVENTS THAT GBN RESPONDS TO?

Invocation from above

Receipt of an ACK

A timeout event

28)WHAT IS SR PROTOCAL?

It is expanded as Selective Repeat Protocal. This is used to replace

GBN because in GBN if an error occurs in a single packet then large number of

packets are to be re-transmitted,but in SR only the packet with error is re-

transmitted.

29)DEFINE THREE-WAY-HANDSHAKE:

First a TCP connection is established between the TCP client and

server and a special TCP segment is passed from client, then the server responds

with another special TCP segment(both these segments do not carry any

payload),then finally the client responds with another TCP segment which may



carry payload. Since three segments are established between two hosts its called

three-way handshake.

30)WHAT IS MSS?

It is expanded as Maximum Segment Size.The maximum amount of

data that can be grabbed and placed in a segment is limited by MSS.

31)WHAT ARE THE DIFFERENT BITS FO FLAG FIELD?

It has 6bits.

ACK: to indicate that the valued carried in the acknowledgement field is valid.

RST,SYN,FIN : used for connection setup and teardown.

PSH: if set,then should pass the data to upper layer immediately.

URG:there is a data in this segment that has been marked urgent.

32)WHWT IS SEQUENCE NUMBER OF A SEGMENT?

The sequence number of a segment is defined as the byte stream

number of the first byte in the segment.

33)WHAT IS ACKNOLEDGEMENT NUMBER?

The acknowledgement number the host A puts in its segment is

the sequence number of the next byte host A puts is expecting from host B.

34)WHEN DOES AN ACKNOLEDGEMENT IS SAID TO BE PIGGYBACKED?

The acknowledgement for client-to-server data is carried in a segment

carrying server-to-client data;this acknowledgement is said to de piggybacked on

the server-to-client data segment.

35)WHAT IS RTT?



It is expanded as Round Trip Time.RTT for a segment is defined as the

amount of time between when the segment is sent and when an

acknowledgement for that segment is received.

36)WHAT IS THE USAGE OF FIN?

FIN is used for connection removal between the client and server.First

FIN is passed by client which is acknowledged by the server,then FIN is passed by

the server which is then acknowledged by the client.Then after some time out

connection is removed.

37)WHAT IS EFCI ?

EFCI is a bit expanded as Explicit Forward Congestion Indication bit. A

congested network switch can set the EFCI bit in a data cell to 1 to signal

congestion to the destination host.

38) PURPOSE OF NI AND CI BIT?

Both these bits are used to indicate congestion to the destination, but

there is a little difference in the function of both the bits. Setting NI bit is used to

indicate mild congestion and setting CI bit indicates severe congestion.

39)WHAT ARE RM CELLS?

These cells are called Resource-Management cells. They are used to

convey congestion related informations.RM cells can be used to provide both

direct network feedback and network-feedback-via-the-receiver.

40) WHAT IS TCP CONGESTION CONTROL ALGORITHM?

This algorithm is used to detect and treat congestion. This algorithm

has three major components, they are

Additive- increase,multiplicative-decrease.

Slow start.

Reaction to timeout events.



41)WHAT IS CBR ATM NETWORK SERVICE?

This is called constant bit rate ATM network service,this was the first

ATM service model to be standardized,its goal is to provide flow of packets with a

virtual pipe,the cells that are lost are less than the specified amount.

42) WHAT IS ABR ATM NETWORK SERVICE?

It is called as Available Bit rate network service.This is little better

than the best-effort service.Minimum transmission rate is ordered for ABR and if

additional resourses are available then transmission rate can be more than the

specified MCR.

43) WHAT ARE THE THREE PHASES OF A VIRTUAL CIRCUIT?

VC setup: a path is set between the sender and receiver.

Data transfer: packets begin to flow along the VC.

VC teardown: after the flow of packets they decide to terminate the VC.

44) WHAT ARE THE IMPORTANT PARTS OF THE ROUTER ARCHITECTURE?

There are four main parts in the router architecture, they are,

Input port.

Output port.

Switch fabric.

Routing processor.

45) FUNCTIONS OF INPUT PORTS?

Physical layer functions-terminating incoming physical link to a router.

Datalink layer functions-at te remote side of the incoming link.

46)FUNCTIONS OF SWITCHING FABRIC:



The switching fabric is present between the input ports and the output

ports.This is used to connect the input ports to the corresponding output ports.

47)FUNCTIONS OF OUTPUT PORTS:

They store the packets that have been forwarded to it through the

switching fabric and then transmits the packets on the outgoing link.Thus they

perform reverse datalindk and physical layer functions of the input port.

48)FUNCTIONS OF ROUTING PROCESSOR?

The routing processor is connected to the switching fabric.The

function of this routing processor is to execute the routing protocols within the

router.

49)WHAT ARE THE SWITCHING TECHNIQUES USED IN SWITCHING FABRIC?

Switching technique using memory.

Switching technique using bus.

Switching technique using crossbar.

50)PURPOSE OF TIME -TO-LIVE?

TTL is used inorder to ensure that datagrams do not circulate forever in

the network.This field is decremented by one each time the datagram is

processed by a router.If the TTL field reaches 0(zero)the datagram must be

dropped.

51) WHAT ARE THE DIFFERENT WAYS TO ASSIGN IP ADDRESS TO THE HOST?

