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Overload Control Algorithms in SIP: Team Overview and Simulation Results

The Cisco Design Team, established in January 2007, is comprised of experts developing simulations to understand overload mechanisms in SIP. The team has agreed on a simulation model that evaluates various response strategies during overload situations, such as stateless vs. stateful 503 responses. Recent results indicate that stateless 503 transactions substantially degrade performance, despite their quicker processing time. Algorithms from AT&T and Nortel are being utilized to manage overload effectively. The team is currently awaiting the final implementations of these algorithms to compare results and proceed with further simulations.

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Overload Control Algorithms in SIP: Team Overview and Simulation Results

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  1. Overload Design Team Status Jonathan Rosenberg Cisco

  2. 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

  3. 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]

  4. Baseline Results (Volker)

  5. Baseline Results (Shen)

  6. 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

  7. 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

  8. Results

  9. 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,

  10. Results

  11. 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

  12. 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.

  13. 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

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