Link Metrics for the Mobile Ad Hoc Network (MANET) Routing Protocol OLSRv2 - Rationale
draft-ietf-manet-olsrv2-metrics-rationale-04

[Ballot comment]
I believe the mail exchange between Suresh and Cristopher has been useful, and should result in some document changes. It looks the authors have this under control, but I'm hoping the thread finishes before the document is cast in stone.

[Ballot comment]
I like this type of rationale document. This is something that the IETF generally doesn't do, with the consequence that resolved issues are revisited on regular basis. I wish I had this document at the time of reviewing draft-ietf-manet-olsrv2. It could have been an appendix in draft-ietf-manet-olsrv2 btw.

-
There is no "manageability considerations section". http://tools.ietf.org/html/rfc5706#appendix-A for a list of questions.
Specifically regarding the metrics, the following question comes to mind: what about connecting different MANET networks together, if the metric convention (for a lack of a better word) is not the same. For example: delay, hop count. Note that this metric "convention" is only the operator head AFAIK.

  In a well-designed network, all routers will use the same metric
  type.  It will not produce good routes if, for example, some link
  metrics are based on data rate and some on path loss (except to the
  extent that these may be correlated).  How to achieve this is an
  administrative matter, outside the scope of OLSRv2.

Yes, there is the above sentence, but that's all there is in terms of manageability and operations.
Topics such as merging network, potential notification or polling) for metric mismatch (*), etc..
Maybe that's fine because it's a rational document, that's something that should be solved in the manageability draft http://tools.ietf.org/html/draft-nguyen-manet-management-00 ?

(*)

  Note that, using directional metrics, if router A defines the metric
  of the link from router B to router A, then router B must use router
  A's definition of that metric on that link in that direction.
  (Router B could, if appropriate, use a bad mismatch between
  directional metrics as a reason to discontinue use of this link,
  using the link quality mechanism in [RFC6130].)

- terminology

  All terms introduced in [RFC5444], including "message" and "TLV", are
  to be interpreted as described there.

  All terms introduced in [RFC6130], including "MANET interface",
  "HELLO message", "heard", "link", "symmetric link", "1-hop neighbor",
  "symmetric 1-hop neighbor", "2-hop neighbor", "symmetric 2-hop
  neighbor", and "symmetric 2-hop neighborhood", are to be interpreted
  as described there.

  All terms introduced in [OLSRv2], including "router", "OLSRv2
  interface", "willingness", "MultiPoint Relay (MPR)", "MPR selector",
  and "MPR flooding" are to be interpreted as described there.

This is a typical example where not using capitalized terms (when specified in the terminology section), is a problem.
Specifically because of the common terms such as heard, link, message, willingness, etc...
Let's take the 3 "heard" instances in the paragraph below. Which one(s) is/are a definition coming from RFC 6130?

    When a router reports a 1-hop neighbor in a HELLO message, it may do
    so for the first time with link status HEARD.  As the router is
    responsible for defining and reporting incoming link metrics, it must
    evaluate that metric, and attach that link metric to the appropriate
    address (which will have link status HEARD) in the next HELLO message
    reporting that address on that OLSRv2 interface.  There will, at this
    time, be no outgoing link metric available to report, but a router
    must be able to immediately decide on an incoming link metric once it
    has heard a 1-hop neighbor on an OLSRv2 interface for the first time.


-
A couple of acronyms must be expanded on the first occurrence: TC message, MPR. Potentially others

[Ballot comment]
I like this type of rationale document. This is something that the IETF generally doesn't do, with the consequence that resolved issues are revisited on regular basis. I wish I had this document at the time of reviewing draft-ietf-manet-olsrv2. It could have been an appendix in draft-ietf-manet-olsrv2 btw.

-
There is no "manageability considerations section". http://tools.ietf.org/html/rfc5706#appendix-A for a list of questions.
Specifically regarding the metrics, the following question comes to mind: what about connecting different MANET networks together, if the metric convention (for a lack of a better word) is not the same. For example: delay, hop count. Note that this metric "convention" is only the operator head AFAIK.

  In a well-designed network, all routers will use the same metric
  type.  It will not produce good routes if, for example, some link
  metrics are based on data rate and some on path loss (except to the
  extent that these may be correlated).  How to achieve this is an
  administrative matter, outside the scope of OLSRv2.

Yes, there is the above sentence, but that's all there is in terms of manageability and operations.
Topics such as merging network, potential notification or polling) for metric mismatch (*), etc..
Maybe that's fine because it's a rational document, that's something that should be solved in the manageability draft http://tools.ietf.org/html/draft-nguyen-manet-management-00 ?

(*)

  Note that, using directional metrics, if router A defines the metric
  of the link from router B to router A, then router B must use router
  A's definition of that metric on that link in that direction.
  (Router B could, if appropriate, use a bad mismatch between
  directional metrics as a reason to discontinue use of this link,
  using the link quality mechanism in [RFC6130].)

- terminology

  All terms introduced in [RFC5444], including "message" and "TLV", are
  to be interpreted as described there.

  All terms introduced in [RFC6130], including "MANET interface",
  "HELLO message", "heard", "link", "symmetric link", "1-hop neighbor",
  "symmetric 1-hop neighbor", "2-hop neighbor", "symmetric 2-hop
  neighbor", and "symmetric 2-hop neighborhood", are to be interpreted
  as described there.

  All terms introduced in [OLSRv2], including "router", "OLSRv2
  interface", "willingness", "MultiPoint Relay (MPR)", "MPR selector",
  and "MPR flooding" are to be interpreted as described there.

This is a typical example where not using capitalized terms (when specified in the terminology section), is a problem.
Specifically because of the common terms such as heard, link, message, willingness, etc...
Let's take the 3 "heard" instances in the paragraph below. Which one(s) is/are a definition coming from RFC 6130?

      When a router reports a 1-hop neighbor in a HELLO message, it may do
      so for the first time with link status HEARD.  As the router is
      responsible for defining and reporting incoming link metrics, it must
      evaluate that metric, and attach that link metric to the appropriate
      address (which will have link status HEARD) in the next HELLO message
      reporting that address on that OLSRv2 interface.  There will, at this
      time, be no outgoing link metric available to report, but a router
      must be able to immediately decide on an incoming link metric once it
      has heard a 1-hop neighbor on an OLSRv2 interface for the first time.



A couple of acronyms must be expanded on the first occurrence: TC message, MPR. Potentially others

[Ballot comment]

- intro, "legacy OLSRv2 routers" is an odd phrase, I think I
know what you mean but maybe try clarify. What I think you
mean is "routers that implement OLSRv2 without the putative
link-metrics extension"

- section 4, last para: I hope that some other doc also says
that link metrics should change slower than that update rate.
If not, then this is being a bit more than just background
informational stuff. (Just checking in case it got lost or
something.)

- 5.5, "unless link quality indicates otherwise" seems odd.
You're explaining link metrics via "link quality"?  If that's
not another well known OLSR term, maybe better to just say
"unless the implementation decides otherwise" or something?

- 6.1, s/produce produce/produce/

- section 8: I'm a bit surprised there's nothing to say since
I would have thought that telling lies about metric values
provides another way in which an OLSR router can do bad
things, such as ensure traffic is sent the way the bad router
wants. If that's the case then maybe saying so and how it
doesn't make things worse really would be good. If that's not
the case, the saying why would be good.

- section 8: Just a query: has there been any (good) work on
using routing metrics as a countermeasure? E.g., gossiping
about node reputations? If there were something good along
those lines, here might be a fine place to note that (even if
it wasn't part of the WG discussion).

IESG/Authors/WG Chairs:

IANA has reviewed draft-ietf-manet-olsrv2-metrics-rationale-02, which is
currently in Last Call, and has the following comments:

We understand that, upon approval of this document, there are no IANA
Actions that need completion.

If this assessment is not accurate, please respond as soon as possible.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
CC:
Reply-To: ietf@ietf.org
Subject: Last Call:  (Link Metrics for the Mobile Ad Hoc Network (MANET) Routing Protocol OLSRv2 - Rationale) to Informational RFC


The IESG has received a request from the Mobile Ad-hoc Networks WG
(manet) to consider the following document:
- 'Link Metrics for the Mobile Ad Hoc Network (MANET) Routing Protocol
  OLSRv2 - Rationale'
  as Informational RFC

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf@ietf.org mailing lists by 2013-03-11. Exceptionally, comments may be
sent to iesg@ietf.org instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.

Abstract


  OLSRv2 includes the ability to assign metrics to links and to use
  those metrics to allow routing by other than minimum hop count
  routes.  This document provides a historic record of the rationale
  for, and design considerations behind, how link metrics were included
  in OLSRv2.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-manet-olsrv2-metrics-rationale/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-manet-olsrv2-metrics-rationale/ballot/


No IPR declarations have been submitted directly on this I-D.

Hi,

I have done my usual AD review of your draft prior to issuing IETF
last call. The purpose of the review is to clear up any issues that
might arise during last call or IESG evaluation to save other reviewers
time, and to smooth the passage of the draft in those stages.

This document looks in pretty good shape to me. As a calibration, I
noted a number of questions as I went along, only to find you answered
them about half a page later. Thanks for all the work you must have put
in.

I have a number of comments, but only the first two really need
attention. The others would be "nice to have".

