rpl-mrhof.c

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/*
 * Copyright (c) 2010, Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the Institute nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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 *
 * This file is part of the Contiki operating system.
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/**
 * \file
 *         The Minimum Rank with Hysteresis Objective Function (MRHOF)
 *
 *         This implementation uses the estimated number of
 *         transmissions (ETX) as the additive routing metric,
 *         and also provides stubs for the energy metric.
 *
 * \author Joakim Eriksson <joakime@sics.se>, Nicolas Tsiftes <nvt@sics.se>
 */

/**
 * \addtogroup uip6
 * @{
 */

#include "net/rpl/rpl-private.h"
#include "net/nbr-table.h"

#define DEBUG DEBUG_NONE
#include "net/ip/uip-debug.h"

static void reset(rpl_dag_t *);
static void neighbor_link_callback(rpl_parent_t *, int, int);
static rpl_parent_t *best_parent(rpl_parent_t *, rpl_parent_t *);
static rpl_dag_t *best_dag(rpl_dag_t *, rpl_dag_t *);
static rpl_rank_t calculate_rank(rpl_parent_t *, rpl_rank_t);
static void update_metric_container(rpl_instance_t *);

rpl_of_t rpl_mrhof = {
  reset,
  neighbor_link_callback,
  best_parent,
  best_dag,
  calculate_rank,
  update_metric_container,
  1
};

/* Constants for the ETX moving average */
#define ETX_SCALE   100
#define ETX_ALPHA   90

/* Reject parents that have a higher link metric than the following. */
#define MAX_LINK_METRIC                 10

/* Reject parents that have a higher path cost than the following. */
#define MAX_PATH_COST                   100

/*
 * The rank must differ more than 1/PARENT_SWITCH_THRESHOLD_DIV in order
 * to switch preferred parent.
 */
#define PARENT_SWITCH_THRESHOLD_DIV     2

typedef uint16_t rpl_path_metric_t;

static rpl_path_metric_t
calculate_path_metric(rpl_parent_t *p)
{
  if(p == NULL) {
    return MAX_PATH_COST * RPL_DAG_MC_ETX_DIVISOR;
  }

#if RPL_DAG_MC == RPL_DAG_MC_NONE
  return p->rank + (uint16_t)p->link_metric;
#elif RPL_DAG_MC == RPL_DAG_MC_ETX
  return p->mc.obj.etx + (uint16_t)p->link_metric;
#elif RPL_DAG_MC == RPL_DAG_MC_ENERGY
  return p->mc.obj.energy.energy_est + (uint16_t)p->link_metric;
#else
#error "Unsupported RPL_DAG_MC configured. See rpl.h."
#endif /* RPL_DAG_MC */
}

static void
reset(rpl_dag_t *dag)
{
  PRINTF("RPL: Reset MRHOF\n");
}

static void
neighbor_link_callback(rpl_parent_t *p, int status, int numtx)
{
  uint16_t recorded_etx = p->link_metric;
  uint16_t packet_etx = numtx * RPL_DAG_MC_ETX_DIVISOR;
  uint16_t new_etx;

  /* Do not penalize the ETX when collisions or transmission errors occur. */
  if(status == MAC_TX_OK || status == MAC_TX_NOACK) {
    if(status == MAC_TX_NOACK) {
      packet_etx = MAX_LINK_METRIC * RPL_DAG_MC_ETX_DIVISOR;
    }

    if(p->flags & RPL_PARENT_FLAG_LINK_METRIC_VALID) {
      /* We already have a valid link metric, use weighted moving average to update it */
      new_etx = ((uint32_t)recorded_etx * ETX_ALPHA +
                 (uint32_t)packet_etx * (ETX_SCALE - ETX_ALPHA)) / ETX_SCALE;
    } else {
      /* We don't have a valid link metric, set it to the current packet's ETX */
      new_etx = packet_etx;
      /* Set link metric as valid */
      p->flags |= RPL_PARENT_FLAG_LINK_METRIC_VALID;
    }

