Cisco DPC2203C Installation And Operation Manual page 24

Chapter 1 Introducing the Model DPC2203C VoIP Cable Modem
Downstream Scanning Routine
The cable modem starts its own standard scanning algorithm. The scanning routine
of the cable modem is now optimized to seek out the CMTS downstream channel as
quickly as possible. The actual scanning process varies slightly depending on the
television frequency channel plan for your particular country.
For example, in North America the standard downstream scanning routine works in
three phases and may take several minutes. The cable modem stops scanning when
the cable modem finds a valid downstream data channel. The cable modem then
proceeds to the next stage: obtain upstream parameters.
In this example, the cable modem scans for the downstream channel in the following
three phases.
1 The cable modem starts to scan the network at 453 MHz and scans up in 6 MHz
increments to end at 855 MHz.
2 The cable modem starts scanning the network at 447 MHz and then scans in 6
MHz increments down to 93 MHz.
3 The process is then repeated for the National Television Systems Committee
(NTSC) Harmonic Related Carrier (HRC) frequency plan in 6.0003 MHz
increments.
Important: There are specialized frequency plans to optimize the acquisition of the
downstream signal that depend on the video format used in the country of
deployment. Check with the representative who handles your account for more
information about alternate scanning routines outside of North America.
Improved Downstream Scanning Features
The cable modems contain two outstanding features that can speed up the scanning
process: the Valid CMTS Frequency Table and the WebWizard Gscan function.
Valid CMTS Frequency Table
The Valid CMTS Frequency Table feature works automatically and requires no user
intervention. When a cable modem finds a valid downstream data channel so that it
can complete the ranging stage, the cable modem stores this frequency in nonvolatile
memory (NVM). The cable modem checks the frequencies stored in NVM before
starting the standard scanning algorithm to search for a downstream data channel.
Note: The cable modems store up to 10 valid CMTS frequencies in the table.
The standard scanning algorithm also regularly interrupts progressive scanning to
check the last known valid CMTS frequency, and then the cable modem resumes its
standard scanning algorithm where it left off.
8 72-4017315-01 Rev B