614_Computer Networks

1. 1. What is computer Network? Give the classification and goals of computer network.
Computer Networks:
The old model of a single computer serving all of the organization’s computational needs has
been replaced by one in which a large number of separate but interconnected computers do the
job. These systems are called computer networks.
Types of networks:
I. Personal Area Network (PAN)
II. Local Area Network (LAN)
III. Metropolitan Area Network (MAN)
IV. Wide Area Network (WAN)
Goals of Computer Network:
I. The main goal of networking is "Resource sharing", and it is to make all programs,
data and equipment available to anyone on the network without the regard to the
physical location of the resource and the user.
II. A second goal is to provide high reliability by having alternative sources of supply. For
example, all files could be replicated on two or three machines, so if one of them is
unavailable, the other copies could be available.
III. Another goal is saving money. Small computers have a much better price/ performance
ratio than larger ones. Mainframes are roughly a factor of ten times faster than the
fastest single chip microprocessors, but they cost thousand times more. This imbalance
has caused many system designers to build systems consisting of powerful personal
computers, one per user, with data kept on one or more shared file server machines.
This goal leads to networks with many computers located in the same building. Such a
network is called a LAN (local area network).
IV. Another closely related goal is to increase the systems performance as the work load
increases by just adding more processors. With central mainframes, when the system is
full, it must be replaced by a larger one, usually at great expense and with even greater
disruption to the users.
V. Computer networks provide a powerful communication medium. A file that was
updated/ modified on a network can be seen by the other users on the network
immediately.
2. What is point- to- Point subnet? Draw the possible topologies for point- to- Point
subnet.
On point to point links we actually do not need special broadcast address of that subnet because
there’s only one way you can send a packet across point to point link. All we have is the IP
address on the other side of the link. We know that if we want to send broadcast it will go there no
matter that address is separate broadcast address or any other address. There cannot be more
destination than one and the router will then know that broadcast will be directed on the same link
as the normal unicast for the link destination address.
Router OS (Cisco IOS in this case) will try to be sure that you will use this kind of subneting only
for Point-to-point links.

2. Fig.: point- to- point subnet.
3. Write the principles for designing the layered architecture of a network.
Principles of layered architectures
• The basic principle of Layered Architectures is layer independence – A layer hides
implementation details from other layers – the functions it realizes are encapsulated and
only the service it provides is visible (but not the details of how it is realized)
• Adjacent layers communicate (interact) through an interface (service interface) – A layer
provides a service to the upper layer through a (service) interface
• A layer uses the service provided by the layer below to perform its own functions, thus
adding value to the service it provides to the layer above
4. Write short note on: NSFNET, ARPANET, and Internet.

3. NSFNET: A wide-area network developed under the auspices of the National Science
Foundation (NSF). NSFnet replaced ARPANET as the main government network linking
universities and research facilities. In 1995, however, the NSF dismantled NSFnet and replaced
it with a commercial Internet backbone. At the same time, the NSF implemented a new
backbone called very high-speed Backbone Network Service (vBNS), which serves as a testing
ground for the next generation of Internet technologies.
ARPANET was the network that became the basis for the Internet. Based on a concept first
published in 1967, ARPANET was developed under the direction of the U.S. Advanced
Research Projects Agency (ARPA). In 1969, the idea became a modest reality with the
interconnection of four university computers.
ARPANET was the network that became the basis for the Internet. Based on a concept first
published in 1967, ARPANET was developed under the direction of the U.S. Advanced
Research Projects Agency (ARPA). In 1969, the idea became a modest reality with the
interconnection of four university computers. The initial purpose was to communicate with and
share computer resources among mainly scientific users at the connected institutions.
ARPANET took advantage of the new idea of sending information in small units called packets
that could be routed on different paths and reconstructed at their destination. The development
of the TCP/IP protocols in the 1970s made it possible to expand the size of the network, which
now had become a network of networks, in an orderly way.
INTERNET: A means of connecting a computer to any other computer anywhere in the
world via dedicated routers and servers. When two computers are connected over the Internet,
they can send and receive all kinds of information such as text, graphics, voice, video,
and computer programs.
No one owns Internet, although several organizations the world over collaborate in its
functioning and development. The high-speed, fiber-optic cables (called backbones) through
which the bulk of the Internet data travels are owned by telephone companies in their
respective countries.
The Internet grew out of the Advanced Research Projects Agency's Wide Area Network (then
called ARPANET) established by the US Department Of Defense in 1960s for collaboration in
military research among business and government laboratories. Later universities and other
US institutions connected to it. This resulted in ARPANET growing beyond
everyone's expectations and acquiring the name 'Internet.'
The development of hypertext based technology (called World Wide web, WWW, or just
the Web) provided means of displaying text, graphics, and animations, and
easy search and navigation tools that triggered Internet's explosive worldwide growth.
5. Define layer, protocol, interfaces. Show how communication is provided to the top
layer in the layer based network?
Layers: To reduce their design complexity, most networks are organized as a stack of layers or
levels, each one built upon the one below it. The number of layers, the name of each layer, the
contents of each layer, and the function of each layer differ from network to network. The
purpose of each layer is to offer certain services to the higher layers while shielding those
layers from the details of how the offered services are actually implemented. In a sense, each
layer is a kind of virtual machine, offering certain services to the layer above it.

