What are Transceivers or PHYs?

  • Transceivers (read as Transmitters/Receivers) are  dedicated piece of hardware  used to transmit and receive data through different wired and wireless media.  As they operate at the physical layer, they are also called as PHYs. 
  • PHYs primary duty is to take care of line encoding (converting the bits into electrical/electromagnetic/optical signals) for data transmission and line decoding (converting back the received signals into bits) for data reception. In cases  where the PHYs perform some form of digital/analog modulation of digital data, then such PHYs may also be called as modems (e.g. DSL modem, Cable modem PHYs etc.)
  • As part of line encoding, they also take care of line clocking (i.e. maintaining the bit interval). In the transmission direction, they make sure that the signal value for each bit is sent for a certain fixed duration (bit interval). Similarly, in the receiving direction, they are capable of monitoring each signal value for a duration equal to the bit interval, before deciding whether the bit is a digital 0 or a digital 1
  • Additionally, PHYs may also have the MAC (Media Access Control) functionality built into them. This functionality enables contention resolution among multiple nodes sharing a common link/media (like a bus topology), so that the nodes could cooperatively use the media for transmitting and receiving data.

The diagram given below illustrates some examples of Transceivers/PHYs/modems:

Examples of Physical Layer Transceivers/PHYs/Modems

Examples of Physical Layer Transceivers/PHYs/Modems

As shown in the diagram,

  • the PHYs are dedicated piece of hardware components.
  • there needs to be a dedicated PHY for each physical interface in a device
  • the Wired Ethernet NIC (Network interface card) that is typically found in every PC/laptop has a dedicated PHY implementing the Ethernet line coding protocols.
  • Similary, the wireless NIC card that is typically found in every PC/laptop has a dedicated PHY that implements the line encoding for wireless LAN protocols like 802.11 a/b/g/n. In this case, the PHY would be connected to an antennae for transmitting electromagnetic signals through the wireless media.

 

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