Installation guide

3-22
Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
Chapter 3 Configuring the Cisco Cable Interface
Configuring the Upstream Cable Interface
Note Cisco does not recommend you adjust default values, but enable the automatic dynamic backoff
algorithm. Refer to the “Configuring Dynamic Contention Algorithms (Cable Insertion Interval, Range,
and Data Backoffs)” section on page 5-4.
To set data or ranging backoff values for an upstream port, use one or more of the following commands,
in cable interface configuration mode.
When considering whether to adjust backoff values, keep the following in mind:
• The cable interface reconnection time after a power outage is related to the following factors:
– DHCP, TOD, and TFTP server capacity. These servers often operate well below 1% load under
normal situations, but can jump to over 100% after an outage.
– Adjusting the backoffs to larger numbers slows cable interface reconnection and reduces server
load.
– Backoffs which 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 which 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 between approximately 0 to 10 minutes after all services are
restored (Cisco uBR7100 series, RF transport, DHCP/TFTP/TOD servers). Cable modems taking
longer than 10 minutes could indicate a problem in the cable modem, in CMTS settings, or 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.
Command Purpose
CMTS01(config-if)# cable upstream
usport
data-backoff start end
or
CMTS01(config-if)# cable upstream
usport data-backoff automatic
The automatic setting is optimized for as many as 250
cable interfaces per upstream port. Set manual values for data
backoff windows only when operating with more than 250
cable interfaces per upstream port.
This command configures the default backoff window values
of 0 and 4.
CMTS01(config-if)# cable upstream
usport
range start end
or
CMTS01(config-if)# cable upstream
usport
range automatic
The automatic setting is optimized for as many as 250
cable interfaces per upstream port. Set manual values for data
backoff windows only when operating with more than 250
cable interfaces per upstream port.
This command configures the default backoff window values
of 0 and 4.