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Configuring Subscriber-End Broadband Access Router Features
Subscriber-End Broadband Access Router Initial Power-Up Sequence
MC-627
Cisco IOS Multiservice Applications Configuration Guide
Next, the Cisco uBR900 series performs a series of DOCSIS-mandated procedures for automatic
installation and configuration. These procedures are summarized in Table 40 and in Figure 114.
.
Table 40 Cable Access Router Initialization Sequences and Events
Sequence Event Description
1. Scan for a downstream channel
and establish synchronization
with the CMTS.
The Cisco uBR900 series acquires a downstream
channel by matching the clock sync signal that is
regularly sent out by the CMTS on the downstream
channel. The cable access router saves the last
operational frequency in nonvolatile memory and tries
to reacquire the saved downstream channel the next
time a request is made.
Note An ideal downstream signal is one that
synchronizes QAM symbol timing, FEC
framing, and MPEG packetization, and
recognizes downstream sync MAC layer
messages.
2. Obtain upstream channel
parameters.
The cable access router waits for an upstream channel
descriptor (UCD) message from the CMTS and
configures itself for the upstream frequency specified
in that message.
3. Start ranging for power
adjustments.
The cable access router waits for the next upstream
bandwidth allocation map message (MAP) from the
CMTS to find the next shared request timeslot. The
router then sends a ranging request message on the
next available shared request timeslot, communicating
its UID (its unique MAC address) using a temporary
SID of 0 (zero) to indicate it has not yet been allocated
an upstream channel.
In reply to the cable access router ranging request, the
CMTS sends a ranging response containing a
temporary SID to be used for the initial router
configuration and bandwidth allocation. As needed,
the router adjusts its transmit power levels using the
power increment value given by the CMTS in its
ranging response message.
Note At this point, the cable access router has
established connectivity with the CMTS but is
not yet online. The next steps allocate
“permanent” upstream and downstream
frequencies, and the configuration required for
IP network connectivity.