Cisco RF Gateway 1 Modules, Руководство по настройке

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Chapter 13 Encryption and Scrambling
178 78-4025112-01 Rev H0
Timing Parameters
When the EIS triggers the SCS to start a new CA event using a SCG (ID 1)
provisioning message, the SCS requests a CW (CW 1) from the CWG. Once the SCS
receives the CW from the CWG, the SCS sends the CW together with the AC and
ECM ID extracted from the SCG provisioning message to the ECMG.
The ECMG encrypts the CW and AC and encapsulates this data into an ECM. The
ECMG sends this ECM to the SCS. At a certain time before (t1-t2) starting the CA
event (activation time), the SCS starts sending ECMs for the first Crypto Period at
regular times to the multiplexer.

Transition Start Delay (t1-t2): represents the amount of time between the start of
the first Crypto Period following a clear to scrambled transition, and the start of
the broadcasting of the ECM attached to this period.
The multiplexer multiplexes these ECMs directly into the outgoing Transport
Stream. At the same time, a CA descriptor containing the ECM Packet Identifier
(PID) is inserted into the PMT of the transport stream.
The Transition Start Delay must match the time the descrambler needs to
decapsulate the ECM PID from the PMT and to decrypt the CW and AC. At the start
(t2) of the first Crypto Period (CP 1), the set top box starts descrambling the
scrambled service using CW 1.
At a certain time (t3-t5) before the end of running Crypto Period (CP 1), the SCS
stops transmitting ECMs attached to this CP and at a certain time (t4-t5) before the
next Crypto Period (CP 2), the SCS starts transmitting ECMs for CP 2.

Stop Delay (t3-t5): represents the amount of time between the end of a Crypto
Period and the end of the broadcasting of the ECM attached to this period.

Start Delay (t4-t5): represents the amount of time between the start of a Crypto
Period and the start of the broadcasting of the ECM attached to this period.