PacketShaper TCP Rate Control
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PacketShaper TCP Rate Control


Article ID: 165946


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Symantec's TCP Rate Control is very similar in concept to the "just-in-time" product flow control used in most modern manufacturing plants.


Symantec's TCP Rate Control can do the following:

  1. Measure current, instantaneous end-to-end latency so PacketWise knows how long it will take for a packet to arrive once it "places an order."
  2. Forecast exactly when the packets will be needed in order to meet latency bounds and rate guarantees.
  3. Specify how much data to order (by setting the window size).
  4. Place the order at the appropriate time so that the data will arrive just when PacketWise wants it to (that is, release an ACK).
  5. Maintain a warehouse (queue) to deal with any contingencies (such as an unexpected order or early/late arrival of a shipment). This ensures that things run smoothly even in the face of surprises.

Because packets are arriving in a "just-in-time" fashion, you don't have the waste of unnecessary packets crossing an expensive WAN link. TCP Rate Control also eliminates the inefficiency of having an unneeded inventory of packets sitting around in router queues.

Managing the window size is just one out of the four steps to TCP Rate Control. Window size management alone without these other (patented) steps would do very little to provide precise bandwidth management. A factory that ordered very precise amounts of raw materials but without doing accurate forecasting or specifying when they are to be delivered would be problematic.

For more information, refer to Appendix A in the PacketShaper white paper "Effectively Managing WAN, Internet Link and Application Traffic". To download the document (PDF):

  1. Go to
  2. Under Resources, select White Papers.
  3. Locate and click the name of the document.