[e2e] Packet dropping

Craig Partridge craig at aland.bbn.com
Wed May 2 03:33:08 PDT 2007

For non-real time, the answer I believe is drop the new packet.

Dropping the earlier packet (assuming the earlier packet has a lower
sequence number) is more likely to slow effective delivery of data
to the recipient and require a more complex set of retransmissions to
recover from.


In message <463857A4.1020205 at gmail.com>, Khaled Elsayed writes:

>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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