Manual configuration: A system administrator manually configures the IP

address into the host.



Dynamic Host Configuration Protocal(DHCP): It allows a host to obtain an

IP address automatically,as well as to learnadditional information,such as its

subnet mask,the address of its first-hop router and the address of its local DNS

server.

52)WHAT ARE THE CHANGES INTRODUCED IN IPv6 COMPARED TO IPv4?

Expanded addressing capabilities: IP address is expanded from 32 to

128 bits.

A streamlined 40-byte header: 40 byte fixed length header allows for

faster processing of the IP datagram.

Flow labeling and priority:labeling of packets belonging to

particularflows for which the sender requests specia; handling.

53)WHAT IS TE PURPOSE OF HOP LIMIT?

The contents of this field are decremented by one by each router that

forwards the datagram.If the op limit count reaches zero the datagram is

discarded.

54)WHAT ARE THE METHODS SUGGESTED FOR TRANSITIONING FROM IPv4 to

IPv6?

Dual stack approach.

Tunneling.

55)WHAT IS TUNNELING?

Consider two IPv6 nodes that wants to interpolate,but between them

there are two IPv4 datagrams,these two IPv4 datagrams present between IPv6

nodes is reffered as tunnel.The IPv6 node on the sending side completely takes

the IPv6 datagram and puts it in the datafield of IPv4 node,whichis unaware that

it actually carries the complete IPv6 datagram,at the receiver side data is given to

IPv6 node.This process is called tunneling.



56)WHAT ARE THE CLASSIFICATIONS OF ROUTING ALGORITHMS?

They are broadly classified into two ways,

One way in which we can classify routing algorithms is according to

whether they are global or decentralized.

Second way to classify routing algorithms is according to whether they are

static or dynamic.

57)DEFINE GLOBAL ROUTING ALGORITHM:

This computes the least-cost path between a source and destination

using complete global knowledge about the network.That is,the algorithm takes

the connectivity between all nodes and all link costs as inputs.This is also called as

link-state (LS) algorithm.

58)DEFINE DECENTRALIZED ROUTING ALGORITHM:

In a decentralized routing algorithm the calculation of the least-cost path

is carried out in an iterative,distributed manner.No node has complete

information about the costs of all network links.Instead each node begins with

only the knowledge of the costs of all network links.

60)DEFINE STATIC AND DYNAMIC ROUTING ALGORITHMS?

In ststic routing algorithms routes change very slowly over time,

often as a result of human intervention. In dynamic routing algorithms they

change the routing paths as the network traffic loads or topology change.

61)WHAT IS INTR-AUTONOMOUS SYSTEM ROUTING PROTOCAL?



The routing algorithm that runs within an autonomous system is

called an intra-autonomous system routing protocol.

62)WHAT IS HYPER TEXT TRANSFER PROTOCAL?

The HTTP,the web’s application-layer protocol,is at the heart of

the web.HTTP is implemented in two programs:a client program and a server

program.The client and server program executing on different end systems,talk to

each oter by exchanging HTTP messages.

63)WHAT IS A WEB PAGE?

A web page is also called as document. It consists of objects.An

object is simply a file-such as HTML file,a JPEG image,a GIF image,and so on.

64)WHAT IS A BROWSER?

A browser is a user agent for the web;it displays the requested web

page to the user and provides numerous navigational and configuration

features.Because web browsers also implement the client side of HTTP,in thecontext of the web,we will use the words browser and client interchangeably.

65)WHAT IS A WEB SERVER?

A web server houses web objects,each addressable by a URL.Web

servers also implement the server side of HTTP.Popular web servers include

Apache and Microsoft Internet Information Server.

66)WHICH PROTOCAL IS CALLED STATELESS PROTOCAL?

HTTP protocol is called stateless protocol.Because an HTTP protocol

does not maintain any information about the clients.

67)WHAT IS CALLED REQUEST LINE,HEADER LINES?



The first line of an HTTP request message is called the request

line;the subsequent lines are called the header lines. The request line has three

fields: the method field,the URL field and the HTTP field.

\

68)WHY HTTP IS CALLED A PULL PROTOCAL?

HTTP is mainly a pull protocol because someone loads

information on a web server and users use HTTP to pull the information from the

server at their convenience.

69)WHY AND WHICH PROTOCAL IS CALLED PUSH PROTOCAL?

SMTP is primarily a push protocol.This is because the sending mail

server pushes the file to the receiving mail server.

70)WHAT IS A STREAM?

A stream is a sequence of characters that flow into or out of a

process.Each stream is either an input stream for the process or an output

stream.

71)WHAT IS A MULTICAST GROUP?

The group of receivers associated with class D is called multicast

group.A multicast packet is addressed using address indirection.A single identifier

is used for group of receivers.

72)WHAT IS IGMP?

This is expanded as Internet Group Management Protocal.IGMP

operates locally,between a host and an attached router.Despite its name IGMP is

not a protocol that operates among all the hosts that have joined a multicast

group.

73)WHAT IS AN ADAPTER?



For a given communication link,the link-layer protocol is,for the

most part,implemented in an adapter.An adapter is a board that typically contains

RAM,DSP chips,a host bus interface and a link interface.They are also called as

network interface cards.

74)WHAT IS CRC?

