RE: Transmission Parameters

Charlie — Fri, 20 Nov 2020 14:33:19 GMT

Hi QuentinD,

According to Zephyr CoAP protocol latest implantation coap.c:

/* TODO: random generated initial ACK timeout
 * ACK_TIMEOUT < INIT_ACK_TIMEOUT < ACK_TIMEOUT * ACK_RANDOM_FACTOR
 * where ACK_TIMEOUT = 2 and ACK_RANDOM_FACTOR = 1.5 by default
 * Ref: https://tools.ietf.org/html/rfc7252#section-4.8
 */
#define INIT_ACK_TIMEOUT	CONFIG_COAP_INIT_ACK_TIMEOUT_MS

static int32_t next_timeout(int32_t previous)
{
	switch (previous) {
	case INIT_ACK_TIMEOUT:
	case (INIT_ACK_TIMEOUT * 2):
	case (INIT_ACK_TIMEOUT * 4):
		return previous << 1;
	case (INIT_ACK_TIMEOUT * 8):
		/* equal value is returned to end retransmit */
		return previous;
	}

	/* initial or unrecognized */
	return INIT_ACK_TIMEOUT;
}

The features to configure CoAP connection with ACK_RANDOM_FACTOR, MAX_RETRANSMIT has not been implemented.