I'm confused with some concepts please help me out,

  1. Data link layer manage flow control hop to hop. Flow control requires acknowledgement receiving but If we observe data link layer header, it does not have any ack field.Ethernet frame format

So does that mean data link layer always depend on transport layer for acknowledgement processing?

  1. On receiving a packet from any local nodes does router gives acknowledgement in return? If they do then how it is possible as they operate only up to network layer and ack generate in transport layer?
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1 Answer 1


The Data link layer in Ethernet (802.3) contains two sublayers :

  • Media Access Control (MAC)
  • Logical Link Control (LLC)

LLC does not provide flow control. Incorrect packets are detected and discarded, and the retransmissions rely on higher layer protocols.

The idea behind this behaviour is that wired networks have a very low error ratio, so an ACK and retransmission mechanism is unnecesary and make the network slower.

In 802.11 there is flow control and error management.

It isn't in the LLC sublayer. It is part of the CSMA/CA MAC protocol.

In CSMA/CA The receiving node sends an ACK after receiving a packet. If the ACK is not received, the packet is considered lost and the sender tries a retransmission.

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Wireless networks have higher error ratios. It is necessary to have it.

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