During our initial WISP WAN introduction webinar we discussed the PMU registry. One of the functions
of the registry is that during the registration of the device (PMU, DFR, PDC, etc.) a unique 16-bit
identifier is assigned to the PMU.
A brief discussion of the IEEE C37.118-2005 specification.
The C37.118 data frame format is used to transmit synchrophasor data from a PMU to a PDC and then
from the PDC to a RC PDC as was explained in the webinar. The C37.118 data frame contains a header,
the phasor data, and ends with an error check (CRC). The header is of particular interest, it contains the
device identifier. This identifier is 16 bits long (2 bytes) and in programming terms is known as a 16-bit
unsigned integer. This means it can contain a number between 0 and 65,535. No fractions and no
negative numbers. The numbers 0 and 65,535 are identified as reserved and so cannot be used. As you
can imagine this is not a lot of numbers especially if shared by the entire North American area.