Frame

What is a frame?

Answer #

Container for a chunk of data as it moves across the network. NIC s create and send as well as receive and read frames.

Generic Frame #

| Destination | Source | Type | Data | FCS | | MAC address | MAC address | | | | Usually holds at most 1500 bytes of data.

  • Preamble See below
  • MAC address
  • Type Identifies data encoding at a very basic level. IPv4 vs IPv6, for example.
  • Data Whatever payload the frame carries. IP packet for example
  • Pad The minimum Ethernet frame is 64 bytes. If a frame has fewer than 64 bytes of data the sending NIC will automatically add extra data.
  • FCS
    • FCS: Frame Check Sequence
    • 4 bytes long
    • Uses CRC to check the integrity of the data
    • CRC: cyclic redundancy check

Unicast frame #

Any frame specifically addressed to another device’s MAC address. unicast addressing

Ethernet frame #

Same basic fields as the generic frame.

  • Transmission starts with a preamble and can also include extra filler
  • called a pad.
  • preamble: 7-byte series of alternating 1s and 0s followed by a 1-byte start frame delimiter.