Hi Pascal,
Please find below my review of draft-ietf-6lo-fragment-recovery-03.
In my humble opinion, this is a very readable document. In addition, the
document provides the motivations for some decisions made, which I
appreciated while reading the document.
Below you can find my comments and/or suggestions. They are mostly
editorial, although some of them are technical.
I hope this helps.
Cheers,
Carles
-------------- Review --------------
- Page 2: "in all cases" can be removed
- Page 2: "a firmware upgrades" -> perhaps remove "a" (or apply other
changes)
- Page 3: "10Kbytes" -> "10 kbyte"
- Page 3: "requires to reassemble the full packet at each hop".
The sentence should probably be modified. At least, "requires" is
probably not the right verb here. As e.g. stated in
draft-ietf-6lo-minimal-fragment: "it may be beneficial for a
forwarder not to have to reassemble each packet in its entirety
before forwarding it. This has always been possible with the
original fragmentation design of RFC4944".
- Page 3: "... and trigger the retransmission of the full datagram".
Perhaps "... potentially triggering" the retransmission..." (since
datagram retransmission will only happen if an upper layer
protocol requires so).
- Section 2.2: "in the following documents" --> "in the following document"
- Section 2.4: "miss-associated" -> "misassociated"
- Section 2.4, last paragraph: "MLPS" --> "MPLS"
- Section 3, first paragraph: "A new format for fragment is introduces"
--> "A new format for fragments is introduced"
- Section 3, last paragraph: "... consistently with in Section 2"
--> "... consistently with Section 2"
- Section 4.1, 2nd paragraph: "the fragment number".
This term appears here for the first time. Perhaps some forward
reference might help the reader.
- Section 4.2, 2nd paragraph: "is required protect"
--> "is required to protect"
- Section 4.2, 2nd paragraph: "progressing alon"
--> "progressing along"
- Section 4.3: "The compression of the Hop Limit, of the source and
destination addresses"
--> Perhaps mention that these are IPv6 header fields (even if it
might seem obvious)?
- Section 4.3, 1st paragraph: "datagram_size"
--> Perhaps add a forward reference to section where this field is
defined?
- Section 5, 2nd paragraph: "the node that is the source MAC address"
--> "the node that corresponds to the source MAC address"
- Section 5, 2nd paragraph: "the selected tag"
--> Perhaps better sticking to "Datagram_tag"
- The line above Fig. 1: "page" --> "Page" (as defined in RFC 8025)
- Section 5, last paragraph of intro: "datagram-tag" -> "Datagram_tag"
- Several instances: "recomposition" --> "reassembly" ?
- Section 5.1. The text before Fig. 2 uses terms such as "the sequence
field" that have not yet been introduced. Perhaps indicate they are
introduced later (e.g. in Fig. 2), or some other solution.
- Section 5.1, 2nd paragraph: "seem be" --> "seem to be"
- Page 9: "Fragment_size" field. I was wondering whether this field is
actually needed. Is this used just in case a lower layer technology uses
padding?
- Page 9: "this field indicates the datagram_size of the compressed
datagram"
--> "... of the *potentially* compressed datagram" (or some similar
approach), as perhaps in some (rare) cases, a packet will
not be compressed?
- Page 10, first lines: "may store" --> "may be stored"
- Page 10, 2nd bullet: "When the Sequence is not 0, this field indicates the
offset of the fragment **in the compressed form**."
--> I was wondering what is the meaning of "in the compressed form"
in the previous sentence. Which is the expected representation
of the offset of the fragment?
- End of 5.1: "If the fragment cannot be forwarded or routed, then an abort
RFRAG-ACK is sent back to the source."
--> Perhaps add a forward reference where the concept of "abort
RFRAG-ACK" is defined.
- Page 11: there is no explicit text about "Datagram_tag" in the RFRAG
Acknowledgment subsection, below Figure 5.
- Page 12, 1st paragraph. The terms "All 0's" and "All 1's" may be well
known for LPWANners. :) But I was wondering if perhaps it might be clearer
to say something like "A bitmap with all bits set to 0...", etc.
- If a datagram is carried by 20 fragments, and all fragments are
successfully received, is the FULL bitmap the only way to indicate so? Or
would a bitmap with the first 20 bits set to 1 and the remaining bits set
to 0 also work?
- Section 6, 3rd line: "a one or more fragments" -> "one or more fragments"
- Section 6, 4th line: "a standalone header"
--> Does this mean "without a payload"? If yes, perhaps something
along these lines could be added for extra clarity.
- Section 6, end of 1st paragraph: "by reversing the MPLS operation"
--> "MPLS-like"?
- Section 6, 2nd paragraph: "Te maximum number" --> "The maximum number"
- Section 6, 2nd paragraph: "the 6LoWPAN endpoint that reassembles
the packets at 6LoWPAN level (the receiver)"
--> Swap with "it" in the previous sentence?
- Section 6, 3rd paragraph: "a ARQ timer" --> "an ARQ timer"
- Section 6, 3rd paragraph. A reader may wonder which are the names and
values for the parameters for number of retries, timers, etc. Perhaps a
reference to Section 7 could be added.
- Page 13, 2nd paragraph: "last fragment of a series"
--> Is this the same as "Last fragment of a window"? If yes, perhaps
use "window" (which has been introduced before).
- Page 13, 2nd paragraph: "RFRAG Acknowledgment Request" and
"acknowledgment request" are not defined terms, whereas "Ack-Request bit"
is defined.
- Page 13, 2nd paragraph, last sentence: does "it" refer to "Delaying the
acknowledgment" or to the "round trip delay computation" ?
- In some instances, "cancel" is used. I was wondering if "abort" refers to
the same. If yes, then perhaps just stick to one term?
- Page 14. "alternate routes not possible" -> "alternate routes are not
possible"
- I understand that the document has been designed with Route-Over in mind,
but I was wondering if the document might also work in Mesh-Under. Any
thoughts?
- Page 15, last paragraph: "to the previous router"
--> "to the previous node" (since perhaps the previous node could be a
host?)
- Section 6.2, 2nd paragraph. "until" -> "Until"
- Section 6.2, 3rd paragraph. If the minimal MTU that decreases is in one of
the intermediate hops (i.e. not the first hop), how does the sender detect
such event?
- Section 7.1, 1st paragraph: "as echoing ECN should always be on"
--> "as echoing ECN is always on" (or is the opposite possible?)
- Section 7.1, 1st paragraph: "to the sender that is in control"
--> "to the sender, which is in control"
- Section 7.1. Should there be default values for the parameters defined?
- Section 7.1. There are two UseECN entries!
- Section 7.2. "The management system should monitor..."
--> Any hint on how this could be done? E.g. each node self-monitors
its performance? An external NMS system collects such information
and makes decisions?
- Section 8. Some of the content of Section 7 in
https://tools.ietf.org/html/draft-ietf-core-cocoa-03 may apply here.
- Page 22: "all fragments are resent" --> "all fragments would need to be
resent..."
- Page 22, 4th paragraph. "Mesh Addressing" and "Mesh-Under" are mentioned.
Since the document focuses on Route-Over, are these needed?
- I understand that the document has been designed with Route-Over in mind,
but I was wondering if the document might also enable the same
functionality for Mesh-Under (not sure if with perhaps minor adaptations).
Any thoughts?
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