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).