Re: [Roll] John Scudder's Discuss on draft-ietf-roll-aodv-rpl-10: (with DISCUSS and COMMENT)

[John Scudder <[e-mail]>]

Hi Ines and all,

Thanks for your patience. I hope it will be OK if I don’t review and reply in detail until the week following IETF-112? If it’s more urgent than that, let me know please.

Thanks,

—John

On Nov 5, 2021, at 3:28 PM, Ines Robles <[e-mail]<mailto:[e-mail]>> wrote:


[External Email. Be cautious of content]


Hello John,

Thank you for your comments to improve the document. We believe that v11 addresses your DISCUSS points, please let us know.

Please find comments below corresponding to version 11 in [v11]

----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

A lot of effort has clearly gone into this work, thank you. I do have one topic
I want to DISCUSS, as it seriously impacted the readability of the document
from my point of view. I don’t anticipate that it will be very difficult to
resolve this DISCUSS as it relates to clarity and not to anything fundamental.

My chief difficulty with the document is placing it in context. No hints are
given to the reader as to what the expected network environment is. I think it
would be almost sufficient to say, for example “the network environment is
assumed to be the same as described in RFC 6550, Section 1” for example, but
without that hint and without a strong background in ROLL, I found myself
struggling. Figures 4 and 5 in particular lead me to believe the expected
environment looks similar to a classic ISP network — a collection of nodes
connected by point-to-point links. If this isn’t correct (and I bet it’s not)
that may have led me into incorrect assumptions, which may be reflected in my
other comments below.

[v11] Page 3, new text: The network environment that is considered in this
   document is assumed to be the same as described in Section 1 of<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/rfc6550*section-1__;Iw!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZy79-H5mg$>
   [RFC6550]<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/rfc6550*section-1__;Iw!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZy79-H5mg$>.


Further, it’s not stated anywhere whether AODV-RPL is intended to stand alone
as its own routing protocol, or to be viewed as an extension of RPL. In the
former case, it seems the document is lacking details that are present in RFC
6550. I’m assuming the latter is the case, but a clear statement to that effect
seems indicated.

[v11] Page 3, new text: AODV-RPL reuses and extends the core RPL functionality to support
   routes with bidirectional asymmetric links



----------------------------------------------------------------------
COMMENT:
----------------------------------------------------------------------

1. Section 1:

   Reply.  AODV-RPL currently omits some features compared to AODV -- in
   particular, flagging Route Errors, blacklisting unidirectional links,
   multihoming, and handling unnumbered interfaces.

Your use of language is entirely up to you, but I feel obliged to point out
that there’s been a lot of discussion in the IETF community recently about use
of language that raises sensitive points, and about the term “blacklisting” in
particular. I understand that this is the only place in the document the term
appears, and since it refers to AODV you can’t just use another term, but
placing it in quotation marks might make it clear that it’s referring verbatim
to the language of RFC 3561.

[v11] (Page 3), new text:  AODV-RPL currently omits some features compared to AODV -- in
   particular, flagging Route Errors, "blacklisting" unidirectional
   links ([RFC3561<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/rfc3561__;!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZwouiSuEQ$>]), multihoming, and handling unnumbered interfaces.


2. Section 1:

  support for storing and non-storing modes.  AODV adds basic messages
  RREQ and RREP as part of RPL DIO (DODAG Information Object) control

Did you mean “AODV-RPL adds”?


[v11] Page 3: It was changed to AODV-RPL adds basic messages


3. Section 2:

   Symmetric route
      The upstream and downstream routes traverse the same routers.

Same routers? Or same links? (Or both, if multi-access links are part of the
mix, as I imagine they may be?)

[v11] Page 5, new text: Symmetric route: The upstream and downstream routes traverse the same routers and
      over the same links.


4. Section 4.1:

   OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO
   message.  A RREQ-DIO message MUST carry exactly one RREQ option,

Should that say “one of its IPv6 addresses"? Is it even necessary to restate
this? RFC 6550 §6.3.1 already has a clearer requirement:

   DODAGID: 128-bit IPv6 address set by a DODAG root that uniquely
         identifies a DODAG.  The DODAGID MUST be a routable IPv6
         address belonging to the DODAG root.

