The tokenmt module can be configured as a Single or a Two Rate meter. Packets are deemed to belong to one of the three levels - Red, Yellow or Green - depending on the configured rate(s) and the burst sizes. When configured as a Single Rate meter, tokenmt can operate with just the Green and Red levels.

Configuration parameters for tokenmt correspond to definitions in RFC- 2697 and RFC- 2698 as follows:

Configuring tokenmt as a Single Rate meter (from RFC- 2697):

committed_rate - CIR

committed_burst - CBS

peak_burst - EBS

(thus 'peak_burst' for a single rate meter is actually the 'excess burst' in the RFC. However, throughout the text the parameter name "peak burst" is used.)

Configuring tokenmt as a Two Rate meter (from RFC- 2698):

committed_rate - CIR

peak_rate - PIR

committed_burst - CBS

peak_burst - PBS

The meter is implemented using token buckets C and P, which initially hold tokens equivalent to committed and peak burst sizes (bits) respectively. When a packet of size B bits arrive at time t, the following occurs:

When operating as a Single Rate meter, the outcome (level)
is decided as follows:
 - Update tokens in C and P
 o Compute no. of tokens accumulated since the
 last time packet was seen at the committed rate as
 T(t) = committed rate * (t - t')
 (where t' is the time the last packet was seen)
 o Add T tokens to C up to a maximum of committed burst
 size. Add remaining tokens ((C+T) - Committed Burst),
 if any, to P, to a maximum of peak burst size.
 - Decide outcome
 o If not color aware
 o If B <= C, outcome is GREEN and C -= B.
 o Else, if B <= P, outcome is YELLOW and P -= B.
 o Else, outcome is Red.
 o Else,
 o obtain DSCP from packet
 o obtain color from color_map, color_map[DSCP]
 o if (color is GREEN) and (B <= C), outcome is
 GREEN and C -= B.
 o Else, if (color is GREEN or YELLOW) and
 (B <= P), outcome is YELLOW and P -= B.
 o Else, outcome is RED.
 Note that if peak_burst and yellow_next_actions are
 not specified (that is, a single rate meter with two
 outcomes), the outcome is never YELLOW.

When operating as a Two Rate meter, the outcome (level) is decided as follows:

- Update tokens in C and P
 o Compute no. of tokens accumulated since the last time a
 packet was seen at the committed and peak rates as
 Tc(t) = committed rate * (t - t')
 Tp(t) = peak rate * (t - t')
 (where t' is the time the last packet was seen)
 o Add Tc to C up to a maximum of committed burst size
 o Add Tp to P up to a maximum of peak burst size
 - Decide outcome
 o If not color aware
 o If B > P, outcome is RED.
 o Else, if B > C, outcome is YELLOW and P -= B
 o Else, outcome is GREEN and C -= B & P -= B
 o Else,
 o obtain DSCP from packet
 o obtain color from color_map, color_map[DSCP]
 o if (color is RED) or (B > P), outcome is RED
 o Else, if (color is YELLOW) or (B > C),
 outcome is YELLOW and P -= B
 o Else, outcome is GREEN and C -= B & P -= B

The tokenmt module exports the following statistics through kstat:

Global statistics:

module: tokenmt instance: <action id>
 name: tokenmt statistics class <action name>
 epackets <number of packets in error>
 green_bits <number of bits in green>
 green_packets <number of packets in green>
 red_bits <number of bits in red>
 red_packets <number of packets in red>
 yellow_bits <number of bits in yellow>
 yellow packets <number of packets in yellow>

dlcosmk (4IPP), dscpmk (4IPP), flowacct (4IPP), ipgpc (4IPP), ipqos (4IPP), tswtclmt (4IPP), ipqosconf (8)

RFC 2697, A Single Rate Three Color Marker J. Heinanen, R. Guerin \(em The Internet Society, 1999

RFC 2698, A Two Rate Three Color Marker J. Heinanen, R. Guerin \(em The Internet Society, 1999