IEEE 802.1Qch-2017：循环队列与转发标准
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"802.1Qch-2017.pdf" 是一份关于IEEE 802.1Q标准的修正案，该修正案详细介绍了Cyclic Queuing and Forwarding（循环队列和转发）的技术，是针对IEEE 802.1Q-2014标准的一系列修订之一，包括了对802.1Qca-2015、802.1Qcd-2015、802.1Q-2014/Cor1-2015、802.1Qbv-2015、802.1Qbu-2016、802.1Qbz-2016和802.1Qci-2017的修改。
这篇文档是IEEE LAN/MAN Standards Committee（局域网/城域网标准委员会）发布，用于规范本地和城域网络中的桥接和桥接网络技术。802.1AS是时间同步协议，它在物联网(IoT)、无线通信和数据中心网络中至关重要，确保了设备间的精确时间同步。
802.1AS，全称为“Precision Time Protocol (PTP) for Local and Metropolitan Area Networks”，是一种在网络中实现微秒级精度时间同步的协议。它基于IEEE 1588标准，适用于各种网络架构，如以太网、Wi-Fi等，主要用于需要严格时间同步的领域，如电力系统自动化、电信网络、视频广播、金融交易和交通管理系统。
802.1AS的主要功能包括：
1. **主时钟选举**：网络中的设备通过PTP消息确定一个主时钟，其他设备则同步到这个主时钟。
2. **时间戳处理**：在网络中的数据包上添加时间戳，用于计算传输延迟和校正时间。
3. **同步机制**：通过周期性的PTP消息交换，设备能够调整其内部时钟，以保持与主时钟的一致性。
4. **边界时钟和普通时钟**：802.1AS区分了两种类型时钟，边界时钟可以同时作为PTP端点和网络中间节点，而普通时钟仅作为端点。
802.1Qch-2017的出现，是为了改进网络中的数据包管理和转发策略，通过引入循环队列和转发机制，可能提升了时间敏感网络(TSN)的性能和效率。TSN是一种使能网络在严格的时间窗口内可靠传输数据的技术，尤其适用于实时性和延迟敏感的应用场景。
修正案可能涉及到以下方面：
- **优化时间同步**：802.1Qch可能引入了新的优化算法，以提高PTP消息的处理和转发速度，从而改善整个网络的时间同步性能。
- **增强网络带宽管理**：通过循环队列，可能实现了更精细的带宽分配，确保关键流量优先。
- **降低延迟**：可能提出了新的数据包调度策略，减少数据包在传输过程中的等待时间，降低整体网络延迟。
- **提高可靠性**：循环队列和转发策略可能增强了网络的容错能力，确保即使在某些节点故障时，时间同步服务仍能持续。
802.1Qch-2017是对802.1Q标准的重要补充，旨在提升网络的时钟同步能力和服务质量，特别是对于那些需要高精度时间同步和低延迟传输的网络应用。
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