user manual

Configuring Headend Broadband Access Router Features
Configuring the Upstream Cable Interface
MC-560
Cisco IOS Multiservice Applications Configuration Guide
You can set fixed start and end values for data backoff on the upstream ports, or you can set the upstream
ports for automatic data backoff. You have the same options for ranging backoff. For both backoff
windows, the default start value is 0; the default end value is 4. Valid values are from 0 to 15.
To set data or ranging backoff values for an upstream port, use one or more of the following commands,
beginning in cable interface configuration mode:
When considering whether or not to adjust backoff values, note the following:
• The cable modem 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 percent load
under normal situations, but can jump to over 100 percent after an outage.
– Adjusting the backoffs to larger numbers slows cable modem reconnection and reduces server
load.
– Backoffs that are too small result in cable modems 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 modem performance (brand to brand) in cable modem
restart time.
• All cable modems should recover in approximately 0 to 10 minutes after all services are restored
(Cisco uBR7200 series, RF transport, DHCP/TFTP/TOD servers). If cable modems take longer than
10 minutes to recover, there could be a problem in the cable modem, in the headend settings, or in
the DOCSIS provisioning servers.
Note Upstream segments serving a relatively large number of cable modems (for
example, more than 1600 or so) may suffer recovery times longer than
10 minutes.
Command Purpose
Step 1
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 up to 250
cable modems per upstream port. Set manual values
for data backoff windows only when operating with
more than 250 cable modems per upstream port.
Configures the default backoff window values of 0
and 4.
Step 2
CMTS01(config-if)# cable upstream usport range start
end
or
CMTS01(config-if)# cable upstream usport range
automatic
The automatic setting is optimized for up to 250
cable modems per upstream port. Set manual values
for ranging backoff windows only when operating
with more than 250 cable modems per upstream port.
Configures the default backoff window values of 0
and 4.