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Link-stats: new option to compute ETX from Tx and ACK count. More stable than EWMA.

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This commit is contained in:
Simon Duquennoy 2017-06-28 15:37:42 +02:00
parent ac4558bea0
commit a791f46002
2 changed files with 74 additions and 29 deletions
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79
core/net/link-stats.c
View File

@ -44,43 +44,36 @@
#define PRINTF(...)
#endif
/* Half time for the freshness counter, in minutes */
#define FRESHNESS_HALF_LIFE 15
/* Maximum value for the Tx count counter */
#define TX_COUNT_MAX 32
/* Statistics with no update in FRESHNESS_EXPIRATION_TIMEOUT is not fresh */
#define FRESHNESS_EXPIRATION_TIME (10 * 60 * (clock_time_t)CLOCK_SECOND)
/* Half time for the freshness counter */
#define FRESHNESS_HALF_LIFE (15 * 60 * (clock_time_t)CLOCK_SECOND)
/* Statistics are fresh if the freshness counter is FRESHNESS_TARGET or more */
#define FRESHNESS_TARGET 4
/* Maximum value for the freshness counter */
#define FRESHNESS_MAX 16
/* Statistics with no update in FRESHNESS_EXPIRATION_TIMEOUT is not fresh */
#define FRESHNESS_EXPIRATION_TIME (10 * 60 * (clock_time_t)CLOCK_SECOND)
/* EWMA (exponential moving average) used to maintain statistics over time */
#define EWMA_SCALE 100
#define EWMA_ALPHA 10
#define EWMA_BOOTSTRAP_ALPHA 25
#define EWMA_SCALE 100
#define EWMA_ALPHA 10
#define EWMA_BOOTSTRAP_ALPHA 25
/* ETX fixed point divisor. 128 is the value used by RPL (RFC 6551 and RFC 6719) */
#define ETX_DIVISOR LINK_STATS_ETX_DIVISOR
#define ETX_DIVISOR LINK_STATS_ETX_DIVISOR
/* Number of Tx used to update the ETX EWMA in case of no-ACK */
#define ETX_NOACK_PENALTY 24
#define ETX_NOACK_PENALTY 16
/* Initial ETX value */
#define ETX_DEFAULT 2
#define ETX_DEFAULT 2
/* Per-neighbor link statistics table */
NBR_TABLE(struct link_stats, link_stats);
/* Called every FRESHNESS_HALF_LIFE minutes */
/* Called at a period of FRESHNESS_HALF_LIFE */
struct ctimer periodic_timer;
/* Used to initialize ETX before any transmission occurs. By default,
* infer the initial ETX from the RSSI of previously received packets.
* To use a statuc value of e.g. ETX_DEFAULT, use:
* #define LINK_STATS_CONF_INIT_ETX(stats) (ETX_DEFAULT * ETX_DIVISOR) */
#ifdef LINK_STATS_CONF_INIT_ETX
#define LINK_STATS_INIT_ETX(stats) LINK_STATS_CONF_INIT_ETX(stats)
#else /* LINK_STATS_INIT_ETX */
#define LINK_STATS_INIT_ETX(stats) guess_etx_from_rssi(stats)
#endif /* LINK_STATS_INIT_ETX */
/*---------------------------------------------------------------------------*/
/* Returns the neighbor's link stats */
const struct link_stats *
@ -98,6 +91,7 @@ link_stats_is_fresh(const struct link_stats *stats)
&& stats->freshness >= FRESHNESS_TARGET;
}
/*---------------------------------------------------------------------------*/
#if LINK_STATS_INIT_ETX_FROM_RSSI
uint16_t
guess_etx_from_rssi(const struct link_stats *stats)
{
@ -126,14 +120,17 @@ guess_etx_from_rssi(const struct link_stats *stats)
}
return 0xffff;
}
#endif /* LINK_STATS_INIT_ETX_FROM_RSSI */
/*---------------------------------------------------------------------------*/
/* Packet sent callback. Updates stats for transmissions to lladdr */
void
link_stats_packet_sent(const linkaddr_t *lladdr, int status, int numtx)
{
struct link_stats *stats;
#if !LINK_STATS_ETX_FROM_PACKET_COUNT
uint16_t packet_etx;
uint8_t ewma_alpha;
#endif /* !LINK_STATS_ETX_FROM_PACKET_COUNT */
if(status != MAC_TX_OK && status != MAC_TX_NOACK) {
/* Do not penalize the ETX when collisions or transmission errors occur. */
@ -145,7 +142,11 @@ link_stats_packet_sent(const linkaddr_t *lladdr, int status, int numtx)
/* Add the neighbor */
stats = nbr_table_add_lladdr(link_stats, lladdr, NBR_TABLE_REASON_LINK_STATS, NULL);
if(stats != NULL) {
stats->etx = LINK_STATS_INIT_ETX(stats);
#if LINK_STATS_INIT_ETX_FROM_RSSI
stats->etx = guess_etx_from_rssi(stats);
#else /* LINK_STATS_INIT_ETX_FROM_RSSI */
stats->etx = ETX_DEFAULT * ETX_DIVISOR;
#endif /* LINK_STATS_INIT_ETX_FROM_RSSI */
} else {
return; /* No space left, return */
}
@ -155,6 +156,28 @@ link_stats_packet_sent(const linkaddr_t *lladdr, int status, int numtx)
stats->last_tx_time = clock_time();
stats->freshness = MIN(stats->freshness + numtx, FRESHNESS_MAX);
#if LINK_STATS_ETX_FROM_PACKET_COUNT
/* Compute ETX from packet and ACK count */
numtx = (status == MAC_TX_NOACK) ? ETX_NOACK_PENALTY : numtx;
/* Halve both counter after TX_COUNT_MAX */
if(stats->tx_count + numtx > TX_COUNT_MAX) {
stats->tx_count /= 2;
stats->ack_count /= 2;
}
/* Update tx_count and ack_count */
stats->tx_count += numtx;
if(status == MAC_TX_OK) {
stats->ack_count++;
}
/* Compute ETX */
if(stats->ack_count > 0) {
stats->etx = ((uint16_t)stats->tx_count * ETX_DIVISOR) / stats->ack_count;
} else {
stats->etx = (uint16_t)MAX(ETX_NOACK_PENALTY, stats->tx_count) * ETX_DIVISOR;
}
#else /* LINK_STATS_ETX_FROM_PACKET_COUNT */
/* Compute ETX using an EWMA */
/* ETX used for this update */
packet_etx = ((status == MAC_TX_NOACK) ? ETX_NOACK_PENALTY : numtx) * ETX_DIVISOR;
/* ETX alpha used for this update */
@ -163,6 +186,7 @@ link_stats_packet_sent(const linkaddr_t *lladdr, int status, int numtx)
/* Compute EWMA and update ETX */
stats->etx = ((uint32_t)stats->etx * (EWMA_SCALE - ewma_alpha) +
(uint32_t)packet_etx * ewma_alpha) / EWMA_SCALE;
#endif /* LINK_STATS_ETX_FROM_PACKET_COUNT */
}
/*---------------------------------------------------------------------------*/
/* Packet input callback. Updates statistics for receptions on a given link */
@ -179,7 +203,11 @@ link_stats_input_callback(const linkaddr_t *lladdr)
if(stats != NULL) {
/* Initialize */
stats->rssi = packet_rssi;
stats->etx = LINK_STATS_INIT_ETX(stats);
#if LINK_STATS_INIT_ETX_FROM_RSSI
stats->etx = guess_etx_from_rssi(stats);
#else /* LINK_STATS_INIT_ETX_FROM_RSSI */
stats->etx = ETX_DEFAULT * ETX_DIVISOR;
#endif /* LINK_STATS_INIT_ETX_FROM_RSSI */
}
return;
}
@ -189,7 +217,7 @@ link_stats_input_callback(const linkaddr_t *lladdr)
(int32_t)packet_rssi * EWMA_ALPHA) / EWMA_SCALE;
}
/*---------------------------------------------------------------------------*/
/* Periodic timer called every FRESHNESS_HALF_LIFE minutes */
/* Periodic timer called at a period of FRESHNESS_HALF_LIFE */
static void
periodic(void *ptr)
{
@ -218,6 +246,5 @@ void
link_stats_init(void)
{
nbr_table_register(link_stats, NULL);
ctimer_set(&periodic_timer, 60 * (clock_time_t)CLOCK_SECOND * FRESHNESS_HALF_LIFE,
periodic, NULL);
ctimer_set(&periodic_timer, FRESHNESS_HALF_LIFE, periodic, NULL);
}

