Draft: draft-ietf-quic-manageability

Commentary: Refers to quicwg . This also addresses /extremely limited/ ECN visibility ( limited for sure , but we do n't need to say " extremely " ) . Fixed multiple definitions of RTT Refered to metrics , etc for encrypted traffic wrt network - layer measurement via a REF . 
 Thanks for the suggestions from  and  , they were of course incorporated .
Paragraph (version A):
The round-trip time of QUIC flows can be inferred by observation once
per flow, during the handshake, as in passive TCP measurement; this
requires parsing of the QUIC packet header and recognition of the
handshake, as illustrated in handshake.  It can also be inferred
during the flow's lifetime, if the endpoints use the spin bit
facility described below and in Section 17.3.1 of QUIC-TRANSPORT.
Paragraph (version B):
The round-trip time (RTT) of QUIC flows can be inferred by
observation once per flow, during the handshake, as in passive TCP
measurement; this requires parsing of the QUIC packet header and
recognition of the handshake, as illustrated in handshake.  It can
also be inferred during the flow's lifetime, if the endpoints use the
spin bit facility described below and in Section 17.3.1 of QUIC-
TRANSPORT.
Paragraph (version A):
When in use, the latency spin bit in each direction changes value
once per round-trip time (RTT) any time that both endpoints are
sending packets continuously.  An on-path observer can observe the
time difference between edges (changes from 1 to 0 or 0 to 1) in the
spin bit signal in a single direction to measure one sample of end-
to-end RTT.  This mechanism follows the principles of protocol
measurability laid out in IPIM.
Paragraph (version B):
When in use, the latency spin bit in each direction changes value
once per RTT any time that both endpoints are sending packets
continuously.  An on-path observer can observe the time difference
between edges (changes from 1 to 0 or 0 to 1) in the spin bit signal
in a single direction to measure one sample of end-to-end RTT.  This
mechanism follows the principles of protocol measurability laid out
in IPIM.
Paragraph (version A):
Limited RTT measurement is possible by passive observation of QUIC
traffic; see sec-rtt.  No passive measurement of loss is possible
with the present wire image.  Extremely limited observation of
upstream congestion may be possible via the observation of CE
markings on ECN-enabled QUIC traffic.
Paragraph (version B):
Limited RTT measurement is possible by passive observation of QUIC
traffic; see sec-rtt.  No passive measurement of loss is possible
with the present wire image.  Limited observation of upstream
congestion may be possible via the observation of CE markings on ECN-
enabled QUIC traffic.
Paragraph (version B):
On-path devices can also make measurements of RTT, loss and other
performance metrics when information is carried in an additional
network-layer packet header (Section 6 of I-D.ietf-tsvwg-transport-
encrypt describes use of operations, administration and management
(OAM) information).  Using network-layer approaches also has the
advantage that common observation and analysis tools can be
consistently used by multiple transport protocols, however, these
techniques are often limited to measurements within one or multiple
cooperating domains.