4. Protocol: a protocol is an agreement between the communicating parties on how
communication is to proceed. In another word, Protocol is set of some rules and regulations
that govern data communication over network.
Interface: Between each pair of adjacent layers is an interface. The interface defines which
primitive operations and services the lower layer makes available to the upper one. When
network designers decide how many layers to include in a network and what each one should
do, one of the most important considerations is defining clean interfaces between the layers.
Doing so, in turn, requires that each layer perform a specific collection of well-understood
functions.
A five-layer network is illustrated in Fig. 1-13. The entities comprising the corresponding layers
on different machines are called peers. The peers may be software processes, hardware
devices, or even human beings. In other words, it is the peers that communicate by using the
protocol to talk to each other.
In reality, no data are directly transferred from layer n on one machine to layer n on another
machine. Instead, each layer passes data and control information to the layer immediately
below it, until the lowest layer is reached. Below layer 1 is the physical medium through
which actual communication occurs. In Fig. 1-13, virtual communication is shown by dotted
lines and physical communication by solid lines.
6. Define connection oriented and connectionless networks. Explain how packets are sent
in a simple client server interaction on connection oriented network?
 Connection-oriented Requires a session connection (analogous to
a phone call) be established before any data can be sent. This
method is often called a "reliable" network service. It can guarantee

5. that data will arrive in the same order. Connection-oriented services
set up virtual links between end systems through a network, as
shown in Figure 1. Note that the packet on the left is assigned the
virtual circuit number 01. As it moves through the network, routers
quickly send it through virtual circuit 01.
 Connectionless Does not require a session connection between
sender and receiver. The sender simply starts sending packets (called
datagram’s) to the destination. This service does not have the
reliability of the connection-oriented method, but it is useful for
periodic burst transfers. Neither system must maintain state
information for the systems that they send transmission to or receive
transmission from. A connectionless network provides minimal
services.
7. Name and define services of data link layer. Show the environment of data link layer.
Explain how data link layer work in Internet with diagram.

6. Services
 Encapsulation of network layer data packets into frames
 Frame synchronization
 Logical link control (LLC) sub layer:
 Error control (automatic repeat request, ARQ), in addition to ARQ provided by
some transport-layer protocols, to forward error correction (FEC) techniques provided on
the physical, and to error-detection and packet canceling provided at all layers, including
the network layer. Data-link-layer error control (i.e. retransmission of erroneous packets) is
provided in wireless networks and V.42 telephone network modems, but not in LAN
protocols such as Ethernet, since bit errors are so uncommon in short wires. In that case,
only error detection and canceling of erroneous packets are provided.
 Flow control, in addition to the one provided on the transport layer. Data-link-layer error
control is not used in LAN protocols such as Ethernet, but in modems and wireless
networks.
 Media access control (MAC) sub layer:
 Multiple access protocols for channel-access control, for example CSMA/CD protocols
for collision detection and re-transmission in Ethernet bus networks and hub networks, or
the CSMA/CA protocol for collision avoidance in wireless networks.
 Physical addressing (MAC addressing)
 LAN switching (packet switching), including MAC filtering, Spanning Tree Protocol (STP)
and Shortest Path Bridging (SPB)
 Data packet queuing or scheduling
 Store-and-forward switching or cut-through switching
 Quality of Service (QoS) control
 Virtual LANs (VLAN)

7. Fig.: Internal Environment of Data Link Layer
Fig.: The Data Link Layer in the Internet
8. Name and define key assumptions for dynamic channel allocation protocol. Define
CSMA/ CD protocol with algorithm.

