NOTE: this page is for archival only, see the note at the end of the page.

For QoS/WMM (EDCA) a mac80211 driver needs to have at least four queues. mac80211 will then program the queues according to the advertised access parameters.

Legend:

  • MQ: mac80211 queue

  • AC: Access Class

  • ACI: Access Class Index

mac80211 queue mapping:

AC

MQ

BK

3

BE

2

VI

1

VO

0

802.11 uses the following number scheme (cf. Table 7-36)

AC

ACI

BK

01 (1)

BE

00 (0)

VI

10 (2)

VO

11 (3)

Therefore, we have:

AC

ACI

MQ

BK

1

3

BE

0

2

VI

2

1

VO

3

0

Due to internal collisions (we don't really know what this means either) the queue numbering is important, and queue 0 is highest priority, 3 lowest. If your hardware has a different idea of queue priority, you may need to rewrite the queue number, but make sure to do it everywhere mac80211 passes a queue number (conf_tx, skb_get_queue_mapping).

The user priority is used as follows (802.11-2007 table 9-1):

UP

AC

Priority

1

BK

Lowest

2

BK

.

0

BE

.

3

BE

.

4

VI

.

5

VI

.

6

VO

.

7

VO

Highest

TOS:

mac80211 currently determines the UP based only on the IPv4 TOS field, unless the packet priority is set to 256..263 with setsockopt(SO_PRIORITY), in which case this maps directly to the UP (priority - 256) for testing.

The IPv4 TOS field maps into the UP as follows, but keep in mind that the lowest two bits of the TOS are reserved (or used for ECN):

TOS

UP

0 - 31

0

32 - 63

1

...

224 - 255

7

DSCP (RFC 2474):

Alternatively you can set the IP_TOS with setsockopt, then you need to ask how DSCP maps into the UP. DSCP is defined in the Differentiated Services (DiffServ) model as the six most significant bits of the DiffServ(DS) Field.

DS5 (P2)

DS4 (P1)

DS3 (P0)

DS2

DS1

DS0

ECN

ECN

The classes of DSCP in wide usage are:

DSCP Class

Codepoint(s)

Default

0x00

Expedited Forwarding (EF)

0x2E

Assured Forwarding (AF1)

0xA, 0xC, 0xE

Assured Forwarding (AF2)

0x12, 0x14, 0x16

Assured Forwarding (AF3)

0x1A, 0x1C, 0x1E

Assured Forwarding (AF4)

0x22, 0x24, 0x26

The 3 Precedence bits of DSCP (P2, P1, P0) are used for mapping to 802.1D tags and AC values as:

P2 P1 P0

802.1D

AC

0 0 0

0

BE

0 0 1

1

BK

0 1 0

2

BK

0 1 1

3

BE

1 0 0

4

VI

1 0 1

5

VI

1 1 0

6

VO

1 1 1

7

VO


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