R&S Quick Notes – QOS


  • Class class-default need “fair-queue” if “bandwidth” was not specified.
  • When using “ip rsvp bandwidth” on a sub-interfaces, it is also required to be configured on the main interface.
  • When using multiple sub-interfaces with “ip rsvp bandwidth”, the main interface should be configured to be the sum all sub-interfaces.
  • RSVP requires fair-queue to be enabled. With FRTS, WFQ is disabled by default, re-enable with “frame-relay fair-queue” in the map-class.
  • When doing MQC configurations using the bandwidth percent command, do not forget to change the “max-reserve-bandwidth %”.
  • Custom queueing defaults – Byte-count = 1500 bytes & Queue-limit = 20.
  • Know the NBAR mime categories: “image/*” or “audio/*”  or  “application/*”  or  “text/*”
  • Voice EF class = 46 decimal and 101110 in dscp-binary.
  • FRTS formulas:

Bc = CIR * Tc

Be = (CAR – CIR) * Tc

  • WRED formula:

= (1/MPD)

  • CAR (Police) formula:

Bc = CIR / 8 * Tc           (Default Tc = 1.5 seconds)

Be = 2 * Bc


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