Chapter 1 Introducing the Model DPR2320, DPR2325, EPR2320, and EPR2325 Cable Modem Gateways
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Theory of Operation
This section summarizes the theory of operation for cable modem gateways and
provides a high-level overview of the operational stages for the cable modem
gateway. Reading this chapter provides a better understanding of how cable modem
gateways operate.
Note:
This section is not intended to be a specification for the cable modem gateway.
Cable Modem Initialization
A cable modem gateway must establish a communication link with the headend
before it becomes fully operational. This section describes the eight DOCSIS-
required operational stages through which a cable modem gateway progresses in
establishing this communication link.
This section provides a detailed explanation of each of the following operational
stages.
1
Scan for Downstream Channel
2
Obtain Upstream Parameters
3
Adjust Timing Offset and Power Level
4
Establish IP Connectivity
5
Establish Time of Day
6
Transfer Operational Parameters
7
Register with the Cable Modem Termination System (CMTS)
8
Initialize Baseline Privacy
Scan for Downstream Channel
When a cable modem gateway powers on, the cable modem gateway starts to scan
the network for the CMTS downstream channel. The downstream channel is the
channel used to send data from the CMTS to the cable modem gateway. The cable
modem gateway identifies a valid downstream data channel as a channel that has
QAM signal timing, forward error correction (FEC) framing, MPEG packets, and
downstream media access control (MAC) messages. The CMTS terminates the cable
modem gateway signal at an upstream location and provides the cable modem
gateway with a network connection.
This section discusses the cable modem gateway downstream scanning routine
along with two features that speed up the downstream scanning process: the Valid
CMTS Frequency Table and the WebWizard Gscan function.
