 multiple do- mains (in theory), although a PTP port can belong to only one single domain. The operation of PTP in one domain is independent from the operation of PTP in other domains in the same network- meaning they do not talk to one another. The value for a domain can vary between 0-255, but values of 128-255 are reserved (although 254 is used for the C37.238 Power Profile) and 0 is normally known as the default domain. The legal values for domain number are typically specified (and limited) by the PTP profile, and most profiles take a range of domain numbers from between the values of 4-127. Generally, a limited number of domains are deployed throughout the network, at least in the case of the telecom profiles, which normally include only one or maybe two domains. The use cases of some industries (such as MiFID-II compliance) can deploy several independent domains and allow them all to flow through the network. The slave devices can recover the clock not only from several PTP domains but also NTP and other time transports. They use the diversity of sources to "elect" the time sources most accurately agreeing with each other about the value of the current time- mostly represented by Coordinated Universal Time (UTC). 7.3.1 Message Rates Most message rates for PTP fit within the range of one message every 64 seconds to one every 128th of a second. PTP expresses these message rates as a logarithmic value (to base 2) of the time interval between messages. This gives a value range for the log of inter-message period of -7 to +6 as outlined in Table 7-1. Table 7-1 Log of Inter-Message Interval Rates Message Interval Log of Inter-Message Interval Message Interval Log of Inter-Message Interval 1/128 second 1 second 1/64 second 2 seconds 1/32 second 4 seconds 1/16 second 8 seconds 1/8 second 16 seconds 1/4 second 32 seconds 1/2 second 64 seconds Definitions of message rate in the IEEE 1588-2008 standard are always expressed in these terms, not as a rate, but as the logarithm (base 2) of the interval between messages. 