How are acknowledgement sent at data link layer to the sender when crc of frame is incorrect?

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How are acknowledgement sent at data link layer to the sender when crc of frame is incorrect?

That depends on the Data-Link protocol, but most Data-Link protocols simply drop bad frames. For example, if an ethernet device receives a frame with a bad FCS, the hardware simply discards the frame, and it never reaches the Data-Link layer.

Also, most Data-Link protocols do not perform any type of acknowledgement. They are connectionless protocols that send out a frame, and they do not care that the frame is damaged or dropped.

  • But ARQ or Stop and wait sends NACK if the data was not received. How does it tell the sender which frame to send again since there is no sequencing in frames? – Ajay Pandita Sep 21 '18 at 16:33
  • You are talking about transport-layer protocols, like TCP. Data-Link protocols are like ethernet, frame relay, Wi-Fi, ATM. PPP, token ring, ARCNET, etc. – Ron Maupin Sep 21 '18 at 18:30
  • But data link layer uses flow control methods like ALQ. They send ack or nack according to the situation. How they do it? – Ajay Pandita Sep 21 '18 at 19:09
  • No, they don't. In the real world, what we answer of here, Data-Link protocols are connectionless, as is IP. TCP, a Transport-layer protocol, is connection-oriented, and it uses ACKs. Ethernet and Wi-Fi interfaces are what you get on the PC, printers, laptops, etc., and those, which are series of Physical and a Data-Link protocols , have no such thing as you describe. I have no idea where you are getting your ideas. – Ron Maupin Sep 21 '18 at 19:23
  • So if CRC check fails then that frame will be dropped. But what will the sender do about that? – Ajay Pandita Sep 21 '18 at 19:26

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