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LLQ cannot be applied across DSL on an 800 series router

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Core Issue

Refer to Configuring LLQ 800 series router for the correct service-policy command issued on the dialer interface.

On a Cisco 827 router, however, Low Latency Queuing (LLQ) is functional on a dialer interface only with the ppp multilink command enabled. In a situation where a service provider does not support the ppp multilink command, it should not be enabled.

In this case, the service-policy command can be issued but it has no affect. Issuing the show policy interface dialer command will show all traffic passing through the default queue.

Resolution

Apply the service-policy command to the ATM Virtual Circuit (VC) as shown in this configuration example:

interface ATM0.4 point-to-point

bandwidth 128

pvc 1/35

  vbr-nrt 128 128

  tx-ring-limit 2

             

Optimise the hardware transmit (Tx) buffer for LLQ. For more information, refer to the Impact of Very Small tx-ring-limit Values section of Understanding and Tuning the tx-ring-limit Value.

 

  service-policy output voice

  pppoe-client dial-pool-number 1

Note: Due to the nature of the LLQ implementation on ATM, if an Unspecified Bit Rate (UBR) class is required then the bandwidth (policy-map-class) command must specify a percentage of the bandwidth. If, as shown in the example above, a bandwidth value is preferred or required then another VC class, such as VBR-nrt, must be chosen. In this case arbitrarily large Peak Cell Rate (PCR) and Sustainable Cell Rate (SCR) values can be chosen to emulate the UBR class.

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