overqos: less bandwidth for more reliable service ?? --a criticism hongyu gao gregory peaker
TRANSCRIPT
OverQos: Less Bandwidth for More Reliable Service ??
--A CriticismHongyu 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 r1 and
r2 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 3rd 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