Chapter 11 - DOCSIS Analyzer
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Each DS channel in the system has a unique identification (ID) that is displayed after the
corresponding frequency.
The DS duty factor provides information on how many MPEG packets of the DS data stream, the
DOCSIS PID (pack identification) 0x1FFE carries in relation to all the incoming packets. The load is
shown only for the primary channel marked in green.
11.4.3.2
Upstream analysis
Select the
UPSTREAM
menu item from the main menu to view additional information about the US
channels.
Figure 11-7 DOCSIS upstream analysis
Each bar represents a US 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.
Each US channel in the system has a unique identification (ID) that is displayed after the
corresponding frequency.
Select the
ADVANCED
and
FRQRESP
menu items to view additional US information. This
information is described in more detail in the following sections.
As many DOCSIS modems communicate with the CMTS on the same upstream frequency the
modems must therefore share an upstream channel. The access method to achieve this can be
read on screen. For DOCSIS1.1 only TDMA (time division multiple access) is offered as an access
method. The modems share the upstream bandwidth such that each modem only transmits in
specially reserved time slots. A-TDMA (advanced TDMA) or S-CDMA (synchronous code division
multiple access) are also optionally used for DOCSIS2.0 and 3.0. For A-TDMA, as opposed to
DOCSIS1.1, it is also possible to transmit upstream with 64QAM at a symbol rate of 5120kSymb/s.
For S-CDMA, several modems can transmit simultaneously on one frequency. The CMTS assigns
messages to the individual modems according to special codes and the mathematical formula of
correlation. The CMTS specifies the access method which is binding for all connected modems.
During ranging, the CMTS sends correction values regarding the transmission power to the
modem. You can view the correction values under “Level offset” on the graphic display. The
modem continuously adjusts its transmission power so that the level offset is zero. That means that
messages that are sent by the modem arrive at the CMTS at the required level.