作者：
∙International Business Machines Corporation (IBM)
∙Eurotech
翻译：明歌
协议原文： public./software/dw/webrvices/ws-mqtt/mqtt-v3r1.html
摘要
MQ遥测传输（MQ Telemetry Transport，MQTT）是一个轻量级的基于代理的发布/订阅式消息传输协议，它的设计目标是开放、简单、轻量和易于实现。这些特征使它适用于各种受限环境，比如，但不限于：
∙网络代价昂贵，低带宽或不可靠。
∙在嵌入设备中运行，处理器和内存资源有限。
该协议的特性包括：
∙使用发布/订阅消息模式，提供一对多的消息分发，解除应用程序耦合。
∙消息传输对有效载荷内容不可知。
∙使用TCP/IP提供基础网络连接。
∙有3个消息发布服务质量级别：
▪“至多一次”，消息发布完全依赖于底层TCP/IP网络。消息有可能丢失或重复。这一级别可应用于如下情景，如环境传感器数据，丢失一次读记录无所谓，因为很快下一次读记录就会产生。
▪“至少一次”，确保消息到达，但消息重复有可能发生。
▪“只有一次”，确保消息到达且只到达一次。这一级别可用于如计费系统等场景，在计费系统中，消息丢失或重复可能会导致生成错误的费用。
∙轻量传输，开销很小（固定头部的长度只有2字节），协议交换最小化，以降低网络流量。
∙提供一种机制，当客户端异常中断时，利用 Last Will 和 Testament 特性来通知有关各方。
版权声明
1999-2010 Eurotech, International Business Machines Corporation (IBM). All rights rerved.
Permission to copy and display the MQ Telemetry Transport specification (the "Specification"), in any medium without fee or royalty is hereby granted by Eurotech and International Business Machines Corporation (IBM) (collectively, the "Authors"), provided that you include the f黑色三部曲
ollowing on ALL copies of the Specification, or portions thereof, that you make:
A link or URL to the Specification at one of the Authors' websites. The copyright notice as
shown in the Specification. The Authors each agree to grant you a royalty-free licen, under reasonable, non-discriminatory terms and conditions to their respective patents that they deem necessary to implement the Specification. THE SPECIFICATION IS PROVIDED "AS IS," AND THE AUTHORS MAKE NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PUR三角梅扦插时间和方法
POSE, NON-INFRINGEMENT, OR TITLE; THAT THE CONTENTS OF THE SPECIFICATION ARE SUITABLE FOR ANY PURPOSE; NOR THAT THE IMPLEMENTATION OF SUCH CONTENTS WILL NOT INFRINGE ANY THIRD PARTY PATENTS, COPYRIGHTS, TRADEMARKS OR OTHER RIGHTS. THE AUTHORS WILL NOT BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF OR RELATING TO ANY USE OR DISTRIBUTION OF THE SPECIFICATION.
