Table of Contents

Configuring the ATM Traffic-Shaping Carrier Module

This chapter describes the features and configuration procedures for the ATM traffic-shaping carrier module (TSCAM). The TSCAM is available on the Catalyst 8510 MSR and the LightStream 1010 ATM switch routers.

Note   This chapter provides advanced configuration instructions for the Catalyst 8510 MSR and LightStream 1010 ATM switch routers. For complete descriptions of the commands mentioned in this chapter, refer to the ATM and Layer 3 Switch Router Command Reference publication.

This chapter includes the following sections:

About the ATM Traffic-Shaping Carrier Module

The ATM traffic-shaping carrier module (TSCAM) augments the current traffic-shaping capabilities for the Catalyst 8510 MSR and the LightStream 1010 ATM switch routers by providing variable bit rate (VBR) and best-effort traffic-shaping capabilities. The TSCAM shapes the streams of cells sent over virtual connections (VCs) so they conform to bandwidth parameters, and they do not exceed the expected flow into the network. The TSCAM does this by temporarily holding cells in buffers and dispersing them as bandwidth parameters allow on the outgoing connection. The TSCAM helps ensure that cells are not dropped if they exceed the maximum traffic-flow parameters established between private and public networks.

You can enable traffic shaping on subcard 0 of a slot that is equipped with the TSCAM. For OC-3, T1, E1, and DS3 port adapters, a maximum of four traffic classes can be shaped. For example, if only VBR traffic is shaped, traffic shaping for VBR can be configured on a maximum of four ports (each port shapes two classes). If VBR traffic and best-effort traffic is shaped, a maximum of two ports can be configured for traffic shaping. For OC-12 port adapters, only one traffic class can be shaped.

Note   Traffic-shaping configurations do not apply to regular virtual path (VP) tunnels defined on that interface, except in the case of unspecified bit rate (UBR) VP tunnels. For example, when best-effort traffic shaping is enabled on a physical interface, all the UBR VP tunnels defined on that interface are shaped to their peak cell rate (PCR), but individual VCs within those VP tunnels are not shaped.

The TSCAM schedules the traffic classes constant bit rate (CBR), VBR, and best effort in a strict priority in which CBR is the highest priority and best effort is the lowest priority. The best-effort traffic class includes UBR, available bit rate (ABR) and UBR+ service categories. When traffic shaping is disabled for all the traffic classes on a port, all the traffic from that port is switched unaltered as if it were a single connection at the highest priority.

Note   Traffic shaping in the TSCAM is disabled by default. Any changes to shaping configurations are supported across switch reloads only.

An example of how the ATM TSCAM might work in a network is shown in Figure 22-1. In this example, the TSCAM is in a Catalyst 8510 MSR switch router that is on the edge of a private enterprise network connected to a public ATM network. The TSCAM helps ensure that the maximum number of cells transmit through to the public network.

ATM TSCAM Features

The ATM TSCAM offers the following benefits:

Hardware and Software Restrictions

This section lists the hardware and software restrictions for the TSCAM.

Hardware Restrictions

The following hardware restrictions apply to the TSCAMs of the Catalyst 8510 MSR and LightStream 1010 ATM switch:

Software Restrictions

The following software restrictions apply to the TSCAMs of the Catalyst 8510 MSR and LightStream 1010 switch routers:

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Note    Burst tolerance is not applicable to the shaping of best-effort connections and the PCR-only mode of shaping for VBR connections.

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About Interface Congestion Thresholds

A total of 256K cell buffers are available on the TSCAM. On an interface enabled for shaping, the number of available cell buffers is the same as the maximum threshold for that interface. Table 22-1 lists the maximum threshold values. These values are the defaults and depend on the number of interfaces configured for traffic shaping. The maximum congestion thresholds for interfaces are not configurable.

Configuring the ATM TSCAM

To configure traffic shaping on your ATM TSCAM, perform the following steps, beginning in global configuration mode:

Note   Any changes to the traffic-shaping configuration take effect upon saving the configurations to NVRAM and reloading the switch, or upon performing an OIR on the port adapter in subcard 0 of the ATM TSCAM.

Example

The following example shows how to enable VBR traffic shaping:

Configuring Maximum Thresholds

The ATM TSCAM supports maximum thresholds for traffic class and for VCs. This section describes how to configure these thresholds.

Configuring Maximum Thresholds for Traffic Classes

To configure traffic class thresholds, perform the following steps, beginning in privileged EXEC mode:

Note   Prior to changing the traffic class maximum threshold configuration, you must disable the interface using the shutdown command. You do not have to disable the interface when configuring per-VC maximum thresholds.

Example

The following example shows how to configure a traffic-shaping threshold for a traffic class:

Note   Class maximum thresholds are expressed as percentages of the interface maximum threshold values. To display interface maximum thresholds, enter the show atm interface resource atm slot/subslot/port in privileged EXEC mode.

Configuring Maximum Thresholds for VCs

To configure VC thresholds, perform the following steps, beginning in global configuration mode:

Note   New per-VC maximum thresholds only apply to new VCs created after making the threshold configuration changes. The new threshold configuration is not applied to the maximum threshold values of existing VCs.

Example

The following example shows how to configure traffic-shaping thresholds for VCs:

Displaying Traffic-Shaping Configurations

To show the traffic-shaping configuration of the switch, use the following privileged EXEC commands:

Examples

The following example shows the configured ports on a Catalyst 8510 MSR switch router:

The following example shows the threshold values configured on a Catalyst 8510 MSR switch router:

The following example shows the traffic-shaping statistics on a Catalyst 8510 MSR switch router:

Traffic-shaping Granularity Tables

This section lists the following granularity tables for configuring traffic-shaping rates on ATM interfaces:

The tables display shaping rates in cells per second and can be used for configuring connection traffic table (CTT) rows. When configuring CTT rows, the traffic parameters are specified in kilobits per second (kbps). By referring to the values listed in the tables, you can choose the rate in cells per second that most closely matches the desired kbps rate for CTT rows.

Two granularity tables represent each interface type. For example, Table 22-2 shows rates for best-effort connections and variable bit rate (VBR) connections using PCR-only mode. Table 22-3 shows rates for VBR connections shaped using their PCR, SCR, and MBS parameters (the default VBR shaping mode). The DS3, E3, E1, and T1 interfaces share the same values and are therefore represented in the same granularity tables.

The resource management software uses the following algorithm to convert the rates given in kbps to cells per second. You can also use the algorithm as a guideline for determining the kbps value that must be configured for the CTT rows.

In the following expression, kbps_val represents a rate specified in units of kbps and cps_val is the cell per second equivalent of the specified kbps_val. Also, the following expressions use integer division and the operator % represents modulus operations.

Note   Observed traffic-shaping rates may vary as much as 2% from the values listed in these tables.

Table 22-2 shows the DS3, E3, E1, and T1 rates for best-effort connections and VBR connections when shaped using PCR-only mode.