ATP: Atomic Transport Protocol

ATP provides sequenced, reliable data transfer

ATP is implemented at the user level.

• Communicates with ATOMIC Myrinet host interface over the user-level Myrinet API
• Interleaves memory copy with DMA to reduce memory copy overhead
• ATP paper

ATP software release: atp-1.1.tar.Z

ATP performance

• Experiment configuration:
  • Measured at memory-to-memory level between two Sun SPARC 20/71 stations interconnected through an 8-port Myrinet switch.
  • Device driver version: Myrinet-2.0c
• ATP peak throughput: 164-Mbps
• Why ATP is slower than kernel-TCP for packets smaller than 16K bytes?
  • ATP adopts blocking sending (and keeps packet boundary): an ATP send will not be returned until the packet is ACKed.
  • TCP uses non-blocking sending (in stream fashion): multiple outstanding TCP sends form a pipeline.
• Why kernel-TCP is slower than ATP for packets larger than 16K bytes?
  • ATP interleaves DMA with memcpy in transferring segments each of which is equal to network MTU (8K).
  • The interleaving starts to take effective when packet size exceeds network MTU.
• Tabulated ATP performance

ATP application: high-speed network computing ( PVM )

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Last modified Aug 9, 1995.