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When the SCS receives an SCG provisioning message update from the EIS indicating
the end of the running CA event, the synchronizer extends the last Crypto Period
until the end of the activation time extracted from the SCG provisioning message
update.
Once the activation time (tl) is reached, the set top box stops descrambling the
service. The SCS stops transmitting ECMs attached to this last Crypto Period at time
(tl+1).
Transition Stop Delay (tl-tl+1): represents the amount of time between the end of
last Crypto Period preceding a scrambled to clear transition, and the end of the
broadcasting of the ECM attached to this period.
When the SCS receives a SCG provisioning message containing another AC for the
service(s), the synchronizer stops sending ECMs containing the previous AC at time
t6 in the last Crypto Period and starts sending ECMs with the new AC at time (t7).
AC Start Delay (t7-t8): represents the amount of time between the start of the
first Crypto Period following a change in the AC and the start of the
broadcasting of the ECM attached to this period.
AC Stop Delay (t6-t8): represents the amount of time between the end of the
lastCrypto Period preceding a change in AC and the end of the broadcasting of
the ECM attached to this period.
During the connection setup between the SCS and the ECMG, the SCS receives a
Channel Status Message containing particular timing parameters. When timing
parameters are missing or inaccurate, the Scrambler ECMG settings allow overruling
these parameters.
When a subscriber tunes into a scrambled service in a particular Crypto Period, the
scrambler is not able to scramble the service during the rest of this Crypto period
because he has only the CW for the next period. To solve this problem, an ECM can
be provided with more than one CW. CA Systems allow 1 or 2 CWs in an ECM, for
example, the CW of the current Crypto Period and the CW of the next period.
78-4025112-01 Rev H0
Timing Parameters
179
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