Subject: [sfc] Few Querries from draft-agv-sfc-packet-delay-measurement-00

From: Nobin Mathew <[email-masked]>
Date: Wed, 20 Apr 2016 18:35:06 +0530

Hi Anil Kumar S N, Gaurav Agrawal,Vinod Kumar S,

I have few question with respect to the delay calculation method
described in the draft "draft-agv-sfc-packet-delay-measurement-00".
Please let me know your opinion on this queries.

1)
-------------------------draft section---------------------------------------
   3.6 Incoming Packets Processing at MA

      On receiving the packet with NSH header following operations are
      carried out:

      Step 1: Detection of PM Context Header in a packet, by verifying
              the PM TLV Class as allocated by IANA.
              (If not detected, move to step 6)

      Step 2: Check if PM Type field value is 6 to 10.
              (If not move to step 6).

      Step 3: If PM Type Value = 7 to 10 move directly to Step 5

      Step 4: Check Presence of self Service index in Service Index List
              (If not present, move to step 6)
---------------------------------------------------------------------------

MA can be SF or SFF , but based on the steps given here, SFF cannot do
the time recording or report to collector because
step 4 checks the SI index and SFF we do not have Si index.

[ SI: List of participating Service functions in the SFP. It SHOULD be
   in decreasing order of the SI for optimized traversal of the SI
   participation. ]

So i thing we need to address SFF scenario as well.

2)
     +---+                                          +----+
     |SF |--------------------+        +------------|SF  |
     |   |....... ----------+  \      / /+----------|    |
     +---+                   \  \    / /            +----+
                         +---2 -3-+-4--5--+
                         |   SF Forwarder |
                   -----1|      (SFF)     |6------
                         +-------+--------+

As per the method specified in this draft MA will record 'timestamp'
when a packet ENTER and EXIT and this 'timestamp'
will be notified to the controller. but if we consider the above
topology SFF has multiple entry and exit ports so
each time these entries[timestamp] will be overwritten by the MA when
the packet traverse and we will not get the correct delay
because of this.

I feel we need to track each ENTRY and EXIT separately to track the
delay correctly.

3)
------------------------------draft
section----------------------------------------------------------------
3.8 MA Reporting the statistics to Collector

   Reporting timer will run on Each MA. Consistency of this timer should
   be ensured across the entire MA in the SFP, ensuring the same is out
   of scope of this document.

   On expiry of this timer following information needs to be sent to the
   Collector.

       - Service Index

       - PM Type Value

       - Value of all the collected Rx-Time[P][W], Rx-Sum-Time[P][W],
         & Rx-Sample-Count[P][W] parameters along with the
         corresponding PMF ID and Window Id

       - Value of all the collected Tx-Time[P][W], Tx-Sum-Time[P][W],
         & Tx-Sample-Count[P][W] parameters along with the
         corresponding PMF ID and Window Id

   MA may delete the parameters after sending the same to collector.
-----------------------------------------------------------------------------------------------------------

If the MA is in SFF the what is the ID to track the device, Service
index can be used for SF but not for SFF ?

4)
------------------------draft section------------------------------------------
   - If Value = 0x7, 0x8, 0x9, 0x10
          o No need to encode SI, since the type dictates the involved
            participating MA
-------------------------------------------------------------------------------

I think 0x10 should be 0xA ?

5)
----------------------------draft section---------------------------------------

3.7 Outgoing Packets Processing at MA

      At outgoing port of MA following operations are carried out.

      Step 1: If Option 1 is used then go to Step 2a, if Option 2 is
              used then go to Step 2b

      Step 2: If Option 1 is used then go to Step 2a, if Option 2 is
              used then go to Step 2b
--------------------------------------------------------------------------------

Steps 1 and 2 is same here.

Regards
Nobin