How to select the preferred parent in RPL in contiki cooja?

Description

In routing network Objective function(OF) is responsible to select nodes it’s preferred parent. Which is classified as both best parent and worst parent.Rpl follows DODAG techniques, which node is preferred shortest range first in forwarding direction.

   Open a file at location:Home/
contiki/core/net/rpl/rpl-mrhof.c

   Here the functions handling
the parent selection.

rpl_parent_t *best_parent

Code:

static rpl_parent_t *best_parent
(rpl_parent_t *p1, rpl_parent_t *p2)

{

rpl_dag_t *dag;

rpl_path_metric_t min_diff;

rpl_path_metric_t p1_metric;

rpl_path_metric_t p2_metric;

dag = p1->dag; /* Both parents
are in the same DAG. */

min_diff=RPL_DAG_MC_ETX_DIVISOR/

PARENT_SWITCH_THRESHOL DIV;

p1_metric =
calculate_path_metric(p1);

p2_metric =
calculate_path_metric(p2);

/* Maintain stability of the preferred
parent in case of similar ranks. */

if(p1 == dag->preferred_parent
|| p2 == dag->preferred_parent) {

if(p1_metric < p2_metric + min_diff )

p1_metric > p2_metric - min_diff) {

printf ("RPL: MRHOF hysteresis:
%u <= %u <= %u\n",)

p2_metric - min_diff,

p1_metric,

p2_metric + min_diff);

return dag->preferred_parent;

}

}

return p1_metric
< p2_metric ? p1 : p2;

}

Minimum rank node selected as
parent node.

   Run the simulation

13b
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