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Digital or Analogue CAS
Three to four years ago, cable operators in Europe and America decided
to change their CAS from analogue to digital. Mainly, this was in
an attempt to preserve their business from the satellite (DTH) threat.
They were also being attacked by pirates stealing the signals. History
now tells us this move to digital was a mistake.
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Digital CAS was the vehicle of choice for European cable operators
in the last few years. It promised security, multiple channel line
up and additional services from which the operator could derive
a further revenue stream. Companies such as NTL and Telewest in
the UK, Kirsch in Germany, UCN in Europe and Adelphia in the USA
invested many hundreds of millions in the new technology. They purchased
new headends, new set top boxes but they underestimated the size
of the task required to upgrade their networks to take the digital
signals. All of the above mentioned companies are now in Chapter
11, the American equivalent of bankruptcy, due partially to the
escalating costs of running a digital network.
Digital CAS promised much but delivered little. Security, the much
vaunted holy grail of digital, was compromised. Indeed, the encryption
algorithms of a leading CAS company were posted on the World Wide
Web. This has resulted in a multimillion dollar law suite and a
statement from a prominent CEO admitting there can never be a secure
system. Additional revenue from the added services such as internet
access has failed to emerge as cable operators the world over find
that subscribers are only prepared to pay a certain percentage of
their disposable monthly income on TV services, irrespective of
whether they are video or internet.
Digital set top boxes are not tolerant of input power, slope and
reflections on the network. All of these problems will cause picture
"blocking" resulting in subscriber dis-satisfaction. Solutions to
these problems are usually expensive, take a lot of time and require
bespoke engineering.
Analogue CAS has served cable operators well for many years. Traditional
systems have suffered in recent years from piracy of signals and
the stigma of being associated with old technology. However, today's
facts paint a different picture. Analogue systems based on sync
manipulation and inversion techniques are indeed relatively easy
to defeat. It is to these types of system that people refer when
they claim that analogue CAS cannot be secure.
The more recent and advanced systems use full digital technology,
within the box, to produce a highly secure yet cost effective solution.
Using techniques such as cut and rotate, line shuffle or a combination
of both produces video which is extremely obscure and practically
impossible to reconstruct without massive computing power and access
to extreme electronics. Indeed, a situation exactly the same as
a traditional digital system.
Analogue systems can provide additional services such as NIPPV,
internet access and others where applicable. These are normally
achieved through either a telephone or cable modem. Analogue systems
have the benefit of being extremely tolerant of cable system imperfections.
They can accept a wide range of input powers, at least five or six
times larger than a digital unit; they do not mind about adjacent
channel slope and they are resilient to reflections on the network.
The time and therefore cost to implement an analogue solution is
many times less than that for a digital solution.
* Richard Chamberlain
The author is CEO Dalvi Technology Ltd (UK). The views expressed
in this article are his own.
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