Reading up about the data link layer I found that the logical link control sublayer uses sequence numbers to find duplicate packet frame transmissions.

I understood the sequence number game with respect to one transmitter and receiver but how does it work with multiple transmitters and a single receiver? Does the receiver need to maintain a table with MAC address and the next sequence number?

Or the duplicate frame "data" (or whatever it is called at that layer) detection is done at a higher layer?

  • 2
    Where did you read that logical link control sublayer uses sequence numbers?
    – hertitu
    Feb 6, 2017 at 11:31
  • IEEE 802.2 (LLC) type 2 is connection oriented and does use sequence numbers.
    – JFL
    Feb 6, 2017 at 12:00

1 Answer 1


Connection-oriented protocols are not used in "one transmitter, many receivers" scenarios, because of exactly the problem you mention. This is true not only of 802.2 Type 2, but also for IP multicast, which only uses UDP, not TCP.

Practically speaking, 802.2 type 2 is obsolete -- You would be hard pressed to find it in use anywhere.

  • So you mean to say that the duplicate detection is done at higher layers like TCP? Then how do sliding window techniques detect duplicate frames at the link layer? Feb 6, 2017 at 12:58
  • Sliding window doesn't detect duplicate frames only duplicate segments. Feb 6, 2017 at 13:05
  • Sliding window doesn't detect duplicate frames/packets. It is used to make transmissions more efficient by not requiring every frame to be acknowledged individually. AFAIK, its not used with type 2.
    – Ron Trunk
    Feb 6, 2017 at 13:08
  • There is no reliability control for duplicate frames, lost frames etc. on layer 2. All of this is handled by upper layer protocol. Feb 6, 2017 at 13:13
  • HDLC does provide for reliable transmission on a point to point link through sequence numbers and ACKs (this includes detecting duplicates), I don't know if it's totally obsolete or still alive somehow.
    – JeanPierre
    Feb 6, 2017 at 13:48

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