    PRINTF("RPL: ETX changed from %u to %u (packet ETX = %u)\n",
        (unsigned)(recorded_etx / RPL_DAG_MC_ETX_DIVISOR),
        (unsigned)(new_etx  / RPL_DAG_MC_ETX_DIVISOR),
        (unsigned)(packet_etx / RPL_DAG_MC_ETX_DIVISOR));
    p->link_metric = new_etx;
  }
}

static rpl_rank_t
calculate_rank(rpl_parent_t *p, rpl_rank_t base_rank)
{
  rpl_rank_t new_rank;
  rpl_rank_t rank_increase;

  if(p == NULL) {
    if(base_rank == 0) {
      return INFINITE_RANK;
    }
    rank_increase = RPL_INIT_LINK_METRIC * RPL_DAG_MC_ETX_DIVISOR;
  } else {
    rank_increase = p->link_metric;
    if(base_rank == 0) {
      base_rank = p->rank;
    }
  }

  if(INFINITE_RANK - base_rank < rank_increase) {
    /* Reached the maximum rank. */
    new_rank = INFINITE_RANK;
  } else {
   /* Calculate the rank based on the new rank information from DIO or
      stored otherwise. */
    new_rank = base_rank + rank_increase;
  }

  return new_rank;
}

static rpl_dag_t *
best_dag(rpl_dag_t *d1, rpl_dag_t *d2)
{
  if(d1->grounded != d2->grounded) {
    return d1->grounded ? d1 : d2;
  }

  if(d1->preference != d2->preference) {
    return d1->preference > d2->preference ? d1 : d2;
  }

  return d1->rank < d2->rank ? d1 : d2;
}

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_THRESHOLD_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;
}

#if RPL_DAG_MC == RPL_DAG_MC_NONE
static void
update_metric_container(rpl_instance_t *instance)
{
  instance->mc.type = RPL_DAG_MC;
}
#else
static void
update_metric_container(rpl_instance_t *instance)
{
  rpl_path_metric_t path_metric;
  rpl_dag_t *dag;
#if RPL_DAG_MC == RPL_DAG_MC_ENERGY
  uint8_t type;
#endif

  instance->mc.type = RPL_DAG_MC;
  instance->mc.flags = RPL_DAG_MC_FLAG_P;
  instance->mc.aggr = RPL_DAG_MC_AGGR_ADDITIVE;
  instance->mc.prec = 0;

  dag = instance->current_dag;

  if (!dag->joined) {
    PRINTF("RPL: Cannot update the metric container when not joined\n");
    return;
  }

  if(dag->rank == ROOT_RANK(instance)) {
    path_metric = 0;
  } else {
    path_metric = calculate_path_metric(dag->preferred_parent);
  }

#if RPL_DAG_MC == RPL_DAG_MC_ETX
  instance->mc.length = sizeof(instance->mc.obj.etx);
  instance->mc.obj.etx = path_metric;

  PRINTF("RPL: My path ETX to the root is %u.%u\n",
        instance->mc.obj.etx / RPL_DAG_MC_ETX_DIVISOR,
        (instance->mc.obj.etx % RPL_DAG_MC_ETX_DIVISOR * 100) /
         RPL_DAG_MC_ETX_DIVISOR);
#elif RPL_DAG_MC == RPL_DAG_MC_ENERGY
  instance->mc.length = sizeof(instance->mc.obj.energy);

  if(dag->rank == ROOT_RANK(instance)) {
    type = RPL_DAG_MC_ENERGY_TYPE_MAINS;
  } else {
    type = RPL_DAG_MC_ENERGY_TYPE_BATTERY;
  }

  instance->mc.obj.energy.flags = type << RPL_DAG_MC_ENERGY_TYPE;
  instance->mc.obj.energy.energy_est = path_metric;
#endif /* RPL_DAG_MC == RPL_DAG_MC_ETX */
}
#endif /* RPL_DAG_MC == RPL_DAG_MC_NONE */

/** @}*/