NAME¶
ieee80211_amrr
—
802.11 network driver transmit rate control
support
SYNOPSIS¶
#include
<net80211/ieee80211_amrr.h>
void
ieee80211_amrr_init
(
struct
ieee80211_amrr *,
struct ieee80211vap
*,
int amin,
int amax,
int
interval);
void
ieee80211_amrr_cleanup
(
struct
ieee80211_amrr *);
void
ieee80211_amrr_setinterval
(
struct
ieee80211_amrr *,
int interval);
void
ieee80211_amrr_node_init
(
struct
ieee80211_amrr *,
struct ieee80211_amrr_node
*,
struct ieee80211_node *);
int
ieee80211_amrr_choose
(
struct
ieee80211_node *,
struct ieee80211_amrr_node
*);
void
ieee80211_amrr_tx_complete
(
struct
ieee80211_amrr_node *,
int ok,
int retries);
void
ieee80211_amrr_tx_update
(
struct
ieee80211_amrr_node *,
int txnct,
int success,
int
retrycnt);
DESCRIPTION¶
ieee80211_amrr
is an implementation of the
AMRR transmit rate control algorithm for drivers that use the
net80211
software layer. A rate control
algorithm is responsible for choosing the transmit rate for each frame. To
maximize throughput algorithms try to use the highest rate that is appropriate
for the operating conditions. The rate will vary as conditions change; the
distance between two stations may change, transient noise may be present that
affects signal quality, etc.
ieee80211_amrr
uses very simple information from a driver to do it's job: whether a frame was
successfully delivered and how many transmit attempts were made. While this
enables its use with virtually any wireless device it limits it's
effectiveness--do not expect it to function well in difficult environments
and/or respond quickly to changing conditions.
ieee80211_amrr
requires per-vap state and
per-node state for each station it is to select rates for. The API's are
designed for drivers to pre-allocate state in the driver-private extension
areas of each vap and node. For example the
ral(4) driver defines a vap as:
struct rt2560_vap {
struct ieee80211vap ral_vap;
struct ieee80211_beacon_offsets ral_bo;
struct ieee80211_amrr amrr;
int (*ral_newstate)(struct ieee80211vap *,
enum ieee80211_state, int);
};
The
amrr structure member holds the per-vap
state for
ieee80211_amrr
and
ral(4) initializes it in the vap create method
with:
ieee80211_amrr_init(&rvp->amrr, vap,
IEEE80211_AMRR_MIN_SUCCESS_THRESHOLD,
IEEE80211_AMRR_MAX_SUCCESS_THRESHOLD,
500 /* ms */);
The node is defined as:
struct rt2560_node {
struct ieee80211_node ni;
struct ieee80211_amrr_node amrr;
};
with initialization done in the driver's
iv_newassoc method:
static void
rt2560_newassoc(struct ieee80211_node *ni, int isnew)
{
struct ieee80211vap *vap = ni->ni_vap;
ieee80211_amrr_node_init(&RT2560_VAP(vap)->amrr,
&RT2560_NODE(ni)->amrr, ni);
}
Once
ieee80211_amrr
state is setup, transmit
rates are requested by calling
ieee80211_amrr_choose
() in the transmit
path; e.g.:
tp = &vap->iv_txparms[ieee80211_chan2mode(ni->ni_chan)];
if (IEEE80211_IS_MULTICAST(wh->i_addr1)) {
rate = tp->mcastrate;
} else if (m0->m_flags & M_EAPOL) {
rate = tp->mgmtrate;
} else if (tp->ucastrate != IEEE80211_FIXED_RATE_NONE) {
rate = tp->ucastrate;
} else {
(void) ieee80211_amrr_choose(ni, &RT2560_NODE(ni)->amrr);
rate = ni->ni_txrate;
}
Note a rate is chosen only for unicast data frames when a fixed transmit rate is
not configured; the other cases are handled with the
net80211
transmit parameters. Note also
that
ieee80211_amrr_choose
() writes the
chosen rate in
ni_txrate; this eliminates
copying the value as it is exported to user applications so they can display
the current transmit rate in status.
The remaining work a driver must do is feed status back to
ieee80211_amrr
when a frame transmit
completes using
ieee80211_amrr_tx_complete
(). Drivers that
poll a device to retrieve statistics can use
ieee80211_amrr_tx_update
() (instead or in
addition).
SEE ALSO¶
ieee80211(9),
ieee80211_output(9)