[6tisch] draft-ietf-6tisch-msf-02.txt is published

[Tengfei Chang <[e-mail]>]

Dear all,

draft-ietf-6tisch-msf-02.txt  is just published.

The main changes made in this version are

   - Resolve the issues in Pending Elements section.
   - Using autonomous SHARED and non-SHARED cells.
   - Overall revised the specification.

Additional information about how the issues in the pending elecments
section are resolved is written below.  (issues are separated by "=")

Any reviews or comments are welcome!

Tengfei


Security issue on autonomous cell installation
====================

The autonomous cell to the pledge is installed on the join proxy before the
pledge is authorized, which is a security issue. Related discussion: ttps://
mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao

[Resolved. During join process, only pledge required to install autonomous
SHARED cell to JP, no action required from JP side.]


Handling the case when bandwidth allocation exceeds available capacity
====================

When node A initializes a 6top ADD transaction to node B, but node B does
NOT have enough bandwidth to allocate.
What can node B do to indicate this case in its 6top response, and how
should node A handle the packet after receiving the response?
Related discussion:
https://www.ietf.org/mail-archive/web/6tisch/current/msg06095.html

[ToDo. According to 6top RFC8480, SUCCESS return code will be in the 6top
response with an empty cellList possibly. For this case, I don't have a
prefect solution. One solution I am using is marking the node B as
'no_resource', then updating it's routing table and filtering out the
neighbor marked as 'no_resource'. However, this is a layer-violation
design.]


joining traffic MUST be sent in minimal cell
====================

Joining traffic MUST be sent in minimal cell.
Issues link: https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/11

 [Resolved. Joining traffic will be sent on autonomous cell.]


NumCellsElapsed  shouldn't update on shared dedicated cell
====================
    NumCellsElapsed  is used to track under/overuse of cells.
    If we are backing off, i.e. skipping cells, should those skipped cells
count towards NumCellsElapsed ?
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/13

    [Resolved. The counters are only applied on managed unicast cell.]


non-trusted packet shouldn't be accounted for for adapting traffic
====================
    Mention that the untrusted packet (e.g. join request/response)
shouldn't be counted for adapting the traffic.
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/15

    [Resolved. clarified in adapting traffic section.]


Customize the backoff exponent on dedicated shared cell.
====================
    Use small backoff exponent on dedicated cell since it's only shared by
two nodes.
    Discussion: do we still have this case with the merger of ASF?
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/17
    [NotApplied. After ASF is merged, the dedicated shared cell is not used
anymore. The autonomous SHARED cell is shared among a set of neighbors
hence no need to customize the backoff exponent.]


Adapting 6P Timeout
====================
    After 6P TIMEOUT, the next 6P transaction should be configured using a
larger TIMEOUT.
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/19

    [ToDo. I am not sure this is an issue or not with current version. Need
to discuss with Malisa and Simon.]


Timeout calculation is wrong
====================
    The 6P Timeout is calculated as :
    list style: symbols

    (1/(C+1))*(1/PDR)*SIXP_TIMEOUT_SEC_FACTOR

    It should be
    list style: symbols

    (1/(C+1))*(1/PDR)*SIXP_TIMEOUT_SEC_FACTOR


    according to the paper: https://arxiv.org/pdf/1507.05810.pdf
    Related link is at:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/22

    [Resolved. The comments are taken and applied in the text.]


Separate Cell Counters for TX and RX
====================
    NumCellsUsed and NumCellsElapsed counter should be separated between TX
and RX.
    Question: still applies?
    Related Link is at:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/20

    [Resolved. The comments are taken and applied in the text.]


Two slotframes
====================
    Why are they two slotframes in same length?
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/25

    [Resolved. The length of two slotframes are SHOULD be the same, instead
of MUST.]


