Computer network-CS52
UNIT – I
DATA COMMUNICATION
PART A
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. 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,
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.
3. What are the three fundamental characteristics determine the
effectiveness of 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.
4. 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.
5. 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.
6. 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 to which everyone has agreed.
7. 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)/2
Ring topology
– n
8. 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.
9. 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.
10. 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=15
Number of
ports per device=n-1=6-1=5
11. 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.
12. 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.
13. 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.
14. What is the DC component?
Direct current is a zero-frequency signal with constant amplitude.
15. How does NRZ-L differ from NRZ-I?
In the NRZ-L sequence, positive and negative voltages have specific
meanings: positive for 0 and negative for 1. in the NRZ-I sequence, the
voltages are meaningless. Instead, the receiver looks for changes from one
level to another as its basis for recognition of 1s.
16. Using HDB3, encode the bit stream 10000000000100. Assume the number of
1s so far is odd and the first 1 is positive.
17. What are the functions of a DTE? What are the functions of a DCE?
Data terminal equipment is a device that is an information source or an
information
sink. It is connected to a network through a DCE. Data circuit-terminating
equipment is a device used as an interface between a DTE
and a
network.
18. What does the electrical specification of EIA-232 describe?
The electrical specification of EIA-232 defines that signals other than
data must be sent using OFF as less than -3 volts and ON as greater than +3
volts. The data must be transmitted using NRZ-L encoding.
19. Discuss the mode for propagating light along optical channels.
There are two modes for propagating light along optical channels,
multimode and single mode.
Multimode: Multiple
beams from a light source move through the core in different paths.
Single mode: Fiber with extremely small diameter that limits beams to a few angles, resulting
in an almost horizontal beam.
20. What is refraction?
The phenomenon related to the bending of light when it passes from one
medium to another.
21.How are the guided media differing from unguided transmission media?
Guided transmission media Unguided transmission media
1.Guided
indicate, medium is contained 1.Unguided
medium does not
have any
within physical boundary Physical boundary
2.Transmission
takes place through wire. 2.It is a
wireless transmission.
Amplitude
Time
1 0 0 0 0 0
0 0 0 0 0 1 0 0
22. What are the disadvantages of optical fiber as a transmission medium?
The disadvantages of optical fiber are
- Very expensive.
- Installation and maintenance is difficult.
- Fragility.
23. What are the criteria used to evaluate transmission medium?
The criteria used to evaluate transmission medium are
- Throughput
- Propagation speed
- Propagation time
- Wavelength
24. Give the relationship between propagation speed and propagation time?
Propagation time = distance / propagation speed The time required for a
signal or a bit to travel from one point to another is called Propagation time.
Propagation speed is the distance, a signal or a bit travel through a
medium in
one second.
25.Explain cross talk and what is needed to reduce it?
Effect of one wire on another is called as cross talk. One wire will be
the sending
antenna and the other wire will be the receiving antenna. We can use the
shielded twisted pair cable or coaxial cable for transmission, which contains metal
foil to reduce cross talk.
UNIT-II
DATA LINK LAYER
1.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 errors
a)
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 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 be
b) 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 steps
a) 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 steps
a) 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 correction
b) 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. 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.
19. What is a buffer?
Each receiving device has a block of memory called a buffer, reserved for
storing
incoming data until they are processed.
20. 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.
21. 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.
22. Mention the advantage and disadvantage of stop and wait flow control.
Advantage:
simplicity
Disadvantage:
inefficiency.
23. 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
frame
b) Lost
frame
c) Lost
acknowledgment.
24. Mention the functionof 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.
25. 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.
26. 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 midpoint
links.
27. List the types of stations is HDLC.
HDLC differentiates between 3 types of stations.
a) Primary
b) Secondary
c) Combined
28. Define configuration.
The bond
configuration refers to the relationship of hardware devices on a link.
29. List the various ways of station configuration.
The stations
are configured in 3 ways
a)
Unbalanced configuration
b)
Symmetrical configuration
c) Balanced
configuration
30. 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)
31. 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)
32. 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 layer
and error
controls.