9. 9. What is error control? Error correction and detection using hamming code (odd/ even
parity for the given code).
Error control (automatic repeat request, ARQ), in addition to ARQ provided by some transport-
layer protocols, to forward error correction (FEC) techniques provided on the physical, and to
error-detection and packet canceling provided at all layers, including the network layer. Data-
link-layer error control (i.e. retransmission of erroneous packets) is provided in wireless
networks and V.42 telephone network modems, but not in LAN protocols such as Ethernet,
since bit errors are so uncommon in short wires. In that case, only error detection and canceling
of erroneous packets are provided.
10. Name and define the fields of Ethernet frame format.
A data packet on the wire and the frame as its payload consist of binary data. Data on Ethernet
is transmitted with most-significant octet (byte) first; within each octet, however, the least-
significant bit is transmitted first, except for the frame check sequence (FCS).
The internal structure of an Ethernet frame is specified in IEEE 802.3-2012.[1]
The table below
shows the complete Ethernet frame, as transmitted, for the payload size up to the MTU of 1500
octets. Some implementations of Gigabit Ethernet (and higher speed Ethernets) support larger
frames, known as jumbo frames.

10. 11. Draw a typical ADSL arrangement and explain the function of its.
12. What is Bluetooth technology? Define the goals of Bluetooth. Explain the Bluetooth
architecture. Name five Bluetooth profiles. Define different types of multiplexing.
13. Define the characteristics/ properties of twisted pair and coaxial cables with diagrams.
One of the oldest and still most common transmission media is twisted pair. A twisted pair
consists of two insulated copper wires, typically about 1 mm thick.
Cat 5 replaced earlier Category 3 cables with a similar cable that uses the same connector, but
has more twists per meter. More twists result in less crosstalk and a better-quality signal over
longer distances, making the cables more suitable for high-speed computer communication,
especially 100-Mbps and 1-Gbps Ethernet LANs.
Twisted-pair cabling comes in several varieties. The garden variety deployed in many office
buildings is called Category 5 cabling, or ‘‘Cat 5.’’ A category 5 twisted pair consists of two
insulated wires gently twisted together. Four such pairs are typically grouped in a plastic sheath
to protect the wires and keep them together. This arrangement is shown in Fig. (b).
(a) Category 3 UTP.
(b) Category 5 UTP.

11. 14. What are the major components of an optical system? Write the working principles of
fiber optic.
i. Compact Light Source
ii. Low loss Optical Fiber
iii. Photo Detector
Compact Light Source
Laser Diodes
Depending on the applications like local area networks and the long haul communication systems,
the light source requirements vary. The requirements of the sources include power, speed, spectral
line width, noise, ruggedness, cost, temperature, and so on. Two components are used as light
sources: light emitting diodes (LED’s) and laser diodes.
The light emitting diodes are used for short distances and low data rate applications due to their
low bandwidth and power capabilities.
Low Loss Optical Fiber
Optical fiber is a cable, which is also known as cylindrical dielectric waveguide made of low loss
material. An optical fiber also considers the parameters like the environment in which it is

12. operating, the tensile strength, durability and rigidity. The Fiber optic cable is made of high quality
extruded glass (si) or plastic, and it is flexible. The diameter of the fiber optic cable is in between
0.25 to 0.5mm (slightly thicker than a human hair).
 The purpose of photo detectors is to convert the light signal back to an electrical signal.
Two types of photo detectors are mainly used for optical receiver in optical communication
system: PN photo diode and avalanche photo diode. Depending on the application’s
wavelengths, the material composition of these devices vary. These materials include
silicon, germanium, InGaAs, etc.
Fig.: How fiber optic works

13. (a) Three examples of a light ray from inside a silica fiber impinging on the air/silica
boundary at different angles.
(b) Light trapped by total internal reflection.
(a) Side view of a single fiber.
(b) End view of a sheath with three fibers.
15. Define cabling and cable topologies for Ethernet.

14. Network Topology
Computers in a network have to be connected in some logical manner. The layout pattern of the
interconnections between computers in a network is called network topology. You can think of
topology as the virtual shape or structure of the network. Network topology is also referred to as
'network architecture.'
Devices on the network are referred to as 'nodes.' The most common nodes are computers and
peripheral devices. Network topology is illustrated by showing these nodes and their connections
using cables. There are a number of different types of network topologies, including point-to-point,
bus, star, ring, mesh, tree and hybrid. Let's review these main types.
Point-to-Point
Point-to-point topology is the simplest of all the network topologies. The network consists of a
direct link between two computers. This is faster and more reliable than other types of connections
since there is a direct connection. The disadvantage is that it can only be used for small areas
where computers are in close proximity.
Bus
Bus topology uses one main cable to which all nodes are directly connected. The main cable acts
as a backbone for the network. One of the computers in the network typically acts as the computer
server. The first advantage of bus topology is that it is easy to connect a computer or peripheral
device. The second advantage is that the cable requirements are relatively small, resulting in lower
cost.
One of the disadvantages is that if the main cable breaks, the entire network goes down. This type
of network is also difficult to troubleshoot. For these reasons, this type of topology is not used for
large networks, such as those covering an entire building.

15. Star
In star topology, each computer is connected to a central hub using a point-to-point connection.
The central hub can be a computer server that manages the network, or it can be a much simpler
device that only makes the connections between computers over the network possible.
Star topology is very popular because the startup costs are low. It is also easy to add new nodes to
the network. The network is robust in the sense that if one connection between a computer and the
hub fails, the other connections remain intact. If the central hub fails, however, the entire network
goes down. It also requires more cable than bus topology and is, therefore, more expensive.
Ring
In ring topology, the computers in the network are connected in a circular fashion, and the data
travels in one direction. Each computer is directly connected to the next computer, forming a single
pathway for signals through the network. This type of network is easy to install and manage.
If there's a problem in the network, it is easy to pinpoint which connection is defective. It is also
good for handling high-volume traffic over long distances since every computer can act as a
booster of the signal. On the downside, adding computers to this type of network is more
cumbersome, and if one single computer fails, the entire network goes down.
Mesh
In mesh topology, every node has a direct point-to-point connection to every other node. Because
all connections are direct, the network can handle very high-volume traffic. It is also robust
because if one connection fails, the others remain intact. Security is also high since data travels
along a dedicated connection.
This type of topology requires a lot of cables and is, therefore, expensive. Many of the connections
are also redundant since there are several different paths for data to travel from one node to
another.
Tree
Tree topology combines multiple star topologies onto a bus. Hub devices for each star topology
are connected to the bus. Each hub is like the root of a tree of devices. This provides great
flexibility for expanding and modifying the network.
16. Write short notes on gigabit, switched Ethernet, and Bluetooth technology.
increase performance tenfold while maintaining compatibility with all existing Ethernet
standards. In particular, gigabit Ethernet had to offer unacknowledged datagram service with
both unicast and broadcast, use the same 48-bit addressing scheme already in use, and
maintain the same
frame format, including the minimum and maximum frame sizes. The final standard met all
these goals. Like fast Ethernet, all configurations of gigabit Ethernet use point-to-point links. In
the simplest configuration, illustrated in Fig. 4-20(a), two computers are directly connected to
each other. The more common case, however, uses a switch or a hub connected to multiple
computers and possibly additional switches or hubs, as shown in Fig. 4-20(b). In both
configurations, each individual Ethernet cable has exactly two devices on it, no more and no
fewer.

