ApsaraMQ for MQTT:Terms

Basic terms

• instance

  • An entity that you create when you purchase ApsaraMQ for MQTT. Each ApsaraMQ for MQTT instance corresponds to a globally unique endpoint. You must create an instance in the target region and use its endpoint to access the service. For information about how to create an ApsaraMQ for MQTT instance, see Step 1: Create resources.

• message ID

  • The globally unique identifier of a message. Message IDs are automatically generated by ApsaraMQ for MQTT and are used to track messages and troubleshoot errors. For more information, see Tracing.

• ApsaraMQ for MQTT broker

  • A server node in ApsaraMQ for MQTT that handles MQTT-based messaging between ApsaraMQ for MQTT clients and ApsaraMQ for RocketMQ.

• ApsaraMQ for MQTT client

  • A mobile node that interacts with an ApsaraMQ for MQTT broker.

• P2P messaging

  • A special messaging model provided by ApsaraMQ for MQTT based on the standard MQTT protocol. In this messaging model, messages can be sent to an ApsaraMQ for MQTT client without subscription. For more information, see P2P Messaging model (MQTT).

• parent topic

  • MQTT uses a publish-subscribe (pub/sub) model where each message belongs to a topic. The MQTT protocol supports multiple topic levels, and level-1 topics are called parent topics. You must create a parent topic in the ApsaraMQ for MQTT console or the ApsaraMQ for RocketMQ console before use.

• subtopic

  • A level-2 or level-3 topic under a parent topic. You can specify subtopics directly in your application code without creating them in the console. The naming format is <Name of parent topic>/<Name of level-2 topic>/<Name of level-3 topic>, with levels separated by forward slashes (/). Example: SendMessage/demo/producer. The total length of the full topic name cannot exceed 64 characters in ApsaraMQ for MQTT. Otherwise, a client exception occurs.

• client ID

  • A globally unique identifier for a client in ApsaraMQ for MQTT. If you use a client ID already in use by another client, the access request is denied.

    A client ID consists of a group ID and a device ID. The format of a client ID is <GroupID>@@@<DeviceID>. A client ID cannot exceed 64 characters in length and cannot contain non-printable characters. For more information, see Limits.

• group ID

  • An identifier for a group of nodes that share identical logic and features. A group ID represents a set of devices with the same capabilities. You must create groups in the ApsaraMQ for MQTT console. For information about how to create a group, see Step 1: Create resources.

• device ID

  • A globally unique identifier for each device. For example, you can use the serial number of a sensor as the device ID.

Network-related terms

• endpoint

  • ApsaraMQ for MQTT provides public and internal endpoints. Public endpoints are recommended for mobile devices. In addition to the standard MQTT port 1883, ApsaraMQ for MQTT supports SSL encryption and WebSocket. An endpoint is automatically assigned when an instance is created. For information about how to create an instance, see Step 1: Create resources.

MQTT-related terms

• MQTT

  • An industry-standard protocol for the IoT and mobile Internet fields. The protocol is suitable for data transmission between mobile devices. By default, ApsaraMQ for MQTT supports the MQTT protocol.

• QoS

  • The quality of service (QoS) level in message transmission. You can separately specify QoS levels for producers and consumers.

    • The QoS level of a producer affects the transmission quality of messages that are sent from the producer to ApsaraMQ for MQTT.

    • The QoS level of a consumer affects the transmission quality of messages that are delivered from the ApsaraMQ for MQTT broker to the consumer.

    MQTT provides the following QoS levels:

    • QoS0: Messages are delivered to the intended ApsaraMQ for MQTT clients at most once.

    • QoS1: Messages are received by the intended ApsaraMQ for MQTT clients at least once.

    • QoS2: Messages are delivered to the intended ApsaraMQ for MQTT clients exactly once.

• cleanSession

  • In the MQTT protocol, the cleanSession parameter controls how offline messages and previous subscriptions are handled after a TCP connection is established. This parameter is independent of the producer configuration. Valid values:

    • cleanSession=true: When an offline ApsaraMQ for MQTT consumer client goes online again, all its previous subscriptions and offline messages are cleaned up.

    • cleanSession=false: When an offline ApsaraMQ for MQTT consumer client goes online again, it processes previous offline messages, and its previous subscriptions remain effective.

Take note of the following points when you use QoS levels and the cleanSession parameter together:

• In the MQTT protocol, the value of the cleanSession parameter for each client cannot be modified upon each connection. Otherwise, some messages may be mistaken as offline messages.

• In the MQTT protocol, the cleanSession parameter cannot be set to false for messages with QoS2. If an ApsaraMQ for MQTT client subscribes to such messages, the subscription does not take effect even if the cleanSession parameter is set to false.

• The cleanSession parameter of P2P messages is subject to the configuration of the ApsaraMQ for MQTT client that receives the messages.

The following Combinations of QoS levels and the cleanSession parameter table lists the results of different combinations of QoS levels and the cleanSession parameter in a consumer.

Solution-related terms

• RTC

  • A real-time communication technology for audio and video scenarios, including voice calls, video calls, and video conferencing.

• RTC server

  • A server that hosts audio-and-video media channel services provided by Alibaba Cloud Real-Time Communication (RTC).

• audio-and-video service management server

  • A management node in the RTC system, also called an audio-and-video management service. You can develop your own audio-and-video management services to manage the lifecycles of all RTC sessions. These management nodes are typically deployed on Alibaba Cloud. You can use Alibaba Cloud services to deploy your audio-and-video management services.

• mobile audio-and-video application

  • A terminal application in the RTC system that allows end users to initiate or join voice and video calls.

• smart AP

  • A programmable network device that provides Internet access and manages LAN devices. A smart router is an example of a smart access point (AP).

• digital price tag

  • An electronic screen that is used in places such as shopping malls and supermarkets. Digital price tags are networked by using smart AP nodes based on a wireless sensor network protocol such as Bluetooth or ZigBee.

• digital price tag management service

  • The backend service of a digital price tag system that manages display content on electronic screens and manages and queries manual tasks such as price changes.

• RDS

  • A stable, reliable, and scalable online database service provided by Alibaba Cloud. In a digital price tag system, RDS persistently stores task status changes such as price updates.

• Simple Log Service

  • A log service provided by Alibaba Cloud that persistently stores operation logs in a digital price tag system for auditing and tracing.