Networking

Networking

Security: Specific directories can be password protected to limit access to authorized users. Also, files and programs on a network can be designated as "copy inhibit" so we don’t have to worry about the illegal copying of programs.

1. 
   Security Issues
   One of the major drawbacks of computer networks is the security issues involved. If a computer is a standalone, physical access becomes necessary for any kind of data theft. However, if a computer is on a network, a computer hacker can get unauthorized access by using different tools. In case of big organizations, various network security software’s are used to prevent the theft of any confidential and classified data.
   
2. 
   Rapid Spread of Computer Viruses
   If any computer system in a network gets affected by computer virus, there is a possible threat of other systems getting affected too. Viruses get spread on a network easily because of the interconnectivity of workstations. Such spread can be dangerous if the computers have important database which can get corrupted by the virus.
   
3. 
   Expensive Set Up: The initial set up cost of a computer network can be high depending on the number of computers to be connected. Costly devices like routers, switches, hubs, etc., can add up to the bills of a person trying to install a computer network. He will also have to buy NICs (Network Interface Cards) for each of the workstations, in case they are not inbuilt.
   
4. 
   Dependency on the Main File Server:
   In case the main File Server of a computer network breaks down, the system becomes useless. In case of big networks, the File Server should be a powerful computer, which often makes it expensive.
   

Transmission media is the means or pathway by which data is transmitted and received from one computer to another computer.

There are two types of transmission media, they are:-

1. 
   Guided media
   
2. 
   Unguided media
   

Example:- Twisted pair cable, coaxial cable, optical fiber cable

There are two types of twisted pair cable, they are:-

1. 
   Shielded twisted pair (STP)
   
2. 
   Unshielded twisted pair (UTP)
   

-thin coaxial cable

-thick coaxial cable
Thick coaxial cable has 100base5 bandwidth which means 10-100mbps bandwidth with distance 500 m. thin coaxial cable has 10base2 bandwidth which means 10-100 bandwidth with distance 100-200m. It is better than twisted pair cable and has high bandwidth but expensive in comparison to twisted pair cable.

c) Fiber optics cable/ Optical fiber: - It is the most advanced media in communication. It has the highest bandwidth 100baseFX (which means 100 mbps with distance 2000m) and 1000baseLX (which means 1000mbps with distance 3000m) and has highest speed and is most expensive media in comparison to any other media. It uses light rather than electricity to transmit information. It is very thin media which is measured in microns and is very hard to identify with our necked eye. It has two layers-clad and core. Both the clad and core are made up of same material (glass and plastic). The light is passed through an optical fiber by the process of total internal reflection. Light source for it is ‘Laser’ or ‘Led’ and detector id ‘Pin’. At the source, electrical pulses generated by computer or electronic devices, is converted into light by ‘Laser’ or ‘Led’ which flows from fiber optics in the form of light. At the destination, the light rays are again converted into electrical pulses by ‘Pin’. It doesn’t have any danger of leakage and electrical interference. So it can be used in any environments like under big factories, grounds or airports .It has the highest bandwidth and the highest speed in comparison to any other media and is most expensive than other media.

Satellite: - Satellite acts as relay station for communication signals. The satellite accept data and signals transmitted from an earth station, amplifies them and then retransmit them to another earth station.

History of Internet

The US department of defense laid the foundation of the internet roughly 30 years ago with a network called ARPNET (Advance Research Projects Agency Net). During the 1970’s work an ARPANET consisted of connecting the various networks and developing the necessary internet software. During the early 1980’s the network became known as the internet and it was during that period that business firms began using it but the general public started using internet after the development of world wide web in the early 1990’s. In 1993 there were only 130 websites all over the world now there are millions of websites all over the world.

Internet is not just like one network, it is a coordinated union of a multitude of networks all over the world or we can say internet is the world largest computer networking, the network of networks. Internet is global LAN where millions of computers are connected to each other. any computer user on internet can contact another user on the internet anywhere in the world, very much like telephone user communicates with another user anywhere in the world. Internet is an information superhighway and has seemingly compressed the world into a cyber colony. Internet is available to anyone who wants to use it. A majority of internet users are college students, businessmen, professionals etc and accessing internet has become a way of life.

1. 
   We can exchange e-mail with millions of people with e-mail address in the internet.
   
2. 
   We can get information about people, products, organizations and many other things from the internet.
   
3. 
   We can get search facilities in the internet (such as- google.com) by the help of which we can search lots of information regarding any topic within a second.
   
