Cisco DNCS System Release 2.7 3.7 4.2 Guia Do Desenho
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Frequently Asked Questions
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Questions and Answers,
Continued
How does the OOB data get to the CMTS so that it can use the DOCSIS path to
the DOCSIS-capable DHCT?
DBDS-specific downstream broadcast data that is originated at the DNCS can be
DBDS-specific downstream broadcast data that is originated at the DNCS can be
forwarded through DAVIC QPSK modulators (for DAVIC and Mixed
DOCSIS/DAVIC mode only) and also through the DOCSIS CMTS’s (for DOCSIS
mode only). The DNCS sends the data to the CMTS by encapsulating it within IP
packets and setting the destination IP address to a value that has been configured on
the CMTS. (This same mechanism is used for the DAVIC QPSK transmitters.) For
this data to pass through the CMTS, the CMTS must implement the CableLabs
DOCSIS Set-top Gateway (DSG) Interface Specification. Essentially, the DSG function in
a CMTS accepts data addressed to some provisioned IP address and forwards it to
the DOCSIS downstream channel. The CMTS places a well-known Cisco MAC
address in the “destination address” field of these Ethernet frames. DHCTs that are
operating in DOCSIS mode and are tuned to the DSG CMTS receive the out-of-band
data by accepting all frames with the well-known Cisco MAC address.
Will the DOCSIS-capable DHCT still be able to decode video if the DOCSIS
Will the DOCSIS-capable DHCT still be able to decode video if the DOCSIS
path/CMTS fails?
Yes. Video functions continue to work without interruption. Advanced services that
Yes. Video functions continue to work without interruption. Advanced services that
do not require immediate message exchange also continue to work, though some
interruptions will occur if interactive communication is not restored before protocols
time out. Interactive services are interrupted until the DOCSIS cable modem system
returns to its operational state. The impact of losing the DOCSIS channel is covered
in DHCT Behavior After Initialization in Chapter 1 of this guide.
I have not implemented DOCSIS completely in my system, or I have not yet
I have not implemented DOCSIS completely in my system, or I have not yet
installed System Release 3.0 – can the DOCSIS-capable DHCT be installed in a
DAVIC-only mode?
Yes. When the DOCSIS portion of the system is functional at a later date, the DHCT
Yes. When the DOCSIS portion of the system is functional at a later date, the DHCT
can be rebooted or updated (with a DCM Updated message) to begin using OOB and
high-speed data using the DOCSIS path.