[ippm] review comments on draft-mirsky-ippm-hybrid-two-step-05

[Haoyu Song <[e-mail]>]

Hi authors and IPPM,

I reviewed the draft and see a close link of the proposed method with the other methods in discussion in the IPPMWG. Below are some questions and comments for your consideration.

  1.  I believe HTS has its place in the on-path telemetry branch of technology. In essence, it sits just between IOAM and PBT: collect the telemetry data using one dedicated and separate packet. The benefit of doing so is clear and sound.
  2.  To best progress this work, I think a good strategy is to try to align it with the existing specifications of IOAM Trace and IOAM DEX (e.g., data and header specification). It's even possible to think about it as yet another option for IOAM.
  3.  The nodes on the path need to maintain the states for each trigger (the transport header and timer). This is not a  trivial process and the scalability also needs to be considered.
  4.  How is the trigger implemented and how is the follow-up packet header encapsulated? The current draft doesn't provide enough details on these issues.
  5.  The definition and usage of the sequence number is not very clear to me. It seems to be used to differentiate the internal generated follow-up packets. Based on the description, if a follow-up packet is dropped, then each hop on the remaining path will experience the timer expiration and generate a new follow-up packet. Will these packets all have the same sequence number? If the original follow-up packet is just delayed but not dropped, how will this and the other newly generated follow-up packets are differentiated and processed?
  6.  The specification of the data profile is also missing. Isn't the data profile should be carried by the trigger packet instead of the follow-up packet?
  7.  The telemetry is encoded as TLV. How can the collector tell which data is generated by which node?
Please let me known if I missed or misunderstood anything. Thanks!
Best regards,
Haoyu