[e2e] Packet dropping

Khaled Elsayed kelsayed at gmail.com
Wed May 2 02:19:32 PDT 2007

Given a per-connection queue that could potentially become full (or in 
case of RED, hits dropping threshold), an incoming packet arrives and 
finds the queue full. What would be the best policy:

1) admit the new packet and drop one at the queue front
2) drop the newly arriving packet.

For real-time connections, it is intuitive that dropping at queue front 
would tend to result in better delay responses (this was already shown 
in an early paper by Yin and Hluchyj in IEEE Trans. Comm, June 1993). 
What about data/non-real time connections? Assume an FTP or HTTP session 
subject to above situation, would TCP behave better if packet is dropped 
from front or  the new packet is dropped?

I have no evidence but I tend to feel that if the congestion is 
persistent for some reasonable time, it would make more sense to deliver 
whatever is in the queue right now and drop the new ones at the expense 
of increasing overall avg. packet delay. If the congestion duration is 
small, it would not make a lot of difference (I guess).

Any thoughts?


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