Hi all, I am studying the minstrel rate control mechinsim in mac80211. I have observed a few strange problem with the current implementation of the minstrel on the mac80211. They are explained below: 1. Different DIFS values were used by madwifi 0.9.4 and mac80211. In madwifi 0.9.4, the DIFS is set to 28 from the source code in the calc_usecs_unicast_packet() function. However, according to the IEEE 802.11 2007 standard, the DIFS time for OFDM should be 34, which is 2 slot time plus a SIFS time shown in table 17-15 in page 626 or described in page 271. Why we have different DIFS values? 2. Another question is on how we calculate the frame transmission time In the function "ieee80211_frame_duration()" within util.c on the mac80211 framework, the frame time is calculated as the following. dur = 16; /* SIFS + signal ext */ dur += 16; /* T_PREAMBLE = 16 usec */ dur += 4; /* T_SIGNAL = 4 usec */ dur += 4 * DIV_ROUND_UP((16 + 8 * (len + 4) + 6) * 10, 4 * rate); /* T_SYM x N_SYM */ In mac80211 based minstrel implementation, minstrel uses the able fuction to calculate the time for sending a data frame as well as sending an ack. to our understanding the normal transmission time is calculated as below (assume no retransmission): DIFS + contentionWindow + dataTime + SIFS + ackTime where dataTime=T_PREAMBLE + T_SIGNAL + T_SYM * N_SYM ackTime is similar but in Minstrel's implementation (using the above "ieee80211_frame_duration()" function), we effectively calculate the transmission time as SIFS + contentionWindow + dataTime + SIFS + ackTime So why there are two SIFS??? Any idea? -- regards; Peizhao The information in this e-mail may be confidential and subject to legal professional privilege and/or copyright. National ICT Australia Limited accepts no liability for any damage caused by this email or its attachments. -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
