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Content Addressable NDN Repository - checkpoint
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Content Addressable NDN Repository - checkpoint


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  • 1. CAREPO checkpoint Junxiao Shi
  • 2. Review LAN Internet neighbor repo /%C1.R.SHA256/<hash> Signature ignored consumer remote /repo/file1/version2/metadata Signed by publisher Content: hashes of segments /repo/file1/version2
  • 3. Workload • Files: CCNx releases at • 29 versions from 0.1.0 to 0.8.1, uncompressed TAR • Platform: Ubuntu 12.04, NDNx 0.2
  • 4. Segment Size • Rabin fingerprint chunking: variable segment size • On the network • Small packets waste resource: router states, packet header overhead, etc • Packet size is limited by OS kernel: 8800 octets • Rabin configuration • sliding window size: 31 octets • average block size: 4096 octets • min/max block size: [1024,8192] octets
  • 5. Intra-file Similarity • 2.6% segments are duplicates within a file, eg. license boilerplate, #include • When downloading from remote repository, each unique segment only needs to be downloaded once, using any segment number. 15000 10000 5000 0 total chunks unique chunks
  • 6. Inter-file Similarity • Client has ALL previous versions: 55.3% segments need to be downloaded. • Client has ONE prior version: 60.3% segments need to be downloaded. • Duplicate segment percentage varies with each version. 14000 12000 10000 8000 6000 4000 2000 0 total chunks new chunks from ONE prior version new chunks from ALL previous versions
  • 7. Trust Model • Metadata is signed by publisher. • Strong signatures are unnecessary on segments. • Segment can be verified by hash as listed in metadata, regardless of whether segment is retrieved by Hash Request or Name Request. • ndngetfile expects valid signatures on segments. • If we want to be compatible with legacy downloaders, we must sign segments.
  • 8. Implementation Status • caput, publisher program: implemented • caget, downloader program: implemented • car, repository program: not implemented • We could publish segments and metadata to a regular ndnr repository, show their contents, and download from remote repository. • Current implementation can benefit from intra-file similarity only, and incurs overhead of hash requests for every segment.
  • 9. Quick Performance Test • ccnx-0.5.0.tar, 47MB • Client connects to server directly over UDP tunnel (2 IP hops) • client to server: 0.5Mbps, 20ms delay • server to client: 2.5Mbps, 20ms delay • MTU: 9000 octets • Content-Addressable repository • caput: 9911 segments, 9696 unique segments • caget: download time 183 seconds • traditional repository • ndnputfile: 11921 segments, fixed 4096 octets per segment • ndngetfile: download time 194 seconds