This is expanded as cyclic redundancy check codes.This is also called

as polynomial codes,since it is possible to view the bit string to be sent as a

polynomial whose co efficient are the 0 and 1 values in the bit string.

75)WHAT IS AAL?

AAL is expanded as ATM adaption layer is roughly analoguos to the

internet’s transport layer and is present only at the ATM devices at the edge of

the ATM network.The unit of data handled by the AAL is reffered to by the rather

generic name of AAL protocol data unit(PDU).

76)WHAT IS EDGE?

This is expandeded as Enhanced Data Rates for Global Evolution.The

main goal of EDGE is to increase the data rate capabilities of a GSM/GPRS

network,that is,to better exploit the 200KHz GSM channel with its eight-slot

TDMA frames.

77)WHAT IS UMTS?

UMTS is expanded as Universal Mobile Telecommunications

Service.This is an evolution of GSM to support 3G capabilities.The UMTS network

architecture borrows heavily from the established GSM network architecture.

78)DEFINE WIRELESS HOSTS:

As in case of wired networks,hosts are end-system devices that run

applications.A wireless host might be a laptop,palmtop,PDA,phone,or destop

computer.The hosts themselves may or may not be mobile.



79)DEFINE WIRELESS LINKS:

A host connects to base station or to another wireless host through a

wireless communication link.Different wireless link technologies have different

transmission rates and can transmit over different distances.

80)DEFINE BASE STATION:

The base station is a key part of the wireless network

infrastructure.Unlike the wireless host and wireless link,a base station has no

obvious counterpart in a wired network.A base station is responsible for sending

and receiving data to and from a wireless host that is associated with that base

station.

81)WHAT IS INFRA-STRUCTURE MODE?

Hosts associated with a base station are often reffered to as

operating in infra-structure mode,since all traditional network services are

provided by the network to which a host is connected via the base station.

82)WHAT IS BSS?

The fundamental building block of the 802.11 architecture is the

basic service set.A BSS contains one or more wireless stations and a central base

station, known as an access point(AP).

83)WHAT IS AGENT DISCOVERY?

Mobile IP defines the protocols used by a home or foreign agent

to advertise its services to mobile nodes, and protocols for mobile nodes to solicit

the services of a foreign or home agent.

84)HOW IS REGISTRATION WITH HOME AGENT IS DONE IN MOBILE IP?

Mobile IP defines the protocols used by the mobile node and/or

foreign agent to register and deregister COAs with a mobile node’s home agent.

85)WHAT IS INDIRECT ROUTING OF DATAGRAMS IN MOBILE IP?



The standard also defines the manner in which datagrams are

forwarded to mobile nodes by a home agent,including rules for forwarding

datagrams,rules for handling error conditions, and several forms of encapsulation.

86)WHAT IS VLR?

The visited network maintains a database known as visitor location

register.it contains an entry for each mobile user that is currently in the portion of

the network served by the VLR.

87)WHAT IS PCM?

This is the basic encoding technique called as pulse code

modulation.Speech encoding often uses PCM,with a sampling rate of 8000

samples per second and 8 bits per sample giving a rate of 64 kbps.

88)WHAT IS END-TO-END DELAY?

End-to-end delay is accumulation of transmission,processing and

queuing delays in routers;propagation delays in the links; end system processing

delays.

89)WHAT IS A JITTER?

A crucial component of end-to-end delay is the random queuing

delays in the routers.Because of these varying delays within the network,the time

from when a packet is generated at the source until it is received at the receiver

can fluctuate from packet to packet.This phenomenon is called jitter.

90)WHAT ARE THE METHODS TO REMOVE JITTER?

prefacing each chunk with a sequence number.

prefacing each chunk with a timestamp.

delayind playout of chunks at the receiver.



91)WHAT ARE THE RTP HEADER FIELDS?

RTP has five important header fields.They are

Payload type.

Sequence number field.

Timestamp field.

Synchronization source identifier.

Miscellaneous fields.

92)WHAT IS SSRC?

This is expanded as synchronization source identifier.It is 32 bits

long.It identifies the source of the RTP stream,each stream in an RTP session has adistinct SSRC.

93)WHAT IS THE USE OF SEQUENCE NUMBER FIELD IN RPT?

It is 16 bits long.The sequence number increments by one for each RTP

packet sent,and may be used by the receiver to detect packet loss and to restore

packet sequence.

94)WHAT IS THE USE OF TIMESTAMP FIELD?

This is 32 bits long.It reflects the sampling instant of the first byte in the

RTP data packet.It is also used to remove packet jitter.

95)WHAT IS DNS?



Host name conflicts would occur constantly unless names were centrally

managed, something unthinkable in a huge international network due to the load

and latency. To solve these problems, DNS (the Domain Name System) was

invented.

96)WHAT IS RESOLVER?

To map a name onto an IP address, an application program calls a library

procedure called the resolver, passing it the name as a parameter.

97)WHAT IS CALLED RESOURCE RECORDS?

Every domain, whether it is a single host or a top-level domain, can have

a set of resource records associated with it. For a single host, the most common

resource record is just its IP address, but many other kinds of resource records

also exist. When a resolver gives a domain name to DNS, what it gets back are the

resource records associated with that name. Thus, the primary function of DNS is

to map domain names onto resource records.

98)WHAT IS REVERSE LOKUPS?

