Subject: [6tisch] Minutes 6top discussion 08 April 2014

From: Thomas Watteyne <[email-masked]>
Date: Tue, 8 Apr 2014 23:29:22 -0700

All,

You will find the minutes of the last 6top discussion at
https://bitbucket.org/6tisch/meetings/wiki/140408_webex_6top, also
copy-pasted below.

Please fix anything we might have missed directly in the e-mail and reply.

Thomas

---

Minutes Webex 8 April, 6top call 6TiSCH WG

Note: timestamps in PDT.
Taking notes *(using Etherpad)*

   1. Xavi Vilajosana
   2. Thomas Watteyne

Attendance *(alphabetically)*

   1. Pat Kinney
   2. Qin Wang
   3. Raghuram Sudhaakar
   4. Thomas Watteyne
   5. Xavi Vilajosana

Agenda

   - exercise on implementing 6top negotiation with YANG and CoAP
   - using CoAP to implement 6top management interface
      - How to express node address? use uri-host or not? IP address or MAC
      address?
      - Need observer function? use uri-port?
      - How to fragment data to fit IE payload size? use CoAP block?
   - 6top-to-6top Access Control model.
   - How to express 6top MIB and IEEE802.15.4 PIB in YANG? (comments from
   Juergen)

Slides

   - slides_140408_webex_6top.pptx<https://bitbucket.org/6tisch/meetings/src/master/140408_webex_6top/slides_140408_webex_6top.pptx>:
   slides shared during the call

Action items

   - *Qin* to create a ticket before editing 6top-interface draft.
   - *Raghuram* to work further on how to proceed w.r.t fragmentation.
   - *Qin* to start thread on the ML about 6top-to-6top Access Control
   model.
   - *Thomas* to start thread on the ML about how to express 6top MIB and
   IEEE802.15.4 PIB in YANG.

Minutes

   - _[20:05]_meeting starts
   - *[Thomas]* note well, minutes, attendance, etc.
   - *[20:07]* Qin presents the slides. Implementation exercise of the soft
   cell reservation process.
   - *[Qin]* Presents the steps to negotiate for cells between 2 nodes.
      - BWIE and ScheduleIE are used. BwIE to indicate the number of cells
      required; ScheduleIE to indicate which cells are candidates and
eventually
      selected
      - Soft cell reservation response includes the number of reserved
      cells and the list of cells. Uses same IEs.
   - *[Qin]* Question is how to specify this operations within the scope of
   CoAP.
   - *[Raghuram]* Why not have the response directly in POST response?
   - *[Xavi]* Maybe to stick closely to CoAP spec?
   - *[Qin]* let's go through other options
   - *[Qin]* 3 possible schemes:
      - 2 resources defined: one for reservation request, another for
      response.
         - POST, then GET (2 operations)
      - 1 resource POST and response
         - *[Qin]* problem is how to separate parameters and response in
         the YANG model
      - 1 resource GET. Query by parameters. Response is an object
      representing the result.
   - *[Thomas]* why a payload associated to a YANG model? Consistency of
   the messages across different protocols. The YANG model does not say what
   the payload is, it just describes the MIB.
   - *[Raghuram]* The question if we need to maintain consistency of this
   model across different protocols. If we use RSVP we need to be able to use
   the same semantics.
   - *[Xavi]* do you think the format is important, or the content? Would
   YANG not be translatable to different protocols?
   - *[Raghuram]* might be disadvantageous to be too specific in YANG
   - *[20:21]* *[Raghuram]* Having 2 packets instead of 4 is an advantage
   from 2nd approach.
   - *[Raghuram]* CoAP response can be asynchronous so if computation of
   the schedule takes time still works.
   - *[Thomas]* CoAP has a capability to have requests with separate
   responses. Both piggybacked responses or delayed responses are possible.
   - *[Raghuram]* proposes to keep the GET NegotiationResult as an optional
   operation to be able to query latest result and in case the response is
   time out.
   - *[Thomas]* Representation of what we want to do using YANG model as
   RPC.

   https://tools.ietf.org/html/rfc6020#section-4.2.9

   - *[Thomas]* The CoAP payload then will be represented by this YANG
   model specification.
   - *[Xavi]* Express the reservation process can be expressed using RPCs
   and then this will be supported by any transport mechanism. e.g rsvp, coap,
   xmpp, etc..
   - *[Thomas]* RPC is meant to express this kind of interactions.
   - *[Raghuram]* section 7.1.1 summarizes sub-statements.
   - *[Thomas]* Optional fields?
   - *[Qin]* Need to be check. Some interactions do not need schedule IE,
   so how to make that optional.
   - *[Xavi]* fields cannot be marked as optional, only mandatory
   (RFC65020, section 7.9.4).
   - *[Thomas]* We need to be very clean when editing the draft. As it is a
   WG document now, we need to explain everything to the ML. Create a ticket
   is a good idea as well.

   Action item: *Qin* to create a ticket before editing 6top-interface
   draft.

   - _[20:44]* using CoAP to implement 6top management interface
   - How to express node address? use uri-host or not? IP address or MAC
   address?
      - *[Xavi]* Use MAC layer address as it is a L2.5 thing.
      - *[Raghuram]* +1
      - *[Thomas]* Remove it completely as MAC layer addresses are at L2 so
      we can use them.
      - *[Raghuram]* It is a good idea to keep mechanism identical to L7
      CoAP, but still addresses can be inferred from l2 information as in the
      case of 6lowpan.
      - *[Thomas]* Come back to that issue when more progress in ACE.
   - *[20:50]* Need observer function? use uri-port?
      - *[Thomas]* What is the relation of uri-port and observer function.
      - *[Qin]* Port might be used to indicate which observing server is
      sending the observe.
      - *[Thomas]* That's not right, that's what the token is for.
      - *[Qin]* We need observe in PCE case: if some data changes it will
      trigger some recalculation on the PCE. Analogously, the 6top-to-6top case
      might require to trigger modifications on the neighbors, this might be
      dependent of the algorithm used.
      - *[Thomas]* Observe is optional, so if it is not present, there
      should be a mechanism to know if the mechanism is running on a particular
      node. To be checked.
   - How to fragment data to fit IE payload size? use CoAP block?
      - *[Raghuram]* CoAP Block, we need to come to a decision.
      - *[Raghuram]* Limit the payload length. Candidate list needs to be
      restricted. We need to determine how often this case will happen.
      - *[Thomas]* We need to make sure that everything will work taking
      into account that packets are 127B long.
      - *[Thomas]* As we need to reassemble, we need to have buffers to be
      able to reassemble at a node, this requires RAM, We need to take
that into
      account if we want to be able to run in any very constrained device.

      Action item: *Raghuram* to work further on how to proceed w.r.t
      fragmentation.

      - *[Thomas]* CoAP header and IE go inside the mac layer payload. UDP
      headers are not considered.
   - *[Thomas]* Out of time, continue on ML.

   Action item: *Qin* to start thread on the ML about 6top-to-6top Access
   Control model.

   - How to express 6top MIB and IEEE802.15.4 PIB in YANG?

   Action item: *Thomas* to start thread on the ML about how to express
   6top MIB and IEEE802.15.4 PIB in YANG.

   - *[09:07]* meeting ends.