In a noiseless channel can frames in the 2 layer of OSI model(Data link layer) reach to the destination out of order?
*I am studying from Computer networks 5 Edition of Andrew S. Tanenbaum
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3 Answers
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Yes this is possible. For instance when the protocol sends several frames without waiting for the individual acknowledgements: if one of the frames gets lost it will be retransmitted out of order.
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It depends on the channel and the assumptions you are making. There may well be some communication channels where messages can be re-ordered but will not be dropped or lost or modified in transit.
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A channel is an abstraction. And an asbstraction can only do what it is assumed to be doing. When describing networks, we usually assume channel capabilities related to in-order delivery, which are completely independent of being noisy or not.
If you plug in a singe cable between two single core devices, then probably no reordering can happen. However data link layer is more complicated than this.
- Ethernet is a network with bridges, and as such, frames can be delivered out of order, e.g., when topology changes. Note also, that if packets are dropped in bridges during topology changes, it is not called noise.
- there are technologies (i think link bonding) where a single link consists of several physical wires, and since that packets that are sent over different wires can be reordered
- on a PC with multicore processors, packets can be reordered if you process one packet by one core and one by another, and there is no guarantee that order is preserved
