1 Prepared By Suresh Kumar. M Assistant Professor Department of Computer Science and Engineering 219-Sri Venkateswara College of Engineering QUESTION BANK CS2363 Computer networks UNIT I PART A 1. Define and compare LAN, WAN. LAN 1.Scope of LAN is restricted to a small/ single building 2. LAN is owned by same organization 3. Data rate of LAN 10-100mbps WAN 1. scope of WAN spans over large geographical area country/ Continent 2. a part of n/w asserts are owned or not owned 3 .Data rate of WAN is Gigabyte. 2. What is circuit switching? In a circuit-switched network, a dedicated communication path is established between two stations through the nodes of the network. That path is a connected sequence of physical links between nodes. 3. What is packet switching? In a packet-switched network, it‘s not necessary to dedicate transmission capacity along a path through the network. Rather, data are sent out in a sequence of small chunks, called packets. Packet switching is mainly used in terminal-to-computer and computer-to-computer communications. 4. Define Full Duplex and simplex transmission system. With Full duplex transmission, two stations can simultaneously send and receive data from each other. This mode is known as two-way simultaneous. The signals are transmitted in only one direction. One is the sender and another is the receiver. 5. Draw the diagram of twisted pair cable? 6. Why sliding window flow control is considered to be more efficient than stop and wait flow control. In sliding window flow control, the transmission link is treated as a pipeline that may be filled with frames in transit. But with stop-and-wait flow control only one frame may be in the pipe at a time. 7. List the various frequencies of wireless transmission. Terrestrial Microwave (2GHz to 40GHz), Broadcast Radio (30MHz to 1GHz), Infrared (3 x 10 11 to 2 x 10 14 ).
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
219-Sri Venkateswara College of Engineering
QUESTION BANK
CS2363 Computer networks UNIT I
PART A
1. Define and compare LAN, WAN.
LAN
1.Scope of LAN is restricted to a
small/ single building
2. LAN is owned by same
organization
3. Data rate of LAN 10-100mbps
WAN
1. scope of WAN spans over large
geographical area country/
Continent
2. a part of n/w asserts are owned or
not owned
3 .Data rate of WAN is Gigabyte.
2. What is circuit switching?
In a circuit-switched network, a dedicated communication path is established between
two stations through the nodes of the network. That path is a connected sequence of
physical links between nodes.
3. What is packet switching?
In a packet-switched network, it‘s not necessary to dedicate transmission capacity
along a path through the network. Rather, data are sent out in a sequence of small
chunks, called packets. Packet switching is mainly used in terminal-to-computer and
computer-to-computer communications.
4. Define Full Duplex and simplex transmission system.
With Full duplex transmission, two stations can simultaneously send and receive data
from each other. This mode is known as two-way simultaneous. The signals are
transmitted in only one direction. One is the sender and another is the receiver.
5. Draw the diagram of twisted pair cable?
6. Why sliding window flow control is considered to be more efficient than stop and
wait flow control.
In sliding window flow control, the transmission link is treated as a pipeline that may
be filled with frames in transit. But with stop-and-wait flow control only one frame
may be in the pipe at a time.
7. List the various frequencies of wireless transmission.
Terrestrial Microwave (2GHz to 40GHz), Broadcast Radio (30MHz to 1GHz),
Infrared (3 x 1011
to 2 x 1014
).
2
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
8. Draw the diagram of coaxial cable?
9. Draw the diagram of optical fiber?
10. Differentiate between lost frame and damaged frame? What is the difference
between stop and wait and sliding window protocol?
Lost frame is the frame that fails to arrive at the other side. The damaged frame is a
recognizable frame does arrive, but some of the bits are in error. In stop and wait
protocol, we can send one frame at a time where as in sliding window protocol we can
send multiple frames at a time.
11. What do you mean by error control and Flow Control?
Error control refers to mechanism to detect and correct errors that occur in the
transmission of frames. Flow control is a technique for assuring that a transmitting
entity does not overwhelm a receiving entity with data.
12. Define piggybacking.
The technique of temporarily delaying outgoing acknowledgment so that they can be
hooked onto the next outgoing data frame is widely known as piggybacking.
3
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
13. What is OSI? Define HDLC.
OSI is Open Systems Interconnection and is developed by the International
Organization for Standardization (ISO). HDLC stands for High Level Data Link Control.
It has three stations, two links, and three types of data transfer.
14. What are the key elements of a protocol?
Protocol is used for communications between entities in a system and must speak the same
language. Protocol is the set of rules governing the exchange of data between 2 entities. It
defines what is communicated, how it is communicated, when it is communicated
Key elements of Protocol:
Syntax – It refers to the structure or format of data meaning the order in which they are
presented.
Semantics – It refers to the meaning of each section of bit. How to do interpretation.
Timing – When data should be sent and how fast they can be sent.
15. List the uses of a network access layer.
Exchange of data between the computer and the network
Sending computer provides address of destination
May invoke levels of service
Dependent on type of network used (LAN, packet switched etc.)
