Cisco RF Gateway 1 Modules, Configuration Manual

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Entitlement Control Messages
78-4025112-01 Rev H0 173
Entitlement Control Messages
The SCS triggered from the EIS to start a CA event will get every Crypto Period a
CW for this event from the CWG. For more information, refer to
Event Information
Scheduler (on page 174).
The SCS extracts the AC from the Scrambling Control Group (SCG) information
received from the EIS. The synchronizer sends this AC together with the CW for the
corresponding Crypto Period to the Entitlement Control Message Generator
(ECMG). The ECMG encrypts both the AC and the CW using a particular
cryptographic algorithm with a specific Service Key. This encrypted data is
encapsulated into an ECM and sent to the SCS.
Before the first Crypto Period for this event begins, the SCS starts sending ECMs for
this event to the multiplexer (typically every 200 msec). This start time is necessary
to give the descrambler time to decrypt the encrypted CW and AC. The multiplexer
multiplexes this stream of ECMs with the outgoing Transport Stream. When the
event begins, the SCS sends the CW to the scrambler, which starts scrambling the
service(s) associated with this event.
Before the end of the Crypto Period, the SCS requests a new CW from the CWG,
then sends it together with the AC to the ECMG, and receives a new ECM for this
event from the ECMG. This new generated ECM is multiplexed in the outgoing
Transport Stream. When the Crypto Period is ended, the new CW is sent to the
scrambler, which starts scrambling the service(s) using the new CW. This occurs for
every Crypto Period until the end of the event.