4. 
   We can send or receive data files, programs, images, sound, and animation through the internet from very distant places.
   
5. 
   We can sell or buy products and services through the interent( Such as E-commerce, E-business)
   
6. 
   We can give information about our organization and institution by launching homepage and keeping in the internet which let the other people around the world to know.
   
7. 
   We can conduct surveys; get opinions of people around the world on particular topics through the internet.
   
8. 
   We can learn or we can do courses through the internet, we can give online exam through the internet such as MCSE(Microsoft Certified System Engineering), OCP (Oracle Certified Professional) etc
   

Networking is categorized according to the size of network, speed of data transmission, distance covered, technology used, architecture used, structure of the network etc. There are three types of Networking, they are:-

1. 
   LAN (Local area Network):- A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.
   

2. 
   Metropolitan Area Network - a network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. When LAN grows and spreads in area then it becomes MAN. It is called metropolitan network because it is extended up to a city or a larger geographical area. MAN is typically owned and operated by a single entity such as a government body or large corporation. In this system different communication media can be adopted and different types of protocols can be used. Instead of using guided media (e.g. wire), it can use unguided media (e.g. wireless media). It has more flexibility than the LAN has many advantages over LAN but has very high chances of data leakage or security break.
   

3. 
   WAN:-It is the network that is extended to a large area (e.g. throughout the world or even more) and the communication is done through satellite. A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address. A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. It is the combination of many different types of LAN and MAN networks, so it has massive amount of heterogeneous systems(e.g. operating systems, devices, hardware, topologies, protocols, transmission media etc). Instead of centralizing the transmitting devices in a particular location such devices are distributed in different parts of the world. The largest WAN in existence is internet.
   

Other types of networking are:-

• 
  Wireless Local Area Network - a LAN based on WiFi wireless network technology
  
• 
  Campus Area Network - a network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.
  
• 
  Storage Area Network - connects servers to data storage devices through a technology like Fibre Channel.
  
• 
  System Area Network - links high-performance computers with high-speed connections in a cluster configuration. Also known as Cluster Area Network.
  

There are two types of networking architecture, they are

1. 
   Peer-to –Peer architecture (Point-to Point)
   
2. 
   Client-Server architecture (Broadcasting)
   

It is also called broadcasting architecture, in this architecture computers are connected to a central device and communication is done through it. When computer A wants to send message to computer C then message is sent to the central device. The message is first of all received by the server and the message is broadcasted by the server. All the computers attached to the network receive such packet; each of them read the receiver’s address and compares their own address with the address written on the packet. If it matches, then only the computer accepts it otherwise the packet is discarded or rejected. So in this case, computer C address matches with the packet address, so computer C accepts, other computer discard it. In this architecture server is always fixed which control all other computers and the communication is done through server. All other computers are called clients. The big disadvantage of this architecture is high traffic problem created by broadcasting, because at the time of broadcasting, all the computers remain busy. Its big advantage is its speed.

ISO (International Standard organization) created a model for network communication called OSI (Open System Interconnect) reference model in 1982 which become the primary architectural model for inter-computer communication. The OSI model describes how information from a software application in one computer moves through a network medium to a software application in another computer.

OSI is the system adopted for data communication through internet because there are different sets of technologies, protocols, devices and software used for transmitting data and there is a need of a common language which they can understand, OSI provides such types of facility by which all the devices attached in the network speak same language.

OSI model divides network communication into seven layers. Each layer carries out specific function in transmitting data on the network. The seven layer of OSI reference model can be divided into two categories: Upper layer and Lower layer. The upper layer of the OSI model deal with application issues and the lower layers of the OSI model deal with data transport issue.

The seven layers of OSI model are as follows:-

1. 
   Physical layer ( layer 1)
   
2. 
   Data link layer( layer 2)
   
3. 
   Network layer ( layer 3)
   
4. 
   Transport layer ( layer 4)
   
5. 
   Session layer ( layer 5)
   
6. 
   Presentation layer ( layer 6)
   
7. 
   Application layer ( layer 7)
   

1. 
   Physical Layer: - The main responsibility of this layer is to define voltage levels, timings of voltage changer, physical data rates, maximum transmission distances and physical connectors. The main function of this layer is to put data on the physical medium.
   
