Computer Network – Physical Layer

  1. Functions of Physical Layer
  2. Data and Signals
    1. Analog and Digital Signals
    2. Transmission Impairment
    3. Data rate Limits
    4. Performance
  3. Data Transmission Media
    1. Guided Media
    2. Unguided Media
    3. Satellites
  4. Bandwidth Utilization
    1. Multiplexing
    2. Spreading
  5. Switching
    1. Circuit Switching
    2. Message Switching
    3. Packet Switching
  6. Telephone, Mobile and Cable network for Data Communications

Functions of Physical Layer

The main function of physical layer is to transmit the bitstream over a physical medium. The electricals and mechanical specifications of the interface and transmission medium deals by this layer. However it doesn’t deal with the actual physical medium like light in fiber optics and copper in the wire.

Main Functions

  • Representations of bits : Basically, it involves a stream of bits (what we call as 0s and 1s) without any interpretation. In order to transmit these sequence of 0s and 1s must be encoded into the signals, either that can be in the form of electrical or optical or some waves.
    • This layer defines the type of encoding of those bits
    • It is responsible for the bit-by-bit delivery of the data to its upper layer called the MAC layer (we will discuss about that in next chapter).
    • It is responsible for delivering the signals from a cable, a wi-fi router or an optical fiber
  • Data Rate :
  • Synchronization of bits :
  • Line Configuration :
  • Physical Topology :
  • Transmission Mode :

Data and Signals

Analog and Digital Signals

Transmission Impairment

Data Rate Limits


Data Transmission Media

Guided Media

Unguided Media


Bandwidth Utilization




Circuit Switching

Message Switching

Packet Switching

Telephone, Mobile and Cable network for Data Communications

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