Computer networks allow computers to exchange data. It is a large topic with several section. Key areas include:

  • Network topology. The shape and layout of the network.
    • Network links. This is the media to connect the computers. Typically copper, optical, or radio wave.
    • Network nodes/devices. The devices at the ends of the network links. Typically network interface controllers (NICs), repeaters, hubs, bridges, switches, routers, modems, and firewalls.
    • Network structure/topology. The physical or logical layout of the devices with the links. Typically bus, star, ring, mesh, fully connected, or tree.
  • Network Protocols (aka Communications Protocols). Rules for exchanging messages BETWEEN computers to keep them concurrent (in sync). Within a computer there is shared memory and HW. Between computers there is no shared memory (hence rules for messages) and no shared HW (hence rules for the transmission medium). Protocols are to communications as programming languages are to computations.
    • For most people THE protocol suite is the TCP/IP stack with its 4 layers:
      • Application. OSI: Application (7), Presentation (6), Session (5). EG: HTTP, FTP, DNS, SMTP, SSH, TLS, SSL, IRC, NNTP, NTP, DHCP, DNS.
      • Transport. OSI: Transport(4). EG: TCP, UDP.
      • Internet. OSI: Network (3). EG: IP, IPv4, IPv6, ICMP, IPsec.
      • Link. OSI: Data Link (2), Physical (1). EG: Ethernet, Tunneling.
    • Protocol Data Unit (PDU). A defined unit of data depending on the protocol and layer.
      • OSI Physical (1): bit
      • OSI Data Link (2): frame
      • OSI Network (3): packet (aka IP packet)
      • OSI Tranport (4): segment for TCP, datagram for UDP.
  • Scale. Geographic or organizational.
    • Personal Area Network (PAN)
    • Local Area Network (LAN)
    • Home Area Network (HAN)
    • Storage Area Network (SAN)
    • Campus Area Network (CAN)
    • Backbone Network
    • Metropolitan Area Network (MAN)
    • Wide Area Network (WAN)
    • Enterprise Private Network (EPN)
    • Virtual Private Network (VPN)
    • Global Area Network (GAN)
    • Intranet
    • Extranet
    • Darknet
    • Internet
  • Routing. Selecting the [best] path in a network for the traffic in terms of performance and security.
    • Circuit switching. Physical electrical circut.
    • Packet switching. Examining metadata in a packet of info to determine its route.

Network Scope

Some people distinguish different networks by their scope:

  • A LAN (Local Area Network) connects an office area or floor or building.
  • A MAN (Metropolitan Area Network) connects LANs between buildings or across town.
  • A WAN (Wide Area Network) connects LANs and MANs between cities or countries.
  • The Internet compromises all the individual computers, LANs, MANs, and WANs that have any form of connectivity to any part of the Internet.

Network Components

Computers and Users need to be identified and organized in order for them to work together in a network.

The physical layout of a network can vary with Topologies (different geometrical arrangements) and Media (physical means of communication).

A network can be set up in two ways:

  • Client/Server. This is where there is at least one computer is a server (of its resources) and the other computers are clients (which use the resources of the servers).
  • Peer-to-Peer. This is where each computer is equal and shares resources. In effect each computer is both a server and a client.

There are many different kinds of networks here are a few:

  • Microsoft LAN Manager (DOS)
  • Microsoft Windows for Workgroups 3.x
  • Microsoft Windows NT
  • Microsoft Window 2000
  • Artisoft LANtastic
  • Banyan VINES
  • Novel Netware
  • SunSoft PC-NFS

Each kind of network uses different sets of network components:

  • Network Transports, eg TCP/IP and IPX/SPX.
  • Communications Protocols, eg RPC, NetBIOS, and named pipes.
  • Network device standards, eg NDIS and ODI.

Network Operating System

An OS (operating system) enables the user, the hardware, and the software to communicate and cooperate. A NOS (Network Operating System) enables the OS to communicate across a network with other nodes on the network. Previously, network communication capabilities were add-ons to an OS. EG: Microsoft LAN Manager was an add on to MS-DOS, Windows 3.X, OS/2, and UNIX. These days, the NOS is virtually inseparable from the OS.

Some NOSs support simultaneous connections to multiple networks. EG:

  • Windows 3.X supports 1 connection.
  • Windows for Workgroups 3.11 supports 2 connections.
  • Windows NT has no connection limit.

Just as an OS knows where things are and what they are called on the local system, an OS does the same thing across a network. A NOS has three important client services for that purpose:

  • Redirectors determines if requests are local or remote.
  • Designators map remote resources to drive letters so they appear as if they were local.
  • UNC (Universal Naming Convention) is a cross-platform convention for specifying servers, directories, files, and other resources on a network. This usual format is as follows:

Just as an OS uses a printer driver to enable local applications to print to a local driver, a NOS can enable miscellaneous services for trans-network usage. EG: In Windows:

  • Some services can be enabled with the Network applet in the Control Panel.
  • Some services must be installed from a CD.
  • Some services can be administered from the Services applet in the Control Panel.
  • Some services have a specific application to administer the service.

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