Chapter 19: DOCSIS Set-top Gateway Configuration
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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datagram to allow the DOCSIS 3.0 embedded cable modems (eCMs) to do Multicast DSID Forwarding (MDF). When MDF is
enabled, the DSG agent provides the mapping of the multicast destination MAC address to the DSID in a DA-to-DSID TLV
included in the MAC Domain Descriptor.
Two modes of DSG have been defined — Basic and Advanced. The primary difference between the two modes is the use of
the DSG Downstream Channel Descriptor (DCD) message. Basic mode requires that the DSG Agent create and forward data
over DSG Tunnels with "well-known" DSG Tunnel MAC addresses. The DSG Set-top Gateways are configured to listen for
packets with the well-known destination MAC address. In Advanced mode, the DSG Agent broadcasts a table with entries
for each tunnel on the downstream. The DSG Set-top Gateway uses a multi-format Client ID to search the table for
information about the tunnels to which it needs to listen. One of the possible formats of this Client ID is a well-known MAC
address for compatibility with BASIC DSG Set-top Gateways.
The DSG protocol does not require a two-way cable plant; therefore, it does not require the DSG Set-top eCM to perform
DOCSIS registration if the client application does not need two-way service.
Definitions
Conditional Access Entity — The decision-making entity within a DOCSIS Set-top Gateway that parses the DCD message
and determines what tunnels must be connected to the DSG Client.
Conditional Access (CA) — A technology used to control access to digital television (DTV) services for authorized users by
encrypting the transmitted programming. CA has been used for years for pay-TV services. There are many ATSC and DVB-
compliant CA systems from which a broadcaster can choose. The CA system provider provides the equipment and software
to the broadcaster, who then integrates the CA system into his equipment. CA is not designed solely for DTV. It can be
used for digital radio broadcasts, digital data broadcasts, non-broadcast information, and interactive services.
DCD — DOCSIS Set-top Gateway Downstream Channel Descriptor.
DSG Address Table — The collection of DSG Rules and DSG Classifiers contained within the DCD message. The DSG Client
uses its DSG Client ID as an index into the DSG Address Table to determine what DSG tunnel Address to receive.
DSG Advanced Mode — DSG operation that uses the DCD message. Address assignment is dynamic. The DSG tunnel
Address is determined by the DSG Agent and learned by the DSG Client through the DSG Address Table in the DCD
message.
DSG Agent — The implementation of the DSG protocol within the CMTS. The DSG Agent creates the DSG tunnel, places
content from the DSG Server into the DSG tunnel, and sends the content over the DSG tunnel to the DSG Client.
