Draft: draft-ietf-quic-transport

Commentary: are free to enable sending or not . 2 , Implementations MAY read the ECN code points if they can and send ECN ACKs . MUST accept the 0x03 ACK type and if they are sending ECN SHOULD use the ECN section . I recognize that some people want to have stronger language here , based on this discussion I think this is where we are . I 'll defer to the chairs to judge whether more is needed here and can change the PR as required . 
 I took the discussion to be " MAY " but obviously this is easily changed if the chairs judge consensus otherwise .
Paragraph (version A):
QUIC endpoints use Explicit Congestion Notification (ECN) RFC3168 to
detect and respond to network congestion.  ECN allows a network node
to indicate congestion in the network by setting a codepoint in the
IP header of a packet instead of dropping it.  Endpoints react to
congestion by reducing their sending rate in response, as described
in QUIC-RECOVERY.
Paragraph (version B):
QUIC endpoints can use Explicit Congestion Notification (ECN) RFC3168
to detect and respond to network congestion.  ECN allows a network
node to indicate congestion in the network by setting a codepoint in
the IP header of a packet instead of dropping it.  Endpoints react to
congestion by reducing their sending rate in response, as described
in QUIC-RECOVERY.
Paragraph (version A):
On receiving a QUIC packet with an ECT or CE codepoint, an endpoint
that can access the ECN codepoints from the enclosing IP packet
increases the corresponding ECT(0), ECT(1), or CE count, and includes
these counts in subsequent ACK frames (see processing-and-ack and
frame-ack).
Paragraph (version B):
On receiving a QUIC packet with an ECT or CE codepoint, an ECN-
enabled endpoint that can access the ECN codepoints from the
enclosing IP packet increases the corresponding ECT(0), ECT(1), or CE
count, and includes these counts in subsequent ACK frames (see
processing-and-ack and frame-ack).  Note that this requires being
able to read the ECN codepoints from the enclosing IP packet, which
is not possible on all platforms.
Paragraph (version A):
If an endpoint receives a QUIC packet without an ECT or CE codepoint
in the IP packet header, it responds per processing-and-ack with an
ACK frame without increasing any ECN counts.  Similarly, if an
endpoint does not have access to received ECN codepoints, it does not
increase ECN counts.
Paragraph (version B):
If an endpoint receives a QUIC packet without an ECT or CE codepoint
in the IP packet header, it responds per processing-and-ack with an
ACK frame without increasing any ECN counts.  if an endpoint does not
implement ECN support or does not have access to received ECN
codepoints, it does not increase ECN counts.
Paragraph (version A):
Each endpoint independently verifies and enables use of ECN by
setting the IP header ECN codepoint to ECN Capable Transport (ECT)
for the path from it to the other peer.  Even if ECN is not used on
the path to the peer, the endpoint MUST provide feedback about ECN
markings received (if accessible).
Paragraph (version A):
To verify both that a path supports ECN and the peer can provide ECN
feedback, an endpoint MUST set the ECT(0) codepoint in the IP header
of all outgoing packets RFC8311.
Paragraph (version B):
Each endpoint independently verifies and enables use of ECN by
setting the IP header ECN codepoint to ECN Capable Transport (ECT)
for the path from it to the other peer.  Even if not setting ECN
codepoints on packets it transmits, the endpoint SHOULD provide
feedback about ECN markings received (if accessible).
Paragraph (version B):
To verify both that a path supports ECN and the peer can provide ECN
feedback, an endpoint sets the ECT(0) codepoint in the IP header of
all outgoing packets RFC8311.
Paragraph (version A):
Receivers send ACK frames (types 0x02 and 0x03) to inform senders of
packets they have received and processed.  The ACK frame contains one
or more ACK Blocks.  ACK Blocks are ranges of acknowledged packets.
If the frame type is 0x03, ACK frames also contain the sum of QUIC
packets with associated ECN marks received on the connection up until
this point.
Paragraph (version B):
Receivers send ACK frames (types 0x02 and 0x03) to inform senders of
packets they have received and processed.  The ACK frame contains one
or more ACK Blocks.  ACK Blocks are ranges of acknowledged packets.
If the frame type is 0x03, ACK frames also contain the sum of QUIC
packets with associated ECN marks received on the connection up until
this point.  QUIC implementations MUST properly handle both types
and, if they have enabled ECN for packets they send, they SHOULD use
the information in the ECN section to manage their congestion state.