MPM-1000A Operator Manual
1000-7075 Rev E
15-8
15.14 Network Initiation
Any Terminal designated “NC capable” within the NCW network may operate as the
NC. The first NC capable Terminal to begin operation under the Satellite becomes the
NC. Terminals joining the network after that assume the role of member Terminal.
In order to initiate a network and assume operation as the NC, the Terminal must have
a stored MSK. All MSKs shall have an effective period identified along with the seed key
data. This effective period is set at the MSK generating station and is logically bound to
the MSK seed key data.
The effective period of an MSK is specified by an Effective Date value, which identifies
the beginning of a six-month period in which the MSK may be used for network
initiation. The Modem will not initiate a network if the current UTC date falls outside the
effective period identified within the MSK. MSK Effective Dates are calculated at
12:00:00 AM UTC on the first Monday of the month in January or July in any given year.
It is important to observe that the MSK effective date governs only the use of the MSK
for network initiation. It is possible, and permissible, for operational TRANSEC keys
derived from an MSK to be used outside the effective date period of the MSK. This will
occur during the six-
week “grace” period that follows the nominal six-month effective
period of the MSK. If the network is restarted after the nominal six-month period,
however, it must be restarted using a new MSK.
The soon-to-be NC must determine which one of the 32 MEKs will be used to initiate
the network. The MEK will be selected using the current UTC date, offset from the
effective date of the MSK. This is accomplished as follows. The Modem will determine
which
“week-of-year” the current UTC date falls into. This value will fall between 1 and
52. If greater than 26, the integer 26 will be subtracted from the week-of-year so that
only the integers 1 through 26 are possible. This adjusted week-of-year value identifies
the MEK number that will be used at network initialization.
In addition to the MEK selection, the NC will determine the initial Frame Number. This
value will be derived from the current UTC date and time as follows. First, the second-
of-week is calculated as follows: Second-of-week = 86400(0-6 days) + 3600(0-23
hours) + 60(0-59 minutes) + seconds. This second-of-week value is then divided by
0.400 to obtain the initial Frame Number.
15.15 TRANSEC Key Rollover
TRANSEC key rollover is directed by the NC. The timing of the rollover is tied to the
network frame count, which increments from zero through 1,511,999 during the course
of a TRANSEC crypto-period. Using a frame length of 400 msec, then 1,512,000 frames
exist during a crypto-period. Eight frames prior to frame count 1,512,000, the NC
Terminal begins transmitting Frame Countdown (n) FOWs. The countdown counter
decrements from 7 to 0. The network begins using the new TRANSEC key (MEK) in the
frame immediately following Frame Countdown (0).
