Cisco 7246VXR - uBR Router Software Configuration Manual page 212

Configuring the Upstream Cable Modem Interface
Command
Step 1
Router(config-if)# cable upstream
usport data-backoff start end
or
Router(config-if)# cable upstream
usport data-backoff automatic
Step 2
Router(config-if)# cable upstream
usport range start end
or
Router(config-if)# cable upstream
usport range automatic
When considering whether to adjust backoff values, keep the following considerations in mind:
•
•
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 u0
Cable5/0 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)
Tx Backoff Start 0, Tx Backoff End 4
Modulation Profile Group 1
part_id=0x3137, rev_id=0x03, rev2_id=0xFF
nb_agc_thr=0x0000, nb_agc_nom=0x0000
Range Load Reg Size=0x58
Request Load Reg Size=0x0E
Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
3-20
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 uBR7200 series, 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.
Upstream segments serving a relatively large number of cable interfaces (for example, more
Note
than 1600) might suffer recovery times greater than 10 minutes.
Purpose
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.
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.
Chapter 3 Configuring Cable Modem Interface Features
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