u-blox MQTT User Manual

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describes how to connect and configure Message Queuing Telemetry

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u-connectXpress

MQTT

Application note

Abstract

This application note Transport (MQTT) using u-connectXpress software.

UBX-19005066 - R03 C1-Public www.u-blox.com

u-connectXpress MQTT - Application note

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Document information

Title u-connectXpress

Subtitle MQTT

Document type Application note

Document number UBX-19005066

Revision and date R03 22-Feb-2021

Disclosure restriction C1-Public

This document applies to the following products:

Product name Software version

NINA-W131 2.1.x onwards

NINA-W132 2.1.x onwards

NINA-W151 1.0.x onwards

NINA-W152 1.0.x onwards

NINA-W156 3.1.x onwards

ODIN-W260 7.0.x onwards

ODIN-W262 7.0.x onwards

ODIN-W263 7.0.x onwards

express written permission of u-blox.

-blox assumes no liability for its use. No warranty, either express or

to, with respect to the accuracy, correctness, reliability and fitness for a particular

-blox at any time without notice. For the most recent

-blox.com.

-blox AG.

UBX-19005066 - R03 Document information Page 2 of 18 C1-Public

u-connectXpress MQTT - Application note

1 Overview ................................................................................................................................................ 4

2 MQTT-SN gateway ............................................................................................................................. 5

2.1 Connect MQTT-SN gateway to broker ................................................................................................... 6

2.1.1 URL format (for AT+UDCP and AT+UDDRP) ................................................................................ 6

2.1.2 Example Mosquitto test broker ....................................................................................................... 7

2.2 MQTT-SN client connect/disconnect ..................................................................................................... 8

2.3 MQTT-SN client publish ............................................................................................................................ 9

2.4 MQTT-SN client subscribe ...................................................................................................................... 10

2.5 MQTT-SN client PING ............................................................................................................................... 11

2.6 MQTT-SN sleeping clients ...................................................................................................................... 12

3 MQTT client gateway ...................................................................................................................... 14

3.1 Connect MQTT client gateway to broker ............................................................................................. 14

A Publish packet size limitations .................................................................................................... 15

B Glossary .............................................................................................................................................. 16

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u-connectXpress MQTT - Application note

broker

MQTT-SN

1 Overview

Message Queuing Telemetry Transport (MQTT) is a publish/subscribe, simple messaging protocol, designed for communication between multiple devices. This application note describes how to connect and configure MQTT using u-connectXpress software.

It is possible to configure the gateway as an MQTT-SN gateway. This is intended for end devices that do not support TCP/TLS directly; instead, an end device connects to the gateway using a serial connection such as Bluetooth SPS or SPP and communicates with the gateway using the MQTT-SN protocol, as described in Figure 1.

It is also possible to configure the gateway as an MQTT client gateway. The host of the gateway can then transmit or receive transparent MQTT data directly over the UART.

Figure 1: Gateway using a serial connection such as Bluetooth SPS or SPP with gateway communication using MQTT-SN

MQTT-SN gateway

SPP or SPS

End device

MQTT

TCP / TLS

MQTT client gateway

UART

Host

End device

Different combinations of the configurations described in Figure 1 can also be achieved. Hence, it is possible for the host, and the end devices to communicate with the MQTT broker via the same gateway simultaneously.

For information about how to get started with a module, see the corresponding EVK user guides (EVKODIN-W2 user guide [1] and EVK-NINA-W1 and EVK-NINA-B2 user guide [4].

See the u-connect AT commands manual [3] for details of the AT commands that can be used with ublox short range stand-alone modules and the u-connectXpress user guide [2] for more information on the u-connectXpress software.

Refer to the MQTT-SN v1.2 protocol specification available at http://mqtt.org/documentation for information about the MQTT-SN protocol.

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u-connectXpress MQTT - Application note

MQTT-SN

MQTT

SPP or SPS

TCP/TLS

Streams bound

2 MQTT-SN gateway

An MQTT-SN (SN=Sensor Network) gateway enables end devices with no TCP/TLS support to communicate with an MQTT broker (which requires TCP/TLS). The end device connects to the gateway using a serial connection, such as Bluetooth SPS or SPP, and communicates using the MQTT-SN protocol. The gateway then converts the MQTT-SN packets, from the end device, to MQTT packets and sends to the broker and vice versa.

