How to to set a keep alive value of MQTT while eDRX is enabled in nRF9160?

[Yusuke]

I want to set a keep alive value of MQTT while eDRX is enabled, but it doesn't work well. Any advice?

Environment
- hardware: nRF9160 DK 0.8.2
- firmware: 0.7.0-29.alpha
- nrf ver: 0.4.0
- LTE-M
- eDRX enable
- mqtt_simple works fine with mosquitto MQTT broker
- project based on mqtt_simple
- antenna power is fine
- eDRX service is available here

AT+CEDRXS?
OK
AT+CEDRXS=1,4,"1000"

I added MQTT_KEEPALIVE param to Kconfig and CONF_MQTT_KEEPALIVE param to pro.conf
I've tested several conditions
[condition]
- CONFIG_LTE_EDRX_REQ_VALUE="0110" in prj.conf // 327.68 sec interval
- CONF_MQTT_KEEPALIVE=300 in prj.conf
[result]
- eDRX doesn't work properly. When I send a message to a MQTT broker, the DK receives it right after that. There should be a delay due to the eDRX.

[condition]
- CONFIG_LTE_EDRX_REQ_VALUE="0110" in prj.conf // 327.68 sec interval
- CONF_MQTT_KEEPALIVE=400 in prj.conf
[result]
- The DK does not receive any message after 360sec followed by disconnection.

This is the whole project.

<Kconfig>
menu "MQTT simple sample"
config MQTT_PUB_TOPIC
	string "MQTT publish topic"
	default "my/publish/topic"

config MQTT_SUB_TOPIC
	string "MQTT subscribe topic"
	default "my/subscribe/topic"

config MQTT_CLIENT_ID
	string "MQTT Client ID"
	default "my-client-id"

config MQTT_BROKER_HOSTNAME
	string "MQTT broker hostname"
	default "iot.eclipse.org"

config MQTT_BROKER_PORT
	int "MQTT broker port"
	default 1883

config MQTT_MESSAGE_BUFFER_SIZE
	int ""
	default 128

config MQTT_PAYLOAD_BUFFER_SIZE
	int ""
	default 128

config MQTT_KEEPALIVE
	int ""
	default 60

endmenu

menu "Zephyr Kernel"
source "$ZEPHYR_BASE/Kconfig.zephyr"
endmenu

<prj.conf>

# General config
CONFIG_TEST_RANDOM_GENERATOR=y

# Networking
CONFIG_NETWORKING=y
CONFIG_NET_SOCKETS_OFFLOAD=y
CONFIG_NET_SOCKETS=y
CONFIG_NET_SOCKETS_POSIX_NAMES=y

# LTE link control
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_NETWORK_MODE_LTE_M=y
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n
# CONFIG_LTE_EDRX_REQ_ACTT_TYPE="4"
CONFIG_LTE_EDRX_REQ=y
CONFIG_LTE_EDRX_REQ_VALUE="0110"
# 0100 81.92sec
# 0101 163.84sec
# 0110 327.68sec
# 0111 655.36sec

# LTE link control
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n

# BSD library
CONFIG_BSD_LIBRARY=y

# AT Host
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_AT_HOST_LIBRARY=y

# MQTT
CONFIG_MQTT_LIB=y
CONFIG_MQTT_LIB_TLS=n

# Appliaction
CONFIG_MQTT_PUB_TOPIC="myPubTopic"
CONFIG_MQTT_SUB_TOPIC="mySubTopic"
CONFIG_MQTT_CLIENT_ID="myClientID"
CONFIG_MQTT_BROKER_HOSTNAME="xxxxxxxxxx.com"
CONFIG_MQTT_BROKER_PORT=1883
CONFIG_MQTT_KEEPALIVE=300 # ADD here

# Main thread
CONFIG_MAIN_THREAD_PRIORITY=7
CONFIG_MAIN_STACK_SIZE=4096

CONFIG_HEAP_MEM_POOL_SIZE=1024

<main.c>

#include <zephyr.h>
#include <stdio.h>
#include <uart.h>
#include <string.h>

#include <net/mqtt.h>
#include <net/socket.h>
#include <lte_lc.h>

#define MQTT_USERNAME "username"
#define MQTT_PASSWORD "password"
.
.
.

/**@brief Initialize the MQTT client structure
 */
static void client_init(struct mqtt_client *client)
{
	mqtt_client_init(client);

	broker_init();

    /* Add from here */
    static struct mqtt_utf8 password;
	static struct mqtt_utf8 user_name;

	password.utf8 = (u8_t *)MQTT_PASSWORD;
	password.size = strlen(MQTT_PASSWORD);
	user_name.utf8 = (u8_t *)MQTT_USERNAME;
	user_name.size = strlen(MQTT_USERNAME);
    /* to here */

	/* MQTT client configuration */
	client->broker = &broker;
	client->evt_cb = mqtt_evt_handler;
	client->client_id.utf8 = (u8_t *)CONFIG_MQTT_CLIENT_ID;
	client->client_id.size = strlen(CONFIG_MQTT_CLIENT_ID);
	client->password = &password; // Add here
	client->user_name = &user_name; // Add here
	client->protocol_version = MQTT_VERSION_3_1_0; // originally MQTT_VERSION_3_1_1