U frames –
reserved for systems management.
33. Write the types of frame fields contained in HDLC.
Each frame
in HDLC may contain up to 6 fields.
a) Beginning
flag field
b) An address
field
c) A control
field
d) An
information field
e) A frame
check sequence (FCS) field
f) An ending
flag field.
34. What is meant by bit stuffing?
Bit stuffing is the process of adding one extra 0 whenever there are 5
consecutive in the data so that the receiver doesn’t mistake the data for a
flag.
35. 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.
36. Mention the various architecture in a LAN.
LAN is
dominated by 4 architectures.
a) Ethernet
b) Token bus
c) Token
ring
d) Fiber
distributed data interface (FDDI)
37. Define a standard 802.3
IEEE 802.3 supports a LAN standard originally developed by Xerox and later
extended by a joint venture between digital equipment corporations. Intel
Corporation and Xerox. This was called ‘Ethernet’.
38. 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
39. Mention the different kinds of Ethernet networks.
a) Switched
Ethernet
b) Fast
Ethernet
c) Gigabit
Ethernet
40. Write short notes on 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 ring access method used here is
token passing.
41. 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: The combined station is one which acts either as a primary or a Secondary,
depending upon the nature and direction of the transmission.
Combined
station sends both commands and responses.
42. 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 data frame and an ACK frame can be combined into just one frame
43. Name the four types of S-frames?
The four
types of S-frames are
Receive
ready(RR).The value of the code sub field is 00
Receive not
ready(RNR). The value of the code sub field is 10
Reject(REJ).
The value of the code sub field is 01
Selective
reject(SREJ). The value of the code sub field is 11
44. Name the five categories of U-frames?
The five
categories of U-frames are
- Mode setting
- Unnumbered exchange
- Disconnection.
- Initialization mode.
- Miscellaneous mode
UNIT III
NETWORK 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 – the logical address, control information, and data. These
functions are handled by the IEEE 802.2 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 four
fields.
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.
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 treats it 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,
Adaptive routing
Non-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, 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.
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 are
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 state of the link.
21. How the routers get the information about neighbor?
A router gets its information about its neighbors by periodically sending
them a short greeting packets. If the neighborhood responds to the greeting as
expected, it is assumed to be alive and functioning. If it dose not, a change
is assumed to have occurred and the sending router then alerts the rest of the
network in its next LSP.
22. What are the four internetworking devices?
The four
internetworking devices are,
Repeaters
Bridges
Routers
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.
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.
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.
UNIT IV
TRANSPORT LAYER
1. What is function of transport layer?
The protocol in the transport layer takes care in the delivery of data
from one application program on one device to an application program on another
device. They act as a link between the upper layer protocols and the services provided
by the lower layer.
2. What are the duties of the transport layer?
The services
provided by the transport layer
End-to- end
delivery
Addressing
Reliable
delivery
Flow control
Multiplexing
3. What is the difference between network layer delivery and the transport
layer delivery?
Network layer delivery Transport layer delivery
The network
layer is responsible for
the the
source-to-destination
delivery of
packet
across
multiple network links.
The
transport layer is responsible for
source-to-destination
delivery of the
entire
message.
4. What are the four aspects related to the reliable delivery of data?
The four
aspects are,
Error
control
Sequence
control
Loss control
Duplication
control
5. What is meant by segment?
At the sending and receiving end of the transmission, TCP divides long
transmissions
into 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 network layer datagram or data link layer frame to handle, the
transport protocol divides it into smaller 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 fit together into a single datagram or frame, the transport protocol combines
them into a single data unit. The combining process is called concatenation.
8. What are the types of multiplexing?
The types of multiplexing are,
Upward multiplexing
Downward multiplexing
9. What are the two possible transport services?
Two basic types of transport services are,
Connection service
Connectionless 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 two
end ports. A connection is a single logical path between the source and destination
that is associated with all packets in a message. Creating a connection involves
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 multiplexing
Time-division multiplexing
Wave-division multiplexing
12. What is meant by congestion?
Congestion in a network occur if user send data into the network at a rate
greater than that 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 store arrived packets.