End Device

ANNA-B112 or NINA-B1/B2/B3

Figure 2: End device connects to the gateway using serial connection

MQTT-SN

gateway

ODIN-W2 or

NINA-W15

MQTT broker

The MQTT-SN gateway is an aggregating gateway, which means that there is only one TCP or TLS connection to the MQTT broker. Hence, multiple end devices do not require one connection each as in the case of a transparent gateway. This is good since many brokers limit the number of connections and it is then better for many end nodes to share one TCP/TLS connection.

The end device will act as an MQTT-SN client (or client from here on) and it can publish or subscribe to data identified by a unique topic string. The MQTT broker is data agnostic meaning it considers all data to be a byte array. Hence, a publish data packet consists of:

• A topic string that uniquely identifies the data

• Data as a byte array.

The steps to get the MQTT-SN gateway configured and running typically are:

1. Create one or more MQTT streams by using the AT commands,

AT+UDCP or AT+UDDRP. The first

created stream will setup the actual TCP/TLS connection to the MQTT broker.

2. Create one or more end device streams, Bluetooth SPS or SPP, by using the AT commands,

AT+UDCP, AT+UDDRP or by enabling one of the associated services, AT+UDSC, for the end device to

connect to the gateway.

3. Bind the MQTT stream with the end device stream using one of the following:

o Dynamic bind, AT command o Static bind configured using “

AT+UDBIND (requires host to execute the command)

sys.sid” key in stream URL (automatic bind once both the

connections are active)

End device

MQTT-SN

SPS

MQTT

MQTT on TCP/TLS

MQTT broker

Figure 3: End device acts as MQTT-SN client with agnostic MQTT broker

Gateway

☞ The end device must transmit and receive MQTT-SN packets on the Bluetooth SPS or SPP link.

Hence, some basic MQTT-SN packet parsing is required by the end device.

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u-connectXpress MQTT - Application note

MQTT on TCP/TLS

The gateway does not support the full MQTT-SN specification. Only the following packet types are supported:

• CONNECT / CONNACK (client connects to the gateway)

• DISCONNECT (client disconnects from the gateway or enter sleep mode)

• REGISTER / REGACK (client register topic to the gateway)

• PUBLISH / PUBACK (client or gateway forwards data)

• SUBSCRIBE / SUBACK (client subscribes to data identified with topic)

• PINGREQ / PINGRESP (client checks connection to the gateway or polls for data when in sleep

mode)

☞ To ease implementation of a propriety MQTT-SN end device, it is recommended to use the MQTT-

SN packet parser code available at https://github.com/eclipse/paho.mqtt-sn.embedded-c.

2.1 Connect MQTT-SN gateway to broker

The MQTT-SN gateway is configured using either the connect peer AT command, AT+UDCP, or the default remote peer AT command,

AT+UDDRP.

Figure 4: MQTT-SN gateway connect to broker

Gateway

MQTT broker

☞ One MQTT stream must be setup for every connected MQTT-SN end device. For example, if the

gateway must handle 5 parallel Bluetooth LE connected end devices, then five MQTT streams must be activated. However, for sleeping clients, it is possible to have more clients than the MQTT streams if they do not need to be connected simultaneously.

2.1.1 URL format (for AT+UDCP and AT+UDDRP)

mqtt://<host address>:<port>/?<keys>

• <host address>: Host name or IP address, e.g., test.mosquitto.org or 37.187.106.16

•

<port>: IP address port number, e.g., 1883

•

<keys>: key=value (with separating and character) for gateway to broker connection

MQTT related keys:

o client: Client name, e.g.,

o user: User name, e.g.,

client=my_client

user=my_user

☞ The end devices must ensure that data is transmitted to the broker within the keep-alive timeout.

o passwd: User password, e.g.,

o keepAlive: Keep alive timeout in seconds, e.g., keepAlive=60

o qos: Quality of Service level (0,1,2). Refer to the MQTT specification [5] for details.

If not, the broker may disconnect.

maxSnClients: Number of MQTT-SN clients supported, e.g., maxSnClients=24

Default is 16.

