[Day 3] 3. Physical Layer

Dumb layer. Doesn't have any logic

Examples are

• Cables,
• Crimps ,
• Connectors (RJ45, RJ11 --> used in telephones),
• Voltages (+5V, +2V),
• Bits(0, 1),
• CSU/DSU(Channel Service Unit/ Data Service Unit),
• DTE/DCE, (Data Terminating Equipment, Data Communication Equipment or Data Circuit Terminal Equipment)
  • Parallel Cables are used for shorter device.
  • Serial cables can be taken up to longer distances.
    • Synchronous Serial Communication
      • Out of two devices one of the devices that are communicating one will provide a pulse called as Clocking, that device is called as DCE and the one receiving the pulse is called as DTE. Both of them will communicate with each other in this case even though there is one provider and one receiver of the pulses (not the data).
    • Asynchronous Serial Communication
      • Asynchronous serial communication is a method of data transmission between two devices that doesn't use a common clock signal to synchronize the interfaces of the communicating devices. Instead, start and stop bits are used to indicate the beginning and end of a data message.
      • ATM (Asynchronous Transmission Mode): Asynchronous Transfer Mode (ATM) is a telecommunications standard that uses cells to transmit data, voice, and video over wide-area networks (WANs). ATM is known for its low latency, high quality of service, and scalability. Although ATM was once a popular solution for high-speed networking, its use has declined with the rise of newer technologies like Ethernet and IP-based solutions.
• HUBs: Even when the connection of one device is destroyed, the other devices can still communicate among each other. But has a range of only 100 meters. Due to internal resistance of the material, the strength of the signal goes on increasing which is called as Attenuation.
• Repeater: Amplifies the signal and can send it to next 100 meters.
  • Amplification by HUB and by repeater are different. During the transmission by HUB the noise might distort the transmission, whereas when Repeater amplifies it, it also purifies the signal.