[v11] Page 6-New text: OrigNode selects one of its IPv6 addresses and sets it in the DODAGID
   field of the RREQ-DIO message.


5. Section S4.1:

  TargNode can join the RREQ instance at a Rank whose integer portion
  is equal to the MaxRank.

Not less than or equal, right? Strict equality to MaxRank is required?

[v11] Page 8, new text: TargNode can join the RREQ instance at a Rank whose integer portion
   is less than or equal to the MaxRank.


6. Section 4.2:

   TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO
   message.  A RREP-DIO message MUST carry exactly one RREP option,

Same as #4.

[v11] Page 8, new text: TargNode sets one of its IPv6 addresses in the DODAGID field of the
   RREP-DIO message.


7. Section 4.2:

  Address Vector
     Only present when the H bit is set to 0.  For an asymmetric route,
     the Address Vector represents the IPv6 addresses of the route that
     the RREP-DIO has passed.

The first time I read through this, I didn’t understand it at all. On
re-reading, I think you’re using the word “route” in two different ways in the
same sentence, the first time to mean “route” in the sense of an object in the
protocol, the second time in the more casual sense of “a path through the
network”. If that’s right, I suggest rewriting the second instance, as in “…
represents the IPv6 addresses of the path through the network the RREP-DIO has
Traversed.”

[v11] Page 10, new text: Address Vector
      Only present when the H bit is set to 0.  For an asymmetric route,
      the Address Vector represents the IPv6 addresses of the path
      through the network the RREP-DIO has passed.

Passed was not changed to Traversed.


Also, as in point #4, is it right to say *the* IPv6 addresses? Couldn’t any
given node have various IPv6 addresses? So maybe just lose the definite
article, as in “… represents IPv6 addresses of the path…”?

8. Section 4.3:

  r
     A one-bit reserved field.  This field MUST be initialized to zero
     by the sender and MUST be ignored by the receiver.

The figure doesn’t show an “r” field. I assume the field labeled “X” should be
relabeled as “r”?

[v11] Page 11: changed to X.

9. Section 5:

   Figure 4.  If an intermediate router sends out RREQ-DIO with the S
   bit set to 1, then all the one-hop links on the route from the
   OrigNode O to this router meet the requirements of route discovery,

On first reading I didn’t understand this. Having read the whole document, I
now get it (I think!). Possibly changing “meet” to “have met” would have been
enough to get me past my initial befuddlement.

[v11] Page 11: changed to “has met”

10. Section 5:

   The criteria used to determine whether or not each link is symmetric
   is beyond the scope of the document.  For instance, intermediate

Should be “criterion … is beyond", or "criteria … are beyond", depending on
whether you want singular or plural.

[v11] Page12, Not Corrected. [Can this be addressed by the RFC Editor?]


11. Section 5:

  routers can use local information (e.g., bit rate, bandwidth, number
  of cells used in 6tisch)

I wouldn’t have minded a reference for 6tisch.

[v11]Page 12, reference added, new text: ...cells used in 6tisch [RFC9030<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/rfc9030__;!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZzNb2CTyA$>])...


12. Section 5:

   Upon receiving a RREQ-DIO with the S bit set to 1, a node determines
   whether this one-hop link can be used symmetrically, i.e., both the
   two directions meet the requirements of data transmission.  If the
   RREQ-DIO arrives over an interface that is not known to be symmetric,
   or is known to be asymmetric, the S bit is set to 0.  If the S bit
   arrives already set to be '0', it is set to be '0' on retransmission

The term “retransmission” seems misused here. I guess you mean something like
“when the RREQ-DIO is propagated”.

[v11] Page 12, changed to propagated: ..when the RREQ-DIO is propagated.

13. Section 5:

  Appendix A describes an example method using the upstream Expected
  Number of Transmissions" (ETX) and downstream Received Signal
  Strength Indicator (RSSI) to estimate whether the link is symmetric
  in terms of link quality is given in using an averaging technique.

This sentence needs a rewrite to make it grammatical. It works up until "is
given in using an averaging technique”.

[v11] Page 13, new text: “ Appendix A<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/draft-ietf-roll-aodv-rpl-11*appendix-A__;Iw!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZxX0Ve_6g$> describes an example method using the upstream Expected
   Number of Transmissions (ETX) and downstream Received Signal Strength
   Indicator (RSSI) to estimate whether the link is symmetric in terms
   of link quality using an averaging technique.”

14. Section 6.2.1:

     If the S bit in the received RREQ-DIO is set to 1, the router MUST
     determine whether each direction of the link (by which the RREQ-
     DIO is received) satisfies the Objective Function.  In case that
     the downward (i.e. towards the TargNode) direction of the link
     does not satisfy the Objective Function, the link can't be used
     symmetrically, thus the S bit of the RREQ-DIO to be sent out MUST
     be set as 0.  If the S bit in the received RREQ-DIO is set to 0,
     the router MUST determine into the upward direction (towards the
     OrigNode) of the link.

The last sentence doesn’t make sense.

[v11] Page 14, Step 1 section was re-written, new text:”Step 1:

      The router MUST first determine whether to propagate the RREQ-DIO.
      It does this by determining whether or not the downstream
      direction of the incoming link satisfies the Objective Function
      (OF).  If not the RREQ-DIO MUST be dropped, and the following
      steps are not processed.  Otherwise, the router MUST join the
      RREQ-Instance and prepare to propagate the RREQ-DIO.  The upstream
      neighbor router that transmitted the received RREQ-DIO is selected
      as the preferred parent.”

15. Section 6.2.1:

     If the router is an intermediate router, then it transmits a RREQ-
     DIO via link-local multicast;

On what interface? Routers generally can have multiple interfaces. Again, this
is a place a clear description of the network environment might have helped.

[v11] Page 15, Step 4 new text as follows: “Step 4:

      The router checks whether one of its addresses is included in one
      of the ART Options.  If so, this router is one of the TargNodes.
      Otherwise, it is an intermediate router.

      If the router is an intermediate router, then it transmits the
      RREQ-DIO via link-local multicast; if the H bit is set to 0, the
      intermediate router MUST include the address of the interface
      receiving the RREQ-DIO into the address vector.  Otherwise, the
      router is TargNode; if it was not already associated with the
      RREQ-Instance, it prepares and transmits a RREP-DIO (Section 6.3<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/draft-ietf-roll-aodv-rpl-11*section-6.3__;Iw!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZxWUDAY_A$>).
      If, on the other hand, TargNode was already associated with the
      RREQ-Instance, it takes no further action and does not send an
      RREP-DIO.”

16. Section 6.2.2:

  If the OrigNode tries to reach multiple TargNodes in a single RREQ-
  Instance, one of the TargNodes can be an intermediate router to the
  others, therefore it MUST continue sending RREQ-DIO to reach other
  targets.  In this case, before rebroadcasting the RREQ-DIO

The use of the term “broadcast” here confuses me. Is this “broadcast” in the RF
sense? Again, this is a place a clear description of the network environment
might have helped.

[v11] Page 16, rebroadcasting changed to transmitting, new text states: “ If the OrigNode tries to reach multiple TargNodes in a single RREQ-
   Instance, one of the TargNodes can be an intermediate router to the
   others, therefore it MUST continue sending RREQ-DIO to reach other
   targets.  In this case, before transmitting the RREQ-DIO via link-
   local multicast, a TargNode MUST delete the Target Option
   encapsulating its own address, so that downstream routers with higher
   Rank values do not try to create a route to this TargNode.”

17. Section 6.2.2:

  send out any RREQ-DIO.  For the purposes of determining the
  intersection with previous incoming RREQ-DIOs, the intermediate
  router maintains a record of the targets that have been requested
  associated with the RREQ-Instance.  Any RREQ-DIO message with
  different ART Options coming from a router with higher Rank is
  ignored.

It’s not clear to me if the last sentence goes with the previous and if so,
how. Does it even relate to multiple targets? Also, different from what? If it
has the same ART Options (same as what?) is it *not* ignored?

[v11] Page 16, new text: “ ...If the intersection is empty, it
   means that all the targets have been reached, and the router MUST NOT
   transmit any RREQ-DIO.  For the purposes of determining the
   intersection with previous incoming RREQ-DIOs, the intermediate
   router maintains a record of the targets that have been requested for
   a given RREQ-Instance.  Any incoming RREQ-DIO message having multiple
   ART Options coming from a router with higher Rank than the Rank of
   the stored targets is ignored.”

18. Section 6.3.1:

  implementation-specific and out of scope.  If the implementation
  selects the symmetric route, and the L bit is not 0, the TargNode MAY
  delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await
  a symmetric route with a lower Rank.  The value of RREP_WAIT_TIME is
  set by default to 1/4 of the time duration determined by the L bit.

It’s not an L bit though, it’s an L field.

[v11] L bit was changed to L field in the document

19. Section 6.3.2:

  multicast until the OrigNode is reached or MaxRank is exceeded.  The
  TargNode MAY delay transmitting the RREP-DIO for duration
  RREP_WAIT_TIME to await a route with a lower Rank.  The value of
  RREP_WAIT_TIME is set by default to 1/4 of the time duration
  determined by the L bit.

Again, it’s an L field. Also, what if L is zero? Is RREP_WAIT_TIME set to
infinity, as the text implies?

Please do a global search for “L bit”, as there are additional instances I
haven’t called out.

[v11] L bit was changed to L field in the document

20. Section 6.4:

  Step 4:

      If the receiver is the OrigNode, it can start transmitting the
      application data to TargNode along the path as provided in RREP-
      Instance, and processing for the RREP-DIO is complete.  Otherwise,
      in case of an asymmetric route, the intermediate router MUST
      include the address of the interface receiving the RREP-DIO into
      the address vector, and then transmit the RREP-DIO via link-local
      multicast.  In case of a symmetric route, the RREP-DIO message is

As with #15: on what interface(s)?

[v11] Page 19,  Step 4 first paragraph remains the same,
Charlie made a question: “ Are we assuming a single interface?”
----------------------------------------------------------------------
RESPONSE to Comment 20:
----------------------------------------------------------------------

AODV-RPL routers can have multiple router interfaces.  Per-node
configuration of "RREP-DIO transmission interfaces" is an administrative
feature which is beyond the scope of the document.

21. Section 10:

  fake AODV-RPL route discoveries.  In this type of scenario, RPL's
  preinstalled mode of operation, where the key to use for a P2P-RPL
  route discovery is preinstalled, SHOULD be used.

What type of scenario is that?

[V11] Page 22, new text: When rogue routers might be  present, RPL's preinstalled mode of operation, where the key to use  for route discovery is preinstalled, SHOULD be used.


22. Appendix A:

s/pakcet/packet/

[V11] Page 25, fixed.

23. General remark:

Although “acknowledgements” isn’t a required section I was a little surprised
not to encounter it, as it’s usually present. Your call of course.

[v11] Added


Thank you very much,

Ines.

On Fri, May 7, 2021 at 4:58 AM Charlie Perkins <[e-mail]<mailto:[e-mail]>> wrote:
Hello John,

It's taken a while for me to get to this, please excuse the delay. I
have some followup to your comments interspersed below.

On 4/19/2021 1:31 PM, John Scudder via Datatracker wrote:
> John Scudder has entered the following ballot position for
> draft-ietf-roll-aodv-rpl-10: Discuss
>
> When responding, please keep the subject line intact and reply to all
> email addresses included in the To and CC lines. (Feel free to cut this
> introductory paragraph, however.)
>
>
> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html<https://urldefense.com/v3/__https://www.ietf.org/iesg/statement/discuss-criteria.html__;!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZzWjkQ5DQ$>
> for more information about DISCUSS and COMMENT positions.
>
>
> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-roll-aodv-rpl/<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-ietf-roll-aodv-rpl/__;!!NEt6yMaO-gk!Rstby0bTB7wzJO1NoK_SCiEP-uCChnwCWuKE4nSeCB3Pg-FgUc84JZzbGphdAw$>
>
>
>
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
>
> A lot of effort has clearly gone into this work, thank you. I do have one topic
> I want to DISCUSS, as it seriously impacted the readability of the document
> from my point of view. I don’t anticipate that it will be very difficult to
> resolve this DISCUSS as it relates to clarity and not to anything fundamental.
>
> My chief difficulty with the document is placing it in context. No hints are
> given to the reader as to what the expected network environment is. I think it
> would be almost sufficient to say, for example “the network environment is
> assumed to be the same as described in RFC 6550, Section 1” for example, but
> without that hint and without a strong background in ROLL, I found myself
> struggling. Figures 4 and 5 in particular lead me to believe the expected
> environment looks similar to a classic ISP network — a collection of nodes
> connected by point-to-point links. If this isn’t correct (and I bet it’s not)
> that may have led me into incorrect assumptions, which may be reflected in my
> other comments below.
>
> Further, it’s not stated anywhere whether AODV-RPL is intended to stand alone
> as its own routing protocol, or to be viewed as an extension of RPL. In the
> former case, it seems the document is lacking details that are present in RFC
> 6550. I’m assuming the latter is the case, but a clear statement to that effect
> seems indicated.
How about this text:
    Routing Protocol for Low-Power and Lossy Networks (RPL) [RFC6550] is
    an IPv6 distance vector routing protocol designed to support multiple
    traffic flows through a root-based Destination-Oriented Directed
    Acyclic Graph (DODAG).  Typically, a router does not have routing
    information for most other routers.  Consequently, for traffic
    between routers within the DODAG (i.e., Point-to-Point (P2P) traffic)
    data packets either have to traverse the root in non-storing mode, or
    traverse a common ancestor in storing mode.  Such P2P traffic is
    thereby likely to traverse longer routes and may suffer severe
    congestion near the root (for more information see [RFC6997],
    [RFC6998]). The network environment that is considered in this document
    assumed to be the same as described in Section 1 of [RFC6550].

> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
>
> 1. Section 1:
>
>     Reply.  AODV-RPL currently omits some features compared to AODV -- in
>     particular, flagging Route Errors, blacklisting unidirectional links,
>     multihoming, and handling unnumbered interfaces.
>
> Your use of language is entirely up to you, but I feel obliged to point out
> that there’s been a lot of discussion in the IETF community recently about use
> of language that raises sensitive points, and about the term “blacklisting” in
> particular. I understand that this is the only place in the document the term
> appears, and since it refers to AODV you can’t just use another term, but
> placing it in quotation marks might make it clear that it’s referring verbatim
> to the language of RFC 3561.

This is an evolving issue.  I am fine with using quotes but otherwise
maintaining consistent terminology.  For instance,

     AODV-RPL currently omits some features compared to AODV -- in
     particular, flagging Route Errors, "blacklisting" unidirectional links
     [RFC3561], multihoming, and handling unnumbered interfaces.

If there is an official list of terms to search for please let us know.

>
> 2. Section 1:
>
>    support for storing and non-storing modes.  AODV adds basic messages
>    RREQ and RREP as part of RPL DIO (DODAG Information Object) control
>
> Did you mean “AODV-RPL adds”?
Yes, will fix.

>
> 3. Section 2:
>
>     Symmetric route
>        The upstream and downstream routes traverse the same routers.
>
> Same routers? Or same links? (Or both, if multi-access links are part of the
> mix, as I imagine they may be?)

       The upstream and downstream routes traverse the same routers and over
       the same links.
> 4. Section 4.1:
>
>     OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO
>     message.  A RREQ-DIO message MUST carry exactly one RREQ option,
>
> Should that say “one of its IPv6 addresses"? Is it even necessary to restate
> this? RFC 6550 §6.3.1 already has a clearer requirement:
>
>     DODAGID: 128-bit IPv6 address set by a DODAG root that uniquely
>           identifies a DODAG.  The DODAGID MUST be a routable IPv6
>           address belonging to the DODAG root.

I'm not quite sure what is requested.  Should it be "OrigNode sets the
DODAGID field", relying on the definition provided in RFC 6550? Should
it be "OrigNode sets one of its routable IPv6 address in the DODAGID field"?
Honestly, I thought the meaning was clear.  Unless there is an
objection, I reckon we will use the latter wording.

>
> 5. Section S4.1:
>
>    TargNode can join the RREQ instance at a Rank whose integer portion
>    is equal to the MaxRank.
>
> Not less than or equal, right? Strict equality to MaxRank is required?
The existing text isn't good.  Instead,

    TargNode can join the RREQ instance at a Rank whose integer portion
    is less than the MaxRank.


> 6. Section 4.2:
>
>     TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO
>     message.  A RREP-DIO message MUST carry exactly one RREP option,
>
> Same as #4.
>
> 7. Section 4.2:
>
>    Address Vector
>       Only present when the H bit is set to 0.  For an asymmetric route,
>       the Address Vector represents the IPv6 addresses of the route that
>       the RREP-DIO has passed.
>
> The first time I read through this, I didn’t understand it at all. On
> re-reading, I think you’re using the word “route” in two different ways in the
> same sentence, the first time to mean “route” in the sense of an object in the
> protocol, the second time in the more casual sense of “a path through the
> network”. If that’s right, I suggest rewriting the second instance, as in “…
> represents the IPv6 addresses of the path through the network the RREP-DIO has
> traversed.”
>
> Also, as in point #4, is it right to say *the* IPv6 addresses? Couldn’t any
> given node have various IPv6 addresses? So maybe just lose the definite
> article, as in “… represents IPv6 addresses of the path…”?

Good point.  We will use your formulation.

>
> 8. Section 4.3:
>
>    r
>       A one-bit reserved field.  This field MUST be initialized to zero
>       by the sender and MUST be ignored by the receiver.
>
> The figure doesn’t show an “r” field. I assume the field labeled “X” should be
> relabeled as “r”?
Actually, the description should refer to an "X" field, not an "r"
field.  We will update.


>
> 9. Section 5:
>
>     Figure 4.  If an intermediate router sends out RREQ-DIO with the S
>     bit set to 1, then all the one-hop links on the route from the
>     OrigNode O to this router meet the requirements of route discovery,
>
> On first reading I didn’t understand this. Having read the whole document, I
> now get it (I think!). Possibly changing “meet” to “have met” would have been
> enough to get me past my initial befuddlement.

Yes, that's better.

>
> 10. Section 5:
>
>     The criteria used to determine whether or not each link is symmetric
>     is beyond the scope of the document.  For instance, intermediate
>
> Should be “criterion … is beyond", or "criteria … are beyond", depending on
> whether you want singular or plural.
We will use "criteria … are beyond".

>
> 11. Section 5:
>
>    routers can use local information (e.g., bit rate, bandwidth, number
>    of cells used in 6tisch)
>
> I wouldn’t have minded a reference for 6tisch.
No problem.

>
> 12. Section 5:
>
>     Upon receiving a RREQ-DIO with the S bit set to 1, a node determines
>     whether this one-hop link can be used symmetrically, i.e., both the
>     two directions meet the requirements of data transmission.  If the
>     RREQ-DIO arrives over an interface that is not known to be symmetric,
>     or is known to be asymmetric, the S bit is set to 0.  If the S bit
>     arrives already set to be '0', it is set to be '0' on retransmission
>
> The term “retransmission” seems misused here. I guess you mean something like
> “when the RREQ-DIO is propagated”.
That is better.  We will use that.

>
> 13. Section 5:
>
>    Appendix A describes an example method using the upstream Expected
>    Number of Transmissions" (ETX) and downstream Received Signal
>    Strength Indicator (RSSI) to estimate whether the link is symmetric
>    in terms of link quality is given in using an averaging technique.
>
> This sentence needs a rewrite to make it grammatical. It works up until "is
> given in using an averaging technique”.
How about:
     Appendix A describes an example method using the upstream Expected
     Number of Transmissions" (ETX) and downstream Received Signal
     Strength Indicator (RSSI) to estimate whether the link is symmetric
     in terms of link quality using an averaging technique.


>
> 14. Section 6.2.1:
>
>       If the S bit in the received RREQ-DIO is set to 1, the router MUST
>       determine whether each direction of the link (by which the RREQ-
>       DIO is received) satisfies the Objective Function.  In case that
>       the downward (i.e. towards the TargNode) direction of the link
>       does not satisfy the Objective Function, the link can't be used
>       symmetrically, thus the S bit of the RREQ-DIO to be sent out MUST
>       be set as 0.  If the S bit in the received RREQ-DIO is set to 0,
>       the router MUST determine into the upward direction (towards the
>       OrigNode) of the link.
>
> The last sentence doesn’t make sense.
How about:
                ...  If the S bit in the received RREQ-DIO is set to 0,
      the router MUST determine the upward direction (towards the
      OrigNode) of the link.
>
> 15. Section 6.2.1:
>
>       If the router is an intermediate router, then it transmits a RREQ-
>       DIO via link-local multicast;
>
> On what interface? Routers generally can have multiple interfaces. Again, this
> is a place a clear description of the network environment might have helped.

