Overload Design Team Status

Jonathan Rosenberg

Cisco

Team Overview

• Design team formed January 2007

• Working on simulations of overload mechanisms

• Composed of experts in this area

• Many non-IETF participants

• Bi-Weekly Calls

Current Status

• Agreed on simulation model

• Several indpendendent simulators developed

• Simulations performed to determine baseline behavior– Drop requests on overload, no 503 [sim1]– Send 503 on overload, no retry [sim2]– Retry on 503 [sim3]

Baseline Results (Volker)

Baseline Results (Shen)

Simulation Comparison with Stateless 503

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Simulation 1Simulation 2 StatelessSimulation 3 Stateless

Stateful vs. Stateless 503

• Found that stateless 503 server transactions seriously worsen performance

• Team agreed to use stateless 503 model despite this because faster 503 processing is critical overall

Simulation Comparison with stateful 503

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Simulation 1Simulation 2 StatefulSimulation 3 Stateful

Simulation Comparison with Stateless 503

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Nortel Algorithm

• Use 503/Retry-After and turn off traffic to server during interval

• Retry-After value determined algorithmically from queue sizes

• Equals amount of time for queue to drain to low watermark

ResultsGoodput in the Network

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stateful 503, sim3

Nortel's OverloadControl Algorithmproposal

stateful 503, sim2

AT&T Algorithm

• During each Measurement Interval, Core Proxy estimates:– Mean processing rate t,– Queue length at end of measurement interval qt,

• Core Proxy calculates the retry after period as the time needed for Core Proxy to process the queued messages that exceed the target queueing delay:

Retry-after-delay = qt/t - a x de

• Retry-after-delay updated each Control Interval and distributed to Edge Proxies in 503 responses,

Results

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AT&T Sim3 Statefull 503 gput

AT&T Sim3 Stateless 502 gput

AT&T Sim3 Statefull 503 with ovld gput

AT&T Sim3 Stateless 503 with ovld gput

Columbia Algorithm

• Sending elements send their current load forward

• Receiving elements send back desired load

• Receiving elements can compute fair share bandwidth allocations and fine grained load adjustment

• No simulation results yet

Bell Labs Algorithm

• Overload Control Feedback Loop in SIP– SIP extension that realizes an overload control

feedback loop to upstream neighbors.– Transport vehicle for feedback generated by an

overload control algorithm.• Orthogonal to the specific control algorithm used.

– draft-hilt-sipping-overload-03.txt

• Overload Control Algorithm– Algorithm that determines fine grained load feedback

to adjust incoming load.

• No simulation results yet.

Next Steps

• Waiting for folks to finish implementing their algorithms

• Once done, can do the real work of comparing results and doing additional simulations

• Targeting proposal for Philadelphia