target = "https://www.rfc-editor.org/rfc/rfc9000#section-13.2.3"

# 13.2.3.  Managing ACK Ranges
#
# When an ACK frame is sent, one or more ranges of acknowledged packets
# are included.  Including acknowledgments for older packets reduces
# the chance of spurious retransmissions caused by losing previously
# sent ACK frames, at the cost of larger ACK frames.
# 
# ACK frames SHOULD always acknowledge the most recently received
# packets, and the more out of order the packets are, the more
# important it is to send an updated ACK frame quickly, to prevent the
# peer from declaring a packet as lost and spuriously retransmitting
# the frames it contains.  An ACK frame is expected to fit within a
# single QUIC packet.  If it does not, then older ranges (those with
# the smallest packet numbers) are omitted.
# 
# A receiver limits the number of ACK Ranges (Section 19.3.1) it
# remembers and sends in ACK frames, both to limit the size of ACK
# frames and to avoid resource exhaustion.  After receiving
# acknowledgments for an ACK frame, the receiver SHOULD stop tracking
# those acknowledged ACK Ranges.  Senders can expect acknowledgments
# for most packets, but QUIC does not guarantee receipt of an
# acknowledgment for every packet that the receiver processes.
# 
# It is possible that retaining many ACK Ranges could cause an ACK
# frame to become too large.  A receiver can discard unacknowledged ACK
# Ranges to limit ACK frame size, at the cost of increased
# retransmissions from the sender.  This is necessary if an ACK frame
# would be too large to fit in a packet.  Receivers MAY also limit ACK
# frame size further to preserve space for other frames or to limit the
# capacity that acknowledgments consume.
# 
# A receiver MUST retain an ACK Range unless it can ensure that it will
# not subsequently accept packets with numbers in that range.
# Maintaining a minimum packet number that increases as ranges are
# discarded is one way to achieve this with minimal state.
# 
# Receivers can discard all ACK Ranges, but they MUST retain the
# largest packet number that has been successfully processed, as that
# is used to recover packet numbers from subsequent packets; see
# Section 17.1.
# 
# A receiver SHOULD include an ACK Range containing the largest
# received packet number in every ACK frame.  The Largest Acknowledged
# field is used in ECN validation at a sender, and including a lower
# value than what was included in a previous ACK frame could cause ECN
# to be unnecessarily disabled; see Section 13.4.2.
# 
# Section 13.2.4 describes an exemplary approach for determining what
# packets to acknowledge in each ACK frame.  Though the goal of this
# algorithm is to generate an acknowledgment for every packet that is
# processed, it is still possible for acknowledgments to be lost.

[[spec]]
level = "SHOULD"
quote = '''
ACK frames SHOULD always acknowledge the most recently received
packets, and the more out of order the packets are, the more
important it is to send an updated ACK frame quickly, to prevent the
peer from declaring a packet as lost and spuriously retransmitting
the frames it contains.
'''

[[spec]]
level = "SHOULD"
quote = '''
After receiving
acknowledgments for an ACK frame, the receiver SHOULD stop tracking
those acknowledged ACK Ranges.
'''

[[spec]]
level = "MAY"
quote = '''
Receivers MAY also limit ACK
frame size further to preserve space for other frames or to limit the
capacity that acknowledgments consume.
'''

[[spec]]
level = "MUST"
quote = '''
A receiver MUST retain an ACK Range unless it can ensure that it will
not subsequently accept packets with numbers in that range.
'''

[[spec]]
level = "MUST"
quote = '''
Receivers can discard all ACK Ranges, but they MUST retain the
largest packet number that has been successfully processed, as that
is used to recover packet numbers from subsequent packets; see
Section 17.1.
'''

[[spec]]
level = "SHOULD"
quote = '''
A receiver SHOULD include an ACK Range containing the largest
received packet number in every ACK frame.
'''