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Ethernet

It is a type of communication protocol that helps to connect devices accross network.

Ethernet Frame

  • Ethernet frame starts with Preamble and SFD, both works at the physical layer.
  • Ethernet header contains both Source and Destination MAC address, after which the payload of the frame is present.
  • The last field is CRC which is used to detect the error.
    Ethernet Frame Image

Ethernet Frame Description

  1. Preamble indicates the receiver that frame is coming and allow the receiver to lock onto the data stream before the actual frame begins.
  2. Start of frame delimiter (SFD) indicates that upcoming bits are starting of the frame, which is the destination address. The SFD warns station or stations that this is the last chance for synchronization.
  3. Destination Address contains the MAC address of machine for which data is destined.
  4. Source Address – This is a 6-Byte field which contains the MAC address of source machine.
  5. Data – This is the place where actual data is inserted, also known as Payload. Both IP header and data will be inserted here if Internet Protocol is used over Ethernet.
  6. Cyclic Redundancy Check (CRC) – CRC is 4 Byte field. This field contains a 32-bits hash code of data, which is generated over the Destination Address, Source Address, Length, and Data field. If the checksum computed by destination is not the same as sent checksum value, data received is corrupted.