• Switch Downstream Ports and Root Ports acting as PTM Responders must respond to each PTM Request Message received at their Downstream Ports with either PTM Response or PTM ResponseD according to the following rules: ◦ A PTM Responder must not send a PTM Response or PTM ResponseD Message without first receiving a PTM Request Message. ◦ Upon receipt of a PTM Request Message, a PTM Responder must attempt to issue a PTM Response or PTM ResponseD Message within 10 μs. ◦ A PTM Responder must issue PTM Response when the Downstream Port does not have valid historical timestamps (t3 - t2) with which to fulfill a PTM Request Message. 翻译

• 作为 PTM Responders 的 Switch Downstream Ports 和 Root Ports 必须根据以下规则响应其收到的每个 PTM Request Message，使用 PTM Response 或 PTM ResponseD： ◦ PTM Responder 必须在先收到 PTM Request Message 后才能发送 PTM Response 或 PTM ResponseD Message。 ◦ 在收到 PTM Request Message 后，PTM Responder 必须在 10 微秒内尝试发出 PTM Response 或 PTM ResponseD Message。 ◦ 当 Downstream Port 没有有效的历史时间戳（t3 - t2）来满足 PTM Request Message 时，PTM Responder 必须发出 PTM Response。