CNAME, PTR points to another name. However, unlike CNAME, which isreally just a macro definition, PTR is a regular DNS datatype whose interpretation

depends on the context in which it is found. In practice, it is nearly always used to

associate a name with an IP address to allow lookups of the IP address and return

the name of the corresponding machine. These are called reverse lookups.

99)WHAT IS AUTHORITATIVE RECORD?

An authoritative record is one that comes from the authority that

manages the record and is thus always correct. Authoritative records are incontrast to cached records, which may be out of date.

100)WHAT IS RECURSIVE QUERY?

It is worth mentioning that the query method described here is known

as a recursive query, since each server that does not have the requested



information goes and finds it somewhere, then reports back. An alternative form

is also possible. In this form, when a query cannot be satisfied locally, the query

fails, but the name of the next server along the line to try is returned. Some

servers do not implement recursive queries and always return the name of the

next server to try.

101)WHAT IS LDAP?

While DNS is extremely important to the correct functioning of the

Internet, all it really does is map symbolic names for machines onto their IP

addresses. It does not help locate people, resources, services, or objects in

generalFor locating these things, another directory service has been defined,

called LDAP (Lightweight Directory Access Protocol).

102)WHAT IS COLLISION?

If two frames are transmitted simultaneously, they overlap in

time and the resulting signal is garbled. This event is called a collision. All stations

can detect collisions. A collided frame must be transmitted again later. There are

no errors other than those generated by collisions.

103)WHAT IS CONTENTION SYSTEMS?

Systems in which multiple users share a common channel in a

way that can lead to conflicts are widely known as contention systems.

104)WHAT IS SLOTTED ALOHA?

In Roberts' method, which has come to be known as slotted

ALOHA, in contrast to Abramson's pure ALOHA, a computer is not permitted to

send whenever a carriage return is typed. Instead, it is required to wait for the

beginning of the next slot. Thus, the continuous pure ALOHA is turned into a

discrete one. Since the vulnerable period is now halved, the probability of no

other traffic during the same slot as our test frame is e-G

.

105)WHAT ARE CARRIER SENSE PROTOCALS?



Protocols in which stations listen for a carrier (i.e., a transmission)

and act accordingly are called carrier sense protocols. A number of them have

been proposed. Kleinrock and Tobagi (1975) have analyzed several such protocols

in detail.

106)WHAT IS 1-PERSISTENT CSMA?

When a station has data to send, it first listens to the channel to

see if anyone else is transmitting at that moment. If the channel is busy, the

station waits until it becomes idle. When the station detects an idle channel, it

transmits a frame. If a collision occurs, the station waits a random amount of time

and starts all over again. The protocol is called 1-persistent because the stationtransmits with a probability of 1 when it finds the channel idle.

107)WHAT IS NON-PERSISTENT CSMA?

Before sending, a station senses the channel. If no one else is

sending, the station begins doing so itself. However, if the channel is already in

use, the station does not continually sense it for the purpose of seizing it

immediately upon detecting the end of the previous transmission. Instead, it

waits a random period of time and then repeats the algorithm. Consequently, this

algorithm leads to better channel utilization but longer delays than 1-persistent

CSMA.

108)WHAT IS P-PERSISTENT CSMA?

When a station becomes ready to send, it senses the channel. If it is idle,

it transmits with a probability p. With a probability q = 1 - p, it defers until the

next slot. If that slot is also idle, it either transmits or defers again, with

probabilities p and q. This process is repeated until either the frame has been

transmitted or another station has begun transmitting. In the latter case, the

unlucky station acts as if there had been a collision

109)WHAT IS BIT MAP METHOD?



If station 0 has a frame to send, it transmits a 1 bit during the

zeroth slot. No other station is allowed to transmit during this slot. Regardless of

what station 0 does, station 1 gets the opportunity to transmit a 1 during slot 1,

but only if it has a frame queued. In general, station j may announce that it has a

frame to send by inserting a 1 bit into slot j. After all N slots have passed by, each

station has complete knowledge of which stations wish to transmit.

110)WHAT IS HIDDEN STSTION PROBLEM?

First consider what happens when A is transmitting to B. If C senses

the medium, it will not hear A because A is out of range, and thus falsely conclude

that it can transmit to B. If C does start transmitting, it will interfere at B, wiping

out the frame from A. The problem of a station not being able to detect a

potential competitor for the medium because the competitor is too far away is

called the hidden station problem.

111)WHAT IS EXPOSED STATION PROBLEM?

Now consider that B transmitting to A. If C senses the medium, it will

hear an ongoing transmission and falsely conclude that it may not send to D,

when in fact such a transmission would cause bad reception only in the zone

between B and C, where neither of the intended receivers is located. This is calledthe exposed station problem.

112)WHAT IS TIME DOMAIN REFLECTOMETRY?

By carefully timing the interval between sending the pulse and receiving

the echo, it is possible to localize the origin of the echo. This technique is called

time domain reflectometry.

113)WHAT IS MANCHESTER ENCODING?

In Manchester encoding, each bit period is divided into two equal

intervals. A binary 1 bit is sent by having the voltage set high during the first

interval and low in the second one. A binary 0 is just the reverse: first low and

then high. This scheme ensures that every bit period has a transition in the

middle, making it easy for the receiver to synchronize with the sender.



114)WHAT IS THE DISADVANTAGE OF MANCHESTER ENCODING?

