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Simplify the duration calculations somewhat. 

* Add an intermediate variable, ctsrate, which is currently derived directly
 from rate, but may be handled differently later (especially for 11g).
* Assume ACKs are sent at the same rate as the original data packet, as ath
  does, shortening the ACK reservation time substantially.
* Add a note that we need to deal with not adding the ACK time for some
  packets, though this is not implemented yet.

Questions:
* How do we affect the control rate used to send RTS/CTS packets?
* Is the PLCP header length actually controlled by the preamble length
  selection, or should this be based on the transmit rate?

Of course short preamble is not actually implemented/working yet.
This commit is contained in:
mycroft 2004-12-27 05:35:33 +00:00
parent 60b9b5a6ef
commit e3c9106a08
1 changed files with 25 additions and 30 deletions
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55
sys/net80211/ieee80211_output.c
View File

@ -1,4 +1,4 @@
/* $NetBSD: ieee80211_output.c,v 1.21 2004/12/27 01:57:58 mycroft Exp $ */
/* $NetBSD: ieee80211_output.c,v 1.22 2004/12/27 05:35:33 mycroft Exp $ */
/*-
* Copyright (c) 2001 Atsushi Onoe
* Copyright (c) 2002, 2003 Sam Leffler, Errno Consulting
@ -35,7 +35,7 @@
#ifdef __FreeBSD__
__FBSDID("$FreeBSD: src/sys/net80211/ieee80211_output.c,v 1.10 2004/04/02 23:25:39 sam Exp $");
#else
__KERNEL_RCSID(0, "$NetBSD: ieee80211_output.c,v 1.21 2004/12/27 01:57:58 mycroft Exp $");
__KERNEL_RCSID(0, "$NetBSD: ieee80211_output.c,v 1.22 2004/12/27 05:35:33 mycroft Exp $");
#endif
#include "opt_inet.h"
@ -296,40 +296,46 @@ static int
ieee80211_compute_duration1(int len, uint32_t flags, int rate,
struct ieee80211_duration *d)
{
int ack, bitlen, cts, data_dur, remainder;
int pre, ctsrate;
int bitlen, data_dur, remainder;
/* RTS reserves medium for SIFS | CTS | SIFS | (DATA) | SIFS | ACK
* DATA reserves medium for SIFS | ACK
*
* XXXMYC: no ACK on multicast/broadcast or control packets
*/
bitlen = len * 8;
pre = IEEE80211_DUR_DS_SIFS;
if ((flags & IEEE80211_F_SHPREAMBLE) != 0)
pre += IEEE80211_DUR_DS_SHORT_PREAMBLE + IEEE80211_DUR_DS_FAST_PLCPHDR;
else
pre += IEEE80211_DUR_DS_LONG_PREAMBLE + IEEE80211_DUR_DS_SLOW_PLCPHDR;
#if 0
/* RTS is always sent at 1 Mb/s. (XXX Really?) */
d->d_rts_plcp_len = sizeof(struct ieee80211_frame_rts) * 8;
#endif
d->d_residue = 0;
data_dur = (bitlen * 2) / rate;
remainder = (bitlen * 2) % rate;
if (remainder != 0) {
d->d_residue = (rate - remainder) / 16;
data_dur++;
}
switch (rate) {
case 2: /* 1 Mb/s */
case 4: /* 2 Mb/s */
/* 1 - 2 Mb/s WLAN: send ACK/CTS at 1 Mb/s */
cts = IEEE80211_DUR_DS_SLOW_CTS;
ack = IEEE80211_DUR_DS_SLOW_ACK;
ctsrate = 2;
break;
case 11: /* 5.5 Mb/s */
case 22: /* 11 Mb/s */
case 44: /* 22 Mb/s */
remainder = (bitlen * 2) % rate;
if (remainder != 0) {
data_dur++;
d->d_residue = (rate - remainder) / 16;
}
/* 5.5 - 11 Mb/s WLAN: send ACK/CTS at 2 Mb/s */
cts = IEEE80211_DUR_DS_FAST_CTS;
ack = IEEE80211_DUR_DS_FAST_ACK;
ctsrate = 4;
break;
default:
/* TBD */
@ -338,25 +344,14 @@ ieee80211_compute_duration1(int len, uint32_t flags, int rate,
d->d_plcp_len = data_dur;
d->d_rts_dur = data_dur + 3 * (IEEE80211_DUR_DS_SIFS +
IEEE80211_DUR_DS_SHORT_PREAMBLE +
IEEE80211_DUR_DS_FAST_PLCPHDR) + cts + ack;
d->d_rts_dur =
pre + (IEEE80211_DUR_DS_SLOW_CTS * 2) / ctsrate +
pre + data_dur +
pre + (IEEE80211_DUR_DS_SLOW_ACK * 2) / ctsrate;
/* Note that this is the amount of time reserved *after*
* the packet is transmitted: just long enough for a SIFS
* and an ACK.
*/
d->d_data_dur = IEEE80211_DUR_DS_SIFS +
IEEE80211_DUR_DS_SHORT_PREAMBLE + IEEE80211_DUR_DS_FAST_PLCPHDR +
ack;
d->d_data_dur =
pre + (IEEE80211_DUR_DS_SLOW_ACK * 2) / rate;
if ((flags & IEEE80211_F_SHPREAMBLE) != 0)
return 0;
d->d_rts_dur += 3 * IEEE80211_DUR_DS_PREAMBLE_DIFFERENCE +
3 * IEEE80211_DUR_DS_PLCPHDR_DIFFERENCE;
d->d_data_dur += IEEE80211_DUR_DS_PREAMBLE_DIFFERENCE +
IEEE80211_DUR_DS_PLCPHDR_DIFFERENCE;
return 0;
}