16. What are the uses of transport layer?
Reliable data exchange
Independent of network being used
Independent of application
17. What is protocol data unit (PDU)?
At each layer, protocols are used to communicate and Control information is added to
user data at each layer. Transport layer may fragment user data. Each fragment has a
transport header added and header consists of Destination SAP, Sequence number and
Error detection code.
18. What are the uses of internet layer in TCP/IP?
Systems may be attached to different networks
Routing functions across multiple networks
Implemented in end systems and routers
19. What is a layered Network Architecture?
A layer is created when a different level of abstraction occurs at protocol.
Each layer should perform a well defined function.
Function of each layer should be chosen using internationality standardized
protocols. Boundaries between should be chosen to minimize information flow
across the interfaces.
A set of layers and protocol is called network architecture. A list of protocols
used by a system is called protocol stack.
4
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
20. What is the need for layering?
It reduces the design complexity.
It decomposes the problem of building a network into more manageable
components.
It provides a modular design, if we want to add some new service, you may
only need to modify the functionality at one layer, reusing the functions
provided at all other layers
21.Compare OSI and Internet Protocol.
OSI TCP
It distinguishes between It does not distinguish between
Protocols are well hidden Protocols are not just hidden
Dejure. Standard Fit Model Defacto standard Fit protocol then
then protocol model
In transport layer only connection In Transport layer choice is for
Oriented services are available Connection oriented/connection less.
It contains 7 layers It contains 5 layers
22. How do layers of the internet model correlate to the layers of the OSI model?
OSI TCP/IP
Physical Layer Physical Layer
Data Link Layer Network Access Layer
Network Layer IP Layer
Transport Layer TCP Layer
Session Layer Application Layer
Presentation Layer
Application Layer
23. What is the use of data link layer in OSI?
Frame synchronization: Data is divided by data link layer as frames ,a
manageable unit.
Flow Control: Sending station does not overwhelm receiving station.
Error Control: Any error in bits must be detected and corrected using some
mechanism.
Addressing: Two stations in a multi point that involved in transmission must
be specified using physical address
Access Control: When two or more devices are connected to the same link,
Access control mechanism is needed to determine which device has control
over the link at any given time.
24. Why is flow control and error control duplicated in different layers?
Like the data link layer, the transport layer is responsible for flow and error control .
Flow control and error control at data link layer is node-to-node level. But at transport
layer, flow control and error control is performed end-end rather than across a single
link.
5
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
25. List the key ingredients of technology that determines nature of a LAN. List the
common topologies available for LAN.
Topology, Transmission medium and Medium access control technique are the
technology that determines nature of a LAN. Star Topology, Ring Topology Bus
Topology and Tree Topology are the topologies available for LAN.
26. What are the functions of physical layer and presentation layer?
Encoding/ decoding of signals, preamble generation/removal (for synchronization)
and Bit transmission/ reception are the functions of physical layer. Translation,
Encryption / Decryption, Authentication and Compression are the functions of
presentation layer.
27. 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).
28. 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.
29. 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.
30. 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.
31. 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
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
32. 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 modelor basis for development to which everyone has agreed.
33. For n devices in a network, what is the number of cable links
required for a Mesh and ring toplogy?
Mesh topology – n (n-1)/2, Ring topology – n
34. 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 theattached devices.
35. 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.
36. 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
37. 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.
38. 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.
7
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
39. 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.
40. What is the DC component?
Direct current is a zero-frequency signal with constant amplitude.
41. 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.
42. 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. Amplitude Time
1 0 0 0 0 0 0 0 0 0 0 1 0 0
3
Data circuit-terminating equipment is a device used as an interface between a DTE and a network.
43. 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.
44. 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.
45. What is refraction?
The phenomenon related to the bending of light when it passes from one
medium to another.
8
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
46 What is meant by Ethernet and MAC control?
Ethernet is a networking topology developed in 1970 which is governed by the IEEE
802.3 specification. MAC control field contains any protocol control information
needed for the functioning of the MAC protocol. For example, a priority level could
be indicated here.
47 What is CSMA/CD?
It is a protocol used to sense whether a medium is busy before transmission but it has
the ability to check whether a transmission has collided with another.
48 List the rules for CSMA/CD.
1. If the medium is idle, transmit; otherwise go to step 2.
2. If the medium is busy, continue to listen until the channel is idle, and then transmit
immediately.
3. If a collision detected during transmission, transmit a brief jamming signal to all
station to indicate collision has occurred and then cease transmission.
4. After transmitting a jamming signal, wait for some time, then transmit again.
49 What is preamble?
A 7-octet pattern of alternating 0s and 1s is used by the receiver to establish bit
synchronization is called as preamble.
50 When a transmitting station will insert a new token on the ring?
It will insert a new token when the station has completed transmission of its frame.
The leading edge of the transmitted frame has returned to the station.
51 What is Early Token Release (ETR)?
ETR allows a transmitting station to release a token as soon as it completes frame
transmission, whether or not the frame header has returned to the station.
52 What is Frame Status (FS)?
It contains the error detected (E), address recognized (A), and frame coped (F)
indicators. Each indicator is represented by a symbol, which is R for ―reset‖ or
―false‖ and S for ―set‖ or ―true‖.
