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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
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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]
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
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
AT&T Algorithm • During each Measurement Interval, Core Proxy estimates: • Mean processing rate mt, • 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/mt - a x de • Retry-after-delay updated each Control Interval anddistributed to Edge Proxies in 503 responses,
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