Original text:
The primary function of a connection ID is to ensure that changes in addressing at lower protocol layers (UDP, IP, and below) don't cause <del> packets for a QUIC connection to be delivered to the wrong endpoint. The connection ID is used by endpoints and the intermediaries that support them to ensure that each QUIC packet can be delivered to the correct instance of an endpoint.  At the endpoint, the connection ID is used to identify which QUIC connection the packet is intended for. </del>  The connection ID is chosen by each endpoint using version-specific methods.  Packets for the same QUIC connection might use different

Reviewer comments:
Editorial NiTs when reviewing the invariant text. These NiTs address readability issues, and do not intend to change the meaning of the text.
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Thanks Gorry, these are all quite helpful. 1) I understand the acronyms DCID and SCID, but these aren't really expanded on first use in sect 5.1. 2) There's mention of "the high bit", but there doesn't seem to be any statement of bit order saying. Is it worth declaring network byte/bit order earlier in section 4? This also clarifies the placement of fields within a byte, which was basically assumed knowledge otherwise. 3) Personally, I don't think: "The length of the Destination Connection ID is not specified" is a great choice of words. Surely, this needs to be specified somewhere for a protocol instance to use it? This reads better as something like: The length of the Destination Connection ID is not encoded in packets with a short header and is not constrained by this specification. 4) The brackets here seem to point to connection IDs in general, not the DCID "(see Section 5.3)". Is it worth writing that as "Connection IDs are described in Section 5", rather than use brackets? The same is true for versions. 5) In section 5.3: "the wrong endpoint" is taken as the wrong transport endpoint, but some of our IP and subIP colleagues would use the term endpoint for other uses, so one insertion of "transport" would perhaps help? 6) In the appendix A, this: "QUIC forbids acknowledgments of packets" - still has me wondering what is actually intended to be understood, because the list of bullets is not guarenteed ... : /The last packet before a long period of quiescence might be assumed to contain an acknowledgment (it should be assumed that QUIC could allow acknowledgments of packets that only contain ACK frames)/ I'm not sure what to say here I think the combination of not... forbids threw me off the meaning. Changes proposed in
Thanks for changing SCID/DCID to "Source Connection ID" and "Destination Connection ID", that seems like a good change.

Revised text:
The primary function of a connection ID is to ensure that changes in addressing at lower protocol layers (UDP, IP, and below) don't cause  <ins> packets for a QUIC connection to be delivered to the wrong QUIC endpoint.  The connection ID is used by endpoints and the intermediaries that support them to ensure that each QUIC packet can be delivered to the correct instance of an endpoint.  At the endpoint, the connection ID is used to identify which QUIC connection the packet is intended for. </ins> The connection ID is chosen by each endpoint using version-specific methods.  Packets for the same QUIC connection might use different