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Chapter 11 - DOCSIS Analyzer
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Figure 11-4 DOCSIS selection of modulation scheme
The associated symbol rate is automatically set.
Automatic scan of the DOCSIS variant:
If you enter a new channel, the receiver attempts to synchronize with the current settings (DOCSIS
variants, modulation schemes). If this is not successful, the instrument alternatively uses the other
settings EUDOC64, EUDOC256, USDOC64 or USDOC256 to receive the signal that is present.
The graphic display begins to show a summary relating to the DOCSIS analysis.
In addition to the direct channel entry of a known DOCSIS DS channel, it is also possible to carry
out an automatic scan of the entire TV frequency band (see also chapter 6.2.2.1.2 - Scan).
11.4.1
DOCSIS DS parameters
As soon as the receiver has completed the DS synchronization process, several parameters are
shown in the measured value display. When LOCK appears, it means that the digital receiver is
receiving a valid data stream. In contrast, UNLK means that either the quality of the signal that is
present is insufficient, or that the parameters of the receiver do not agree, or that no DOCSIS
signal can be received at this frequency.
Once the receiver synchronized the DOCSIS analyzer queries whether valid DOCSIS packets are
being received. Is this the case, the indicator on the graphic display under the “Downstream” item
changes from “Scan running...” to “Valid”.
11.4.2
DOCSIS US parameters
After a valid DS is detected, the analyzer automatically extracts the upstream parameters from the
downstream information. The most important are shown on the graphical display.
Communication with the CMTS is now established. During this, the transmitting power and other
important parameters for problem-free communication between the cable modem and head end
are set iteratively. This process is called “ranging.” The current transmitting power is shown on the
graphical display. After the first successful ranging, the screen on the graphical display under the
“Ranging” item switches from “running...” to “finished”.
After the cable modem and the CMTS have been synchronized, the analyzer switches to a mode
for continuous ranging, which means that communication with the CMTS is maintained and the
transmitting power on the graphical display is updated after every data exchange.