2. 
   Data link Layer: - The main responsibility of this layer is to decide which computer to send data, where the data is meant to go and what is the validity of the data frames. In other word these layers define access method for the physical medium.
   
3. 
   Network Layer: - The main responsibility of this layer is to make possible to connect heterogeneous networking systems. It also looks at the media path and helps router to find the short and the best path.
   
4. 
   Transport Layer: - The main responsibility of this layer is to ensure error-free delivery of data. It also makes possible for a faster host to communicate with a slower host or vice versa.
   
5. 
   Session Layer: - The main responsibility of these layers is to establish and maintains communication channel. This layer helps to establish a session/meeting/conference between different people in the network. It also provides synchronization between the systems with different speeds. Practical function like security authentication, Identification, connects and release of connection is done in this layer.
   
6. 
   Presentation Layer: - The main responsibility of this layer is to convert general data formats (ASCII) into network data representation (NDR). This layer is concerned with the syntax and semantics of the information transmitted.
   
7. 
   Application Layer: - The main responsibility of this layer is to define how application interacts with each other. It is totally user-oriented layer. Some of the major responsibility of this layer is file transfer, accessing remote files, accessing remote database, accessing email etc.
   

Protocols are the rules of transmission. As we know that for a transmission of data/information to be successful, each of the devices/computers attached to both ends must speak the same set of languages, must have same set of devices and same types of software. But practically it is impossible in this distributed world. To overcome this limitation, certain set of rules which are common and acceptable by both the parties are developed which play a role of interpreter between the sender and the receiver, which is known as protocols.

For example: - TCP/IP, SMTP, HTTP etc

Intranet: -

Intranet is based on internet technology to build information system with an organization or enterprise. It also uses the same protocols as used by the internet (HTTP, TCP/IP). It inherits all the features of Internet. It is useful for promoting business, education etc. If permission is given to access intranet from remote location then it is termed as extranet.

There are all together six types of LAN topology, they are as follows:-

1. 
   Bus Topology
   
2. 
   Star Topology
   
3. 
   Ring Topology
   
4. 
   Tree Topology
   
5. 
   Mesh Topology
   
6. 
   Hybrid Topology
   

1. 
   Bus Topology: - This is the most popular topology. In this topology a single cable is connected with each computer. The single cable at the middle of all the computers is called ‘Bus’ from which other nodes are connected by some connectors and that node is connected on the LAN port of each computer. In this topology server is located on either side and a terminator is located on other side of the bus. It is based on broadcasting architecture
   

• 
  It is relatively easy to install and extend the network
  
• 
  If any of the computers in network is down, then other computers can continue their work
  
• 
  It is more flexible because we can connect any number of computers by using a connector in the bus
  
• 
  It is not expensive to install
  

• 
  Data traffic is high in this topology because it is based on client/ server architecture
  
• 
  Data collision is high
  
• 
  If the backbone cable fails the entire network is unusuable.
  
• 
  Finding out fault and troubleshooting is hard
  

2. 
   Star Topology:-
   

• 
  It is flexible because in this topology it is easy to add computer and remove existing one.
  
• 
  In this topology it is easy to diagnose fault because of the use of ‘Hub’
  
• 
  In this topology if any of the computers in the network is down, then other computers can carry out their functions as usual
  

• 
  In this topology if the server or hubs fail it makes the whole system unavailable.
  

• 
  In this topology cost of cable is more because all the cable from all the clients must be connected to the server through hub
  

• 
  It is based on client/server architecture so in this topology data traffic is high
  

3. 
   Ring Topology:-
   

• 
  There is no dependence on the central server. So, each computer is capable of acting as server as well as client.
  
• 
  Since data travels in one direction, there is less chance of collision and there is less chance of data- traffic.
  
• 
  Every computer has equal access facility to the resources.
  

• 
  Failure of any one of the computer on the network makes the whole network down
  
• 
  Very hard to find out the errors and troubleshooting
  

• 
  Non- flexible because adding new computer on the network and removing existing computer is very hard
  

4. 
   Tree Topology:
   

• 
  The tree topology is flexible to extend and reduce.
  
• 
  The failure of the leaf node does not affect the whole network.
  

• 
  Failure to any of the hierarchical node will cause the failure to the network on that node.
  
