6.5.2 Ordinary clocks
The model of an ordinary clock is illustrated in Figure 2.
Figure 2 ?Model of an ordinary clock

ordinary clocks通過基于單個物理端口的兩個邏輯接口與網絡通信。 Event interface用于發送和接收事件消息，這些消息由時間戳生成模塊根據本地時鐘的值加上時間戳。general interface 用于發送和接收general messagels。

An ordinary clock in a domain supports a single copy of the protocol and has a single PTP state. The ordinary clock can be the grandmaster clock in a system, or it can be a slave clock in the master?slave hierarchy.

Ordinary clock maintain 兩個類型的data sets，分別是clock data sets 和port data sets

clock data sets 如下：

a) defaultDS: Attributes describing the ordinary clock. （描述ordinary clock屬性）
b) currentDS: Attributes related to synchronization.（與同步相關的屬性）
c) parentDS: Attributes describing the parent (the clock to which the ordinary clock synchronizes) and the grandmaster (the clock at the root of the master?slave hierarchy).(描述parent 和grandmaster 屬性)
d) timePropertiesDS: Attributes of the timescale.（timescale 的屬性）

The port data sets contain attributes of the port, including the PTP state.
The protocol engine:
? Sends and receives PTP messages.(發送和接收PTP message)
? Maintains the data sets.（maintain 數據集）
? Executes the state machine associated with the port.（執行與port關聯的狀態機）
? If the port is in the slave state (synchronizes to a master), it computes the master’s time based on the received PTP timing messages and timestamps that were generated.（如果port是slave port，則通過接收到的PTP timing message以及timestamps計算 master的timing）

如果ordinary clock處于slave 狀態， 則locol clock中的control loop會調整clock，使其與master的time一致。如果port是master state，則local clock是free running的，或者和外部時鐘一致，比如GPS。如果port 是master state，而ordinary clock是domain的grandmaster clock，則通常將local clock同步到可追溯到TAI和UTC的外部時間源，例如GPS系統。

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