A disadvantage of Manchester encoding is that it requires twice as

much bandwidth as straight binary encoding because the pulses are half the

width.

115)WHAT IS DIFFERENTIAL MANCHESTER ENCODING?

Differential Manchester encoding, is a variation of basic

Manchester encoding. In it, a 1 bit is indicated by the absence of a transition at

the start of the interval. A 0 bit is indicated by the presence of a transition at the

start of the interval.

116)WHAT IS FRAME BURSTING?

Frame bursting allows a sender to transmit a

concatenated sequence of multiple frames in a single transmission. If the total

burst is less than 512 bytes, the hardware pads it again. If enough frames are

waiting for transmission, this scheme is highly efficient and preferred over carrier

extension.

117)WHAT IS PICONET?

The basic unit of a Bluetooth system is a piconet, which consists of a

master node and up to seven active slave nodes within a distance of 10 meters.

Multiple piconets can exist in the same (large) room and can even be connected

via a bridge node. An interconnected collection of piconets is called a scatternet.

118)WHAT IS SCO?

SCO(synchronous connected orientation) links are used for real-time

data, such as telephone connections. This type of channel is allocated a fixed slot

in each direction. Due to the time-critical nature of SCO links, frames sent over

them are never retransmitted. Instead, forward error correction can be used to

provide high reliability. A slave may have up to three SCO links with its master.

Each SCO link can transmit one 64,000 bps PCM audio channel.



119)WHAT IS BENT PIPE?

In its simplest form, a communication satellite can be thought of

as a big microwave repeater in the sky. It contains several transponders, each of

which listens to some portion of the spectrum, amplifies the incoming signal, and

then rebroadcasts it at another frequency to avoid interference with the incoming

signal. The downward beams can be broad, covering a substantial fraction of the

earth's surface, or narrow, covering an area only hundreds of kilometers in

diameter. This mode of operation is known as a bent pipe.

120)WHAT IS FOOTPRINT?

The first geostationary satellites had a single spatial beam that

illuminated about 1/3 of the earth's surface, called its footprint.

121)WHAT IS TOLL CONNECTING TRUNKS?

If the called telephone is attached to another end office, a

different procedure has to be used. Each end office has a number of outgoing

lines to one or more nearby switching centers, called toll offices (or if they are

within the same local area, tandem offices). These lines are called toll connecting

trunks.

122)WHAT IS CALLED AS INTERTOLL TRUNKS?

Primary, sectional, and regional offices form a network by

which the toll offices are connected. The toll, primary, sectional, and regional

exchanges communicate with each other via high-bandwidth intertoll trunks (also

called interoffice trunks).



123)WHAT IS DATAGRAM SUBNET?

If connectionless service is offered, packets are injected into the

subnet individually and routed independently of each other. No advance setup is

needed. In this context, the packets are frequently called datagrams (in analogywith telegrams) and the subnet is called a datagram subnet.

124)WHAT IS VIRTUAL- CIRCUIT SUBNET?

If connection-oriented service is used, a path from the

source router to the destination router must be established before any data

packets can be sent. This connection is called a VC (virtual circuit), in analogy with

the physical circuits set up by the telephone system, and the subnet is called a

virtual-circuit subnet.

125)DEFINE THE USE OF ROUTING ALGORITHM?

The routing algorithm is that part of the network layer

software responsible for deciding which output line an incoming packet should be

transmitted on. If the subnet uses datagrams internally, this decision must be

made anew for every arriving data packet since the best route may have changedsince last time.

126)WHAT IS SESSION ROUTING?

If the subnet uses virtual circuits internally, routing

decisions are made only when a new virtual circuit is being set up. Thereafter,

data packets just follow the previously-established route. The latter case is

sometimes called session routing because a route remains in force for an entire

user session (e.g., a login session at a terminal or a file transfer).

127)WHAT IS FORWARDING?

It is sometimes useful to make a distinction between

routing, which is making the decision which routes to use, and forwarding, which

is what happens when a packet arrives. One can think of a router as having two



processes inside it. One of them handles each packet as it arrives, looking up the

outgoing line to use for it in the routing tables. This process is forwarding.

128)EXPLAIN DISTANCE VECTOR ROUTING?

Distance vector routing algorithms operate by having each router

maintain a table (i.e, a vector) giving the best known distance to each destination

and which line to use to get there. These tables are updated by exchanging

information with the neighbors.

129)WHAT IS CHOKE PACKET?

The router sends a choke packet back to the source host, giving it the

destination found in the packet. The original packet is tagged (a header bit is

turned on) so that it will not generate any more choke packets farther along the

path and is then forwarded in the usual way.

130)WHAT IS LOAD SHEDDING?

Load shedding is a fancy way of saying that when routers are being

inundated by packets that they cannot handle, they just throw them away. The

term comes from the world of electrical power generation, where it refers to the

practice of utilities intentionally blacking out certain areas to save the entire grid

from collapsing on hot summer days when the demand for electricity greatly

exceeds the supply.

131)GIVE BLUETOOTH ARCHITECTURE?

The basic unit of a Bluetooth system is a piconet, which

consists of a master node and up to seven active slave nodes within a distance of

10 meters. Multiple piconets can exist in the same (large) room and can even be



connected via a bridge node. An interconnected collection of piconets is called a

scatternet.

132)WHAT IS ACL?