53 Give the applications of wireless LANs.
LAN extension, cross building interconnect, nomadic access, and advantages hoc
networks.
54 What is a bridge? List the reason for using bridges in LAN.
Bridge is a hardware networking device used to connect two LANs. A bridge
operates at data link layer of the OSI layer.
Reliability, performance, security, and geography are the reason for using bridges in
LAN
9
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
55 What is No-transition?
A station of this type is either stationary or moves only within the direct
communication range of the communicating stations of a single BSS
(basic service set)
56 What are the functions of a bridge?
The function of a bridge between two LANs A and B are:
Reads all frames transmitted on A and accepts those addressed to stations on B
Using medium access control protocol for B, retransmits the frames onto B
Does the same for B-to-A traffic.
57 What is spanning tree routing?
The spanning tree approach is a mechanism in which bridges automatically develop a
routing table and update that table in response to changing topology.
58 Compare FDDI with token ring 802.5.
FDDI 802.5
No priority and reservation bits It has priority scheme by using
reservation bits.
No need of converting a token to start of
data frame by inverting token bits because
of high data rate
It converts a token to data frame
changing token frame.
A station that transmits data frames
releases a new token as soon as it
completes data.
A station that data transmissions after
releasing back its own transmission,
release the token.
59 Ethernet stipulates a minimum size of a frame. Why is it necessary?
To detect collision. To identify valid frame from garbage, valid full format
should contain 64 bytes from destination address to checksum. So if the data portion is less
than 46 bytes, pad field is used to fill out the frame to minimize size.
60 Give the format of Ethernet address.
Preamble
64
Dest addr
48
Src addr
48
Type
16
Body CRC
32
61 What is meant by the contention period of Ethernet? How many lines are
required to connect n – systems in Direct Mesh topology?
When several stations on an Ethernet have data to send, there are contention periods during
which collisions happen and no data is successfully transmitted.
n(n-1)/2 lines are required.
62 What does IEEE 10 Base 5 standard signify?
10 represents data rate 10 Mbps.
5 refers to segment length 5* 100 m that can run without repeaters
Base represents Base band communication
10
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
63 Define Repeater, Hub.
Repeaters and hubs are interconnecting devices.
Repeater: Repeaters extends the Ethernet segment and it repeats the signal. It does
not amplifies the signal.
Hub: A Hub has several point to point segments coming out. It is a multi way
repeater. It broadcasts any signal through all outgoing lines.
64 What is meant by Exponential back of algorithm?
After first collision, each station waits either 0 or 1 slot time before trying again. If 2
stations collide and each one picks same random number 0/1,. .After second collision,
each one picks either 0,1,2 or 3 slot at random and waits. If collision occurs again , then
next time the number of slots to wait is chosen at random from 0 to [23 – 1]. This
algorithm is called binary exponential ―back off algorithm‖.
65. Define a switch and a bridge. Switches are hardware or software device capable of creating temporary connections between
more devices which are not directly connected. It is a multi input/output port device. It transfers
data coming from one input port to one or more output ports. This function is called as
forwarding. Bridges are used to interconnect LANs. A bridge observes and forwards all frames
that it receives.
66.Define Spanning Tree Algorithm.
Bridge connects n/w and removes loop in the path using spanning tree algorithm It constructs
a spanning tree of edges between hosts that maintain connectivity of the graph with no loops.
It is a dynamic algorithm. The algorithm works as Frame Forwarding, Address Learning and
Loop Resolution.
67. What are different types of bridge? What are the limitations of bridges?
Simple Bridge connect 2 LAN
Multi port Bridge connect more than 2 LANs
Transparent Bridge it learns on its own about connected LANs.
limitations of bridges:Scalability and Hetrogenity
68. Mention the functions of Bridges.
1. A bridge should have enough buffer space to store the frames until it is transmitted.
2. It should be able to distinguish addresses of host on different LAN.
3. It can contain information about other bridges.
. 4. It should follow congestion control mechanisms to overcome congestion.
5. It works at layer 1 and layer 2 level.
69.Name any two network connecting devices? Can a bridge replace repeater for
interconnecting 2 segments of a n/w?
Repeater repeats the signal to the actual strength so that they can travel and works at
physical layer. Repeater operates on the physical layer level. Here collision
probability is more.
Bridge is an network connecting device. It does forwarding & filtering frames using
LAN destination address. Bridges are used to connect LAN or WAN and works at
data link layer level. Collision Probability is more.
11
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
A bridge cannot replace repeater for interconnecting 2 segments of a network because
functions of them are entirely different.
70.What are the advantages of switches? Write the frame format for FDDI.
In switches, the sending information are directly transmitted to the concern receiver.
8 8 48 48 32 8 24
Start of
Control
Dest Src
Body
CRC
End of
Status
frame addr addr
frame
71. What is Token ring? What is the use of bit stuffing?
Token ring is a set of nodes are connected together in a ring. Data flow always in a particular
direction around the ring. Bit stuffing is bit oriented protocol. It is used to detect the error
during the transmission of the stream of bits.
