System Administration Guide: IP Services

Meter Module

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:

A metering action on a packet can result in one of three outcomes:

You can configure each outcome with different actions in the IPQoS configuration file. Committed rate and peak rate are explained in the next section.

tokenmt Metering Module

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. You can find more general information about token buckets in Kalevi Kilkki's Differentiated Services for the Internet and on a number of web sites.

Configuration parameters for tokenmt are as follows:

Configuring tokenmt as a Single-Rate Meter

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 34–3.

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.

Configuring tokenmt as a Two-Rate Meter

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.

Configuring tokenmt to Be Color Aware

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 37–1 Color-Aware tokenmt Action for the IPQoS Configuration File

action {
    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 turn on 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.

tswtclmt Metering Module

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. The rate estimation algorithm is taken from RFC 2859, A Time Sliding Window Three Colour Marker.

You use the following parameters to configure tswtclmt:

For technical details on tswtclmt, refer to thetswtclmt(7ipp) man page. For general information on rate shapers that are similar to tswtclmt, see RFC 2963, A Rate Adaptive Shaper for Differentiated Services.