14. How will the congestion be avoided?
The
congestion may be avoided by two bits
BECN - Backward Explicit Congestion Notification
FECN - 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
to this 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 sender
and receiver are communicating with each other and are using some types of flow
control at 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 the connection. For each connection, the user can request a
particular attribute each service class is associated with a set of attributes.
18. What are the two categories of QoS attributes?
The two main
categories are
User Oriented
Network Oriented
19. List out the user related attributes?
User related
attributes are
SCR – Sustainable Cell Rate
PCR – Peak Cell Rate
MCR- Minimum Cell Rate
CVDT – 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
dedicated to each sending device.
22. What is interleaving?
The switch moves from device to device at a constant rate and fixed order.
This process is called interleaving.
23. What is framing bits?
One or more synchronization bits are usually added to the beginning of each
frame. These bitts are called framing bits.
24. What is the difference between service point address, logical address
and physical address? Service point addressing Logical addressing Physical
addressing
The 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, the data link layer adds the which makes a
data delivery from a specific process on one 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 defines
the source machine’s address and the destination machine’s address.
UNIT – V
APPLICATION LAYER
1. What is the purpose of Domain Name System?
Domain Name
System can map a name to an address and conversely an address to name.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. 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
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.
8. 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.
9. Give the format of HTTP request message.
10. Give the format of HTTP response message.
Status Line
Headers
A Blank Line
Body
(present
only in
some
messages)
Request Line
Headers
A Blank Line
Body
(present
only in
some
messages)
11. 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.
12. 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, embedded
graphics and hypertext links.
13. Define CGI.
CGI is a
standard for communication between HTTP servers and executable
programs. It
is used in crating dynamic documents.
14. 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 from a
specific sender.
15. How is a secret key different from public key?
In secret
key, the same key is used by both parties. The sender uses this key and an
encryption algorithm to encrypt data; the receiver uses the same key and the corresponding
decryption algorithm to decrypt the data.
In public
key, there are two keys: a private key and a public key. The private key is
kept by the receiver. The public key is announced to the public.
16. What is a digital signature?
Digital
signature is a method to authenticate the sender of a message. It is similar to
that of signing transactions documents when you do business with a bank. In network
transactions, you can create an equivalent of an electronic or digital
signature by the way you send data.
17. What are the advantages & disadvantages of public key encryption?
Advantages:
a) Remove
the restriction of a shared secret key between two entities. Here each entity
can create a pair of keys, keep the private one, and publicly distribute the other
one.
b) The no.
of keys needed is reduced tremendously. For one million users to
communicate,
only two million keys are needed.
Disadvantage:
If you use
large numbers the method to be effective. Calculating the cipher text using the
long keys takes a lot of time. So it is not recommended for large amounts of
text.
18. What are the advantages &
disadvantages of secret key encryption?
Advantage:
Secret Key
algorithms are efficient: it takes less time to encrypt a message. The reason
is that the key is usually smaller. So it is used to encrypt or decrypt long messages.
Disadvantages:
a) Each pair
of users must have a secret key. If N people in world want to use this method,
there needs to be N (N-1)/2 secret keys. For one million people to communicate,
a half-billion secret keys are needed.
b) The
distribution of the keys between two parties can be difficult.
19. Define permutation.
Permutation
is transposition in bit level.
Straight permutation: The no. of bits in the input and output are preserved.
Compressed permutation: The no. of bits is reduced (some of the bits are dropped).
Expanded permutation: The no. of bits is increased (some bits are repeated).
20. Define substitutional &
transpositional encryption.
Substitutional: A character level encryption in which each character is replaced by another
character in the set.
Transpositional: A Character level encryption in which the characters retain their plaintext
but the position of the character changes.
No comments:
Post a Comment