Ethan Banks Not writing about IT.

OECG – Chapter 16


Moving onto frame-relay traffic shaping (FRTS), we have a whole new set of tools that can be used to shape in a frame environment. Here’s a list of the notable differences between class-based and frame-relay traffic shaping.

  • FRTS, obviously enough, only works on frame-relay interfaces. CB shaping can be used with any L2 protocol.
  • FRTS does not allow you to use queuing tools on the physical interface at the same time you’re running FRTS.
  • FRTS shapes the traffic on each virtual circuit independently.
  • FRTS cannot classify traffic so that you can shape a certain class of traffic on a specific virtual circuit.
  • FRTS can, on the fly, learn the CIR, Bc and Be values on the upstream frame switch using enhanced local management interface (ELMI).
  • FRTS does not use MQC commands, thus the config looks different. You end up with a “map-class frame-relay” command with a “frame-relay class” or “class” command referencing those map-classes and then defining the shaping parameters.
    • If there’s a “class <name>” command under the interface-dlci command, then that’s the map-class that define FRTS for that specific virtual circuit.
    • If there is no “class <name>” command under the interface-dlci command, then the “frame-relay class <name> command under the sub-interface defines the FRTS parameters for the virtual circuits mapped into that subinterface.
    • If there’s no “class <name>” under the interface-dlci and no “frame-relay class <name>” under the subinterface, then the “frame-relay class <name>” command under the physical interface will define FRTS for that subinterface.
    • And if none of the above are present, then FRTS will use a default shaper of 56Kbps, with a committed burst (Bc) of 7000 bits and a transmit interval (Tc) of 125 ms.

When configuring FRTS shaping, there’s a couple of approaches you can take.

  • One is to allow the router to calculate Bc and Be, assuming a Tc rate of 125 ms.
    • “frame-relay traffic-rate <average rate> [<peak rate>]” allows you to take this approach.
    • Bc and Be will be calculated, based on a transmit interval of 125 ms.
  • The other is to specify Bc and Be yourself.
    • “frame-relay cir <rate>” will define the committed information rate.
    • “frame-relay bc <rate>” will define the amount of data to normally be sent at an interval.
    • “frame-relay be <rate>” will define the burst rate.

FRTS also supports a low-latency queue. You can feed the packets into a priority queue by referencing a priority queue in the “map-class frame-relay” paragraph.

FRTS also supports adaptive shaping, where the shaper will decrease the bitrate in the presense of a BECN or “foresight” frame.

  • “frame-relay adaptive-shaping [becn | foresight]” must be added to the appropriate map-class.
  • “frame-relay mincir <rate>” will allow you to set the minimum information rate to something other than the default of 50% of the shaping rate.
By Ethan Banks
Ethan Banks Not writing about IT.

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