PART-B
1. List and discuss the various techniques available in error detection. (ReferWilliam
stallings)
2. Explain about internet architecture (ReferWilliam stallings)
3. Explain about OSI network architecture (ReferWilliam stallings)
4. Explain Sliding window flow control and stop and wait flow control in detail.(Refer
Peterson)
5. Explain about Token Ring andfiber distributed data(FDDI) interface in detail.(Refer
Peterson)
6. Explain in detail about IEEE 802.11 with example
7. Describe about link layer Flow Control. .(Refer Peterson)
8. Explain about Physical links and Channel access on links. (ReferWilliam stallings)
9. Discuss about Framing. .(Refer Peterson)
10. Describe about the layering and protocols. .(Refer Peterson)
11.Discuss the various line encoding techniques used to send analog and digital data on
digital channels. .(Refer Peterson)
12. Explain the Mesh and star topologies of the networks in detail with diagram.(Refer my
notes)
13. write short notes on transmission media. .(Refer Peterson)
14. with an example ,illustrate how CRC will calculate with an example. .(Refer my notes)
15. compare and contrast the Go-Back-N ARQ Protocol with selective repeat ARQ.
ReferWilliam stallings)
16. Explain in detail the error detection and error corrections.(ReferWilliam stallings)
17.Write in detail about Bluetooth and Wi-Fi. .(Refer Peterson)
18.Explain about learning Bridges and the spanning tree algorithm in detail. .(Refer
Peterson)
19. Explain the following: Switches and Bridges.(Refer Peterson)
12
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
UNIT – II
PART A
1. Differentiate Packet Switching and circuit Switching.
Issue Datagram subnet Circuit Switching
2. What is Virtual circuit Switching? In the virtual circuit approach, the relationship between all packets belonging to a
message or session is preserved single route is chosen between sender and receiver at the
beginning of the session. When the data are sent all packets of the transmission travel one
after another along that route Virtual circuit transmission is implemented in two formats -
PVC, SVC.
3. What is Switched virtual circuit?
Here virtual circuit is created wherever is needed and exist only for duration of the
specific exchange. It can be used with connection establishment and connection termination.
4. What are the different types of source routing approach?
Rotation, Stripping off and Using pointers are the different types of source routing approach.
5. Define Unicasting, Broadcasting and Multicasting.
Unicasting: Transmitting data from a single sender to a single receiver.
Broadcasting: Transmitting data from a single source to all the other nodes in the network
Multicasting: Transmitting data from a single source to a group of destination nodes.
6. Classify the following addresses
23.85.48.119 --------- Class A, 127.24.34.56 ------------- Class A
159.78.9.10 ------------ Class B, 195.20.10.11. ------------ Class C
220.36.123.47 ------------ Class D, 245.31.220.225------------ Class 3
7. What is IP address?
An Internet Address is made of four bytes (32 bits) that define a host‘s connection to a
network. There are currently 5 different field lengths patterns, each define a class of
addresses. These are designed to cover the needs of different types of organizations, class A,
B, C, D, E.
Class Netid Hostid
Circuit setup Not Required Required
Transmission path No Transmission path dedicated path
Delay Packet transmission delay Call setup delay
Addressing Each packet contains the full
source and destination address
Only data is sent
Bandwidth Dynamic Bandwidth Fixed Bandwidth
Routing Each packet is routed
independently
Entire data is sent through the
same path
Congestion control Difficult Easy if enough buffers can be
allocated in advance for each VC
set up
Complexity In the transport layer In the network layer
Suited for Connection-oriented and
connectionless service
Connection-oriented service
13
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
8. How many network addresses and host addresses are supported by class A, class B
networks?
Class A: Number of networks = 127
Number of hosts = 224
-1
Class B : Number of networks = 214
-1
Number of hosts = 216
– 1 = 65,535
9. Differentiate Physical Address and Logical Address.
Physical Address Logical Address
1. It is implemented by data link layer. It is implemented by n/w layer.
2. It contains 48 bits. It contains 32 bits
3. It is a local addressing system. It is an universal address system.
4. Another name MAC address. Another name IP address.
5. It is flat in nature Hierarchical in nature
6. Does not give any clue for routing Its structure gives clue for routing
10. Define Router.
A router operates as the physical, data link and network layer of the OSI model ,
A router is termed as an intelligent device. Therefore, its capabilities are much
more than those of a repeater or a bridge.
11. What does a router do when it receives a packet with a destination address that it
does not have an entry for, in its routing table?
Default Router: If IP Software is not able to find the destination, from routing table then it
sends the datagram to default router. It is useful when a site has small set of local address
connected to it and connected to the rest of the Internet.
12. Define ARP.
Associates an IP address with physical address. It is used to find the physical address of the
node when its Internet address is known. Any time a host/router needs to find the physical
address of another host on its network, it formats an ARP query packet that includes the IP
address and broadcasts it. All hosts in the network process the ARP packet but only the
required station sends back physical address.
13. Define RARP
Allows a host to discover its internet address when it knows only its physical address ( a
diskless computer). The host wishing to retrieve its internet address broadcasts an RARP
query packet that contains its physical address to every host on its physical network. A
server on the network recognizes the RARP packet and returns the host‘s internet address.