	/* MQTT buffers configuration */
	client->rx_buf = rx_buffer;
	client->rx_buf_size = sizeof(rx_buffer);
	client->tx_buf = tx_buffer;
	client->tx_buf_size = sizeof(tx_buffer);

	/* MQTT transport configuration */
	client->transport.type = MQTT_TRANSPORT_NON_SECURE;
}

.
.

void main(void)
{
	int err;

	printk("The MQTT simple sample started\n");

	modem_configure();

    /* ADD here */
    err = lte_lc_edrx_req(true);
    if (err) {
        printk("ERROR: set edrx %d\n", err);
        return;
    }
    /* ADD here */

	client_init(&client);

	err = mqtt_connect(&client);
	if (err != 0) {
		printk("ERROR: mqtt_connect %d\n", err);
		return;
	}

	err = fds_init(&client);
	if (err != 0) {
		printk("ERROR: fds_init %d\n", err);
		return;
	}

	while (1) {
		err = poll(&fds, 1, K_SECONDS(CONFIG_MQTT_KEEPALIVE)); 
		if (err < 0) {
			printk("ERROR: poll %d\n", errno);
			break;
		}

        err = mqtt_live(&client);
		if (err != 0) {
			printk("ERROR: mqtt_live %d\n", err);
			break;
		}

		if ((fds.revents & POLLIN) == POLLIN) {
			err = mqtt_input(&client); // if a publish event comes, mqtt_evt_handler is called here
			if (err != 0) {
				printk("ERROR: mqtt_input %d\n", err);
				break;
			}
		}

		if ((fds.revents & POLLERR) == POLLERR) {
			printk("POLLERR\n");
			break;
		}

		if ((fds.revents & POLLNVAL) == POLLNVAL) {
			printk("POLLNVAL\n");
			break;
		}
	}

}

This is a test condition.
Ideally, I want to set a longer keepalive value, like 1200(sec) to decrease power consumption.
- keep alive of MQTT: 1200 sec
- eDRX interval value: 655 sec

I have been struggling with this issue more than two weeks, but I don't really get the eDRX behavior. Any advice?

[Martin Lesund]

Hi Yusuke,

I am sorry for the delay, but I would like you to test the newest up to date versions before we continue.

Could you please update following this small guide and do a re-test?

[Yusuke]

I updated the firmware, but it doesn't work out yet.

KeepAlive function works fine after the firmware were updated. However, eDRX function doesn't work correctly. Even I set 327 sec interval, it receives a message around 30 ~ 60 sec after it was sent. 

# LTE link control
CONFIG_LTE_LINK_CONTROL=y
CONFIG_LTE_NETWORK_MODE_LTE_M=y
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n
CONFIG_LTE_EDRX_REQ=y
CONFIG_LTE_EDRX_REQ_VALUE="0110"
# 0100 81.92sec
# 0101 163.84sec
# 0110 327.68sec
# 0111 655.36sec

I want an example of eDRX.

[Yusuke]

Thank you for your reply.

I'll test including the at command later.

I really want edrx example project or tutorial.

And one more question. For example, if you set 327 sec in edrx interval, does it operate in the interval right after edrx starts? Or the device takes some steps and finally reaches to 327sec like 30, 60, ..., 327? I want to know the specification of nRF9160 eDRX.

[Yusuke]

Hi, Martin

condition:
LTE-M, eDRX, interval = 327("0110")

result:

+CEDRXRDP: 4,"0110","0110","0000"

<Paging_time_window>: "0000"

 Is this OK?

[Martin Lesund]

Hi Yusuke,

From the 3GPP spec:

• The eDRX interval is 102,4 seconds

• The Paging Time Window in your case is 1.28 seconds. 

[Yusuke]

Hi, Martin.

Can you show me the link of the whole document?

Those values are different what I found.
https://www.arib.or.jp/english/html/overview/doc/STD-T63V12_00/5_Appendix/Rel13/24/24008-d50.pdf

see page 597.

max value of eDRX interval should be around 43 min = 2580 sec.

[Yusuke]

OK. I got it.

3GPP TS 24.008 has several versions and some values vary depending on versions. Nordic should specify which version users should read. That's so confusing.

This would be the latest version now.

https://www.etsi.org/deliver/etsi_ts/124000_124099/124008/14.08.00_60/ts_124008v140800p.pdf

[Martin Lesund]

Hi Yusuke,

This is the official 3gpp site with the version of the specification #24.008

I would recommend using Release 15

[Yusuke]

which version do you recommend in Rel15 ? 15.6.0?

[Martin Lesund]

Correct

[Yusuke]

Thanks

So, is this correct understanding?

CONFIG_LTE_EDRX_REQ_VALUE="1010"
# 0101 81.92sec
# 1001 163.84sec
# 1010 327.68sec => current state
# 1011 655.36sec

[Martin Lesund]

Correct: