0ffset Posted October 23, 2011 Share Posted October 23, 2011 I just can't get my head around this. Considering a system using stop-and-wait ARQ, does the PER include the packets that has to be resent? I mean, isn't the PER value the probability of a packet containing an error? If so, every time a packet is received, there's a PER chance it's erroneous. If the packet is indeed erroneous a second time, it has to be resent, and that resent packet also has a probability of PER that it arrives with an error, and if that one also contains an error, it has o be resent, and so on... This would imply that there's a difference of a total PER and the PER given by the BER value. Or isn't the PER value really the probability of one packet containing a bit error, but rather the total ratio between correct and incorrect packets received over time including the packets that were resent? I would really appreciate it if somebody would try to explain so i'd understand. Link to comment Share on other sites More sharing options...
Xittenn Posted October 23, 2011 Share Posted October 23, 2011 I don't think there is a standard that defines Packet Error Rate explicitly. And if somewhere in the megatons of literature there is one, well there are several different standards, so you would be required to be more specific. I think it's safe to say that most would just include the resent packages in their figures, but these would represent some small fractions of their values. Your statement "This would imply that there's a difference of a total PER and the PER given by the BER value." is kind of 52 card pick up and I prefer to not spend my time guessing at the meaning of these kinds of statements. If a packet is resent and has an error a second time, and the error is different then the measured PER and BER may be different in contrast to such a package never having ever existed. This said I think that it is safe to say that claims given of PER and BER in real life communications are in fact averages of observed and measured PER and BER during testing or from logging of such events. What does it really matter though? These figures simply give an idea as to the effectiveness of the system in use and do not play such important roles beyond that of guesstimating figures for settings in traffic control. Given the small discrepancies in the difference between the two possibilities well .. . . . Link to comment Share on other sites More sharing options...
khaled Posted October 29, 2011 Share Posted October 29, 2011 Such rates that are considered from a real system .. are not taken by a constant, equation, or a thought They are statistically given based on an existing networks at a given time in history, Link to comment Share on other sites More sharing options...
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