Change:
server MUST NOT use the same ETag value for different representations of a resource. <del> The ETag is opaque in nature, but it is RECOMMENDED that the server treats it as an unsigned integer of 8 bytes in length.  An implementation may want to consider limiting this to 4 bytes to reduce packet overhead size.  The client still treats it as an opaque entity.  The ETag value MUST be different for distinct bodies or sets of blocks of data and SHOULD be incremented whenever a new body of data is being transmitted between peers.  The initial ETag value SHOULD be randomly generated by the server. </del> <ins> The ETag is opaque, the client still treats it as opaque but the server SHOULD ensure that it is unique for every different body of transmitted data. It is suggested that the server treats the ETag as an unsigned integer of 8 bytes in length.  An implementation may want to consider limiting this to 4 bytes to reduce packet overhead size. The initial ETag value SHOULD be randomly generated and then subsequenty incremented by the server whenever a new body of data is being transmitted between peers. </ins> If the client detects that some of the payloads are missing, the missing payloads are requested by issuing a new GET, POST, PUT,

Discussion:
Hello Med, hello Jon, here's a few concrete points I'd like to suggest for new-block: Applicability: I'd have expected to read something like this in the introduction: Separation of layers, sub-topic "congestion control": It should be possible to phrase all congestion control parts of this in a dedicated section (which may also make sense as an appendix). I'd avoid all other mentions of things like PROBINGRATE: For example, Section 3.4 right in the middle of a paragraph on re-requesting missing blocks states that Yes it is, but so is every single CoAP request until the client hears back from the server. Repeating these things in places where are not a new requirement may make it easier for some implementers that try to build the whole stack in a single go, but even for them is prone to the authors missing a spot -- and for everyone else this will each time trigger the question of "is this new here or isn't this already handled by a component two layers down the stack?". I haven't tracked every single retransmission and rate limiting statement throughout the document, but I expect that this section could boil down to something like (The latter replaces MAXPAYLOADS, and I'm not sure whether it is better to express this in terms of package count or bytes on the wire, just giving an example here. All numbers in the above were pulled out of uninformed air.) Separation of layers, sub-topic "Tokens": Same thing, next layer. Whenever you're tempted to talk of a token, consider some of these replacement phrases as a first step: "MUST be sent with a new token" -> "is a new request". "Tokens MUST be included" -> (nothing -- transports use tokens by construction) "MUST be sent with the same token as the response" -> "is sent as a response to" / "is sent as an additional response to that request". (Here it may make sense to refer to the tokens in an additional " (which means it uses the same token, the same way an observation response uses the requests's token for multiple responses)"). Naming: It's technically a minor thing, but people have already complained to me about how hard the Block[12] names are to comprehend, and introducing these options as Block[34] would not help here. I'd like to suggest QuickBlock-Block[12].

(I know that this part of designing a new option is annoying. In the interest of winding up with something that can be learned easily, it is unfortunately essential). In connection with that, it may make sense to briefly think about a draft name before it is submitted as a WG draft. new-block sounds like a 7959bis, which in my understanding this does not aim to be. 4.TBA3 Missing Payloads: I don't quite see why this needs a distinct code. 4.08 Request Entity Incomplete sounds perfectly suitable to me. If you think that sending an existing 4.xx code in the middle of a block-wise transfer would cancel the transfer, there's still two ways out of this: You're just defining what a block-wise transfer is; just allow it. (In a RFC7959 block-wise transfer that runs over a proxy, the proxy may be currently incapable of doing any forwarding and return 5.03 Service Unavailable Max-Age:5. The client would then just pause 5 seconds and send the latest block again.) For all but the last block, it may also be an option to send it as a payload to a 2.31 code -- I don't think that would be outright forbidden (and at any rate, all involved clients speak the protocol anyway).
We don't have an objection to this proposal. We asked the Chairs for guidance before we submitted -00 with "new-block" instead or "quick-block". This one is thus closed.