/share/man/man9/ieee80211_amrr.9

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 26.\" $FreeBSD$
 27.\"
 28.Dd August 4, 2009
 29.Dt IEEE8021_AMRR 9
 30.Os
 31.Sh NAME
 32.Nm ieee80211_amrr
 33.Nd 802.11 network driver transmit rate control support
 34.Sh SYNOPSIS
 35.In net80211/ieee80211_amrr.h
 36.Ft void
 37.Fo ieee80211_amrr_init
 38.Fa "struct ieee80211_amrr *"
 39.Fa "struct ieee80211vap *"
 40.Fa "int amin"
 41.Fa "int amax"
 42.Fa "int interval"
 43.Fc
 44.\"
 45.Ft void
 46.Fn ieee80211_amrr_cleanup "struct ieee80211_amrr *"
 47.\"
 48.Ft void
 49.Fn ieee80211_amrr_setinterval "struct ieee80211_amrr *" "int interval"
 50.\"
 51.Ft void
 52.Fo ieee80211_amrr_node_init
 53.Fa "struct ieee80211_amrr *"
 54.Fa "struct ieee80211_amrr_node *"
 55.Fa "struct ieee80211_node *"
 56.Fc
 57.\"
 58.Ft int
 59.Fo ieee80211_amrr_choose
 60.Fa "struct ieee80211_node *"
 61.Fa "struct ieee80211_amrr_node *"
 62.Fc
 63.\"
 64.Ft void
 65.Fo ieee80211_amrr_tx_complete
 66.Fa "struct ieee80211_amrr_node *"
 67.Fa "int ok"
 68.Fa "int retries"
 69.Fc
 70.\"
 71.Ft void
 72.Fo ieee80211_amrr_tx_update
 73.Fa "struct ieee80211_amrr_node *"
 74.Fa "int txnct"
 75.Fa "int success"
 76.Fa "int retrycnt"
 77.Fc
 78.Sh DESCRIPTION
 79.Nm
 80is an implementation of the AMRR transmit rate control algorithm
 81for drivers that use the
 82.Nm net80211
 83software layer.
 84A rate control algorithm is responsible for choosing the transmit
 85rate for each frame.
 86To maximize throughput algorithms try to use the highest rate that
 87is appropriate for the operating conditions.
 88The rate will vary as conditions change; the distance between two stations
 89may change, transient noise may be present that affects signal quality,
 90etc.
 91.Nm
 92uses very simple information from a driver to do it's job:
 93whether a frame was successfully delivered and how many transmit
 94attempts were made.
 95While this enables its use with virtually any wireless device it
 96limits it's effectiveness--do not expect it to function well in
 97difficult environments and/or respond quickly to changing conditions.
 98.Pp
 99.Nm
100requires per-vap state and per-node state for each station it is to
101select rates for.
102The API's are designed for drivers to pre-allocate state in the
103driver-private extension areas of each vap and node.
104For example the
105.Xr ral 4
106driver defines a vap as:
107.Bd -literal -offset indent
108struct rt2560_vap {
109        struct ieee80211vap     ral_vap;
110        struct ieee80211_beacon_offsets ral_bo;
111        struct ieee80211_amrr   amrr;
112
113        int      (*ral_newstate)(struct ieee80211vap *,
114                      enum ieee80211_state, int);
115};
116.Ed
117.Pp
118The
119.Vt amrr
120structure member holds the per-vap state for
121.Nm
122and
123.Xr ral 4
124initializes it in the vap create method with:
125.Bd -literal -offset indent
126ieee80211_amrr_init(&rvp->amrr, vap,
127    IEEE80211_AMRR_MIN_SUCCESS_THRESHOLD,
128    IEEE80211_AMRR_MAX_SUCCESS_THRESHOLD,
129    500 /* ms */);
130.Ed
131.Pp
132The node is defined as:
133.Bd -literal -offset indent
134struct rt2560_node {
135        struct ieee80211_node   ni;
136        struct ieee80211_amrr_node amrr;
137};
138.Ed
139.Pp
140with initialization done in the driver's
141.Vt iv_newassoc
142method:
143.Bd -literal -offset indent
144static void
145rt2560_newassoc(struct ieee80211_node *ni, int isnew)
146{
147        struct ieee80211vap *vap = ni->ni_vap;
148
149        ieee80211_amrr_node_init(&RT2560_VAP(vap)->amrr,
150            &RT2560_NODE(ni)->amrr, ni);
151}
152.Ed
153.Pp
154Once
155.Nm
156state is setup, transmit rates are requested by calling
157.Fn ieee80211_amrr_choose
158in the transmit path; e.g.:
159.Bd -literal -offset indent
160tp = &vap->iv_txparms[ieee80211_chan2mode(ni->ni_chan)];
161if (IEEE80211_IS_MULTICAST(wh->i_addr1)) {
162	rate = tp->mcastrate;
163} else if (m0->m_flags & M_EAPOL) {
164	rate = tp->mgmtrate;
165} else if (tp->ucastrate != IEEE80211_FIXED_RATE_NONE) {
166	rate = tp->ucastrate;
167} else {
168	(void) ieee80211_amrr_choose(ni, &RT2560_NODE(ni)->amrr);
169	rate = ni->ni_txrate;
170}
171.Ed
172.Pp
173Note a rate is chosen only for unicast data frames when a fixed
174transmit rate is not configured; the other cases are handled with
175the
176.Nm net80211
177transmit parameters.
178Note also that
179.Fn ieee80211_amrr_choose
180writes the chosen rate in
181.Vt ni_txrate ;
182this eliminates copying the value as it is exported to user applications so
183they can display the current transmit rate in status.
184.Pp
185The remaining work a driver must do is feed status back to
186.Nm
187when a frame transmit completes using
188.Fn ieee80211_amrr_tx_complete .
189Drivers that poll a device to retrieve statistics can use
190.Fn ieee80211_amrr_tx_update
191(instead or in addition).
192.Sh SEE ALSO
193.Xr ieee80211 9 ,
194.Xr ieee80211_output 9