Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 989)

Quality of Service (QoS) Introduction
Software Reference for x310 Series Switches
C613-50046-01 REV A AlliedWare Plus TM Operating System - Version 5.4.4C 38.17
Policing (Metering) Your Data
Once you have set-up your classification and created your class-maps, you can start
conditioning your traffic flows. One tool used for traffic conditioning is the policer (or
meter). The principle of policing is to measure the data flow that matches the definitions
for a particular class-map; then, by selecting appropriate data rates, allocate the flows into
one of three categories: Red, Yellow, or Green. You then decide what action to apply to the
colored data.
Single-rate Three-color Policing
This policing method is based on that defined in RFC 2697. The principle of single-rate
three-color policing is shown in
Figure 38-7 . For a given class-map, a meter monitors both
the token count in the buckets, and the input data flow.
Figure 38-7: Single-rate Three-color Policing
Each byte entering the meter is paired with a token in one of the buckets, and a token is
removed as each byte is accepted. If the input data rate is the same as the CIR then the
data passes through the port at the same rate as its bucket fills. Hence the bucket level
remains constant. In this model, the data buffer is represented by two data buckets. You
can specify the CIR using the
police single-rate action command.
M
e
t
e
r
Te = Tokens in
Excess Bucket
Tc = Tokens
in Committed
Bucket
Green tokens
enter the
Committed Bucket
Yellow tokens
enter the
Excess Bucket
SR-TC_bucket_meter
CBS
(minburstsize)
EBS
(maxburstsize)
Data packets (at data rate > CIR)
packet size < Tc
packet size >Te
Packets marked after metering
Used green and yellow
tokens are replaced at the
Committed Information
Rate (CIR)
green green
green, yellow or red
yellow
red (no token top-up)
Bucket
Excess
Committed
Bucket
yellow
red
yellow
red
Single-Rate Three-Color Policing (color aware mode)
green
yellow
red red
Tc
Note that although the data is metered in bytes, coloring is applied per packet.