WinlabMadwifi → MIT's SampleRate Algorithm

SampleRate Algorithm:

implemented by

- sample.c
- sample.h

This algorithm conducts a per-MAC destination rate control. For each different destination, link statistics are stored separately.

Description of functions in sample.c:

I. static __inline int best_rate_ndx(struct sample_node *sn, int size_bin, int require_acked_before)

The objective of this function is to return the bit-rate with the lowest avg. pkt. tx. time.

Process information starting from the lowest rate: 1. if ((avg. pkt. tx. time for this pkt. size and bit-rate <= 0) or ((packets have not been acked for this pkt. size and bit-rate) and (multi-rate retry is disabled))) process next higher bit-rate; 2. if (processing 9Mbps) process next higher bit-rate; // 9Mbps is never better than 12Mbps 3. if (successive failures at this rate > 3) process next higher bit-rate; 4. if (avg. pkt. tx. time for this rate is lowest so far) set best_rate_index to that of current rate; if (best rate index found) return best_rate_index; else return -1;

II. static __inline int pick_sample_ndx(struct sample_node *sn, int size_bin)

The objective of this function is to return the index of a "suitable" bit-rate that can be sampled.

1. if (no packets have been sent successfully at any of the higher bit-rates) return (index of lowest bit-rate); 2. current_tx_time = avg. tx. time for the bit-rate at which the card was operating in the previous interval; 3. Process information starting from the index of the lowest rate (for (i = 0); i < max_rate_index; i++)): 1. Choose 1 + the index of the last rate that was sampled + i; 2. if (i == current_rate_index) proceed to next higher bit-rate; 3. if (perfect_tx_time(rate(i)) > avg. tx. time (current rate)) proceed to next higher bit-rate; 4. if ((last tx. at rate(i) was less than 10 seconds ago) and (successive failures at rate(i) > 3)) proceed to next higher bit-rate; 5. if ((rate(i) > 11Mbps) and (rate(i) > current rate + 2)) proceed to next higher bit-rate; 6. if (rate(i) == 9Mbps) process next higher bit-rate; // 9Mbps is never better than 12Mbps 7. if ((current rate == 11Mbps) and (rate(i) > 12Mbps)) proceed to next higher bit-rate; 8. return i;

Last modified
18 years ago
Last modified on Feb 28, 2006, 12:46:23 PM

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