The meter tracks the transmission rate of flows on a per-packet basis. The meter then determines whether the packet conforms to the configured parameters. The meter module determines the next action for a packet from a set of actions that depend on packet size, configured parameters, and flow rate.
The meter consists of two metering modules, tokenmt and tswtclmt, which you configure in the IPQoS configuration file. You can configure either module or both modules for a class.
When you configure a metering module, you can define two parameters for rate:
committed-rate – Defines the acceptable transmission rate in bits per second for packets of a particular class
peak-rate – Defines the maximum transmission rate in bits per second that is allowable for packets of a particular class
A metering action on a packet can result in one of three outcomes:
green – The packet causes the flow to remain within its committed rate.
yellow – The packet causes the flow to exceed its committed rate but not its peak rate.
red – The packet causes the flow to exceed its peak rate.
You can configure each outcome with different actions in the IPQoS configuration file.
The tokenmt module uses token buckets to measure the transmission rate of a flow. You can configure tokenmt to operate as a single-rate or two-rate meter. A tokenmt action instance maintains two token buckets that determine whether the traffic flow conforms to configured parameters.
The tokenmt (7ipp) man page explains how IPQoS implements the token meter paradigm.
Configuration parameters for tokenmt are as follows:
committed_rate – Specifies the committed rate of the flow in bits per second.
committed_burst – Specifies the committed burst size in bits. The committed_burst parameter defines how many outgoing packets of a particular class can pass onto the network at the committed rate.
peak_rate – Specifies the peak rate in bits per second.
peak_burst – Specifies the peak or excess burst size in bits. The peak_burst parameter grants to a traffic class a peak-burst size that exceeds the committed rate.
color_aware – Enables the awareness mode for tokenmt.
color_map – Defines an integer array that maps DSCP values to green, yellow, or red.
To configure tokenmt as a single-rate meter, do not specify a peak_rate parameter for tokenmt in the IPQoS configuration file. To configure a single-rate tokenmt instance to have a red, green, or a yellow outcome, you must specify the peak_burst parameter. If you do not use the peak_burst parameter, you can configure tokenmt to have only a red outcome or green outcome. For an example of a single-rate tokenmt with two outcomes, see Example 3–3.
When tokenmt operates as a single-rate meter, the peak_burst parameter is actually the excess burst size. committed_rate and either committed_burst or peak_burst must be nonzero positive integers.
To configure tokenmt as a two-rate meter, specify a peak_rate parameter for the tokenmt action in the IPQoS configuration file. A two-rate tokenmt always has the three outcomes (red, yellow, and green). The committed_rate, committed_burst, and peak_burst parameters must be nonzero positive integers.
To configure a two-rate tokenmt to be color aware, you must add parameters to specifically add “color awareness.” The following is an example action statement that configures tokenmt to be color aware.
Example 6-1 Color-Aware tokenmt Action for the IPQoS Configuration Fileaction {
module tokenmt
name meter1
params {
committed_rate 4000000
peak_rate 8000000
committed_burst 4000000
peak_burst 8000000
global_stats true
red_action_name continue
yellow_action_name continue
green_action_name continue
color_aware true
color_map {0-20,22:GREEN;21,23-42:RED;43-63:YELLOW}
}
}
You enable color awareness by setting the color_aware parameter to true. As a color-aware meter, tokenmt assumes that the packet has already been marked as red, yellow, or green by a previous tokenmt action. Color-aware tokenmt evaluates a packet by using the DSCP in the packet header in addition to the parameters for a two-rate meter.
The color_map parameter contains an array into which the DSCP in the packet header is mapped. Consider the following color_map array:
color_map {0-20,22:GREEN;21,23-42:RED;43-63:YELLOW}Packets with a DSCP of 0–20 and 22 are mapped to green. Packets with a DSCP of 21 and 23–42 are mapped to red. Packets with a DSCP of 43–63 are mapped to yellow. tokenmt maintains a default color map. However, you can change the default as needed by using the color_map parameters.
In the color_action_name parameters, you can specify continue to complete processing of the packet. Or, you can add an argument to send the packet to a marker action, for example, yellow_action_name mark22.
The tswtclmt metering module estimates average bandwidth for a traffic class by using a time-based rate estimator. tswtclmt always operates as a three-outcome meter. The rate estimator provides an estimate of the flow's arrival rate. This rate should approximate the running average bandwidth of the traffic stream over a specific period or time, its time window.
You use the following parameters to configure tswtclmt:
committed_rate – Specifies the committed rate in bits per second
peak_rate – Specifies the peak rate in bits per second
window – Defines the time window, in milliseconds, over which history of average bandwidth is kept
For technical details about tswtclmt, refer to the tswtclmt (7ipp) man page.