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How does data over coaxial
cable work ?
Two way
transmission of digital data
over coaxial cable uses a
digitally modulated signal
either QPSK or QAM to
transmit data in downstream
direction using any one of
the 6MHz or 8MHz (EuroDOCSIS)
channels. The downstream
signal uses any one channel
between 88MHz to 850MHz.
» Click Here to See Diagram
For
upstream it utilizes the
same cable but frequencies
in the range of 5MHz to
42MHz (65MHz for EuroDOCSIS).
Upstream modulation can be
QPSK or 64QAM. For DOCSIS/EudroDOCSIS
1.0/1.1 a TDMA based
bandwidth allocation
mechanism is used. One
common myth is that two
coaxial cables are required
to provide two way data
communication. Only one
coaxial cable can carry both
downstream and upstream data
over coaxial cable.
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How does data flow
through the IRIS subsystem?
IRIS is a powerful router
that manages the cable
modems on the coaxial cable
network and links them to
the Internet. On both its
cable interface and the
uplink interface you can
activate a rule based
firewall to protect the
cable network. Other
subscribers can be protected
by rules based firewall on
its cable interface with PCs
that may be affected with
malicious viruses.
On the cable interface you
can activate multiple
subnets and put different
users or cable modems in
separate private subnets. On
the cable interface sits the
upstream bandwidth manager
that regulates each cable
modem upstream bandwidth
needs. Cable modems can be
added or deleted from the
subscription list very
easily. New firewall rules
can be applied without
rebooting or any system
downtime. reboot.
» Click Here to See Diagram
IRIS can easily be
configured to operate in a
bridge mode, if you wish to
handle the routing in an
outside router.
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Power level of a digitally
modulated signal
A
digitally modulated
carrier's average power
level is 6dB to 10dB below
the amplitude of what an
analog TV channel at the
same frequency would be.
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What power level is required
at the input to Cable Modem?
The
average power level of the
downstream digitally
modulated carrier at the
cable modem input should be
in the range of -15dBmv to
+15dBmV.
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What is the
carrier-to-noise ratio
required by DOCSIS?
The
DOCSIS minimum
carrier-to-noise ratio is
35dB for both 64 and 256 QAM.
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