14. What do you mean by ICMP?
ICMP is an error reporting mechanism. It does not specify the action to be taken for each
possible error. The source must relate the error to an individual application program and take
other actions to correct the problem.
15. List out functions of IP.
IP services unreliable, best-effort, connectionless packet system.
Unreliable – delivery is not guaranteed
Connectionless – each pocket is treated independent from others
Best-effort delivery – it makes an earnest attempt to deliver packets.
14
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
It defines basic unit of data transfer through TCP/IP.
IP s/w performs routing function – finds a path from source to destination.
IP includes a set of rules that embody the idea of unreliable packet delivery
16. What is the use of TTL in IP header?
It lets how long that datagram is allowed to live in the network. The source sets that
time. Routers and hosts in the path of that datagram should decrement TTL and
removes it when TTL = 0 and send an error message to the source. TTL is written hops or
time in seconds.
17. What is internetworking and what are its principles?
Internet is an interconnected set of networks. From outside it looks like a simply layer
n/w. A collection of communication networks interconnected by routers is called
internetworking. The principle of inter networks are provide a link between networks and
routing for delivery of packets.
18. What are the important fields in a routing table?
Destination, Cost and Next Hop
19. What is Trace route option?
Record Route/ Trace Route: Here source creates an empty list of IP addresses and
each router on the path of the datagram adds its IP address to the list whereas a router get a
datagram that has record route option, it adds its addresses to the list. To add, it compares
pointer & length. If pointer > length, the list is full. So host forwards a datagram without
inserting its address to it. Record route is useful only if source & destination agrees.
0 8 16 24 31
Code (7) Length Pointer
First IP address
Second IP address
20. Write the difference between Distance vector routing and Link state routing.
Distance Vector Routing Link state routing
1. Basic idea is each node sends its
knowledge about the entire network to its
neighbours.
1. Basic idea is every node sends its
knowledge about its neighbours to the
entire network
2. It is dynamic routing 2. It is dynamic routing
3. RIP uses Distance vector routing 3. OSPF uses link state routing
21. List some of the unicast routing protocols. Routing Information Protocol (RIP) for IP Open Shortest Path First (OSPF)
22. To whom ICMP reports error message?
ICMP allows routers to send error messages to other router or hosts. ICMP is an error
reporting mechanism. It does not specify the action to be taken for each possible error. It is
informing the source that the error has occurred and the source has to take actions to rectify the
errors.
15
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
23. Which class IP addresses are used for multicast and unicast?
Unicast : Class A, Class B , Class C Multicast: Class D
24. What is Permanent virtual circuit ?
In this technique the same virtual circuit provided between two users on a continuous basis.
The circuit is dedicated to a specific user. No one else can use it. Because it always in place,
it can be used without connection establishment and connection termination
25. What is the use of a router?
A router is useful for interconnecting two or more heterogeneous networks that differ in
their physical characteristics such as frame size, transmission rates, topologies, addressing
etc. A router has to determine the best possible transmission path among several available
paths.
26. 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.
27. 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.
28. 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.
30. 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
Control field
Information field
31. 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.
16
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
32. 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.
33. 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.
PART B (Refer all in Peterson)
1. What do you mean by switching? Explain Virtual circuit switching techniques.
2. (i) Explain Packet switching technique in detail.
(ii) Explain in detail about source routing approach.
3. Explain about Address Resolution Protocol.
4. Explain in detail about Dynamic Host Configuration Protocol and Internet Control
Message Protocol.
5. Explain the differences between the adaptive and non adaptive routing
6. (i) Explain in detail about IP addressing.
(ii) Explain the Datagram delivery and Forwarding in Internet Protocol.
7. Explain the IP datagram format, fragmentation and reassembly.
8. Explain the Routing Information protocol/Distance vector routing in detail.
9. Explain about the OSPF and Interdomain routing (BGP)routing algorithms.
10. Describe about Queuing discipline
11. Discuss about Subnetting and CIDR.
12. Describe about Ipv6
13. Describe distance Vector Routing
14. compare The distance Vector and Link state routing Protocol
15. Discuss in detail about the OSPF routing Protocol
16. Define fragmentation and Explain Why the IPV4 and IPV6 Protocol need to fragment
some packets
17. . Discuss in detail the various aspects of IPv6
18. Write short Notes on (1.)internet Protocol (2).Routers
19. Explain in detail about Distance vector routing protocol with an example
20. Discuss the various Switching Techniques used in networks
21. For The Routing Table shown Below, what does the router do with packets addressed to
Transport layer performs multiplexing/ demultiplexing function. Multiple
applications employ same transport protocol, but use different port number. According
to lower layer n/w protocol, it does upward multiplexing or downward multiplexing.
(eg) X.25 can have 4095 VC. Multiple services can use that single VC using upward
multiplexing. (eg) X.25 can use only 3bit/7bit/15bit sequence number. So a high
speed network may need a larger sequence space. For that downward multiplexing /
splitting used to improve throughput.
