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Cisco Broadband Cable Command Reference Guide
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Chapter 2 Cisco CMTS Configuration Commands
cable map-advance
Usage Guidelines
The
max-delay
option, which was introduced in Cisco IOS Release 12.1(10)EC, specifies the maximum
possible round-trip delay between the cable plant and furthest CM in the cable network. A CM will not
be allowed to exceed the maximum timing offset given by the
max-delay
value (in
static
mode) or given
by the combination of the
max-delay
and
safety
values (in
dynamic
mode). If a CM reports a timing
offset beyond the maximum value, the CMTS will reset its offset to the maximum value and put an
exclamation point (!) next to its offset value in the
show cable modem
display.
In dynamic MAP operation, Cisco IOS 12.1(10)EC also implements a regular polling of the furthest CM,
to determine if that CM is now offline. If the furthest CM has gone offline, the CMTS scans the currently
online CMs to determine which CM is now the furthest offline and updates the dynamic MAP advance
algorithm with the new value.
Tip
The
show cable modem
command displays the CM timing offset in DOCSIS ticks. Use the following
method to convert microseconds to DOCSIS ticks:
ticks = microseconds*64/6.25
. To
Note
Dynamic map advance might need to be temporarily turned off if the first modem to be connected outside
of the CMTS is close to the 100-mile limit of the DOCSIS specification.
Tip
To reset the timing offset values on an upstream, use the
shutdown
and
no shutdown
commands to reset
the upstream port. This will temporarily force all CMs on that upstream offline until they reacquire the
upstream.
Examples
The following example shows how to configure the dynamic map advance to 4000 microseconds:
router(config-if)#
cable map-advance dynamic 4000
Related Commands
show cable modem
Displays statistics for the connected CMs.
