IEEE1588协议P2PTC端口的时钟模块是什么作用

[aa45698]

希望知道的给解答以下
6.5.5 Peer-to-peer transparent clocks
The peer-to-peer transparent clock has an additional per port block as indicated in Figure 7. This block is
used to compute the link delay between each port and a similarly equipped port on another node sharing the
link, i.e., the link peer. The link peer exists in another clock supporting the peer delay mechanism since
non-peer-to-peer devices are not expected between peer-to-peer transparent clocks. The computation of link
delay is based on an exchange of Pdelay_Req, Pdelay_Resp, and possibly Pdelay_Resp_Follow_Up
messages with the link peer. As a result of these exchanges, the link delay is known for each port of the
peer-to-peer transparent clock. Unlike the end-to-end transparent clock, which corrects and forwards all
PTP timing messages, the peer-to-peer transparent clock only corrects and forwards Sync and Follow_Up
messages. The appropriate correctionField in these messages is updated for both the residence time of the
Sync message within the peer-to-peer transparent clock and the link delay on the port receiving the Sync
message.
就是这一节，这个时间模块意思P2P和E2ETC都有，只是处理消息的方法不同。但是P2P遇到Follow—up消息会直接丢掉，又怎么会修正。另一个As a result of these exchanges, the link delay is known for each port of the peer-to-peer transparent clock. P2P知道链路延迟，E2ETC也同样知道啊，所以不理解为什么能从这两个方面来说明P2P比E2E的时间同步精度高

[fabs2016]

我也刚看1588协议。理论上，主时钟是需要发送包含有真实的sync帧发送时间的follow_up帧的，实际上，很多产品都是硬件上实现时间戳功能的，时间戳可以记录sync的实际发送时刻，故就不需要follow_up了。end-to-end的透明时钟是修正和转发所有的PTP时间信息， peer-to-peer的透明时钟只修正和转发