WEEK-III

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PERSPECTIVES ON NETWORKING

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From the end-user perspective, whether at home, at work, or at school, what happens behind the wall plug is magic. Just as most people do not really understand how cars work, how TVs work, and so on, most people who use networks do not understand how they work. Nor do they want to! 

END USER PERSPECTIVES ON NETWORKING AND INTERNET

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• Enterprise Network
• Small Office Home Network (SOHO)

Overview of Networking

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• A computer network is a system that connects two or more computing devices for transmitting and sharing information.
• Computing devices include everything from a mobile phone to a server.
• These devices are connected using physical wires such as fiber optics, but they can also be wireless.

Key Components of a Computer Network

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• A computer network is built with two basic blocks: nodes or network devices and links.
• The links connect two or more nodes with each other.
• The way these links carry the information is defined by communication protocols.
• The communication endpoints, i.e., the origin and destination devices, are often called ports.

Key Components of a Computer Network

1.Network Devices

Network devices or nodes are computing devices that need to be linked in the network. Some network devices include:

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Computers, mobiles, and other consumer devices: These are end devices that users directly and frequently access. For example, an email originates from the mailing application on a laptop or mobile phone.

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Servers: These are application or storage servers where the main computation and data storage occur. All requests for specific tasks or data come to the servers.

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Routers: Routing is the process of selecting the network path through which the data packets traverse. Routers are devices that forward these packets between networks to ultimately reach the destination. They add efficiency to large networks.

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Switches: Repeaters are to networks what transformers are to electricity grids—they are electronic devices that receive network signals and clean or strengthen them. Hubs are repeaters with multiple ports in them. They pass on the data to whichever ports are available. Bridges are smarter hubs that only pass the data to the destination port. A switch is a multi-port bridge. Multiple data cables can be plugged into switches to enable communication with multiple network devices.

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Network Devices

Gateways: Gateways are hardware devices that act as ‘gates’ between two distinct networks. They can be firewalls, routers, or servers.

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2. Links

Links are the transmission media which can be of two types:

Wired: Examples of wired technologies used in networks include coaxial cables, phone lines, twisted-pair cabling, and optical fibers. Optical fibers carry pulses of light to represent data.

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Wireless: Network connections can also be established through radio or other electromagnetic signals. This kind of transmission is called ‘wireless’. The most common examples of wireless links include communication satellites, cellular networks, and radio and technology spread spectrums. Wireless LANs use spectrum technology to establish connections within a small area.

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3. Communication protocols

A communication protocol is a set of rules followed by all nodes involved in the information transfer. Some common protocols include the internet protocol suite (TCP/IP), IEEE 802, Ethernet, wireless LAN, and cellular standards. TCP/IP is a conceptual model that standardizes communication in a modern network. It suggests four functional layers of these communication links:

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Network access layer: This layer defines how the data is physically transferred. It includes how hardware sends data bits through physical wires or fibers.

Internet layer: This layer is responsible for packaging the data into understandable packets and allowing it to be sent and received.

Transport layer: This layer enables devices to maintain a conversation by ensuring the connection is valid and stable.

Application layer: This layer defines how high-level applications can access the network to initiate data transfer.

4. Network Defense

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While nodes, links, and protocols form the foundation of a network, a modern network cannot exist without its defenses. Security is critical when unprecedented amounts of data are generated, moved, and processed across networks. A few examples of network defense tools include firewall, intrusion detection systems (IDS), intrusion prevention systems (IPS), network access control (NAC), content filters, proxy servers, anti-DoS devices, and load balancers.

CATEGORIES OF NETWORKS-LAN

LAN - Local Area Network

• Group of computers connected to each other in a small area eg: Building, office, University Campus.
• Used for connecting two or more personal computers through a communication medium such as twisted pair, coaxial cable, etc.
• Less costly as it is built with inexpensive hardware such as hubs, network adapters, and Ethernet cables.
• Extremely faster rate of data transmission
• Provides higher security.

Computer Science & Engineering – 20CS33P

LAN (local area network)

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Computer Science & Engineering – 20CS33P

WAN – Wide Area Network

• A network that extends over a large geographical area such as states or countries
• Quite bigger network than the LAN.
• Not limited to a single location
• Spans over a large geographical area through a telephone line, fiber optic cable or satellite links
• The internet is one of the biggest WAN in the world.
• Widely used in the field of Business, government, and education
• Eg: KSWAN

Computer Science & Engineering – 20CS33P

WAN - Wide Area Network

Computer Science & Engineering – 20CS33P

MAN - Metropolitan Area Network

• A network that covers a larger geographic area by interconnecting a different LAN to form a larger network.
• Government agencies use MAN to connect to the citizens and private industries.
• In MAN, various LANs are connected to each other through a telephone exchange line.
• It has a higher range than Local Area Network(LAN).

Computer Science & Engineering – 20CS33P

MAN (Metropolitan area network)

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Computer Science & Engineering – 20CS33P

Internetworking

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• Is the practice of interconnecting multiple computer networks, such that any pair of hosts in the connected networks can exchange messages irrespective of their hardware-level networking technology.
• The resulting system of interconnected networks are called an internetwork, or simply an internet.

