Chapter 22: Channel Bonding
STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved. 686
CM Channel Selection
Pre-3.0 DOCSIS cable modems and CMs that have been configured to operate in a pre-3.0 DOCSIS mode use only one
upstream channel and one downstream channel.
Bonded DOCSIS 3.0 CMs
A DOCSIS 3.0 CM assists in the channel allocation effort by determining its own MAC domain downstream service group
(MD-DS-SG). It does this by comparing the MD-DS-SG information that is passed in MAC Domain Descriptor (MDD)
messages against the list of downstream channels that it can find. The MD-DS-SG identifier is transmitted from the CM to
the chassis during the initial upstream ranging process.
As part of the ranging process, the CER also attempts to locate the MD-CM-SG of the CM. It does this by using the MD-DS-
SG that was reported in the initial ranging message and the upstream channel that the CM ranged upon. If these two
pieces of information do not uniquely identify the CM’s MD-CM-SG, then the chassis uses signaling in the ranging response
message to move the CM to another upstream channel which might help resolve its location. In extremely complicated
topologies, multiple upstream channel moves may be necessary.
Once the topology resolution process is complete, the CM downloads its configuration file and begins the registration
process. The CM includes an indicator of the downstream receiver parameters in what is known as a Receive Channel
Profile identifier (RCP-ID) in the registration request. Standard RCPs, which are defined by CableLabs, are supported
natively. Another supported RCP is the vendor-specific one supported by Broadcom 3381-based CMs. RCP-IDs which are
not natively supported in the C4/c CMTS may be supported via explicit RCC provisioning (see Configuration Examples for
Static RCC (page 697)) or by enabling verbose RCPs (see Verbose RCP Reporting (page 695)).
The C4/c CMTS attempts to match candidate RCCs for that RCP-ID to the Channels that are found in the MD-DS-SG. These
RCCs may either be individually provisioned by the operator or they may be automatically determined by the chassis, if it is
provisioned to do so.
During cable modem registration, the ARRIS C4/c CMTS channel assignment algorithm will attempt to fully utilize the
transmission and reception capabilities of each cable modem. The C4/c CMTS will assign channels to the CM based upon
the flow information that is available at registration time — specifically the flow information that is available in the cable
modem's configuration file. Once the receive channel set and transmit channel set for a CM is assigned at CM registration
time, it is not modified during the normal course of operation.
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