24
core/net/link-stats.h
View File

@ -37,17 +37,35 @@
/* ETX fixed point divisor. 128 is the value used by RPL (RFC 6551 and RFC 6719) */
#ifdef LINK_STATS_CONF_ETX_DIVISOR
#define LINK_STATS_ETX_DIVISOR LINK_STATS_CONF_ETX_DIVISOR
#define LINK_STATS_ETX_DIVISOR LINK_STATS_CONF_ETX_DIVISOR
#else /* LINK_STATS_CONF_ETX_DIVISOR */
#define LINK_STATS_ETX_DIVISOR 128
#define LINK_STATS_ETX_DIVISOR 128
#endif /* LINK_STATS_CONF_ETX_DIVISOR */
/* Option to infer the initial ETX from the RSSI of previously received packets. */
#ifdef LINK_STATS_CONF_INIT_ETX_FROM_RSSI
#define LINK_STATS_INIT_ETX_FROM_RSSI LINK_STATS_CONF_INIT_ETX_FROM_RSSI
#else /* LINK_STATS_CONF_INIT_ETX_FROM_RSSI */
#define LINK_STATS_INIT_ETX_FROM_RSSI 1
#endif /* LINK_STATS_CONF_INIT_ETX_FROM_RSSI */
/* Option to use packet and ACK count for ETX estimation, instead of EWMA */
#ifdef LINK_STATS_CONF_ETX_FROM_PACKET_COUNT
#define LINK_STATS_ETX_FROM_PACKET_COUNT LINK_STATS_CONF_ETX_FROM_PACKET_COUNT
#else /* LINK_STATS_CONF_ETX_FROM_PACKET_COUNT */
#define LINK_STATS_ETX_FROM_PACKET_COUNT 0
#endif /* LINK_STATS_ETX_FROM_PACKET_COUNT */
/* All statistics of a given link */
struct link_stats {
clock_time_t last_tx_time; /* Last Tx timestamp */
uint16_t etx; /* ETX using ETX_DIVISOR as fixed point divisor */
int16_t rssi; /* RSSI (received signal strength) */
uint8_t freshness; /* Freshness of the statistics */
clock_time_t last_tx_time; /* Last Tx timestamp */
#if LINK_STATS_ETX_FROM_PACKET_COUNT
uint8_t tx_count; /* Tx count, used for ETX calculation */
uint8_t ack_count; /* ACK count, used for ETX calculation */
#endif /* LINK_STATS_ETX_FROM_PACKET_COUNT */
};
/* Returns the neighbor's link statistics */