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passwd=my_passwd

u-connectXpress MQTT - Application note

TLS related keys:

encr: TLS encryption without validating certificates if set to 1, e.g., encr=1

ca: Server CA for gateway to validate the server, e.g., ca=ca.pem

cert: Gateway client certificate, e.g., cert=client.pem

privKey: Gateway client private key, e.g., privKey=client.key

Static bind key:

sys.sid: Static bind of the MQTT stream to another stream, e.g., sys.sid=100



sys.sid 100-106: Incoming SPS service connections



sys.sid 200-206: Incoming SPP service connections

☞ A new incoming service connection will use the lowest free id currently.

•

sys.sid < 100: Used to bind two streams configured using +UDCP or +UDDRP. For

this case, use the same id for both streams.

The static bind will be activated when both streams have been connected or reconnected.

☞ Since all MQTT streams share the same connection to the MQTT broker, most of the above

parameters must be identical for all the MQTT streams. The exception is the will be different between the streams.

sys.sid key, which

☞ The certificates must be uploaded to the gateway using the security manager AT command

AT+USECMNG, or by using the s-center tool “Advanced connection and settings->Wi-Fi certificates”

tab.

2.1.2 Example Mosquitto test broker

List certificates

AT+USECMNG=3 "CA","mosquitto.org.crt" "CC","client.pem" "PK","client.key" OK

TCP

at+udcp=mqtt://test.mosquitto.org:1883/?sys.sid=100 +UDCP:1 OK +UUDPC:1,2,2,0.0.0.0,0,37.187.106.16,1883

TLS Encryption

at+udcp=mqtt://test.mosquitto.org:8883/?encr=1&sys.sid=100 +UDCP:1 OK +UUDPC:1,2,2,0.0.0.0,0,37.187.106.16,8883

to make sure they are already uploaded:

TLS 1-way authentication

at+udcp=mqtt://test.mosquitto.org:8883/?ca=mosquitto.org.crt&sys.sid=100 +UDCP:1 OK +UUDPC:1,2,2,0.0.0.0,0,37.187.106.16,8883

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u-connectXpress MQTT - Application note

TLS 2-way-authentication

at+udcp=mqtt://test.mosquitto.org:8884/?ca=mosquitto.org.crt&cert=client.pem&privKey=clien t.key&sys.sid=100 +UDCP:1 OK +UUDPC:1,2,2,0.0.0.0,0,37.187.106.16,8884

☞ For the tests, the Mosquitto test broker (http://test.mosquitto.org/) is used. Note that this is an

open server and published data is visible to anyone. Hence, use only for initial testing.

☞ The “sys.sid=100” key would automatically bind the MQTT-SN stream to the first incoming SPS

connection.

☞ For the +UUDPC event, the local IP and port is not supported and is always set to 0.

2.2 MQTT-SN client connect/disconnect

For an end device to setup an MQTT-SN connection to the gateway, the CONNECT packet must be sent. To terminate a previously setup MQTT-SN connection, the DISCONNECT packet is sent.

Figure 5: MQTT-SN client connect/disconnect

Sample packets:

CONNECT: 0x0A040001000041424344 Length: 0x0A Type: 0x04 (CONNECT) Flags: 0x00 Protocol id: 0x01 Duration: 0x0040 (Keep alive duration in seconds) Client id: 0x41424344 (“ABCD”)

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u-connectXpress MQTT - Application note

CONNACK 0x030500 Length: 0x03 Type: 0x05 (CONNACK) Result: 0x00 (OK)

DISCONNECT: 0x0218 Length: 0x02 Type: 0x18 (DISCONNECT)

☞ It is recommended to set duration for the connect message. This prevents the gateway from

keeping track of clients that are no longer available. When the duration timer for a client has elapsed, the gateway will delete the client.

☞ If the connection (for example, SPS or SPP) is lost and setup again, the end device should send

another

CONNECT (“unique client id”) or PINGREQ (“unique client id) to identify itself once again.

☞ For the CONNECT flags parameter, it is not supported.

2.3 MQTT-SN client publish

Before an MQTT-SN client can publish data to the MQTT broker, it must first register the data topic to the gateway. It registers the topic name (string) and gets back a two-byte id, which is then used for publishing data of that topic.

