Re: [Dots] [core] WG Last Call on draft-ietf-core-new-block (Congestion Control)

[[e-mail]]

Re-,

You are completely right that the default probing-rate is to be increased for the DOTS case. FYI, this is why we went with the following in RFC8782:

      |  Given that the size of the heartbeat request cannot exceed
      |  ('heartbeat-interval' * 'probing-rate') bytes, 'probing-rate'
      |  should be set appropriately to avoid slowing down heartbeat
      |  exchanges.  For example, 'probing-rate' may be set to 2 *
      |  ("size of encrypted DOTS heartbeat request"/'heartbeat-
      |  interval') or (("size of encrypted DOTS heartbeat request" +
      |  "average size of an encrypted mitigation request")/'heartbeat-
      |  interval').  Absent any explicit configuration or inability to
      |  dynamically adjust 'probing-rate' values (Section 4.8.1 of
      |  [RFC7252]), DOTS agents use 5 bytes/second as a default
      |  'probing-rate' value.

We also allow DOTS peers to negotiate the transmission parameters (and probing rate) with the following as default: 

   "The RECOMMENDED values of
   transmission parameter values are 'ack-timeout' (2 seconds), 'max-
   retransmit' (3), and 'ack-random-factor' (1.5).  In addition to those
   parameters, the RECOMMENDED specific DOTS transmission parameter
   values are 'heartbeat-interval' (30 seconds) and 'missing-hb-allowed'
   (15)."

We avoided to include a pointer to these details as these are application-specific and that, even if the draft is motivated by the DOTS use case, other applications can make use of the new block functionality. 

For NSTART, we already have the following: 

  " NSTART will also need to be increased from the default
   (1) to get faster transmission rates."

Cheers,
Med

> -----Message d'origine-----
> De : Christian Amsüss [mailto:[e-mail]]
> Envoyé : mercredi 23 décembre 2020 06:01
> À : [e-mail]
> Cc : [e-mail] WG ([e-mail]) <[e-mail]>; [e-mail]
> Objet : Re: [core] WG Last Call on draft-ietf-core-new-block
> 
> * Also on parameters: This document is describing flow control stuff
>   around a situation CoAP was not originally designed for. Wouldn't
> it
>   make sense to include a set of parameters (PROBING_RATE,
> MAX_LATENCY,
>   ACK_TIMEOUT) that's suitable for the DOTS use case? I doubt that
>   PROBING_RATE will be left to 1 byte/second for any DOTS
> application
>   using this (for sending 10KiB in the initial 10-package
> MAX_PAYLOADS
>   burst would mark that connection as unusable for about 3 hours if
> they
>   all get lost), so better give justifiable numbers here than rely
> on
>   implemnetors to come up with unreviewed numbers or disregard
>   PROBING_RATE altogether.
> 
>   I don't know if it needs additional justification, but an
> increased
>   N_START may be justifiable there.
> 

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