network

• A computer network is a set of interconnected machines that exchange information and share hardware resources
• Sharing of hardware, software, and data resources


  • Communication between remote users and/or remote applications (exchange of information)
  • Collaboration between remote users to perform common tasks
  • Fault tolerance: continuity of services, and data duplication
• Today, it's the Internet: e-commerce, banking transactions, etc.
• Physical elements


  Interconnection interfaces, connection cables, connection equipment, computers, etc.
• Logical elements (software)


  Browsers, protocols, services (web, mail, ftp)
• Personal Area Network (PAN)


  • Connects a machine to its peripherals, and is used by only one person
• PAN examples


  • A mobile phone with its accessories
  • A computer with its peripherals
• Local Area Network (LAN)


  • Connects machines in a location that is geographically limited
• LAN examples


  • University campus network
  • Network in a factory
  • Network in a building
  • Network in a house
• Metropolitan Area Network (MAN)


  • Covers a city, generally used to connect multiple local networks
• MAN examples


  • Connecting multiple university campuses
  • Connecting multiple city administrations
  • Connecting multiple health centers in a city
  • Jointly broadcasting cable television with the internet
• Wide Area Network (WAN)


  • Covers a country, a continent, or even the whole world, generally the interconnection of several LAN or MAN networks
• WAN examples


  • Algeria Post connects its branches, located throughout the national territory, through a WAN network
  • The Internet
• Broadcast Mode


  Involves sharing a single transmission medium, where each message sent by a device on the network is received by all other devices
• Point-to-Point Networks


  The physical medium (cable) connects only a pair of devices. When two devices that are not directly connected want to communicate, they do so through the other nodes on the network
• Bus Topology


  • All machines are interconnected to a single cable, the bus
• Star Topology


  • All machines are interconnected through a single point of concentration
• Tree Topology


  • Multiple points of concentration in the network, connected to each other to form a tree-shaped network
• Mesh Topology


  • Machines are connected in the form of a graph, which is not necessarily a tree
• Ring Topology


  • Each node is connected to two other nodes to form a ring
• Transmission channel


  The physical tools of transmitting information (a signal), characterized by the bandwidth which represents the range of frequencies in which signals are correctly transmitted over the medium
• Connection-oriented mode


  Any communication between 2 devices follows a process of establishing a connection, transferring data, and releasing the connection
• Connectionless mode


  Data blocks, called datagrams, are sent without checking in advance whether the equipment to be reached, as well as any interim nodes, are active. The network manages the routing and delivery of the message
• Complex network functions are grouped into modules (layers) to reduce the complexity
• Layer


  One level of abstraction, where a layer uses the services of layer n-1 and its own means to offer services more appropriate to layer n+1
• Communicating requires interpreting the exchanged information and speaking the same language (syntax and semantics)
• Protocol


  A set of rules designed for a particular communication task, where two computers must use the same protocol to be able to communicate with each other
• Syntax


  The different fields found in each message and the number of bits occupied by each field
• Semantics


  The meaning of each field
• Standards are documented agreements describing specifications for products or services, to eliminate incompatibilities
• Standard


  Defined by national and international organizations
• Layers of the OSI model


  • Physical layer
  • Data Link layer
  • Network layer
  • Transport layer
  • Session layer
  • Presentation layer
  • Application layer
• TCP/IP model


  The standard on which the development of the Internet has been based, consisting of 4 layers: application, transport, internet, and network access
• TCP


  Transmission Control Protocol
• IP


  Internet Protocol
• Network layer


  Provides a communication service that enables a machine to communicate with others
• Network layer


  • Data is encapsulated in packets (also called datagrams)
• Roles of the network layer


  • Addressing (Identification of machines)
  • Routing (Finding a machine in a network through a route)

  
• Addressing


  Each machine must be equipped with a unique logical address in a network
• Routing


  The network layer allows for finding a machine in a network through a route specifying how the machine can be reached