2. Reliability : [ Error Control and Flow Control ]
2. How an application process running in one host is addressed by another process
through TCP?
It uses socket address (host, port).
Port represents a particular transport service in a host.
3. What are the various adaptive retransmission policy of TCP.
Simple average
Exponential / weighted average
Exponential RTT backoff
Jacobson‘s Algorithm
4. What is the wrap around time for TCP Sequence Number. What is the Wrap
around time for T3 link with 45 Mbps data rate?
Once a segment with sequence x survives in Internet, TCP cannot use the same sequence
no. How fast 32-bit sequence no space can be consumed? 32-bit sequence no is adequate
for today‘s network. Wrap Around Time for T3-45Mbps (232
x 8)
/45Mbps=763.55sec=12.73 min
5. What do you mean by congestion?
Any given node has a number of I/O ports attached to it. There are two buffers at each
port—one to accept arriving packets & another one to hold packets that are waiting to
depart. If packets arrive too fast node than to process them or faster than packets can be
cleared from the outgoing buffers, then there will be no empty buffer.
The first such strategy is to discard any incoming packet for which there is no
available buffer space. The alternative is for the node that is experiencing these
problems to exercise some sort of flow control over its neighbors so that the traffic flow
remains manageable.
6. Name the policies that can prevent congestion.
a. Additive Increase Multiplicative decrease
b. Slowstart mechanism
c. Fast retransmit and fast recovery
18
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
7. What is TINYGRAM?
1byte data + 20 byte IP header + 20 byte TCP header=41 byte => known as ‗
TINYGRAM‘overhead is more . ( - for one byte data over head is 40 byte)
8. Give the datagram format of UDP.
Source port address:- It is the address of the application program that has created the
message.
Destination port address:- It is the address of the application program that will receive
the message.
Source port
Address
16 bits
Destination port
Address
16 bits
Total Length
16 bits
Checksum
16 bits
Total Length :- It defines the total length of the user datagram in bytes.
Checksum :- It is a 16 – bit field used in error correction.
9. 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.
9. 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
11. What is the difference between network layer delivery and the
transport layer delivery?
Network layer delivery: * The network layer is responsible for the the source-to-destination delivery of packet
* The transport layer is responsible for source-to-destination delivery
of the entire message. Transport layer delivery across multiple network links. The transport layer
is responsible for source-to-destination delivery of the entire message.
19
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
12. What are the four aspects related to the reliable delivery of data?
The four aspects are, Error control, Sequence control, Loss control,
Duplication control.
13. 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.
14. 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.
15. What are the types of multiplexing?
The types of multiplexing are,
Upward multiplexing
Downward multiplexing
10. What are the two possible transport services?
Two basic types of transport services are,
Connection service
Connectionless services
16. 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.
17. What is meant by congestion?
Congestion in a network occurs if user sends data into the network at a rate greater than that allowed by network resources.
18. Why the congestion occurs in network?
Congestion occurs because the switches in a network have a limited
20
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
buffer size to store arrived packets. 19. 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.
20. What are the two categories of QoS attributes?
The two main categories are
User Oriented
Network Oriented
21. 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
22. 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)
23. 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.
24. Define Gateway.
A device used to connect two separate networks that use different
communication protocols.
25. 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.
21
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
26. What is the main difference between TCP & UDP?
TCP UDP
It provides Connection oriented service Provides connectionless service.
Connection Establishment delay will be
there
No connection establishment delay
Provides reliable service Provides unreliable, but fast service
It is used by FTP, SMTP It is used by audio, video and
multimedia applications.
27. Give some examples for situations using UDP.
It is very useful for audio or video delivery which does not need
acknowledgement. It is useful in the transmission of multimedia data.
28. How does TCP sender window size change using effective window?
Calculation of effective window: TCP on Receiver side must keep
Last Byte Received – Last Byte Read <= Max Rcv Buffer.
It advertises a window size of Advertised window = Max Rev buffer – (Last
ByteReceived – Last ByteRead )(i.e.) free space in received buffer.
TCP on sender side
Sender calculates an effective window,
Effective Window = Advertised window –(Last Byte sent – Last Byte Acknowledged)
If Effective. Window > 0 Source can send data.
29. What are the different phases in TCP state machine?
Connection Establishment, Data transfer and Connection Release
30. How check sum is calculated in TCP?
To compute checksum, UDP/TCP prepends a pseudo header to datagram.
Source IP address
Destination IP address
Zero Protocol TCP
Length
Pseudo header is not transmitted nor they included in length. To compare checksum,
Store zeroes in CHECKSUM field
Entire object (pseudo header, header , data) is divided into 16 bits.
Added & taken ones complemented.
31. What is SYN segment?
It is used to start a TCP connection and provides agreement between sender and
receiver on sequence number
32. Name the policies that can prevent congestion.
a. DEC bit.
b. Random Early Detection(RED).
c. Source based congestion avoidance.
22
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
33. How do transport services differ from the data link layer services?
The data link layer services are at node to node level. But the transport layer services are
end to end level. Both the layers are having the flow control and error control mechanisms.
