QoS Bandwidth Estimation

Allocating adequate bandwidth is key to ensuring the network performance required for applications. However, allocating too much bandwidth can be costly. The QoS Bandwidth Estimation feature in Cisco IOS software uses Corvil Bandwidth technology to allow you, as a network manager, to determine the bandwidth requirements to achieve user-specified quality of service (QoS) targets for networked applications.

Corvil Bandwidth can determine the minimum bandwidth required to deliver traffic within customer-specified QoS targets with statistical reliability. From a network management perspective, an application’s QoS requirements are characterized with respect to its sensitivity to delay and packet loss. Corvil Bandwidth provides a way to specify limits for delay and packet loss, and get a tight estimate of the minimum bandwidth essential to achieve desired application performance.

Corvil Bandwidth achieves its results by taking very short timescale (8-millisecond) snapshots of traffic and summarizing them in traffic descriptors that place very low overhead on the router because each descriptor has fewer than 300 bytes. These traffic descriptors record the exceptional events (bursts) and are input to the Corvil Bandwidth algorithm to calculate the minimum bandwidth required to deliver the user-specified QoS target for the observed traffic. (The QoS target is specified in terms of sensitivity to traffic delay and packet loss. For example, voice over IP [VoIP] traffic is very sensitive to both, whereas e-mail file transfer is sensitive to neither.)

As a result, turning on Corvil Bandwidth in the router allows you to obtain bandwidth values that can be used directly to configure the existing Cisco IOS QoS mechanisms on the router to achieve the required application performance as efficiently as possible.

For example, in the figure below, Corvil Bandwidth is enabled on the router so that the serial interface can deliver the WAN traffic within the customer-specified QoS targets with statistical reliability.

• Applying Corvil Bandwidth
  

The table below shows the features and benefits of QoS Bandwidth Estimation using Corvil Bandwidth technology.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    policy-map policy-map-name

4.    class [class-name | class-default]

5.    bandwidth [bandwidth-kbps | remaining percent percentage | percent percentage]

6.    estimate bandwidth [drop-one-in n] [delay-one-in n milliseconds n]

7.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	policy-map policy-map-name Example: Router(config)# policy-map my-policy	Specifies the name of the policy map to be created. Enters policy-map configuration mode. Enter the policy-map name.
Step 4	class [class-name | class-default] Example: Router(config-pmap)# class my-class	Specifies the class so that you can configure or modify its policy. Enters policy-map class configuration mode. Enter the class name or use the class-default keyword.
Step 5	bandwidth [bandwidth-kbps | remaining percent percentage | percent percentage] Example: Router(config-pmap-c)# bandwidth percent 20	Specifies or modifies the bandwidth allocated for a class belonging to a policy map. Enter the bandwidth to be set or modified.
Step 6	estimate bandwidth [drop-one-in n] [delay-one-in n milliseconds n] Example: Router(config-pmap-c)# estimate bandwidth drop-one-in 100 delay-one-in 100 milliseconds 50	(Optional) Estimates the bandwidth needed per traffic class for given quality of service (QoS) targets based on traffic data. Enter values for the packet loss target, the delay target, and the delay threshold.
Step 7	end Example: Router(config-pmap-c)# end	(Optional) Exits policy-map class configuration mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number [name-tag]

4.    service-policy {input| output} policy-map-name

5.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number [name-tag] Example: Router(config)# interface fastethernet0/1	Configures the specified interface and enters interface configuration mode. Enter interface type and number.
Step 4	service-policy {input| output} policy-map-name Example: Router(config-if)# service-policy output my-policy	Specifies the name of the policy map to be attached to the interface. Note    You can configure policy maps on ingress or egress routers and attach them in the input or output direction of an interface. The direction (input or output) and the router (ingress or egress) to which the policy map should be attached vary according to your network configuration. For this feature, only the output direction is supported. Enter the output keyword followed by the policy map name.
Step 5	end Example: Router(config-if)# end	(Optional) Exits interface configuration mode.

SUMMARY STEPS

1.    enable

2.    show policy-map interface interface-name [vc [vpi /]vci][dlci dlci][input | output]

3.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	show policy-map interface interface-name [vc [vpi /]vci][dlci dlci][input | output] Example: Router# show policy-map interface fastethernet0/1	Displays the packet statistics of all classes that are configured for all service policies either on the specified interface or subinterface or on a specific PVC on the interface. Enter the interface name.
Step 3	exit Example: Router# exit	(Optional) Exits privileged EXEC mode.