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tokenmt - Single and Two Rate Three Conformance Level Meter
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) - Commited 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>
/kernel/ipp/sparcv9/tokenmt
See attributes(5) for descriptions of the following attributes:
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ipqosconf(1M), dlcosmk(7ipp), dscpmk(7ipp), flowacct(7ipp), ipqos(7ipp), ipgpc(7ipp), tswtclmt(7ipp)
RFC 2697, A Single Rate Three Color Marker J. Heinanen, R. Guerin --- The Internet Society, 1999
RFC 2698, A Two Rate Three Color Marker J. Heinanen, R. Guerin --- The Internet Society, 1999
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