Parameters for SAX is missing
====================
    It'd be nice to have an example or a test vector in the draft in order
to validate a SAX implementation used for MSF.
    This is critical for interoperability.
    Related discussion:
https://mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao

    [Resolved. An appredix of how to implement the sax is added.]


Wrong end state statement
====================
    In Section 1, one of the end states of the join process is having "one
default unicast cell to/from each of its neighbors".
    It should be an autonomous TX cells to its Join Proxy.
    Related discussion: hhttps://
mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao

    [Resolved.Comments are taken and applied in v2.]


Dependency on RFC8180 shouldn't be a MUST
====================
    Section 2 states
    "A node implementing MSF MUST implement the Minimal 6TiSCH
Configuration [RFC8180], which defines the "minimal cell", a single shared
cell  providing minimal connectivity between the nodes in the network".
    MUST here is too strong.
    Some may want to use MSF with a base schedule other than the one
defined in RFC8180, with full understanding on the implications by not
following RFC8180.
    Proposal is to replace MUST by SHOULD.
    Related discussion:
https://mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao

    [Resolved. Comments are taken and applied in v2.]


DIO can be unicast packet as indicated in RFC6550
====================
    Section 2 states
    "DODAG Information Objects (DIOs), defined by [RFC6550].  These are
broadcast frames."
    However, the DIO as a response to a DIS is a unicast frame.
    Related discussion: hhttps://
mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao

    [Resolved. Comments are taken and applied in v2.]


Rules for broadcast frames is out of scope of MSF
====================
    In Section 2, the rules for broadcast frames on the minimal cell seem
to be an implementation-specific optimization.
    And it is beyond of the scope of this draft.
    This idea is about how to use the minimal cell efficiently; it's not
directly related to how to use cells scheduled by MSF.
    Related discussion:
https://mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao

    [ToDo. I agree with this comment. Should we remove those text or keep
them in the draft but mentioned those rules are not a MUST but a
RECOMMENDED?]


Wrong statement in Step 4
====================
    In Section 4.4 Step 3, the statement "After joining" in the explanation
of step 3 should be "After having chosen a JP"?
    At this step 3, "joining" is not done.
    Related discussion:
https://mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao

    [Resolved. Comments are taken and applied in v2.]


Rephrase NumCellsElapsed  to NumCellsElapsed
====================
    Rephrase NumCellsElapsed  to NumCellsElapsed
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/14

    [Resolved. Comments are taken and applied in v2.]


Create a list of packets that be able to be sent on minimal cell
====================
    The current text enumerates explicitly EBs and DIOs.
    The other broadcast packets are not mentioned.
    For example: RPL DIS or application-layer broadcast?
    It should mention EBs and DIOs but also say "any other broadcast
packet".
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/24

    [Resolved. Comments are taken and applied in v2.]


Clarify term 'dedicated cell'
====================
    Terminology: "dedicated" needs to be clarified in MSF.
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/26

    [Resolved. dedicated cells are not used in v2. The type of cell used in
the specification are autonomous non-SHARED cell, autonomous SHARED cell
and managed unicast cell.]


text is missing
====================
    The text that describes the 6P command with cell options etc. was
accidentally removed.
    Needs adding back somewhere.
    The text was:
    Step 5 - 6P ADD to Preferred Parent
    After having selected a preferred parent, the joined node MUST issue
    a 6P ADD command to that parent, with the following fields:
    list style: symbols
     CellOptions: set to TX=1,RX=1,SHARED=1
     CellOptions: set to TX=1,RX=1,SHARED=1
     NumCells: set to 1
     CellList: at least 5 cells, chosen according to Section 7
    /list>
    After the 6P Transaction is finished, the node MUST synchronize only
    to its preferred parent.  At this point, the node has a dedicated
    cell which allows for bidirectional communication with its preferred
    parent.
    Issues link:
https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/29

    [NotApplied. This comments is referring to the version before ASF is
merged.]

-- 
Chang Tengfei,
Pre-Postdoctoral Research Engineer, Inria