 increase by approxim- ately 2,600,000 per month or 31,100,000 per year. The nanosecond field can range from zero to 999,999,999 even though it is a 32-bit integer. PTP can run one of two timescales: PTP timescale: The epoch is the PTP epoch. ARB timescale: Arbitrary = the epoch is specific to the implementation. The ARB timescale can be basically whatever the operator or engineer desires it to be. Under nor- mal operations, it is, like PTP, a continuous timescale. However, under normal deployments in the telecoms world, you should not see ARB, SO seeing it means that something is wrongly configured or there is an operational issue. 7.3.1 The Announce Message The Announce message is sent out regularly to announce the capabilities of the PTP port, and de- pending on the profile, it is transmitted at a rate between eight every second to once every eight seconds. There is also a timeout mechanism whereby the operator configures the slave port with a timeout value that fixes the maximum number of messages allowed to be "missed." For proper op- eration, it is recommended that the Announce timeout should be uniform across a domain. For example, if the configured rate of Announce is four per second, and the timeout is four mes- sages, then the slave would declare a timeout after not receiving any Announce messages for one second. According to IEEE 1588-2008, the allowable timeout range is from 2-255 messages but can be further constrained by a PTP profile. IEEE 1588 suggests that the minimum value should be 3. See IEEE 1588-2008 section 9.2.6.11 on the Announce receipt timeout expiry for more details. The Announce message contains the following fields (see IEEE 1588-2008 section 13.5): Common PTP header: Includes the domain number, clock identity, and port identity. There are also flag fields in the header that are used in combination with the Announce message. This in- cludes information about upcoming leap events, whether the GM is traceable to sources of time and frequency, and whether the UTC offset value is valid. 