Figure 6: MQTT-SN client publish

Sample packets:

REGISTER: 0x090A00001234303132 Length: 0x09 Type: 0x0A (REGISTER) Topic Id: 0x0000 Message id: 0x1234 (id or sequence number returned in the REGACK message) Topic name: 0x303132 (“012”)

REGACK 0x070B0001123400 Length: 0x07 Type: 0x0B (REGACK) Topic Id: 0x0001 (Returned topic id to used in PUBLISH) Message id: 0x1234 (id or sequence number of the REGISTER message) Result: 0x00 (OK)

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u-connectXpress MQTT - Application note

PUBLISH: 0x0A0C0000012345010203 Length: 0x0A Type: 0x0C (PUBLISH) Flags: 0x00 Topic Id: 0x0001 Message id: 0x2345 (id or sequence number returned in the PUBACK message) Data: 0x010203

PUBACK 0x070D0001234500 Length: 0x07 Type: 0x0D (PUBACK) Topic Id: 0x0001 Message id: 0x2345 (id or sequence number of the PUBLISH message) Result: 0x00 (OK)

☞ Set the PUBLISH flags parameter to 0 as it is not supported. The gateway will use DUP=0 (first

time), which is 2-byte id)

QoS=0 (send once), Retain=0 (do not store), Will=0 (no will), TopicIdType=0 (normal topic id,

2.4 MQTT-SN client subscribe

An MQTT-SN client can subscribe on topics using the SUBSCRIBE message. When data for a subscribed topic is updated, the

PUBLISH message is received from the gateway.

Figure 7: MQTT client subscribe

SUBSCRIBE: 0x0812001234303132 Length: 0x08 Type: 0x12 (SUBSCRIBE) Flags: 0x00 Message id: 0x1234 (id or sequence number returned in the SUBACK message) Topic name: 0x303132 (“012”)

SUBACK 0x0813000001123400 Length: 0x08 Type: 0x13 (SUBACK) Flags: 0x00 Topic Id: 0x0001 (Returned topic id used in PUBLISH) Message id: 0x1234 (id or sequence number of the SUBSCRIBE message) Result: 0x00 (OK)

PUBLISH: 0x0A0C0000010000010203 Length: 0x0A

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u-connectXpress MQTT - Application note

Type: 0x0C (PUBLISH) Flags: 0x00 Topic Id: 0x0001 Message id: 0x0000 (not used by gateway for PUBLISH messages) Data: 0x010203

☞ Flags in the SUBSCRIBE message is not supported. Hence, set to 0. Gateway will use DUP=0 (first

time),

QoS=0 (send once), TopicIdType=0 (topic name as string).

☞ The message id (sequence number) of the PUBLISH message is always 0 when sent by the

gateway.

☞ For the subscribe topic, neither the multi-level character, “#”, or the single-level character, “+”, is

supported.

2.5 MQTT-SN client PING

An MQTT-SN client may use the PING message to check that the connection to the gateway is alive.

Also, if the keep-alive duration for the MQTT-SN connection is set, it is the client that must assure that data is transmitted to avoid a disconnection. The PINGREQ can then be used.

Figure 8: MQTT-SN client PING

The PINGREQ with client identifier can also be used if the serial connection, e.g., SPS or SPP, is lost and reconnected. It may then be necessary for the client to identify itself in order for the gateway to associate the client with a new stream. Hence, it is recommended to always start with a PINGREQ including the unique client id after a reconnection of the serial link, for example, SPS or SPP.

PINGREQ: 0x0216 Length: 0x02 Type: 0x16 (PINGREQ)

PINGREQ with client id: 0x0816434C49454E54 Length: 0x08 Type: 0x16 (PINGREQ) Client id: 0x434C49454E54 (“CLIENT”)

PINGRESP 0x0217 Length: 0x02 Type: 0x17 (PINGRESP)

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u-connectXpress MQTT - Application note

☞ If a response to a PINGREQ is a DISCONNECT (instead of a PINGRESP), it means that the gateway

has lost track of the client or even deleted it. It may then be needed to do a CONNECT, REGISTER, SUBSCRIBE to restore the connection.

2.6 MQTT-SN sleeping clients

It is possible for an MQTT-SN client that is in sleep mode to terminate the serial connection (for example, SPS or SPP), enter low power mode (to save power), wake-up and setup the serial connection and poll if there has been any data transmitted to the client while asleep. The gateway will store the messages subscribed by the client while asleep.

