The user can configure one or more service type IDs for each RLBG. The
user can also configure the Cisco CMTS, using CLI or SNMP, to restrict a
particular cable modem to a certain STID and RLBG ID. However, if such a
configuration is made, both the STID and RLBG ID in the configuration file are
ignored by the Cisco CMTS.
When the STID is
configured by CLI or SNMP or the STID is present in the cable modem
configuration file, the Cisco CMTS selects an upstream and downstream channel,
which offers the signaled service type, from a RLBG, if such channels exist.
However, if an upstream and downstream channel do not exist that provide the
signaled service type the Cisco CMTS assigns an upstream and downstream channel
that does not offer the signaled service type.
When the LBG ID is
configured by CLI or SNMP or the LBG ID is present in the cable modem
configuration file, the Cisco CMTS examines the available choices for upstream
and downstream channels and, if they include a channel pair associated with the
signaled LBG, the Cisco CMTS assigns the cable modem to the signaled LBG. If
these conditions are not met, the Cisco CMTS disregards the LBG ID.
If there are
multiple upstream and downstream channels available that meet the requirements
of the STID, if present, and the LBG ID, if present, the Cisco CMTS selects an
upstream and/or downstream channel that meet the cable modem required and
forbidden attribute masks requested in the configuration file. If upstream and
downstream channels are not available that meet these criteria, the Cisco CMTS
can disregard the cable modem attribute masks and select an alternative
upstream and/or downstream channel.
In determining a
target channel pair for a cable modem during registration time, the Cisco CMTS
tries to find the target channel pair that can actually reach the cable modem
by checking the current channel pair, the MD-DS-SG-ID (Media Access Control
Domain Downstream Service Group Identifier) of cable modem (CM-DS-SG-ID) and
the MD-US-SG-ID (Media Access Control Domain Upstream Service Group Identifier)
of cable modem (CM-US-SG-ID), if present, and fiber node (FN) configurations.
If the target channel pair is available to the cable modem and is different
from the current channel pair, the Cisco CMTS is required to move the CM by
means of DCC technique 0 or downstream frequency override (DFO).
When the Cisco CMTS identifies multiple
candidate RLBGs for a CM, but cannot determine which fiber node configuration
the cable modem is actually wired to, or cannot determine if the wired RLBG is
unusable (when interfaces in the load balance group are disabled or in an
administratively down state), the Cisco CMTS assigns the cable modem to the
RLBG with the lowest group index. This assignment causes the Cisco CMTS to
attempt to move the cable modem to interfaces it is not physically connected
to, resulting in service outages for the CM.
The Cisco CMTS enforces fiber node
checking during RLBG assignment.
The Cisco CMTS
follows the following RLBG assignment rules:
- If there is no fiber node
configuration, there is no change in the candidate RLBG list. However, if the
fiber node is configured, the fiber node must be configured correctly to
reflect the real fiber node connection.
- If the cable modem is
inside a fiber node, only those RLBGs that are inside that fiber node are
- If the cable modem is not
inside any fiber node, that is, the fiber node configuration does not cover all
the channels, only those RLBGs that are not inside any fiber node are selected.
- If an RLBG spans across
multiple fiber nodes, it is not considered to be inside any fiber node.
- If no candidate RLBG is found, cable
modems are assigned to the GLBG, if the GLBG exists.