workload data:  meta-challenges

splintered & competitive core 
limited access to data
so difficult to argue `representativeness'

network performance impact 
higher b/w increasing difficult to measure
faster speeds and changing transport technologies complicate data acquisition and processing 
e.g. monitor gone when AIX converts to POS

user privacy volatile issue
hard to get data in researchers hands

    CAIDA's UCSD/CERFnet link monitor available:
    https://anala.caida.org/CoralReef/Demos/