If you can respin the document addressing these comments, I will issue
last call. As usual, all my comments are open for discussion.

Thanks,
Adrian

---

The punctuation and clause order in the Abstract is a little ambiguous.
The document does not "describe in order to allow routing". I have
some suggested wording which I have rolled into my next point.

---

The document was clearly useful during the production of OLSRv2, and
after discussion with the WG chairs I understand why the WG wants to
pursue publication even after all of the decisions have been made and
OLSRv2 accepted for publication.  However, the *current* purpose of the
document is not particularly clear so I have two suggestions:

In the Abstract add a few words as follows. I have also re-ordered the
clauses to cover my previous point.

  OLSRv2 includes the ability to assign metrics to links and to use
  those metrics to allow routing by other than minimum hop count
  routes.  This document provides a historic record of the rationale
  for and design considerations behind how link metrics were included
  in OLSRv2.

Add a new 3rd paragraph in Section 1

  During the development of OLSRv2 the working group and authors
  repeatedly revisited discussion with others about how and why some
  choices were made in the protocol specification particularly at the
  metric integration level.  Some of the issues were non-intuitive
  and this document is presented as a record of the considerations and
  decisions to provide informational discussion about motivation and
  historic design choices.  This will be a useful reference document
  when those questions arise again.

The wording on these is not mandatory, but the inclusion of some sort
of statement is going to make the document more useful and get it
through the IESG more easily.

(BTW. Thank you for Section 3.)

---

Section 1 bullets

The use of "can use only" is a bit confusing. Suggest...

OLD
      routers can use only metrics of the physical type that they are
      configured to use.
NEW
      routers can be configured to use only a subset of the available
      metric types.
END

---

There is a mismatched double quote at symmetric link in the middle
paragraph.

---
                                                                             
I wonder whether you want to make any comments about node metrics.
Obviously, you don't have them (neighbor metrics being a different
thing), but you could comment on why you don't have them (if this was
ever discussed).

The question is slightly touched on in 5.2 in discussion of "delay".

---

Section 8

Were there any security considerations that cropped up while designing
metric support in OSLRv2? If so, here would be the place to mention
them.

> (1) What type of RFC is being requested (BCP, Proposed Standard,
> Internet Standard, Informational, Experimental, or Historic)? Why
> is this the proper type of RFC? Is this type of RFC indicated in the
> title page header?

This document is requested to be published as an Informational RFC.

OLSRv2 reflects ~8 years of experiences with OLSR, published as RFC3626
(Experimental), and multiple independent implementations and deployments
exist, and this protocol is in final review by the IESG for publication
as a Proposed Standard. (The single DISCUSS outstanding is not related
to the subject matter of this document.)

This document presents the design rationale behind the way in which
OLSRv2 incorporated metrics. It does not mandate any protocol behaviors.

> (2) The IESG approval announcement includes a Document Announcement
> Write-Up. Please provide such a Document Announcement Write-Up. Recent
> examples can be found in the "Action" announcements for approved
> documents. The approval announcement contains the following sections:

> Technical Summary
>
>  Relevant content can frequently be found in the abstract
>  and/or introduction of the document. If not, this may be
>  an indication that there are deficiencies in the abstract
>  or introduction.

The abstract of this document is included below.

  This document describes the rationale for and design considerations
  behind how link metrics are included in OLSRv2, in order to allow
  routing by other than minimum hop count routes.

> Working Group Summary
>
>  Was there anything in WG process that is worth noting? For
>  example, was there controversy about particular points or
>  were there decisions where the consensus was particularly
>  rough?
o OLSRv2 was first submitted as an individual draft in July 2005
(draft-clausen-manet-olsrv2-00), and accepted as a Working Group
document in August 2005.

o OLSRv2 is close to approval as a Propose Standard by the IESG
              (one DISCUSS to resolve).
o A key difference between RFC3626 and OLSRv2 is the introduction of
support for link metrics. An individual draft
(draft-dearlove-olsrv2-metrics-00) was submitted in 2007, discussing
the design options, culminating in 2010 with
draft-dearlove-olsrv2-metrics-05 documenting Working Group consensus
on this matter. Metrics support was, then, folded into OLSRv2.

o This document retains and documents the design rationale, and important
decisions for how metrics were integrated into OLSRv2.

> Document Quality
>
>  Are there existing implementations of the protocol? Have a
>  significant number of vendors indicated their plan to
>  implement the specification? Are there any reviewers that
>  merit special mention as having done a thorough review,
>  e.g., one that resulted in important changes or a
>  conclusion that the document had no substantive issues? If
>  there was a MIB Doctor, Media Type or other expert review,
>  what was its course (briefly)? In the case of a Media Type
>  review, on what date was the request posted?

There is a number of independent implementations of OLSRv2, as was
indicated in the write-up for that OLSRv2.
This document does not propose a protocol, or mandate protocol behavior,
but rather presents part of the design rationale for OLSRv2.
> Personnel
>
>  Who is the Document Shepherd? Who is the Responsible Area
>  Director?

Adrian Farrel is the Responsible Area Director;  Stan Ratliff is the Document Shepherd.

> (3) Briefly describe the review of this document that was performed by
> the Document Shepherd. If this version of the document is not ready
> for publication, please explain why the document is being forwarded to
> the IESG.

The shepherd has read and reviewed the document. no issues exist; the document is ready for publication.

> (4) Does the document Shepherd have any concerns about the depth or
> breadth of the reviews that have been performed?

No concerns exist.

> (5) Do portions of the document need review from a particular or from
> broader perspective, e.g., security, operational complexity, AAA, DNS,
> DHCP, XML, or internationalization? If so, describe the review that
> took place.

The authors do not believe that - outside the usual directorate reviews
during  IETF Last Call - additional reviews are required.

> (6) Describe any specific concerns or issues that the Document Shepherd
> has with this document that the Responsible Area Director and/or the
> IESG should be aware of? For example, perhaps he or she is uncomfortable
> with certain parts of the document, or has concerns whether there really
> is a need for it. In any event, if the WG has discussed those issues and
> has indicated that it still wishes to advance the document, detail those
> concerns here.

There are no issues that the ADs and/or the IESG should be aware of.

> (7) Has each author confirmed that any and all appropriate IPR
> disclosures required for full conformance with the provisions of BCP 78
> and BCP 79 have already been filed. If not, explain why.

All authors have confirmed that they are unaware of any IPR needing disclosure,
indeed that there are no known IPR claims related to this document.

> (8) Has an IPR disclosure been filed that references this document?
> If so, summarize any WG discussion and conclusion regarding the IPR
> disclosures.

No IPR disclosures have been filed.

> (9) How solid is the WG consensus behind this document? Does it
> represent the strong concurrence of a few individuals, with others
> being silent, or does the WG as a whole understand and agree with it?

> (10) Has anyone threatened an appeal or otherwise indicated extreme
> discontent? If so, please summarise the areas of conflict in separate
> email messages to the Responsible Area Director. (It should be in a
> separate email because this questionnaire is publicly available.)

> (11) Identify any ID nits the Document Shepherd has found in this
> document. (See http://www.ietf.org/tools/idnits/ [^] and the Internet-Drafts
> Checklist). Boilerplate checks are not enough; this check needs to be
> thorough.

IDnits returns no errors or warnings

> (12) Describe how the document meets any required formal review
> criteria, such as the MIB Doctor, media type, and URI type reviews.

This document does not specify a protocol, a format, a media type or reserve
any code-points. Thus, such reviews are not needed.

> (13) Have all references within this document been identified as
> either normative or informative?

Yes.

> (14) Are there normative references to documents that are not ready for
> advancement or are otherwise in an unclear state? If such normative
> references exist, what is the plan for their completion?

No. There are no normative references in this document.

> (15) Are there downward normative references references (see RFC 3967)?
> If so, list these downward references to support the Area Director in the
> Last Call procedure.

No. There are no normative references.

All informative references are, furthermore, to already published RFCs or
soon-to-be-RFCs (OLSRv2 currently in IESG review)

> (16) Will publication of this document change the status of any
> existing RFCs? Are those RFCs listed on the title page header, listed
> in the abstract, and discussed in the introduction? If the RFCs are not
> listed in the Abstract and Introduction, explain why, and point to the
> part of the document where the relationship of this document to the
> other RFCs is discussed. If this information is not in the document,
> explain why the WG considers it unnecessary.

Publication of this document will not change the status of any existing RFCs.

> (17) Describe the Document Shepherd's review of the IANA considerations
> section, especially with regard to its consistency with the body of the
> document. Confirm that all protocol extensions that the document makes
> are associated with the appropriate reservations in IANA registries.
> Confirm that any referenced IANA registries have been clearly
> identified. Confirm that newly created IANA registries include a
> detailed specification of the initial contents for the registry, that
> allocations procedures for future registrations are defined, and a
> reasonable name for the new registry has been suggested (see RFC 5226).

This document has no actions for IANA.

> (18) List any new IANA registries that require Expert Review for future
> allocations. Provide any public guidance that the IESG would find
> useful in selecting the IANA Experts for these new registries.

This document has no actions for IANA.

> (19) Describe reviews and automated checks performed by the Document
> Shepherd to validate sections of the document written in a formal
> language, such as XML code, BNF rules, MIB definitions, etc.

No automated checks, other than IDnits, performed; the document does not
specify a protocol, but documents a design rationale.