Figure 9: MQTT-SN sleeping clients

Once the client has set up the connection, it uses the PINGREQ message with the unique client identifier to poll the gateway for data. The gateway then sends stored messages to the client and ends with the PINGRESP message to indicate that no more data is available.

☞ The gateway only stores the latest update for each topic.

☞ By default, the gateway can serve a maximum of 16 clients. It is possible to change this by using

the URL

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maxSnClients keyword when configuring the MQTT stream(s).

u-connectXpress MQTT - Application note

☞ If the gateway needs to store a lot of messages for many clients, it is possible that it may run out

of RAM memory, which will cause the gateway to restart. Hence, it is very important to test every specific configuration to make sure that the gateway is not overloaded.

☞ The number of active MQTT-SN streams limits the number of parallel active clients.

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u-connectXpress MQTT - Application note

MQTT

3 MQTT client gateway

The gateway can also be configured as an MQTT client gateway and not as a full MQTT-SN gateway. It is then possible for a host to transmit and receive MQTT data on the UART transparently.

In data mode, transmitted data will be published to one configured publish topic and received data will be received from one configured subscribe topic.

In EDM (extended data mode) mode, it is possible to configure one publish topic and one subscribe topic for every EDM channel. The host can then transmit and receive data on separate channels and thus publish and subscribe to as many topics as there are defined by the channels.

Host MQTT gateway

UART

(data mode or EDM)

ODIN-W2 or NINA-W13/

Figure 10: MQTT client gateway

NINA-W15

TCP/TLS

MQTT

broker

The data transmitted and received on the UART is the actual MQTT data only without any topic information (configuration specifies what topic it is). For the data mode, it means that if the host transmits two consecutive packets of size 5 and 10 bytes, it may be written to the MQTT Broker as one packet of 15 bytes since there is no delimiting information. Similarly, long packets may be split before being sent to the MQTT broker. For EDM, this is not an issue since every EDM write packet is transmitted separately to the MQTT broker. For EDM related restriction refer to the u-blox Extended Data Mode protocol specification [6].

An MQTT client stream is configured using the commands

+UDCP or +UDDRP. The first created stream

will setup the actual TCP/TLS connection to the MQTT broker.

3.1 Connect MQTT client gateway to broker

The MQTT client gateway support is implemented as an MQTT stream according to the u-connect software concepts. This means that it is configured using URLs either with the connect command (AT+UDCP) or the default remote peer command

AT+UDDRP.

Gateway

MQTT on TCP/TLS

MQTT broker

Figure 11: MQTT client connect to broker

The URL format is similar to the MQTT-SN URL format, except for the following keys:

•

pt: Publish topic, e.g., pt=ubx/test/1

•

st: Subscribe topic, e.g., st=ubx/test/1

•

maxSnClients: Not used

☞ If an MQTT stream is configured without the “pt” and “st” keys, the stream will be an MQTT-SN

stream. If any of the “

pt” or “st” keys are used, the stream will be an MQTT client stream.

☞ For the subscribe topic, the multi-level character, ‘#’, is supported, as in st=ubx/test/#. The single-

level character ‘

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+’ is not supported.

u-connectXpress MQTT - Application note

Appendix

A Publish packet size limitations

NINA-W13/NINA-W15 MQTT MQTT-SN

u-connectXpress 3.0 onwards topic length + payload length + 8 <=1024 topic length + payload length + 8 <=1024

u-connectXpress 2.1 and earlier topic length + payload length + 8 <= 320 MQTT-SN header length + payload length

<= 255 bytes

Table 1 NINA-W1x packet size limitations (bytes).

ODIN-W2 MQTT MQTT-SN

SW 7.2 and earlier topic length + payload length + 8 <= 320 MQTT-SN header length + payload

length <= 255 bytes

SW 8.0 and later topic length + payload length + 8 <= 320 topic length + payload length + 8 <= 320

Table 2 ODIN-W2 packet size limitations (bytes).

☞ MQTT header length is 8 bytes (6 bytes with QOS=0) ☞ MQTT-SN header is 2-4 bytes. ☞ MQTT-SN payload also contains 5 bytes of flags, TopicId and MsgId. ☞ The memory used for MQTT messages is a ring buffer and maximizing message size and sending messages frequently

may result in buffer overruns.

