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The old model of a single computer serving all of the organization’s computational needs has been replaced by one in which a large number of separate but interconnected computers do the job.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. 

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.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.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 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.

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)

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. 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.

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.

14. What are the major components of an optical system? Write the working principles of fiber optic.

i. Compact Light Sourceii. Low loss Optical Fiberiii. 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

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

(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.

Network TopologyComputers 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-PointPoint-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.

BusBus 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.

StarIn 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.

RingIn 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.

MeshIn 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.

TreeTree 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 sameframe 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.

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.

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.

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 of servers that comprises the largest digital database on the planet. This database is maintained, managed and regulated by several 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 mistakenly refer to them as either the same thing or completely separate 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.

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, particularly a server that is managed by a web host that is specifically designated for managing the domain names that are 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 system showing the SMTP and POP3 protocol environment?23. Explain the architecture framework of WWW with diagram. Write the steps that

occur when a URL is selected in the browser.