Subject: [6tisch] 6P Timeout in MSF

From: Tengfei Chang <[email-masked]>
Date: Fri, 23 Aug 2019 14:48:57 +0200

Hi All,

For the current version (06) of MSF,  we defined the 6P Timeout as the
result of following equation:

6PTIMEOUT = ((2^MAXBE)-1)*MAXRETRIES*SLOTFRAME_LENGTH

   o  MAXBE is the maximum backoff exponent used
   o  MAXRETRIES is the maximum retransmission times
   o  SLOTFRAME_LENGTH represents the length of slotframe

What I believed is this is the right timeout value according the definition
of RFC8480:

The value of the 6P
   Timeout should be greater than the longest possible time it takes to
   receive the 6P Response or Confirmation.

However, this value could be super large depending the value of MAXBE and
SLOTFRAME_LENGTH.

For example, MAXBE = 5, MAXRETRIES=8 (to get a better reliability),
SLOTFRAME_LENGTH=101.
for 10 ms slot duration, the 6P timeout is more than 4 minutes. This
could cause large delay for 6P transaction, for example at network
forming phase.

So my concerns on the 6P Timeout are

- do you think this is an issue or not

- if yes,  what's your suggestion?

Thanks!

Tengfei

-- 
Chang Tengfei,
Postdoctoral Research Engineer, Inria