Jennifer Rexford wrote:
An example is reasonable. A forward pointer to trajectory sampling might work?- page 13-14: Under "content-dependent sampling" or "non-uniform probabilistic sampling," it may be helpful to include "sampling packets in proportion to their length" as an example.Doesn't "sampling packets in proportion to their length" fall into the content _independent_ sampling? If you sample periodically by time, you'll get sampling of packets in proportion to their length.I was trying to think of a meaningful example to make it more clear why content dependent sampling would be useful. The one thing that came to mind was sampling on the packet-length field in the IP header. That said, you are right that there are content-independent ways to sample this way, too, so perhaps it isn't a good choice for an example. In any case, I think including an example might be helpful here.
Yes, if the PSAMP selector is embedded in a router, that router should be able to access routing state at line rate. However, the PSAMP selector may not be implemented in the fast path that is able to access routing state at line rate. It could be implemented as another stage in the fast path that does not have line-rate access to routing state or in the slow path that cannot access routing state at line-rate."However, if prior selection not based on routing state has reduced the packet stream to below line rate, subselection based on routing state may be feasible."Easier to parse, though still a little confusing. How could the packet stream on the line be above line rate? (Or, are you talking about the packets before they go into the output queue? Or, is the "line rate" the bandwidth allocated for psamp records? Is the idea that subselecting routing state [such as the prefix entry that matched the packet?] is not reasonable unless the sampled stream is low-rate enough to enable the look-ups to take place? But, isn't the lookup already done as part of regular packet handling? Hmmm, I think I still don't quite understand what the sentence is driving at.)
However, if there are selectors that first reduce the packet stream to a more manageable rate (somewhere under line rate), it's possible that the slow path selector could select based on routing state.
I think that's what this sentence is trying to say.
Thanks! -- Jen