Faisal's Notebook

Recent Notes

Computer Networks, Communication Technologies, and Topologies

6 min read

Sources

  1. Nader F. Mir, Pearson, “Computer and communication networks” - 2015
  2. Ed Tittel, McGraw-Hill, “Schaum’s outline of theory and problems of computer networking” - 2002
  3. Greg Tomsho, Cengage, “Guide to networking essentials”, - 2020

Essential Concepts and Technologies in Computer Networking

LAN and Topologies

  • terms
    • Nader F. Mir
      • frames - packets with additional headers for local routing
      • LAN - facilitates the communication and resource sharing between devices in a small community
  • concepts
    • Nader F. Mir
      • One LAN can be connected to another LAN so that a device in that LAN can forward data to a device from the other LAN
      • There are a variety of ways to interconnect hosts in a LAN
    • Ed Tittel
      • a path is required to connect sending and receiving devices
      • the types of paths are called topologies
      • a physical network topology refers to the tangible property of the topology
      • a logical network topology refers to the behavior property of the topology
    • Greg Tomsho
      • physical topology - the arrangement and the way in which cables connect devices in a network
      • logical topology - represents the network technology used for transferring frames between devices
      • 4 basic physical topologies often used in LAN
        • bus - computers tethered using a single cable segment in series
          • strengths:
            • simplest
            • a new machine can be added by extending the cable length and connecting the last computer in the bus to the new computer
          • weaknesses:
            • 30 computers per cable segment max
            • 185 meters cable length limit
            • damages in the bus damages the entire network
            • addition/removal of devices entail temporary network shutdown
            • utilizes coaxial cabling, thereby restricting connected machines to 10 Mbps half-duplex communication
        • star - a single and central device, either a hub or switch, connects the hosts. A larger scale network can utilize the extended star topology, wherein the central device connected to and is the center of other switches which are connected to a set of computers
          • strengths:
            • faster technologies used compared to bus topology. For example, central device can be 1000 Mbps and enable full-duplex communication; whereas physical bus is limited to 10 Mbps and half-duplex only.
            • offers centralized monitoring and network traffic management
            • easier network upgrades. As long as the computer’s Network Interface Card supports (NIC) it, the network speed can be significantly improved by replacing the central device with a better switch. Nonetheless, if the NIC doesn’t support it, it can also be replaced with one that does support upgrades.
          • weaknesses:
            • there is a single point of failure—the central device; it shutting down would result in the shut down of the entire network.
        • ring - devices are connected in a loop
          • two devices which are directly connected to one another. Similar to a bus but does not terminate at each end, rather the cable at the last device is connected back to the first device.
          • was not used to connect computers in a LAN, but connect LANs (which use a star topology) with each other with the support of Fiber Distributed Data Interface (FDDI) technology1 Weakness:
            • unreliable: doesn’t travel in all directions because there is no beginning or end, as a result, it needs each station to forward and reproduce data and the data arrives at its destination. Issue here is that if one of the station fails, the ring breaks and data cannot be passed
          • FDDI overcomes the weakness of rings by using dual data rings (wherein data can travel forward and backward) to mitigate ring failure. Nonetheless, it is costly.
      • Dominant logical topologies
        • bus - one computer transmits the data to all other computers in the network. In a physical star topology that utilizes wired Ethernet, its central device will play the role of the Ethernet hub
        • ring - data sequentially travels from computer to computer until destination is reached
        • switched - a dynamic connection/switch is formed between two devices communicating with each other. This connection begins when data is sent and ends once it is not needed (i.e., they stop communicating).

Cables

  • Nader F. Mir
    • Cables, or data links, offers a physical path for signals to move between two communication entities
    • 3 most common data link types
      • twisted-pair links
        • guided media
        • usually made of copper and is made up of two insulated wires
        • twisting reduces crosstalk interference originating from the two pairs of transmission links
        • frequency range - 0 to 1 MHz
        • popular application - telephone network transmission line
      • coaxial cable links
        • offers faster data transmission for longer distances than twisted pairs
        • is composed of a hollow outer cylindrical conductor which surrounds the inner wire. between them is a solid dialectric material.
        • concentric architecture is for mitigating interference
        • applications include LAN, telephone, cable TV
        • frequency range - 0 to 750 MHz
      • fiber-optic links
        • can achieve a higher-bandwidth
        • uses a thin glass or plastic to guide an optical ray
        • has a cylindrical layout like coaxial cables. the three concentrics are the core, cladding, and jacket.
        • the core is made up of very thin fibers, each with its own cladding. the boundary between the core and the cladding allows for light reflection and transmission
        • the jacket is used to protect the cable from interference and damage
        • advantages of fiber optic links compared to coaxial cable:
          • higher bandwidths
          • lighter weights
          • lower signal attenuation
          • less affected by signal interference
        • is used in all types of data communication LAN and WAN application
        • frequency range - 180THz to 330 THz

Connectors

  • Greg Tomsho
    • list of fiber-optic connectors
      1. straight tip - usually used in ethernet networks that uses fiber-optic for their backbone. it locks to jack when twisted.
      2. straight connection - are pushed on, therefore requiring less installation effort and space for attachment. One key feature is their strong connection and their usability when the cables are spliced.
      3. locking connection - pushes and pull off with an RJ-45 latching mechanism. They are suited for applications where many fibers are focused in one small area.
      4. mechanical transfer registered jack - a mechanical transfer registered jack (MT-RJ) connector. They can be used for high-density applications since they only take half the space for the same number of cable terminations.
      5. fiber channel - they are used in some measurement equipment applications and together with single-mode lasers
      6. medium interface connector -are one-piece constructions that are used for FDDI
      7. subminiature type a - have two common versions: 905, which uses a metal sleeve for strengthening known as straight ferrule; and 906, which uses a stepped ferrule instead that has a plastic sleeve, thereby guaranteeing the fibers precise alignment.

Footnotes

  1. FDDI is a cabling that was fast and reliable. It is primarily used to enable communication between switches/LANs ↩

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