. If it is excessive, this time error will consume all the phase alignment budget that is allowed for the application. However, if you can measure the asymmetry, then PTP could be configured to correct for it and eliminate that error from the calculations. Now that the slave has an accurate timestamp from the master, and an estimate of the delay in a packet getting from the master to the slave, the slave can calculate the present time. This process occurs repeatedly (depending on the profile) but in the range of between once every 8 seconds to 128 times per second. 7.3.1 Overview of PTP Clocks To read about and comprehend the core components of PTP, you need to understand the features and functions of PTP clocks; however, to discuss PTP clocks in much detail requires significant knowledge of other concepts. For this reason, this section provides a simplified overview of PTP clocks and the subject is revisited in much more detail in the section "PTP Clocks" later in the chapter. In IEEE 1588-2008, there are three basic types of PTP clocks (it gets more nuanced later): The ordinary clock (OC) The boundary clock (BC) The transparent clock (TC) Clocks contain PTP ports, which are simply communications channels to other clocks. In most cases, a PTP port is either a master port (giving out time) or a slave port (recovering it). IEEE 1588 defines ordinary clocks as those that have only one PTP port, and under normal condi- tions, that port can be placed into either master or slave state via algorithmic control. The clock can also be restricted to be a slave-only clock, in which case it can never enter master state. As previ- ously mentioned, the ultimate master clock in the timing network is called the grandmaster clock. In some PTP profiles, the port state is fixed, and therefore, there are two types of ordinary clock: an ordinary master with one master port and an ordinary slave clock with a single slave port. In this case, master clocks cannot take time from another clock, and slave clocks cannot give time to an- oth