The data link layer offers at node to node level. But the transport layer offers at end to end
level. Data link layer is responsible for node to node delivery of the frames while transport
layer is responsible for end to end delivery of the entire message.
34. What are the TCP services to provide reliable communication?
Error control,Flow control,Connection control and Congestion control
35. Define the DEC bit mechanism.
Each router under this mechanism monitors the load and explicitly notifies the end nodes
when congestion is going to occur. This notification is implemented by setting a binary
congestion bit which is known as DEC bit, in the header of the packet that follows to the
router. The destination host copies this DEC bit into the corresponding ACK and sends back
to source. Now source can adjust its sending rate to avoid congestion.
36.List out various congestion control and congestion avoidance techniques
congestion control: AIMD, slow start, Fast retransmit and Recovery
congestion avoidance techniques: DEC bit , RED
37. What is a bus topology?
Bus topology uses a multipoint medium and all stations are attached through
appropriate hardware interfacing known as a tap. A full duplex operation is used for
transmission and reception of data in a bus.
38. What is tree topology?
Tree topology is generalization of bus topology. Transmission medium is a branching
cable with no closed loops. It begins at a point known as headend, where one or more
cables start, and each of these may have branches.
39. What is ring topology?
In the ring topology, the network consists of a set of repeaters joined by point-to-
point links in a closed loop. The repeater is a device which receives data in one link
and transmits them in other link.
40. What is star topology? List the advantages of it.
In star topology, each station is directly connected to a common central node. Central
node is referred as star coupler which uses two point-to-point links, one for transmission
in each direction. Its advantages are scalable and easy to identify the fault.
41. What is ARQ? What are the two types of error in flow control and error control?
Automatic Repeat Request is used to retransmit the information automatically when
the packet is lost while transmit. The two types of error in flow control and error control are
single bit error and burst error.
23
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
42. What is peer to peer process?
Communication between peer to peer process, a protocol defines a communication
service that it exports locally, along with a set of rules governing the messages that
the protocol to implement this service.
PART B [Refer only in Peterson]
1. Write short notes on (i) TCP segment format.(ii) Wrap around time.
iii) silly window syndrome.
2. Explain TCP sliding window algorithm for flow control.
3. (i) Explain DECbit mechanism in detail. (8)
(ii)Explain the slow start mechanism. (8)
4. Describe about congestion control algorithms in detail
5. Discuss about congestion avoidance algorithm in detail.
6. Explain Adaptive retransmission policy in detail.
7. Explain the real transport protocol of UDP and how will you calculate checksum in
UDP? What is the significance of Pseudo Header in UDP?
8. Explain the TCP Connection establishment and termination using Timeline diagram.
9. Explain TCP state Transition diagram.
10. Explain the significance of Clark‘s solution and Nagle‘s algorithm
11. Explain connection establishment and connection closing in TCP.
12. What is PUSH mechanism? Explain CODE BITS in TCP header.
13. Explain the working of TCP using The state Diagram
14. Explain adaptive flow control in detail and its uses
15. How the connection is established using three-way handshaking, explain in detail
16. Discuss briefly about the techniques used to improve Qos
24
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
UNIT – IV
PART A
1.lossless compression
Ensures that the data recovered from the compression/decompression process
is exactly the same as the original data. A lossless compression algorithm is used to
compress file data, such as executable code, text files, and numeric data, because programs
that process such file data cannot tolerate mistakes in the data.
2. lossy compression
does not promise that the data received is exactly the same as the data
sent. This is because a lossy algorithm removes information that it cannot later restore.
Hopefully, however, the lost information will not be missed by the receiver. Lossy algorithms
are used to compress still images, video, and audio.
3. Delta encoding,
simply encodes a symbol
as the difference from the previous one. Thus, for example, AAABBCDDDD would
be represented as A001011000. Note that delta encoding is likely to work well for
encoding images where adjacent pixels are similar. It is also possible to perform RLE
after delta encoding, since we might find long strings of 0s if there are many similar
symbols next to each other.
4. Block Diagram for JPEG Compression
5. DCT phase
In jpeg compression,The first phase applies the discrete cosine transform (DCT) to the block.
If the image is a signal in the spatial domain, then DCT transforms this signal
into an equivalent signal in the spatial frequency domain. This is a lossless operation
but a necessary precursor to the next, lossy step. It takes
an 8 × 8 matrix of pixel values as input and outputs an 8 × 8 matrix of frequency
coefficients.
6.Quantization phase:
It is the second phase of JPEG compression where the insignificant bits of the frequency
coefficients obtained from DCT phase are dropped. This phase is lossy.
7.Encoding phase:
This is the final phase of JPEG compression where the quantized frequency coefficients are
encoded in a compact form. This results in additional compression, but this compression is
lossless.
25
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
8.Data compression:
The goal of data compression,
is to remove as much redundancy from the data as possible,
so that we may encode it in as few bits as possible. There is a requirement that the sending
and receiving hosts to process every byte of data in the
message
9. Authentication means verifying the identity of the remote Participant.
10.Digital signature:
A digital signature is a special case of a message integrity code, where the code can have
been generated only by one participant.eg. RSA signature, where, a given participant
is the only one that knows its own private key, the participant uses this key to produce
the signature
11.Public and Private key:
Any of several encryption algorithms (e.g., RSA), in which
each participant has a private key (shared with no one else) and a public key (available
to everyone). A secure message is sent to a user by encrypting the data with that user‘s
public key; possession of the private key is required to decrypt the message, and so
only the receiver can read it.
