Re: [6tsch] simulation for random schedule allocation

[Maria Rita PALATTELLA <[e-mail]>]

Hello Xavi,
first of all many thanks for having built the code and run this first set of simulations for the WG.
I have some questions about the simulations. Please, feel free to ignore my comments, if they are inappropriate.

1)"Each node requests a link to each of its neighbors."
Is it really what we want? In my point of view, each node will ask a set of links (i.e., cells) according to the paths along which it will transmit its own traffic, and forwards the traffic received by other neighbors. In other words, the number of requested cells per node should be less than what we are simulating right now. For sure, in the actual scenario, we have higher probability of collision.

2) " the network is represented by a boolean square matrix of num_nodes*num_nodes. Two nodes are neighbours if the cell for that two nodes (indexed by node ids) is true. if X is neighbour of Y the cells (x,y) and (y,x) will be true."
This way of representing the network can create somehow a bit of confusion with the TSCH schedule representation, where we have (timeslot, channeloffset) cells.
Can't we find a different way for representing the network, and defying the set of neighbors? Moreover, this point 2) is linked with point 1) I guess, i.e., assuming each node will request a link to each of its neighbors.

3) "Topology: Random, where each node requests a random number of neighbours between 2 and 10.”
Even though I am in favor of having a random topology, and a random number of neighbors, maybe, for having a preliminary idea of the network behavior, we could run a set of simulations, where we fix the number of neighbors (i.e., having it constant). Basically, my suggestion is to keep some parameters constant, while we change others, in order to see how each of them impact the cells allocation.

Thank you!
Maria Rita


________________________________
From: [e-mail] [[e-mail]] on behalf of Xavier Vilajosana Guillen [[e-mail]]
Sent: Thursday, June 27, 2013 2:27 AM
To: [e-mail]
Cc: [e-mail]
Subject: Re: [6tsch] simulation for random schedule allocation

Hi Yoshihiro,

the network is represented by a boolean square matrix of num_nodes*num_nodes. Two nodes are neighbours if the cell for that two nodes (indexed by node ids) is true. if X is neighbour of Y the cells (x,y) and (y,x) will be true.
When a node requests a link it always requests a TX link, the counter part sets it to RX links so a link allocation happens at both sides. In a particular node Number of allocated links is the accumulation of both TX and RX allocated in that node.

Regarding your question, if X requests a TX link to Y the schedule of X allocates a TX link to Y and the schedule of Y allocates a RX link from X. If Y requests a TX link to X, X allocates a RX link from Y.

A link is not allocated in either side if there is a collision, and then I increment the collision counter.

The code is here in case someone wants to play. Sorry it is not very clean but I will clean it as soon as I can. If someone modifies it or improves it, feel free to commit your changes to the repository so the simulator becomes better.

https://github.com/xvilajosana/6TSCH

hope this makes things clear.

regards,
X


Xavi


On Wed, Jun 26, 2013 at 3:56 PM, <[e-mail]<mailto:[e-mail]>> wrote:
Hi Xavi,

Thanks for your explanation.  I have better understanding now.

I have one more question.

You mentioned “there might be more than one link to a neighbor”.   Say Node X selected only one neighbor Node Y and requests one link to Node Y.  The resulting number of links associated with Node X can be two (2) when Node Y also selected Node X as its neighbor and requested one link to Node X.  Is my understanding correct?

Yoshihiro Ohba


From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]<mailto:[e-mail]>] On Behalf Of Xavier Vilajosana Guillen
Sent: Thursday, June 27, 2013 1:33 AM
To: ohba yoshihiro
Cc: [e-mail]<mailto:[e-mail]>
Subject: Re: [6tsch] simulation for random schedule allocation

Hi Yoshihiro,
you are right, the formulation of the sentence is not correct. Should be:

“Topology: Random, where each node requests a random number of neighbours between 2 and 10.”
this means that each node when created requests a number of neighbors between 2 and 10, meaning that other nodes when are created also request that number of neighbours and therefore a node can have more than 10 neighbours, because other nodes selected it as a neighbour. From the simulation results I see that nodes have between 5 and 11 neighbours usually.
However, from the numbers you point, 28 represents the number of allocated links (number of allocated cells in the schedule) to its neighbours, there might be more than one link to a neighbour in that case.
regards,
Xavi

Xavi

On Wed, Jun 26, 2013 at 7:28 AM, <[e-mail]<mailto:[e-mail]>> wrote:
Hi Xavi,

Thank you very much for the simulation.

I am trying to understand the simulation model from your description and the result.

“Topology: Random, where each node has a random number of neighbors between 2 and 10.”

“
************************ requesting 1 links
Node,Allocated Links,Collisions,Percentage
0,28,0,0.0
“

In the above result, does Node 0 actually have 28 neighbors?

Regards,
Yoshihiro Ohba

From: [e-mail]<mailto:[e-mail]> [mailto:[e-mail]<mailto:[e-mail]>] On Behalf Of Xavier Vilajosana Guillen
Sent: Wednesday, June 26, 2013 3:46 AM
To: [e-mail]<mailto:[e-mail]>

Subject: [6tsch] simulation for random schedule allocation


Hi all,

I prepared a little simulation to see how random schedule allocation behaves. (I have the code in Java in case someone is interested)

here there are some details (everything can be tuned in case someone wants to point me to a special case)

Network: 50 nodes

Topology: Random, where each node has a random number of neighbors between 2 and 10.

Each node requests a link to each of its neighbors. This is done from 1 to 10 times (i.e 10 tests, the first requesting 1 link to each neighbour, the second 2, etc.. up to 10 links to each of the neighbors, can be configured)

The slotframe is 101 slots and 16 channels.

The simulation prints statistics for the test (and the collisions if we are interested.)
I used pseudo random generator from the java language assuming it provides uniform or almost uniform distribution.
The allocation counter counts both the number of links allocated as tx and the number of links allocated as rx due to a neighbour allocating a link to the actual node. The percentage is the % of collisions w.r.t the allocated links.
Worst case is around 11% when allocating 10 links to each neighbour in that 50 node network.
I can play more on it but I wanted to share that initial results.
please see attached file for the results.
regards,
Xavi