The ACL (Asynchronous Connection-Less) link, which is used for

packet-switched data available at irregular intervals. These data come from the

L2CAP layer on the sending side and are delivered to the L2CAP layer on the

receiving side. ACL traffic is delivered on a best-efforts basis. No guarantees are

given. Frames can be lost and may have to be retransmitted. A slave may have

only one ACL link to its master.

133)WHAT IS PROMISCUOUS MODE?

Most LAN interfaces have a promiscuous mode, in which all frames are

given to the computer, not just those addressed to it. Spies and busybodies lovethis feature. By inserting bridges at various places and being careful not to

forward sensitive traffic, a system administrator can isolate parts of the network

so that its traffic cannot escape and fall into the wrong hands.

134)WHAT IS BACKWARD LEARNING?

The algorithm used by the transparent bridges is backward

learning.As mentioned above, the bridges operate in promiscuous mode, so they

see every frame sent on any of their LANs. By looking at the source address, they

can tell which machine is accessible on which LAN.

135)WHAT ARE THE RESULTS OF BROADCAST STORM?



The results of broadcast storm are that (1) the entire LAN capacity

is occupied by these frames, and (2) all the machines on all the interconnected

LANs are crippled just processing and discarding all the frames being broadcast.

136)WHAT IS VLAN?

In response to user requests for more flexibility, network vendors

began working on a way to rewire buildings entirely in software. The resulting

concept is called a VLAN (Virtual LAN) and has even been standardized by the 802

committee. It is now being deployed in many organizations. Let us now take a

look at it. For additional information about VLANs.

137)GIVE THE FUNCTIONS OF DATALINK LAYER?

The data link layer has a number of specific functions it can carry out. These

functions include

1. Providing a well-defined service interface to the network layer.

2. Dealing with transmission errors.

3. Regulating the flow of data so that slow receivers are not swamped by fast

senders.

138)WHAT ARE THE DIFFERENT METHODS OF FRAMING?

1. Character count.

2. Flag bytes with byte stuffing.

3. Starting and ending flags, with bit stuffing.

4. Physical layer coding violations.

139)WHAT IS REACHABILITY ANALYSIS?

From the initial state, some, perhaps all, of the other states can be

reached by a sequence of transitions. Using well-known techniques from graphtheory (e.g., computing the transitive closure of a graph), it is possible to

determine which states are reachable and which are not. This technique is called

reachability analysis.

140)WHAT IS DEADLOCK?



A deadlock is a situation in which the protocol can make no more forward

progress (i.e., deliver packets to the network layer) no matter what sequence of

events happens. In terms of the graph model, a deadlock is characterized by the

existence of a subset of states that is reachable from the initial state.

141)WHAT ARE THE PROPERTIES OF DEADLOCK?

It has two properties:

1. There is no transition out of the subset.

2. There are no transitions in the subset that cause forward progress.

Once in the deadlock situation, the protocol remains there forever. Again, it is

easy to see from the graph that protocol 3 does not suffer from deadlocks.

142)WHAT ARE THE DIFFERENT TYPES OF FRAMES?

There are three kinds of frames:

Information.

Supervisory.

Unnumbered.

143)WHAT ARE THE FEATURES OF PPP PROTOCAL?

PPP provides three features:

1. A framing method that unambiguously delineates the end of one frame and

the start of the next one. The frame format also handles error detection.



2. A link control protocol for bringing lines up, testing them, negotiating

options, and bringing them down again gracefully when they are no longer

needed. This protocol is called LCP (Link Control Protocol). It supports

synchronous and asynchronous circuits and byte-oriented and bit-oriented

encodings.

144)WHAT IS TRANSPORT ENTITY?

The hardware and/or software within the transport layer that does

the work is called the transport entity. The transport entity can be located in the

operating system kernel, in a separate user process, in a library package bound

into network applications, or conceivably on the network interface card.

145)WHAT IS LDAP?

While DNS is extremely important to the correct functioning of the

Internet, all it really does is map symbolic names for machines onto their IP

addresses. It does not help locate people, resources, services, or objects in

general. For locating these things, another directory service has been defined,

called LDAP (Lightweight Directory Access Protocol).

146)WHAT IS CALLED PAGES?

From the users' point of view, the Web consists of a vast, worldwide

collection of documents or Web pages, often just called pages for short. Each

page may contain links to other pages anywhere in the world. Users can follow a

link by clicking on it, which then takes them to the page pointed to.

147)WHAT IS HYPERTEXT?

Each page may contain links to other pages anywhere in the world.

Users can follow a link by clicking on it, which then takes them to the page

pointed to. This process can be repeated indefinitely. The idea of having one page

point to another, now called hypertext.

148)WHAT IS CYPHER?



A cipher is a character-for-character or bit-for-bit transformation,

without regard to the linguistic structure of the message.

149)WHAT IS CODE?

A code replaces one word with another word or symbol. Codes are not

used any more, although they have a glorious history.

150)DEFINE PLAIN TEXT AND KEY:

The messages to be encrypted, known as the plaintext, are transformed

by a function that is parameterized by a key.

151)WHAT IS CYPHER TEXT?

The output of the encryption process, known as the ciphertext, is then

transmitted, often by messenger or radio. We assume that the enemy, or

intruder, hears and accurately copies down the complete ciphertext.