• 
  The performance of the root node and other hierarchical nodes will affect the performance of the network.
  
• 
  It is not easy to install.
  
• 
  It is not easy to troubleshoot the network problem.
  

5. 
   Mesh topology:
   

• 
  Because of the multiple paths to reach the nodes the failure of any node will not affect the operation of the entire network.
  
• 
  There is no traffic problem as it has multiple paths.
  

• 
  It is very complex network and is difficult to find the faults and troubleshoot problems.
  
• 
  A lot of network cable is needed, so it is costly.
  
• 
  It is difficult to install and extend the network.
  

6. 
   Hybrid topology:
   

Hybrid topology is the combination of two or more topologies together. It has advantages of more than one topologies as well as disadvantages, too

Q.9 what are the different networking devices? Explain each of then in brief.

ANS:-

The different networking devices are-

• 
  Hub
  
• 
  Bridge
  
• 
  Repeater
  
• 
  Router
  
• 
  Modem
  

Hub is a device with multiple ports for connecting different computers on the network.

Usually, each file servers has only one NIC. Therefore, it would be impossible to connect every workstation directly to the file server. To solve this problem, LANs use hubs, which are very common networking devices. So, it has the following properties:

• 
  It operates on Physical layer of OSI model
  
• 
  It accepts data, amplify them and then transmit
  
• 
  It is used to split network segments and propagate signals through it.
  
• 
  It does not need path determination and switching
  

Its big disadvantage is that it can’t filter network traffic and it imposes limitation to the number of computer that can be connected

It is a device, which connects different network segments and passes data with the same communication protocols. It is the connecting device between two or more hubs. Some of the characteristics are:

• 
  It operates at layer 2 ( Data Link) of OSI model
  
• 
  It reduces unnecessary traffic problem by controlling broadcasting
  
• 
  Bridges are more intelligent then hubs because they maintain MAC address tables in them and forward data looking on it.
  
• 
  Bridges collect and pass packets between 2 network segments
  

• 
  It operates at layer-1 (Physical layer) of OSI model
  
• 
  It receives signals, amplifies them and sends it.
  
• 
  If the signals are weakened because of long wire, then repeater can amplify, clean the signal and we can increase length of cable.
  

It is also a type networking device which are used to connect separate network and to access internet. It is similar to Bridge in many ways

Some of the characteristics of routers are:

• 
  It operates at layer -3 (Network layer).
  
• 
  Router finds the shortest and the best path to forward data between different paths available
  
• 
  It use IP address for accessing and forwarding data packets
  
• 
  It is just like bridge or hub but provides more functionality and is more intelligent
  

In other words modem is a device which has responsibility of modulating (coding) the data before transmission and demodulating (decoding) the same data with the same rule at the receiving end.

A signal is called analog signal if the signal is continuously varying with respect to time. The example of analog signal are the voice signals,music signals, human voice,temperatue etc. A signal is called digital signal if the signal is discrete or discontinuous.Digital signals are the language of modern day computers. Digital signal is represented only by digits that are 1 and 0.The examples of digital signal are the digitized audio and video signals stored in media such as CD/DVD. The digital signaling has more advantages than analog signaling. The advantage of the digital signaling is that it is cheaper than analog signaling and is more tolerant to noise interference.

Depending on the direction of flow of signals during the communication, mode of communication can be divided into three types. They are:-simplex, half duplex and full duplex.

When data flows in both the direction from sender to receiver and receiver to sender simultaneously then the communication flow is known as full duplex communication. For example:-email and web chatting etc.

In this system when one dials a number from his home, the circuitry system in the telecommunication office automatically finds the appropriate path from the caller to the called telephone switch. When such path is determined, then a dedicated line is established between them till the duration of the conversation. This system is referred to as switching system.

There are three type of switching, they are as fallows:-

2. 
   Circuit switching
   
3. 
   Message switching
   
4. 
   Packet switching
   

1. 
   circuit switching
   

2. 
   Message switching :
   

3. 
   Packet switching
   

It is one of the most frequently used features of the internet. Many people sigh up for internet service just so that they can send and receive e-mail message. The internet is now the world’s largest electronic mail system. More than 30 million people are directly connected to the internet and can send and receive electronic mail.

