Change:
merging.
We currently use PNs for ordering, but that runs afoul of requirements at the receiver specified in .

Discussion:
ACK-FREQUENCY frames have a type of 0xXX, and contain the following fields: <ins> A variable-length integer representing the sequence number assigned to the ACK-FREQUENCY frame by the sender, see multiple- frames. </ins> A variable-length integer representing the maximum number of ack- eliciting packets after which the receiver sends an acknowledgement.  A value of 1 will result in an acknowledgement

5. On receiving an ACK-FREQUENCY frame, an endpoint will have an updated <del> maximum delay for sending an acknowledgement, and a packet threshold as well.  The endpoint MUST send an acknowledgement when either of the two thresholds are met. loss and batch section describes exceptions to this strategy. </del> <ins> "max_ack_delay" and a "Packet Tolerance" threshold for sending an acknowledgement.  The endpoint MUST send an acknowledgement when either of the two thresholds are met.  That is, an endpoint MUST send an acknowledgement when one of the following conditions are met: Since the last acknowledgement was sent, the number of received ack-eliciting packets is greater than or equal to "Packet Tolerance". Since the last acknowledgement was sent, "max_ack_delay" amount of time has passed. loss and batch section describes exceptions to this strategy. </ins> An endpoint is expected to bundle acknowledgements when possible. Every time an acknowledgement is sent, bundled or otherwise, all

6. An endpoint can send multiple ACK-FREQUENCY frames, and each one of <del> them can have different values. If a received ACK-FREQUENCY frame is the first one in this connection, the endpoint MUST immediately record any values from the frame and start using them.  The endpoint MUST also record the packet number of the enclosing packet. If a received ACK-FREQUENCY frame is not the first one in this connection, the endpoint MUST check if this is a more recent ACK- FREQUENCY frame than any previous ones, as follows: If the enclosing packet number is greater than the recorded one, the endpoint MUST immediately replace old recorded state with values received in this frame.  The endpoint MUST also replace the value of the recorded packet number with that of the enclosing packet. If the enclosing packet number is not greater than the recorded one, the endpoint MUST ignore this ACK-FREQUENCY frame. </del> <ins> them can have different values.  An endpoint MUST use a sequence number of 0 for the first ACK-FREQUENCY frame it constructs and sends, and a strictly increasing value thereafter. An endpoint MUST allow reordered ACK-FREQUENCY frames to be received and processed, see Section 13.3 of QUIC-TRANSPORT. On the first received ACK-FREQUENCY frame in a connection, an endpoint MUST immediately record all values from the frame.  The sequence number of the frame is recorded as the largest seen sequence number.  The new Packet Tolerance and Update Max Ack Delay values MUST be immediately used for delaying acknowledgements; see sending. On subsequently received ACK-FREQUENCY frames, the endpoint MUST check if this is a more recent frame than any previous ones, as follows: If the enclosing packet number is not greater than the largest one seen so far, the endpoint MUST ignore this frame. If the sequence number in the frame is greater than the largest one seen so far, the endpoint MUST immediately replace old recorded state with values received in this frame.  The endpoint MUST start using the new values immediately for delaying acknowledgements; see sending.  The endpoint MUST also replace the recorded sequence number. </ins> 7.