Frame Relay Traffic Shaping

Traffic shaping with Frame Relay applies to both PVCs and SVCs. You can configure Frame Relay traffic shaping by performing the following tasks:

Enable Frame Relay encapsulation on an interface (covered earlier in this chapter).
Define VCs for different types of traffic.
Enable Frame Relay traffic shaping on an interface.
Enable LMI.
Specify a traffic-shaping map class for an interface.
Define a map class with queuing and traffic-shaping parameters.
Define an ACL.
Define priority queue lists for the map class.
Define custom queue lists for the map class.

The following traffic-shaping features are available when you use Cisco IOS Release 11.2 or above:

Rate enforcement on a per-VC basis The peak rate for your outbound traffic. This value can be set to match CIR or any other value.
Dynamic traffic throttling on a per-VC basis When BECN packets indicate congestion on the network, the outbound traffic rate is automatically stepped down; when congestion eases, the outbound traffic rate is increased.
Enhanced queuing support on a per-VC basis Either custom queuing or priority queuing can be configured for individual VCs.

Defining VCs for Different Types of Traffic

You can perform virtual TDM on the same line by defining separate VCs for different types of traffic and specifying queuing and an outbound traffic rate for each VC. In this manner, you can provide guaranteed bandwidth for each traffic type that crosses the line. This enhances your ability to throttle outbound traffic from a high-speed LAN line in your central office to a lower-speed WAN line going to your remote locations, easing congestion and data loss in your network. Enhanced queuing mechanisms can also prevent congestion-caused data loss.

Enabling Frame Relay Traffic Shaping on the Interface

By enabling Frame Relay traffic shaping on an interface, you enable both traffic shaping and per-VC queuing on all PVCs and SVCs defined on the interface. Remember that traffic shaping lets your FRAD control the circuit's output rate and, if configured, react to congestion notification information.

You can use the following command to enable Frame Relay traffic shaping on a specified interface:

R2(config-if)#frame-relay traffic-shaping

Specifying a Traffic-Shaping Map Class for the Interface

When you specify a Frame Relay map class for a main interface, all the VCs you define on its subinterfaces also inherit the traffic-shaping parameters defined for the class.

You can use the following command to specify a map class for a specified interface:

R2(config-if)#frame-relay class map-class-name

You can override the default for a specific DLCI on a specific subinterface by using the class VC command to explicitly assign the DLCI to a different class.

Defining a Map Class with Queuing and Traffic-Shaping Parameters

You can specify the average and peak rates, in bits per second, that you want to allow on a VC by defining and associating it with a map class. You can also specify a custom queue list or a priority queue group for use by the VC associated with the map class. You can use the following commands to define a map class:

This command specifies a map class:

R2(config)#map-class frame-relay map-class-name

This command defines the traffic rate:

R2(config-map-class)#frame-relay traffic-rate average [peak]

This command specifies a custom queue list:

R2(config-map-class)#frame-relay custom-queue-list list-number

This command specifies a priority queue list:

R2(config-map-class)#frame-relay priority-group list-number

To select BECN or ForeSight as a congestion backward-notification mechanism to which traffic shaping adapts, use this command:

R2(config-map-class)#frame-relay adaptive-shaping {becn | foresight}

Defining ACLs

When you use custom queuing, you can specify an ACL to identify the traffic it will use. You associate the lists through the list numbers. For more information on defining ACLs, refer to the Traffic Filtering and Firewalls configuration guide for the IOS version you are using.

Defining Priority Queue Lists for the Map Class

You have the option of defining a priority list for a protocol and also a default priority list. You use the number you specified for a specific priority list to associate it to the Frame Relay priority group defined for a specified map class.

For example, when you enter the frame-relay priority-group 2 command for the map class fast_vcs, and then you enter the priority-list 2 protocol decnet high command, that priority list is used for the fast_vcs map class. The average and peak traffic rates you defined for the fast_vcs map class are used for DECnet traffic.

Defining Custom Queue Lists for the Map Class

You have the option of defining a queue list for a protocol and a default queue list. You also have the option of specifying the maximum number of bytes to be transmitted in any given cycle. You use the number you specified for a specific queue list to associate it to the Frame Relay custom queue list defined for a specified map class.

For example, when you enter the frame relay custom-queue-list 1 command for the map class slow_vcs and then you enter the queue-list 1 protocol ip list 100 command, that queue list is used for the slow_vcs map class. The access-list 100 definition is also used for that map class and queue. The average and peak traffic rates you defined for the slow_vcs map class are used for IP traffic that meets the access-list 100 criteria.

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