Cisco DNCS System Release 2.7 3.7 4.2 デザインガイド
4000358 Rev B
Introducing DOCSIS
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System Description,
Continued
DOCSIS Settop Gateway (DSG)
For DHCTs operating in DOCSIS mode, DBDS broadcast data must be carried over
the DOCSIS channel through a DSG-compliant CMTS. To accomplish this
communication, DSG definitions are established on the CMTS to act as gateways for
the DBDS broadcast data that must be delivered to the DHCTs in each of the
DOCSIS MAC domains of the CMTS as specified in the DOCSIS Set-top Gateway
(DSG) Interface Specification.
Each CMTS DOCSIS MAC domain has a single definition for DBDS broadcast data.
Each CMTS DOCSIS MAC domain has a single definition for DBDS broadcast data.
Each DSG definition takes IP packets matching its destination address and
encapsulates them in an Ethernet frame, using a well-known Cisco MAC address.
All DSG definitions use the same well-known Cisco MAC address; the DHCT filters
on the well-known Cisco MAC address. By using this MAC address, DHCTs
operating in DOCSIS mode can receive DBDS broadcast data without establishing an
interactive communications path with the CMTS. Therefore, if the upstream plant is
impaired, there is no impact on the DHCT’s ability to receive DBDS broadcast data.