16. Also like fast Ethernet, gigabit Ethernet supports two different modes of operation: full-duplex
mode and half-duplex mode. The ‘‘normal’’ mode is full duplex mode, which allows traffic in
both directions at the same time.
The heart of this system is a switch containing a high-speed backplane that connects all of
the ports, as shown in Fig. 4-17(b). From the outside, a switch looks just like a hub. They are
both boxes, typically with 4 to 48 ports, each with a standard RJ-45 connector for a twisted-
pair cable. Each cable connects the switch or hub to a single computer.
Inside the switch, however, something very different is happening. Switches only output
frames to the ports for which those frames are destined. When a switch port receives an
Ethernet frame from a station, the switch checks the Ethernet addresses to see which port the
frame is destined for.
In 1994, the L. M. Ericsson company became interested in connecting its mobile phones to
other devices (e.g., laptops) without cables. Together with four other companies (IBM, Intel,
Nokia, and Toshiba), it formed a SIG (Special Interest Group, i.e., consortium) in 1998 to
develop a wireless standard for interconnecting computing and communication devices and
accessories using short-range, low-power, inexpensive wireless radios. The project was
named Bluetooth, after Harald Blaatand (Bluetooth) II (940–981), a Viking king who unified
(i.e., conquered) Denmark and Norway, also without cables.

17. The basic unit of a Bluetooth system is a piconet, which consists of a master node and up to
seven active slave nodes within a distance of 10 meters. Multiple piconets can exist in the
same (large) room and can even be connected via a bridge node that takes part in multiple
piconets.
17. Manchester and differential Manchester code with time diagram.
(a) Binary encoding,
(b) Manchester encoding,
(c) Differential Manchester encoding.
18. How can you define active repeaters for optical fiber? Name the ways of connecting
fiber optical cable.

18. At the bottom, in the physical layer, we find the repeaters. These are analog devices that work
with signals on the cables to which they are connected. A signal appearing on one cable is
cleaned up, amplified, and put out on another cable. Repeaters do not understand frames,
packets, or headers. They understand the symbols that encode bits as volts. Classic Ethernet,
for example, was designed to allow four repeaters that would boost the signal to extend the
maximum cable length from 500 meters to 2500 meters.
19. How DNS works? Define DNS namespace with diagram.
How DNS works
If you've ever used the Internet, it's a good bet that you've used the Domain Name System,
or DNS, even without realizing it. DNS is a protocol within the set of standards for how computers
exchange data on the Internet and on many private networks, known as the TCP/IP protocol suite.
Its basic job is to turn a user-friendly domain name like "howstuffworks.com" into an Internet
Protocol (IP) address like 70.42.251.42 that computers use to identify each other on the network.
It's like your computer's GPS for the Internet.
Computers and other network devices on the Internet use an IP address to route your request to the
site you're trying to reach. This is similar to dialing a phone number to connect to the person you're
trying to call. Thanks to DNS, though, you don't have to keep your own address book of IP
addresses. Instead, you just connect through a domain name server, also called a DNS
server or name server, which manages a massive database that maps domain names to IP
addresses.
Whether you're accessing a Web site or sending e-mail, your computer uses a DNS server to look
up the domain name you're trying to access. The proper term for this process is DNS name
resolution, and you would say that the DNS server resolves the domain name to the IP address.
For example, when you enter "http://www.howstuffworks.com" in your browser, part of the network
connection includes resolving the domain name "howstuffworks.com" into an IP address, like
70.42.251.42, for HowStuffWorks' Web servers.
Definition and diagram
The DNS (Domain Name System) is a massive network ofservers that comprises the largestdigital database
on the planet.This database is maintained,managed and regulated byseveral internet authorities,including
the IANA (Internet Assigned Numbers Authority) and ICANN (Internet Corporation for Assigned Names and
Numbers).
Many people confuse the various terms associated with the DNS and mistakenlyrefer to them as either the
same thing or completelyseparate entities.In truth, they are neither separate nor are they the same thing;
rather, they are integral pieces to the puzzle that is the world wide web.

19. 20. What are resource records? Explain with example.
21. What is name server? Explain with example how resolver looks- up a remote name in
DNS namespace?
A name server is a web server that has DNS software installed on it, particularlya server that is managed by a
web hostthat is specificallydesignated for managing the domain names thatare associated with all of the
hosting provider's accounts.
Name servers are often called DSN servers as well, and this is likely the origin of all of the confusion
associated with name servers and the DNS.
22. Define e- mail systemshowing the SMTP and POP3 protocol environment?
23. Explain the architecture framework of WWW with diagram. Write the steps that
occur when a URL is selectedin the browser.