[e2e] why fair sharing? ( Are we doing sliding window in the Internet?)

Sergey Gorinsky gorinsky at arl.wustl.edu
Fri Jan 12 14:54:49 PST 2007


> How hard it is to turn the Fair Queueing knob to "on" on the gateways?

  To put my 2 kopecks in... First, since an application can masquerade as 
multiple flows, fairness enforcement with FQ is not effective. To lend 
itself to meaningful enforcement, fairness should be defined not in terms 
of flows or even hosts/processes generating them. Instead, fairness 
should be linked to humans behind the communications but this requires 
a very different network architecture.  

  Second, packet-by-packet FQ and end-to-end TCP strive to approximate 
instantaneous PS (Processor Sharing) which is not a good fit for any 
natural application. Multimedia streams need a minimal rate, not a fair 
share. Elastic applications are not well served by PS either because 
average message delay is much larger than under SRPT (Shortest Remaining 
Processing Time), in agreement with Internet experiences where deviations 
from short-term fair sharing improves overall efficiency.

  While minimizing the average message delay, SRPT also might starve large 
messages. However, one can have it both ways: the rich can get richer 
without making the poor poorer. ViFi (Virtual Finish Time First), which 
schedules messages preemptively in the order of their finish times under 
PS, is close to SRPT (and much better than PS) with respect to the average 
message delay and guarantees that no message is delivered later than 
under PS. You can read more on ViFi in:

  S. Gorinsky and N. S. V. Rao, "Dedicated Channels as an Optimal 
Network Support for Effective Transfer of Massive Data", Proceedings of 
High-Speed Networking (HSN 2006), April 2006.

The paper and respective simulation suite are available at:


  In the context of web servers, ViFi was independently proposed under  
a name of FSP (Fair Sojourn Protocol):

   E. J. Friedman and S. G. Henderson, "Fairness and Efficiency in 
Web Server Protocols", Proceedings of ACM SIGMETRICS 2003, June 2003, 
available through:

  Thank you,


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