WEEK-1
Network Definition
A network is a group of two or more computer systems linked together. There are many types of computer networks , including:
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Local-area networks (LANs) : The computers are geographically close together (that is, in the same building).
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Wide-area networks (WANs) : The computers are farther apart and are connected by telephone lines or radio waves.
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Campus-area networks (CANs) : The computers are within a limited geographic area, such as a campus or military base.
 metropolitan-area networks MANs) : A data network designed for a town or city.
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Home-area networks (HANs) : A network contained within a user's home that connects a person's digital devices.
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Topology : The geometric arrangement of a computer system. Common topologies include a bus, star, and ring. See the Network topology diagrams in the Quick
Reference section of Webopedia .
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Protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called
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Ethernet .
Another popular LAN protocol for PCs is the IBM token-ring network .
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Architecture : Networks can be broadly classified as using either a peer-topeer or client/server architecture.
OSI Model
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The Open Systems Interconnection model (OSI) is a conceptual model that characterizes and standardizes the internal functions of a communication system by partitioning it into abstraction layers.

The seven layers of the OSI Basic Reference Model are (from bottom to top):
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The Physical Layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. Ex: this layer defines the size of Ethernet coaxial cable, the type of BNC connector used, and the termination method.
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The Data Link Layer describes the logical organization of data bits transmitted on a particular medium. Ex: this layer defines the framing, addressing and check summing of
Ethernet packets.
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The Network Layer describes how a series of exchanges over various data links can deliver data between any two nodes in a network. Ex: this layer defines the addressing and routing structure of the Internet.
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The Transport Layer describes the quality and nature of the data delivery. Ex: this layer defines if and how retransmissions will be used to ensure data delivery.
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The Session Layer describes the organization of data sequences larger than the packets handled by lower layers. Ex: this layer describes how request and reply packets are paired in a remote procedure call.
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The Presentation Layer describes the syntax of data being transferred. Ex: this layer describes how floating point numbers can be exchanged between hosts with different math formats.
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The Application Layer describes how real work actually gets done. Ex: this layer would implement file system operations.