Subject: [ippm] A question about using the STAMP in the loopback mode

From: Greg Mirsky <[email-masked]>
Date: Mon, 8 Nov 2021 14:40:50 -0800

Hi Rakesh, Authors et al,
I much appreciate it if you can help me understand what is expected to be
standardized in Section 4.2.3
<https://datatracker.ietf.org/doc/html/draft-gandhi-spring-stamp-srpm#section-4.2.3>
of the draft. As I understand it, the transmitting test probe node
constructs a packet that it receives back without any modification. It
appears that there's no interaction with any other node in the network is
defined. It is not clear how that is related to STAMP. As I can see, a test
probe in the loopback mode can be anything since that is completely local
to the sending system decision. As a result, I cannot find what needs
standardization in that mechanism.
I further have a question about the quality of the delay measurement that
the loopback method can provide. It appears that you are concerned with how
local processing at the STAMP Session-Reflector affects the accuracy of the
measurement. But the STAMP enables a real one-way delay measurement that
provides accurate statistical information about the condition of the
particular path. The loopback method described in Section 4.2.3 measures
the round-trip delay and, as a result, the accuracy of the downstream
one-way delay is impacted by the choice of the upstream part of the
engineered route that loops the test probe back to the sender. As a result,
using the loopback mechanism may produce measurements that don't represent
the network conditions in the downstream direction, on the path that is of
interest and the real importance to the operator. The loopback mode may be
producing results that are very far from the real conditions, lowering or
inflating the measured delay.

I am looking forward to your feedback.

Regards,
Greg