152)WHAT IS CRYPTOLOGY?

The art of breaking ciphers, called cryptanalysis, and the art devising

them (cryptography) is collectively known as cryptology.

153)WHAT IS CALLED AS TRANSPOSITION CIPHERS?

Transposition ciphers, in contrast, reorder the letters but do not disguise

them. It is a common transposition cipher, the columnar transposition. The

cipher is keyed by a word or phrase not containing any repeated letters.

154)WHAT ARE THE DIFFERENT WAYS TO ASSIGN IP ADDRESS TO THE HOST?

Manual configuration: A system administrator manually configures the IP

address into the host.



Dynamic Host Configuration Protocal(DHCP): It allows a host to obtain an

IP address automatically,as well as to learnadditional information,such as its

subnet mask,the address of its first-hop router and the address of its local DNS

server.

155)WHAT IS ONE-TIME PAD?

The ciphertext cannot be broken, because in a sufficiently large

sample of ciphertext, each letter will occur equally often, as will every digram,

every trigram, and so on. This method, known as the one-time pad, is immune to

all present and future attacks no matter how much computational power the

intruder has.

156)WHAT IS ACCESS NETWORKS?

The access networks are defined as the physical link(s) that

connect an end system to its edge router,which is the first router on a path from

the end system to any other distant end system.

157)WHAT IS RECTILINEAR BASIS?

Consider two sets.

Set one consists of a vertical filter and a horizontal filter.

This choice is called a rectilinear basis.

158)WHAT IS DIAGONAL BASIS?

The second set of filters is the same, except rotated 45 degrees,

so one filter runs from the lower left to the upper right and the other filter runs

from the upper left to the lower right. This choice is called a diagonal basis.

159)WHAT ARE THE TWO PRINCIPLES OF CRYPTOGRAPHY?



The two basic principles of cryptography are

Redundancy.

Freshness.

160)WHAT IS REDUNDANCY?

The first principle is that all encrypted messages must contain some

redundancy, that is, information not needed to understand the

message.According to cryptographic principle one:messages must contain some

redundancy.

161)WHAT IS FRESHNESS?

The second cryptographic principle is that some measures must be

taken to ensure that each message received can be verified as being fresh, that is,

sent very recently. Cryptographic principle 2: Some method is needed to foil

replay attacks.

162)WHAT IS A WEB SERVER?

A web server houses web objects,each addressable by a URL.Web

servers also implement the server side of HTTP.Popular web servers include

Apache and Microsoft Internet Information Server.

163)WHAT IS DES?

In January 1977, the U.S. Government adopted a product cipher

developed by IBM as its official standard for unclassified information. This cipher,

DES (Data Encryption Standard), was widely adopted by the industry for use in

security products. It is no longer secure in its original form, but in a modified form

it is still useful.



164)DEFINE WHITENING?

A technique that is sometimes used to make DES stronger is called

whitening. It consists of XORing a random 64-bit key with each plaintext block

before feeding it into DES and then XORing a second 64-bit key with the resultingciphertext before transmitting it. Whitening can easily be removed by running the

reverse operations.

165)WHAT IS TRIPLE DES?

As early as 1979, IBM realized that the DES key length was too short and

devised a way to effectively increase it, using triple encryption (Tuchman, 1979).

Here two keys and three stages are used. In the first stage, the plaintext is

encrypted using DES in the usual way with K1. In the second stage, DES is run in

decryption mode, using K2 as the key. Finally, another DES encryption is done with

K1.

166)GIVE EXPANSIONS FOR EEE AND EDE?

EDE (Encrypt Decrypt Encrypt) .

EEE (Encrypt Encrypt Encrypt).

167)WHY EDE IS USED INSTEAD OF EEE?

The reason that two keys are used is that even the most paranoid

cryptographers believe that 112 bits is adequate for routine commercial

applications for the time being.

168)WHAT IS NIST?

NIST (National Institute of Standards and Technology), the agency of

the U.S. Dept. of Commerce charged with approving standards for the U.S.

Federal Government, decided that the government needed a new cryptographic

standard for unclassified use.

169)WHAT ARE THE BACK-OFF RULES IN AES?



The bake-off rules were:

1. The algorithm must be a symmetric block cipher.

2. The full design must be public.

3.

Key lengths of 128, 192, and 256 bits must be supported.4. Both software and hardware implementations must be possible.

5. The algorithm must be public or licensed on nondiscriminatory terms.

170)WHAT IS ECB MODE?

The straightforward way to use DES to encrypt a long piece of plaintext

is to break it up into consecutive 8-byte (64-bit) blocks and encrypt them one

after another with the same key. The last piece of plaintext is padded out to 64

bits, if need be. This technique is known as ECB mode (Electronic Code Book

mode).

171)WHAT IS CYPHER BLOCK CHAINING?

In this method, each plaintext block is XORed with the previous

ciphertext block before being encrypted. Consequently, the same plaintext blockno longer maps onto the same ciphertext block, and the encryption is no longer a

big monoalphabetic substitution cipher. The first block is XORed with a randomly

chosen IV (Initialization Vector), which is transmitted (in plaintext) along with the

ciphertext.

172)WHAT IS CYPHER FEEDBACK MODE?

