NSG 9000-6G - Harmonic Inc

Chapter 5
Conditional Access System (CAS)
5.1 CAS Overview
The Conditional Access System (CAS) prevents unauthorized viewing of programs by
scrambling services that later on can be decrypted using the correct decrypting key.
NSG devices support the following CAS modes:
• DVB SCR scrambling - an encryption mode for the DVB protocol.
• Privacy Mode - an encryption mode developed by Motorola Inc.
5.1.1 DVB SCR Scrambling Overview
A typical CAS is comprised of a few elements. The NSG 9000 includes the SCS, CWS and
scrambling modules. Following is a short description of the CAS elements.
• Event Information Scheduler (EIS) - in charge of all of the headend’s schedule information
and the CAS configuration to ensure that services are encrypted correctly. It initiates the
Scrambler Control Group (SCG) message, the actual request sent by the EIS to the NSG
9000 that encryption is required.The SCG message includes the service ID, time slot and
the access criteria.
• SimulCrypt Synchronizer (SCS) - controls and manages the scrambling parameters to
allow encryption. It receives requests for encryption and passes them on to the Control
Word (CW) generator. Once a CW is initiated the SCS passes it to ECMG.
• Control Word Server (CWG) - generates the encryption key.
• Scrambling Unit - encrypts the services.
• Entitlement Control Message Generator (ECMG) - receives control words and access
criteria and generates an Entitlement Control Message (ECM) stream in return.
ECMG
ECM
CW & ACC
EIS
SCG
message
SCS
CWG
NSG 9000
clear input
stream
Scrambling
unit
scrambled Output
stream
The EIS sends the NSG 9000 an SCG message, a request to encrypt a service component. In
turn, the NSG 9000 sends a message to the ECMG which contains the following:
• Control Word (CW) - the encryption key generated by the NSG 9000.
© 2012 Harmonic Inc. 101 NSG 9000-6G, Version 2.7, Rev B