The Communication Rules

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There are six different communication rules followed in a computer network. Viz…

1. Rule Establishment
2. Message Encoding
3. Message Formatting and Encapsulation
4. Message size
5. Message Timing
6. Message Delivery Options

Protocols

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Protocol is a set of rules that govern data communications. A Protocol defines-

• what is communicated
• how it is communicated
• When it is communicated

The key elements of a protocol are

• syntax
• semantics
• timing

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Internet

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• The Internet is a globally connected network system that facilitates communication and data services through a vast collection of private, public, business, academic, and government networks.
• The Internet is decentralized, which means there is no central authority governing its operations.
• To enable communication between devices, the internet relies on protocols and standards that govern how small units of data are formatted, addressed, and transmitted.
• The terms internet and World Wide Web (WWW) are often used as synonyms, but technically they are not the same thing.
• The Internet is a global network of interconnected computers and networks.

• The World Wide Web is a service that uses the Internet’s infrastructure to provide digital devices and applications with access to websites.
• Popular internet services include email, VoIP (Voice over IP), and SMS (Short Message Service).

The Network Standard Organizations

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1. International Standard Organization (ISO)
1. ISO is the International Organization for Standardization.
2. It creates set of rules and standards for graphics, document exchange , data communication etc.

2) Consultative Committee for International Telephony and Telegraphy (CCITT)

• CCITT is now standard organization for the United States.
• CCITT developer’s recommended set of rules and standards for telephone and telegraph communication.

It has developed 3 set of specifications :

V Series for Modern Interfacing.

X series for Data Communication.

Q series for Integrated Services Digital Network(ISDN).

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3) American National Standard Institute (ANSI)

• ANSI is primary organization for fostering the development of technology standards in the United States and providing various set of rules and standard for  Data Communication.

4) Institute of Electrical and Electronic Engineering (IEEE)

• It is US based professional organization of electronic , computer and communication engineering.
• It provides various set of rules and standard in communication and networking field.

5) Electronic Industries Association(EIA)  

• This organization establish and recommends industrial standards.
• EIA has developed the RS(Recommended Standards) series of Standards for data and telecommunication.

6) Standard Council of Canada (SCC)

• It is an official Standard Agency for Canada .
• It has Similar responsibilities as ANSI has. 

Protocol Stack

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• Protocol stacks are a layered collection of protocols that work together to provide communication services.
• Each protocol in the stack is responsible for a specific task, and by layering them, we can create a more robust and reliable system.
• A protocol stack or protocol suite is the architecture of a protocol that follows the layered architecture design principle.
• The functionality of the whole protocol is broken down into component protocols that are separately managed and can be treated and designed mostly independently from one another.

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• A protocol stack typically contains a set of protocols where each protocol in the stack performs a specific task and is responsible for a well-defined function.
• The protocols are often referred to as layers with each layer providing services to the layer above it and receiving services from the layer below it.

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OSI Model

• Open Systems Interconnection (OSI)
• Each layer support the layers above it and offers services to the layers below
• Each layer performs unique and specific task
• A layer only has knowledge of its neighbour layers only
• A layer service is independent of the implementation

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7. Application Layer

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• The application layer is used by end-user software such as web browsers and email clients.
• It provides protocols that allow software to send and receive information and present meaningful data to users.
• A few examples of application layer protocols are the Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), Post Office Protocol (POP), Simple Mail Transfer Protocol (SMTP), and Domain Name System (DNS).

6. Presentation Layer

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• The presentation layer prepares data for the application layer.
• It defines how two devices should encode, encrypt, and compress data so it is received correctly on the other end.
• The presentation layer takes any data transmitted by the application layer and prepares it for transmission over the session layer.

5. Session Layer

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• The session layer creates communication channels, called sessions, between devices.
• It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends.
• The session layer can also set checkpoints during a data transfer—if the session is interrupted, devices can resume data transfer from the last checkpoint.

4. Transport Layer

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• The transport layer takes data transferred in the session layer and breaks it into “segments” on the transmitting end.
• It is responsible for reassembling the segments on the receiving end, turning it back into data that can be used by the session layer.
• The transport layer carries out flow control, sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, requesting it again.

3. Network Layer

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• The network layer has two main functions. One is breaking up segments into network packets, and reassembling the packets on the receiving end.
• The other is routing packets by discovering the best path across a physical network.
• The network layer uses network addresses (typically Internet Protocol addresses) to route packets to a destination node.

2. Data Link Layer

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The data link layer establishes and terminates a connection between two physically-connected nodes on a network. It breaks up packets into frames and sends them from source to destination. This layer is composed of two parts—Logical Link Control (LLC), which identifies network protocols, performs error checking and synchronizes frames, and Media Access Control (MAC) which uses MAC addresses to connect devices and define permissions to transmit and receive data.

1. Physical Layer

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The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable or wireless technology connecting the devices, and is responsible for transmission of the raw data, which is simply a series of 0s and 1s, while taking care of bit rate control.

Advantages of OSI Model

The OSI model helps users and operators of computer networks:

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Determine the required hardware and software to build their network.

Understand and communicate the process followed by components communicating across a network. 

Perform troubleshooting, by identifying which network layer is causing an issue and focusing efforts on that layer.

OSI Encapsulation Terminology

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• Encapsulation is the process of adding additional information when data is traveling in OSI or TCP/IP model.
• The additional information has been added on sender’s side, starting from Application layer to Physical layer.