In my simulation platform, I noticed three new parameters to me:

  1. Hierarchical Token Bucket (TBF scheduling).
  2. Explicit Congestion Notification (ECN)
  3. Random Early Detection (RED)

When I googled them, I roughly understood them as: 2 and 3 are primarily used for congestion control while 1 is used for queue scheduling. In this case, would it be reasonable to enable TBF with RED or ECN in my simulation's routers and switches? Would that make sense?


Each of those three things does something very different.

  1. Token buckets can be used for shaping. That is, bandwidth assignment for various protocols or interfaces.
  2. ECN is used by TCP to inform the hosts about network congestion.
  3. RED is used to prevent queues from filling up by randomly dropping queued packets. Full queues lead to tail-drop, and this can cause multiple TCP flows to become globally synchronized, simultaneously shrinking and expanding their windows, alternately starving and filling queues.

All three could be used at the same time because they do very different things.

  • Thank you .. Does it mean ENC is used to inform hosts only? How about routers? Can they use it to inform each other about congestion points? – Michael Jan 17 '17 at 0:00
  • 1
    ECN is only useful for the hosts that are part of the TCP connection. ECN will let a sending host modify its behavior, but a router has no choice but to forward any traffic coming to it. Routers don't really care anything about protocols above OSI layer-3. TCP is a layer-4 protocol, and it plays no part in routing. – Ron Maupin Jan 17 '17 at 0:04

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