Physical layer functions and Servicers

• Establishment and termination of a connection to a communications medium.
  
• Participation in the process whereby the communication resources are effectively shared among multiple users
  
• Conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel.
  
• Bit by bit or symbol by symbol delivery
  
• Providing a standardized interface to physical transmission media,
  
• Modulation
  
• Line coding
  
• Bit synchronization
  
• Circuit switching
  
• Multiplexing
  
• Forward error correction
  
• Auto negotiation
  
• Serial or parallel communication
  
• Bit-interleaving 
  
• channel coding
  
• Equalization filtering