For byte-by-byte encryption, cipher feedback mode, using (triple)

DES is used. For AES the idea is exactly the same, only a 128-bit shift register is

used. In this figure, the state of the encryption machine is shown after bytes 0

through 9 have been encrypted and sent. When plaintext byte 10 arrives, the DES

algorithm operates on the 64-bit shift register to generate a 64-bit ciphertext.

173)WHAT IS MIDDLEWARE?



Often a layer of software on top of the operating system, called

middleware, is responsible for implementing this model.

174)WHAT IS CLIENT SERVER MODEL?

In a client server model any number of clients can get information

from the server through the network.Here the clients are connected to the server

through the network.

175)WHAT ARE TE TWO TYPES OF TRANSMISSION TECHNOLOGY?

1. Broadcast links.

2. Point-to-point links.

176)WHAT IS POINT TO POINT NETWORK?

The point-to-point networks consist of many connections between

individual pairs of machines.

177)WHAT IS UNICASTING?

Point-to-point transmission with one sender and one receiver is

sometimes called unicasting.

178)WHAT IS MULTICASTING?

Sometimes broadcast systems also support transmission to a subset of the

machines, something known as multicasting. One possible scheme is to reserve

one bit to indicate multicasting. The remaining n - 1 address bits can hold a group

number. Each machine can ''subscribe'' to any or all of the groups. When a packet

is sent to a certain group, it is delivered to all machines subscribing to that group.

179)DEFINE TRAP MESSAGE:

Trap messages are used to notify a managing entity of an exceptional

situation that has resulted in canges to MIB object values.

180)WHAT IS POLLING PROTOCAL?



The polling protocol requires one of the nodes to be designated as the

master node.The master node polls each of the nodes in a round-robin fashion.

181)WHAT ARE THE DISADVANTAGES OF POLLING PROTOCAL?

The protocol introduces a polling delay.Another drawback is more

serious,ie if the master node fails,then the entire channel becomes inoperative.

182)WHAT IS TOKEN PASSING PROTOCAL?

Here a token is passed among the nodes.The node can hold a token only if it has

some data to transmit.

183)WHAT ARE THE DISADVANTAGES OF TOKEN PASSING PROTOCAL?

Failure of one node can crash the entire channel.If a node accidentally neglects

to release the token then some recovery procedure must be done to get back that

token.

184)WHAT IS MAC ADDRESS?

The link layer address is called MAC address.It is 6bytes long.It gives 2(to the

power)48 possible MAC addresses.These MAC addresses are permanent.

185)WHAT IS DHCP SERVER DISCOVERY?

The first task of the host is to find a DHCP server to interact.This is done

using DHCP server discovery.This contains a transaction ID that allows subsequent

responses to be matched to the discovery request.

186)ADVANTAGES OF LAN?

first widely deployed high-speed LAN.

higher data rate.

comparitively cheaper.



187)WHAT ARE THE FRAMES OF ETHERNET FRAME?

This consists of 6 fields.

Preamble,destination address,source address,type field,cyclic redundancy check.

188)USE OF PREAMBLE BITS:

It has 8 bytes.Each of the first 7bytes of the preamble has a value of

10101010 ;the last byte is 10101011.The first 7bytes of the preamble serve to

“wake up” the receiving adapters.

189)DEFINE FILTERING?

Filtering is the ability of a switch to determine whether the frame shouldbe forwarded to some interface or should just be dropped.

190)DEFINE FORWARDING:

Forwarding is the ability to determine the interfaces to which a frame

should be directed,then directing the frames to those interfaces.

191)WHAT IS PACKET FRAMING?

The PPP protocol link-layer must be able to take a network-level packetand encapsulate it within the PPP link layer frame such that the receiver will be

able to identify the start and the end.

192)WHAT IS CARRIER SENSING?

A node listens to the channel before transmitting.If a frame from

another node is currently being transmitted into the channel,it waits for a random

amount of time and then again senses the channel.

193)WHAT IS COLLISION DETECTION?

A transmitting node listens to the channel while transmitting.If it detects

that another node is transmitting then it stops transmitting and uses some

protocol to find when it can start its next transmission.



194)DEFINE WEIGHTED FAIR QUEUING?

A generalized abstraction of round robin queing that has found

considerable use in QoS architectures is te so-called weighted fair queuing.

195)WHAT IS PER-HOP BEHAVIOUR?

When a DS marked packet arrives at a diffserv-capable router,the packet

is forwarded onto its next hop according to the so-called per-hop behavior.

196)WHAT IS TRAFFIC PROFILE?

The traffic profile might contain a limit on the peak rate,as well as the

burstiness of the packet flow,with the leaky bucket mechanism.

197)WHAT IS THE ROLE OF METERING FUNCTION?

The role of metering function is to compare the incoming packet flow

with the negotiated traffic profile and to determine whether a packet is within

the negotiated traffic profile.

198)WHAT ARE THE CHARACTERISTICS OF RSVP?

it provides reservation for bandwidth in multicast trees.

it is receiver oriented.

199)WHAT IS EAP?

It is expanded as extensible authentication protocol.It defines the end-to-

end message formats used in simple request/response mode of interaction

between the client and authentication server.

200)FILTERING DECISIONS ARE TYPICALLY BASED ON?

IP source or destination address.

TCP or UDP source and destination port.



ICMP message type.

connection-initialization datagrams using the TCP SYN or ACK bits.

computer netwirk 2 marks 1

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