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Cell Relay Retreat>List Archive>month:1998-Feb> msg00097



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Re: Explanation of PPD

  • From: jbasrur@sahana.bellcore.com (33150-basrur)
  • Date: Tue, 24 Feb 1998 09:52:08 -0500

> 
> Hello:
> 
> Can somebody explain to me what PPD is?  And how it is different from EPD.
> 
> Thanks In Advance
> 
> Rodger Higgins
> rhiggins@westell.com
> 
> -----== Posted via Deja News, The Leader in Internet Discussion ==-----
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> 


PPD is partial packet discard where the atm switch begins discarding
atm cells when it begins to experience buffer overflow. That results in only 
parts of the IP packet being discarded and therefore reduces TCP thourghput.

EPD or early packet discard is a scheme where the switch discards a whole
IP packet even before it experiences buffer overflow....i.e when it begins to forsee congestion. 

There are numerous papers which describe TCP throughput and flow control 
problems related to ABR/ UBR+PPD/UBR+EPD etc.

Jyotin