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)

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

Results

AT&T Algorithm During each Measurement Interval, Core Proxy estimates: –Mean processing rate  t , –Queue length at end of measurement interval q t, 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 = q t /  t - a x d e Retry-after-delay updated each Control Interval and distributed to Edge Proxies in 503 responses,

Results

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