• 
  Fast: Most system can relay our message to the recipient in a matter of minutes or seconds. Many system let us check to see whether the recipient has accessed our message or not
  
• 
  Easy: - When we open our email box we see a list of the message we have received, first we read the message and then decide how to respond. We can reply to the message if we like, or just delete if it requires no reply. We can save it or print it. We can even forward the message to the other
  
• 
  Fun:- International electronic mail system enable us to find ‘pen pals’ all over the world
  
• 
  Cheap:- World- wide electronics mail access is available through services such as CompuServe, these services charge less than we would expect to pay for monthly telephone service.
  
• 
  Flexible: - We can send a message to more than one person if we like.
  

1. 
   Workstation:-A workstation is a computer intended for individual use that is faster and more capable than a personal computer. It's intended for business or professional use (rather than home or recreational use). Workstations and applications designed for them are used by small engineering companies, architects, graphic designers, and any organization, department, or individual that requires a faster microprocessor, a large amount of random access memory (RAM), and special features such as high-speed graphics adapters. Historically, the workstation developed technologically about the same time and for the same audience as the UNIX operating system, which is often used as the workstation operating system. Among the most successful makers of this kind of workstation are Sun Microsystems, Hewlett-Packard and IBM.
   

2. 
   Terminal:- A terminal is an end-user device (usually with display monitor and keyboard) with little or no software of its own that relies on a mainframe or another computer (such as a PC server) for its intelligence.
   

3. 
   Network Adapters (NIC Card):- Network Adapters often called as Network Interface Card (NIC) is a computer circuit board or card that is installed in a computer so that it can be connected to a network. Personal computers and workstations on a local area network (LAN) typically contain a network interface card (NIC) specifically designed for the LAN transmission technology, such as Ethernet.
   

4. 
   Gateway:- Gateway is a device that enables communication between different network architectures. A gateway takes the data from one network architecture and repackages it and sends it to network architecture. Gateway is just like an interpreter between two network architectures. There can be a physical connection between two network architectures but need a gateway to translate network communication. For example if two groups of people can physically talk to each other but speak different languages, they need an interpreter to communicate.
   

1. 
   Satellite: - a satellite is a specialized wireless receiver/transmitter that is launched by a rocket and placed in orbit around the earth. There are hundreds of satellites currently in operation. They are used for such diverse purposes as weather forecasting, television broadcast, amateur radio communications, Internet communications, and the Global Positioning System, (GPS). Satellite act as a relay station for communication signals. The satellite accepts data and signal transmitted from one earth station, amplifies them and then retransmits them to another earth station.
   
2. 
   IP Address and MAC Address: - An Internet Protocol (IP) address is a numerical label that is assigned to devices participating in a computer network that uses the Internet Protocol for communication between its nodes. Each of the computers attached in the networking are given some name (or address) by the network administrator in 32-bit digits in 4 octets (for example-192.168.0.1) which is known as IP address. IP address has two parts network number and host number. Network number is used to identify the network to which the computer is connected and the host number is used to identify the particular machine connected to that network.
   

61-8C-01-02-04)

3. 
   Electronic mail (E-mail):- E-mail is an electronic message sent from one computer to another. E-mail systems allow us to send letters and files containing data of all types from our computer to any other computer with e-mail address and a modem, simply by typing the recipient’s name and pressing the send button.
   

1. 
   A message can be sent anywhere in the world for the price of a local, without having to leave our desk.
   
2. 
   The same massage can be sent simultaneously to a group of people.
   
3. 
   The message will arrive in a few min and can be picked up the next time the recipient looks at their email.
   
4. 
   It is very easy to send a reply to an e-mail as soon as it is received using a reply button of forward it to someone else with our comments.
   

4. 
   Microwave systems:- Microwave systems transmit voice and data through the atmosphere as super-high-frequency radio waves. Microwave systems transmit microwaves. Microwaves are the electromagnetic waves that vibrate at 1 gigahertz per second or higher. These frequencies are used not only to operate microwave ovens but also to transmit messages between ground-based earth stations and satellite communication systems. Today we see dish or horn-shaped microwave antennas nearly everywhere on towers, buildings and hilltops.
   
5. 
   Infrared Transmission:- It operates by using an infrared light beam to carry the data between devices. There must be a clear line of sight between the transmitting and receiving devices, anything that blocks the infrared signals prevents communication. These systems must generate very strong signals because weak transmission signals are susceptible to interference from light sources
   

Ans:- Difference between Distributed System and Centralized System