12. Cryptographic hash functions
typically don‘t involve the use of keys. Instead, the idea is to map a potentially large
message into a small fixed-length number, analogous to the way a regular hash function
maps values from a large space into values from a small space.
13.Define PKI.
Public Key Infrastructure(PKI), is a complete scheme for certifying binding between
public key and identities. PKI starts with ability to verify the identities and bind them to keys
OUT-of-Band.(range something ouside the n/w).
14. Define X.509 authentication.
One of the major standard for certicates is known as X.509.It includes
a) Identity of the entity being certified
b) Public key of the entity being certified
c) Identity of the signer
d) Digital signature
e) Dig Sig Algorithm identifier
f) Timer Expiration(optional)
15.Define CA.
Certification Authority(CA) is an entity claim to be trust worthy for verifying identities
and issuing public key certificates. They are classified as Commercial CA, Govermental
CA and Even Free CA. You must use own keys if CA is used. It is also known as Self
certifying certificates.
17.Define Nonce.
Nonce is the random number which is used only once in the message.
26
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
18. Define PGP.
Pretty good Privacy(PGP) is the widely used approach to provide security for Email.
It provides authentication, confidentiality, data integrity and Non-repudiation.
19. Define Handshake protocol in security.
A pair of of TLS participants negotiate at run time which cryptography to use.
The participants negotiate the choice of
a) data integrity Hash, MD5 or SHA used to implement HMAC.
b) Symmetric key cipher for confidentiality among the possibilities are DES, AES ,
3DES
c) Session key establishment approach .
20. Define Record Protocol.
With in session establish by the handshake protocol TLS record protocols add
confidentialty and integrity to the underline transport services. Messages handed down from
the application layer are
a) Fragmented or coalesced into blocks of convenient size.
b) Optionally compressed
c) Integrity protected using Hmac.
d) Encrypted using a symmetric key cipher.
e) Past to the transport layer for transmission.
21.Define Firewalls.
A firewall is a system that is a sole point of connectivity between the sited it protects and
the rest of the network.
22. Define Demilitarized Zone(DMZ).
DMZ is used to hold services such as DNS and Email server that need to be accessible to
the outside.
22. Define Packet filter.
It filter the packet from third person using firewall mechanism, but it will not detect the
state of the packet where it arrive.
Part B.
1.Explain in detail about Video Compression.(Refer in Peterson)
2. Explain in detail about Image Compression.(Refer in Peterson)
3.Explain in detail about Audio Compression.(Refer in Peterson)
4.Explain in detail about PGP.(Refer in William stallings)
5. Explain in detail about TLS and IP security. .(Refer in Peterson)
6. Discuss in Detail about Firewalls. .(Refer in William stallings)
7.Disucuss in detail about Kerberos. .(Refer in Peterson)
8. Explain in detail about key predistribution. .(Refer in Peterson)
9.Explain in detail abot Diffie-Hellmann Algorithm.(Refer in Peterson)
10.Explain in detail about modes of operation in security.(Refer in William stallings)
27
Prepared By Suresh Kumar. M Assistant Professor
Department of Computer Science and Engineering
UNIT – V
PART A
1. List the capabilities provided by the SIP (Session Intimation Protocol).
User location
User availability
User capabilities
Session setup
Session management
2. What is the Domain Name System responsible for?
The Domain Name System converts domain names (of the form www.vtubooks.com)
into IP numbers.
3. Why do we need a Domain Name System? What role does the DNS Resolver play
in the DNS system?
IP numbers uniquely identify hosts on the Internet: however they are difficult to remember.
We therefore need a memorable way of identifying hosts. A DNS Resolver is responsible for
making requests of the local DNS server in behalf of clients.
4. How does a DNS Resolver bootstrap the Domain Name Lookup process?
A DNS Resolver must know the IP address of at least one DNS server. It uses this
address to start the DNS Lookup process.
5. What are the four main properties of HTTP?
Global Uniform Resource Identifier.
Request-response exchange.
Statelessness.
Resource metadata.
6. What are the four groups of HTTP Headers?
The four groups of HTTP headers are General headers, Entity Headers, Request
Headers and Response Headers.
7. What is WWW and SMTP?
The SMTP is used for connection between sending mail. WWW is an internet
application that allows user to view pages and move from one web page to another.
8. What do you mean by active web pages?
When a client send a HTTP request for an active Web page, the Web server sends back an
HTTP response that contains an HTML page as usual. HTML page also contains a small
program that executes on the client computer inside the Web browser.
9. What are the transmission modes of FTP?
i. Stream mode: Default mode and data is delivered from FTP to TCP as a continuous
stream of data.
ii. Block mode: Data is delivered from FTP to TCP in terms of blocks. Each data block