OverQos: Less Bandwidth for More Reliable Service ?? --A Criticism Hongyu Gao Gregory Peaker

Overview OverQos provides the following services:  A) smoothing packet losses  B) prioritizing packets within an aggregate  C) statistical loss and bandwidth guarantee

Congestion in Routers & Computers Overlays route around congestion points  We’ve seen direct paths, normally taken by routers have improved over the past 10 years Overlay paths longer Routers & Electrical Components are the bottleneck to delivering better Internet Service, not the Terbits in optical fibers in backbones

Smoothing packet loss Given: Bursty line loss rates from 0.5% to 3.3% Outcome: Loss rate guaranteed at.1% Reality: many failures due to outages, loss zero or high thus average is meaningless Doesn’t reduce the packet loss rate Some sample applications might benefit, but it’s not a general solution. (e.g. file transfer application)

Prioritizing Requires input from application programmer. Specify the priority of packets + rewrite legacy applications  --Difficult for people to change the programming habbit

Prioritizing (cont ’ d) Why would application programmer honestly specify the priority of the packets? Programmers have incentive to specify all the packets as the highest priority. Result:  Prioritizing not achievable

Statistical loss and bandwidth guarantees Sounds appealing, but not indeed We look at the one by one

Slabg (loss guarantee) (Refer to Section 3.2) Minimizing the bandwidth overhead of r 1 and r 2 to achieve the target loss constraint -> No guarantee on the bandwidth limit Given the bandwidth limit -> manually drop traffic that exceeds the limit -> No guarantee on the loss rate

Slabg (bandwidth guarantee) (refer to the end of the 3 rd page) “Statistical bandwidth guarantees can be provided only to a subset of the OverQos flows, potentially at the expense of other flows”

Slabg (cont ’ d) A more accurate description of OverQos:  OverQos can provide statistical loss guarantee, NOT considering the extra bandwidth consumption  OverQos can provide statistical bandwidth guarantee to a subset of flows, NOT considering other concurrent flows

Slabg (cont ’ d) A closer look at the loss rate guarantee:  At the first time, transmit the packet as normal TCP does.  At the retransmission, add redundancy to recover from loss, using FEC software library It’s a pure usage of existing tools. You call it a contribution?

Actual Delay

The authors started with a nice goal. The system is poorly designed and implemented. It doesn’t achieve any meaningful improvement. Conclusion