Ryan Mounce rmounce

## docsis-cake-notes.md

      
        
          
            
              
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                rmounce
                / docsis-cake-notes.md
            
            
              Last active
              January 25, 2017 07:56
            
              
                Thoughts on precise shaping of constrained DOCSIS upstream links with cake AQM
              
          
        
      
        
  
      
    Theoretical vs experimental results for Telstra EuroDOCSIS 3.0 (with "Ultimate Speed Boost" add-on) upstream rates at various packet sizes

Telstra's supplied modem (CG3100D-2BPAUS) appears to be shaping (through a ~94KiB FIFO) based on ethernet frames (inc. FCS, excl. preamble etc). The 6-byte DOCSIS MAC header and 4-byte "Upstream Privacy EH version 2 Element" are not a factor.
Theoretical vs actual throughput at various UDP payload sizes (with iperf)

12 byte payload

Naive:

(12 / (12 + 8 + 20 + 14 + 4))*2500 = 517

Accounting for minimum datagram size of 64 bytes: