Re: [Roll] WGLC - Working Group Last Call - draft-ietf-roll-trickle-mcast-05

[peter van der Stok <[e-mail]>]

Hi Michael,
corresponding questions can be:

1) What are the maximum and minimum 1-hop MPL router neighbours of all 
the MPL routers?
2) what is the arrival rate of new packets that need repetition in a MPL 
router
3) Is there a deadline associated with the packets
4) What is the shortest number of hops of the longest path between 
sources and destinations
5) What are the values of the MAC: back-off values, retries, buffer 
size.
6) What is the background load of other non MPL applications.
7) arrival probability of 1-hop packets
8) other parameters I did not stumble on.

The corresponding design space is incredibly large, and probably only a 
limited subset of the design space is viable.
I have gone through only a limited number of possibilities, and 
analysing the consequences for MPL took me quite a large amount of time.

In one of my scenarios:
1) 5 neighbours
2) once every 100 ms (rate at sources is once every 300-500 ms)
3) yes, 200 ms
4) 5 hops, with mostly 1 hop
5) no buffer, retry 1, back-off 2
6) absent
7) 100-80%

leading to k=3-5, Imin =30-70 ms, repeat = 2, Imax n/a.

It may help that operational boundary conditions together with 
appropriate MPL parameter values are published in the applicability 
statements.
All applicability statements together may give a good hint which MPL 
parameters and boundary conditions to choose.

My 5 cents,

peter





Michael Richardson schreef op 2013-09-16 17:15:
> peter van der Stok <[e-mail]> wrote:
> >> various settings for IMIN, IMAX and k. A process similar to this 
> (with
> >> knowledge of the topology and messaging profile) is needed for 
> tuning
> >> these values in a real deployment setting.
> 
> peter> After looking for an appropriate setting for Imin, Imax and k, I
> peter> slowly learnt that these settings depend on the topology of the
> peter> network, the load of the network, the setting of the MAC, and
> peter> eventual real-time requirements (e.g. there is a deadline), and
> peter> the value of that deadline.  The setting of k for example is
> peter> related to the number of MPL repeaters that receive a new 
> message
> peter> and start to resend it, possibly interfering with each other and
> peter> probably incrementing the c value of the next hop, where the
> peter> maximum value of c is related to the Imin value.  Sending a 
> packet
> peter> takes as little as 3 ms, but when the MAC stores three packets 
> and
> peter> the they all back-off a maximum number of times, delays of a few
> peter> hundred milliseconds to seconds become possible.  When there is
> peter> buffer space for packets before and in the MAC, the Imin value 
> can
> peter> be chosen as low as 1 ms, the resend of packets is then 
> completely
> peter> determined by the load on the network.
> 
> This is an excellent template discussion... can I put it into the MPL
> parameter part of the RPL applicability template?
> 
> Do you think you could rephrase this in the form of questions to be
> answered?
> 
> --
> Michael Richardson <[e-mail]>, Sandelman Software Works
> IETF ROLL WG co-chair.    http://datatracker.ietf.org/wg/roll/charter/