Introduction
IRD, Encoder, SMS,, QAM and CAS are five essential part of every Digital Headend. All the processes done by these four Headend Equipments are demodulated and unscrambled by a small device STB. There are many more devices which used in digital headend we have explained that in our other articles.
So today in this article we will cover internal architecture and communication between QAM CAS STB in a single diagram step by step. How these devices are linked with one another and communicating.
Internal Architecture Of QAM CAS & STB
As shown above in the figure there is a brief internal architecture of QAM, CAS Server and STB with communication links. This is the step by step process for understanding the functions of QAM, CAS and STB only. Which make us more easy to understand the working of digital headend.
This QAM have two inputs DVB-S2 and IP Inputs that depends upon your requirement, you need to just change the module. A DVB-S2 input signal contains both FTA and Encrypted services. The encrypted services passes through de-scrambler which gets descrambled by using the Control Word from Smart Card Section. After that it gets demuxed.
On the other hand if you are using IP Input port then your IP goes directly into the MUX for multiplexing. Now the output of the MUX goes into the scrambler. Now this Scrambler gets the CW for scrambling from Control Word Generator. It provides scrambled output. Meanwhile this control word is also sent to the ECM Encryptor. Now the output of ECM Encryptor and EMM Encryptor goes for mixing.
Now this scrambled output after mixing goes into the STB. Where ECM EMM goes to smart card section to provide the Control Word to Descrambler. Now this decrambler receive the streams and descramble it by using the Control Word. Then after it goes for Demultiplexing which is performed by DEMUX as shown in STB sections above.
After demultiplexing the final output of stb goes into the Televison.
Conclusion
In this article we have explained internal architecture of QAM CAS and STB and their working how they works. A diagram have shown above which explain itself its working. Because it is step by step process. This diagram explain many hidden concepts of Digital Headend.
Above shown QAM is a standard which can accept DVB-S2,or DVB-T2 or IP inputs of services for multiplexing and scrambling.
The Smart Card Section contains the CAM Module so that we can insert the smart card for decryption of premium services. If you want to know more about CAM Module then you can find it here
If you want to know more about DVB-S2 then you can find it here
Supportive Articles
What Is Statistical Multiplexing ?
What Is AES Encryption Algorithm ?
