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Chapter 11 - DOCSIS Analyzer
10713 Vxx.11
11.6
Sequence of a measurement
After the measuring receiver is connected to a multimedia socket (or another point at which the
DOCSIS connection can be tested, for example, a return channel amplifier), the measuring receiver
should be tuned either by entering the channel of a known DOCSIS DS channel directly or by
scanning for a valid DS channel. A summary of the US measuring parameters starts in the
graphical display. The DS can be assessed qualitatively in the measured value display.
Since, in practice, a measured value update comes once every 5 to 20 seconds during continuous
ranging, the instrument-internal beeper signals when the measured values were updated and the
CMTS sent positive feedback (“Ranging complete”) on the last data exchange. This makes the
work easier, such as, when adjusting the return channel amplifiers. If the beeper is activated, the
user knows that a correct value for the required US transmitting power is present.
If a cable network operator offers several US and DS channels, ranging may not function on the
selected DS. In this case, scanning should take place after the next DOCSIS downstream, or, if
known, a new DS frequency should be entered directly.
As was described above, the DOCSIS 3.0 analyzer can be used to perform further tests, in addition
to pure US and DS level tests, after successful ranging.
11.7
Ingress measurement
An important measuring parameter with return channel capable systems is ingress (interference
level through external stray pick-up in the coaxial cable).
The measuring receiver can assess ingress with the aid of the spectrum analyzer (see also chapter
15.13 - Ingress measurement in the return path and Chapter 8 - RC (Return Channel) Measuring
Range)).
11.8
Notes regarding compatibility
Basically, up to DOCSIS 3.0 the different DOCSIS standards (1.0, 1.1, 2.0 and 3.0) are downward
compatible with one another. This means that the DOCSIS analyzer generally operates with any
head end.
However, if a cable network operator has issued only DOCSIS 2.0 modems to its customers, for
example, and no longer has any 1.1 modems in circulation, it can switch off mixed mode and
change over to pure DOCSIS 2.0 or DOCSIS 3.0 operation.
Starting from DOCSIS 3.1, only a downward compatibility down to DOCSIS 3.0 is possible, older
standards are not supported.
Additionally, there are some network operators that identify a modem using the MAC address and
assign it to a customer during the very first ranging. It can therefore happen that measurement is
only possible once the measuring receiver's MAC address has been configured in the head end.
The MAC address can be read out. (see chapter 17.6- MAC ).
However, the above aspects are dependent on the operator.
11.9
Further information
Further information for measuring using the DOCSIS 2.0/3.0 analyzer can be found in application
note “AN004 – DOCSIS 3.0 analyzer“. This is available from the homepage www.kws-electronic.de
in the support section (“SUPPORT” – “Application Notes”).
For DOCSIS 3.1 topics you can refer the Application Note "DOCSIS 3.1 Analyzer".