The link-local multicast should go out over all local interfaces.

>
> 16. Section 6.2.2:
>
>    If the OrigNode tries to reach multiple TargNodes in a single RREQ-
>    Instance, one of the TargNodes can be an intermediate router to the
>    others, therefore it MUST continue sending RREQ-DIO to reach other
>    targets.  In this case, before rebroadcasting the RREQ-DIO
>
> The use of the term “broadcast” here confuses me. Is this “broadcast” in the RF
> sense? Again, this is a place a clear description of the network environment
> might have helped.
This needs to be reformulated to avoid suggesting anything about RF
broadcast.  TBD.

>
> 17. Section 6.2.2:
>
>    send out any RREQ-DIO.  For the purposes of determining the
>    intersection with previous incoming RREQ-DIOs, the intermediate
>    router maintains a record of the targets that have been requested
>    associated with the RREQ-Instance.  Any RREQ-DIO message with
>    different ART Options coming from a router with higher Rank is
>    ignored.
>
> It’s not clear to me if the last sentence goes with the previous and if so,
> how. Does it even relate to multiple targets? Also, different from what? If it
> has the same ART Options (same as what?) is it *not* ignored?
How about:
                   .....                     For the purposes of
determining the
   intersection with previous incoming RREQ-DIOs, the intermediate
   router maintains a record of the targets that have been requested
   associated with the RREQ-Instance. Any incoming RREQ-DIO message having
   multiple ART Options coming from a router with higher Rank than the
Rank of
   the stored targets is ignored.

>
> 18. Section 6.3.1:
>
>    implementation-specific and out of scope.  If the implementation
>    selects the symmetric route, and the L bit is not 0, the TargNode MAY
>    delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await
>    a symmetric route with a lower Rank.  The value of RREP_WAIT_TIME is
>    set by default to 1/4 of the time duration determined by the L bit.
>
> It’s not an L bit though, it’s an L field.
Good point!

>
> 19. Section 6.3.2:
>
>    multicast until the OrigNode is reached or MaxRank is exceeded.  The
>    TargNode MAY delay transmitting the RREP-DIO for duration
>    RREP_WAIT_TIME to await a route with a lower Rank.  The value of
>    RREP_WAIT_TIME is set by default to 1/4 of the time duration
>    determined by the L bit.
>
> Again, it’s an L field. Also, what if L is zero? Is RREP_WAIT_TIME set to
> infinity, as the text implies?
Thanks for pointing this out.  We need to be explicit about it.  I don't
think the RREP_WAIT_TIME should ever be zero or infinity. But, if it
were, the implementations would still be interoperable in a sense.  Do
we really want to get into exactly what wait times make sense in this
context?


>
> Please do a global search for “L bit”, as there are additional instances I
> haven’t called out.
>
> 20. Section 6.4:
>
>    Step 4:
>
>        If the receiver is the OrigNode, it can start transmitting the
>        application data to TargNode along the path as provided in RREP-
>        Instance, and processing for the RREP-DIO is complete.  Otherwise,
>        in case of an asymmetric route, the intermediate router MUST
>        include the address of the interface receiving the RREP-DIO into
>        the address vector, and then transmit the RREP-DIO via link-local
>        multicast.  In case of a symmetric route, the RREP-DIO message is
>
> As with #15: on what interface(s)?
It should go out to all the neighbors over multiple interfaces if necessary.

>
> 21. Section 10:
>
>    fake AODV-RPL route discoveries.  In this type of scenario, RPL's
>    preinstalled mode of operation, where the key to use for a P2P-RPL
>    route discovery is preinstalled, SHOULD be used.
>
> What type of scenario is that?

  "In this type of scenario" -> "When rogue routers might be present"

>
> 22. Appendix A:
>
> s/pakcet/packet/
Check.
>
> 23. General remark:
>
> Although “acknowledgements” isn’t a required section I was a little surprised
> not to encounter it, as it’s usually present. Your call of course.
Acknowledgements are due to a lot of people - thanks for the reminder!

Naturally Yours,
Charlie P.