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Chapter 11 - DOCSIS Analyzer
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The primary channels in the downstream contain SYNC and UCD messages; the secondary
channels do not. Primary channels can be used to create a connection between a modem and
CMTS; secondary channels are used only for data rate multiplication. The primary downstream
channel is shown in green in the graphic. The channels bundled with the primary channel appear in
yellow. In some systems, all bundled downstream channels are primary channels. Other systems
contain only one primary downstream. In the latter case, the download data rate is higher because
the sync and UCD messages are sent on one channel only, which avoids the associated overhead.
For the upstream channels, there is no distinction between primary and secondary channels. In the
diagram, the upstream through which the modem was able to successfully establish a connection
with the CMTS is shown in green. The upstream channels bonded to this during subsequent
registration are shown in yellow in the diagram.
The DOCSIS 3.0 analyzer supports the bundling of up to 8 downstream channels, although these
must be within 64 MHz. Up to 4 bundled upstream channels are supported.
The top figure shows the graphic screen of the DOCSIS 3.0 analyzer following successful ranging
in a DOCSIS 3.0 system.
Depending on the cable network operator, the US or DS frequency could automatically change
during measurement. This is because in systems with several upstream and downstream
frequencies, CMTS can force the modem onto other frequencies in order to balance the load
across all channels. In the measurement parameter range, you can always read the frequency or
channel on which the modem is currently using to receive data. The same applies to the DOCSIS
analyzer display. The frequency on which the modem is currently using to transmit is always
marked on the upstream display. In theory it is also possible for further US parameters to change
during measurement.
11.4.3.1
Downstream analysis
You can open the menu by pressing the
MODE
key. You can navigate around the menu using the
arrow keys and the
ENTER
key. The figure below shows the graphic that appears after choosing
the
DOWNSTREAM
menu item.
Figure 11-6 DOCSIS downstream analysis
Each bar represents a DS channel. You can use the
←/→
keys to select the relevant channel in
the graphic. The currently selected channel is highlighted in red. The information shown below
applies to the selected channel.