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u-connectXpress MQTT - Application note

B Glossary

Abbreviation Definition

CA Certification Authority

EDM Extended Data Mode

IP Internet Protocol

LE Low Energy

MQTT Message Queuing Telemetry Transport

MQTT-SN MQTT for Sensor Networks

QOS Quality Of Service

SN Sensor Network

SPP Serial Port Profile

SPS Serial Port Service

TCP Transmission Control Protocol

TLS Transport Layer Security

UART Universal Asynchronous Receiver/Transmitter

Table 3: Explanation of the abbreviations and terms used.

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u-connectXpress MQTT - Application note

W2 in some

W1x modules in some

Revision history

Revision Date Name Comments

R01 19-Mar-2019 tfri, cmag Initial release.

R02 30-Oct-2019 flun Included NINA-W13 v2.1.x and NINA-W15 v1.0.x in the applicable products

table on page 2. Provided reference to NINA-W1x modules in addition to ODIN-

sections. Provided reference to ANNA-B112/NINAfigures. Added links to related documents.

R03 22-Feb-2021 mape Added appendix A. Included NINA-W156 and ODIN-W263. Other minor fixes.

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u-connectXpress MQTT - Application note

Contact

For complete contact information, visit us at www.u-blox.com.

u-blox Offices

North, Central and South America

u-blox America, Inc.

Phone: +1 703 483 3180 E-mail: info_us@u-blox.com

Regional Office West Coast:

Phone: +1 408 573 3640 E-mail: info_us@u-blox.com

Technical Support:

Phone: +1 703 483 3185 E-mail: support@u-blox.com

Headquarters Europe, Middle East, Africa

u-blox AG

Phone: +41 44 722 74 44 E-mail: info@u-blox.com Support: support@u-blox.com

Asia, Australia, Pacific

u-blox Singapore Pte. Ltd.

Phone: +65 6734 3811 E-mail: info_ap@u-blox.com Support: support_ap@u-blox.com

Regional Office Australia:

Phone: +61 3 9566 7255 E-mail: info_anz@u-blox.com Support: support_ap@u-blox.com

Regional Office China (Beijing):

Phone: +86 10 68 133 545 E-mail: info_cn@u-blox.com Support: support_cn@u-blox.com

Regional Office China (Chongqing):

Phone: +86 23 6815 1588 E-mail: info_cn@u-blox.com Support: support_cn@u-blox.com

Regional Office China (Shanghai):

Phone: +86 21 6090 4832 E-mail: info_cn@u-blox.com Support: support_cn@u-blox.com

Regional Office China (Shenzhen):

Phone: +86 755 8627 1083 E-mail: info_cn@u-blox.com Support: support_cn@u-blox.com

Regional Office India:

Phone: +91 80 405 092 00 E-mail: info_in@u-blox.com Support: support_in@u-blox.com

Regional Office Japan (Osaka):

Phone: +81 6 6941 3660 E-mail: info_jp@u-blox.com Support: support_jp@u-blox.com

Regional Office Japan (Tokyo):

Phone: +81 3 5775 3850 E-mail: info_jp@u-blox.com Support: support_jp@u-blox.com

Regional Office Korea:

Phone: +82 2 542 0861 E-mail: info_kr@u-blox.com Support: support_kr@u-blox.com

Regional Office Taiwan:

Phone: +886 2 2657 1090 E-mail: info_tw@u-blox.com Support: support_tw@u-blox.com

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u-blox MQTT User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

Document information

Contents

1 Overview

2 MQTT-SN gateway

2.1 Connect MQTT-SN gateway to broker

2.1.1 URL format (for AT+UDCP and AT+UDDRP)

2.1.2 Example Mosquitto test broker

2.2 MQTT-SN client connect/disconnect

2.3 MQTT-SN client publish

2.4 MQTT-SN client subscribe

2.5 MQTT-SN client PING

2.6 MQTT-SN sleeping clients

3 MQTT client gateway

3.1 Connect MQTT client gateway to broker

Appendix

A Publish packet size limitations

B Glossary

Related documents

Revision history

Contact