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Cisco uBR10012 Universal Broadband Router Software Configuration Guide
OL-1520-05
Chapter 3 Configuring Cable Interface Features for the Cisco uBR10012 Router
Configuring the Upstream Cable Interface
When considering whether to adjust backoff values, keep the following considerations in mind:
•
The cable interface reconnection time after a power outage is related to the following factors:
–
DHCP, ToD, and TFTP servers often operate well below 1 percent load under normal situations,
but can jump to over 100 percent after an outage.
–
Adjusting the backoffs to larger numbers slows cable interface reconnection and reduces server
load.
–
Backoffs that are too small result in cable interfaces failing to range the upstream RF levels
correctly and cycling to maximum power, thus increasing connection time and reducing
network performance.
–
Backoffs that are too large result in increased recovery time after a large service outage.
–
There is significant variation in cable interface performance (brand to brand) in cable interface
restart time.
•
All cable interfaces should recover in 0 to 10 minutes after all services are restored
(Cisco uBR10012 router, RF transport, DHCP, TFTP, and ToD servers). A CM that takes longer than
10 minutes could be experiencing a problem with the modem itself, a problem with CMTS settings,
or a problem in the DOCSIS provisioning servers.
Note
Upstream segments serving a relatively large number of cable interfaces (for example,
more than 1600) might suffer recovery times greater than 10 minutes.
Verifying Upstream Data Backoff
To verify backoff window settings, enter the
show controllers cable
command for the upstream port you
have just configured:
Router#
show controllers cable5/0/0 u0
Cable5/0/0 Upstream 0 is up
Frequency 24.016 MHz, Channel Width 1.600 MHz, QPSK Symbol Rate 1.280 Msps
Spectrum Group is overridden
SNR 33.2560 dB
Nominal Input Power Level 0 dBmV, Tx Timing Offset 2288
Ranging Backoff automatic (Start 0, End 3)
Ranging Insertion Interval automatic (60 ms)
Command
Purpose
Step 1
Router(config-if)#
cable upstream
usport
data-backoff
start end
or
Router(config-if)# cable upstream
usport
data-backoff automatic
Optimizes the
automatic
setting for as many as 250 cable interfaces per
upstream port. Sets manual values for data backoff windows only when
operating with more than 250 cable interfaces per upstream port.
Configures the default backoff window values of 0 and 4.
Step 2
Router(config-if)#
cable upstream
usport
range
start end
or
Router(config-if)#
cable upstream
usport
range automatic
Optimizes the
automatic
setting for as many as 250 cable interfaces per
upstream port. Sets manual values for data backoff windows only when
operating with more than 250 cable interfaces per upstream port.
Configures the default backoff window values of 0 and 4.