Case study debugging multicast problems from an applications perspective
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Case Study: Debugging Multicast Problems from an Applications Perspective. Steven Senger, Ph.D. Dept. of Computer Science University of Wisconsin - La Crosse. HAVnet Project. Parvati Dev, PI, Stanford SUMMIT National Library of Medicine, NGI & SII programs since 1999.

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Case study debugging multicast problems from an applications perspective

Case Study: Debugging Multicast Problems from an Applications Perspective

Steven Senger, Ph.D.

Dept. of Computer Science

University of Wisconsin - La Crosse


Havnet project
HAVnet Project Applications Perspective

  • Parvati Dev, PI, Stanford SUMMIT

  • National Library of Medicine, NGI & SII programs since 1999.

  • Applications of high-performance networks to anatomical and surgical education.

  • http://havnet.stanford.edu

  • http://visu.uwlax.edu


Immersive segmentation
Immersive Segmentation Applications Perspective


Remote stereo viewer
Remote Stereo Viewer Applications Perspective


Nomadic anatomy viewer
Nomadic Anatomy Viewer Applications Perspective


Other apps and components
Other Apps and Components Applications Perspective

  • Information Channels

    • Multicast based announcement/discovery mechanism.

    • Supports other app requirements such as logging.

  • Access Grid


Testbed
Testbed Applications Perspective


Network app monitoring
Network/App Monitoring Applications Perspective


Potholes along the way
Potholes Along the Way Applications Perspective

  • Stanford / CENIC

    • Multicast setup delay

  • WiscNet

    • Conflict between sender and receiver

  • Michigan / Merit

    • Multicast setup delay

    • Inbound flow stops after 209 secs


Stanford cenic
Stanford / CENIC … Applications Perspective

  • Longstanding problem (observed in ‘01).

  • Large delays (~15 min) in multicast setup.

  • Stanford / La Crosse / NLM

    • Significant delays except for La Crosse / NLM

  • Originally thought to be at Stanford Border and RP.

  • 04 hardware/ios upgrades at Stanford.

  • Situation improved.


Stanford cenic1
Stanford / CENIC … Applications Perspective

  • Only Michigan to Stanford delayed, ~6 mins.

  • Oct 04, Phone calls, Stanford, CENIC, Vendor support, La Crosse. Escalate through 3 layers of vendor support.

  • Test/Debug every couple of weeks through March ‘05.

  • Identified as MSDP propagation delay related to encap/unencap data received by MSDP.


Stanford cenic2
Stanford / CENIC Applications Perspective

  • Delay occurred at each CENIC router.

  • At some point problem had been internally found and resolved by vendor.

  • Solution: upgrade OS on CENIC routers.


La crosse wiscnet
La Crosse / WiscNet … Applications Perspective

  • First observed spring 05 using AccessGrid.

  • La Crosse sender and Stanford receiver OK.

  • Starting a La Crosse receiver breaks the flow.

  • WiscNet identified problem router.

  • Vendor support engaged.

  • Discovered rpd restart sufficient to fix.

  • Reoccurs every 2 months.


La crosse wiscnet1
La Crosse / WiscNet … Applications Perspective

  • When failing

    • Upstream interface on router gets set to unreasonable value.

    • Sender continues to send data in encapsulated PIM-register messages.

    • Router never sends register-stop messages.


La crosse wiscnet2
La Crosse / WiscNet Applications Perspective

  • Problem has survived router chassis upgrade.

  • No solution as yet.


U michigan merit
U. Michigan / Merit … Applications Perspective

  • Discovered after CENIC problem solved.

  • Small delay in setup for Michigan to Stanford.

  • Varies between 0 and 60 sec.

  • Similar behavior for Milwaukee to Stanford.

  • Does not appear to be in CENIC?


U michigan merit1
U. Michigan / Merit … Applications Perspective

  • Presence of other receivers seems to change the setup delay.

  • Merit engaged in isolating problem.

  • No solution as yet.


U michigan merit2
U. Michigan / Merit Applications Perspective

  • Discovered Jan ‘06 using AccessGrid.

  • Traffic from Stanford to MCBI/Merit starts correctly but stops after 208 seconds.

  • When stopped IPLSng shows as pruned.

  • Merit identified problem with a switch in Chicago not allowing streams to setup correctly.

  • Problem resolved with OS upgrade.


Diagnostic help
Diagnostic Help Applications Perspective

  • Debugging strategies

  • Tools

  • Monitoring


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