Usage Guidelines
The DOCSIS ping
is a unique Cisco patented technology that allows a cable operator to quickly
diagnose the health of a channel between the CMTS router and any particular
DOCSIS cable CPE device. The DOCSIS ping is similar in concept to the IP ping
but uses the lower MAC layer instead of the datalink or transport layers. Using
the MAC layer has two major advantages:
- A DOCSIS ping uses only
1/64 of the bandwidth of an IP ping.
- A DOCSIS ping can be
used with CMs that have not yet acquired an IP address. This allows cable
operators to ping CMs that were not able to complete registration or that were
improperly configured at the IP layer.
In addition to
providing connectivity information, the
ping
docsis command provides a real-time view and plot
of requested power adjustments, frequency, timing offset adjustments, and a
measure of optimal headend reception power.
If a CM
responds to the
ping
docsis
command, but does not respond to an IP ping, the problem could
be one of the following:
- The CM is still in the
registration process and has not yet come completely online. In particular, the
CM could be waiting for the DHCP server to assign it an IP address.
- Severe interference or
other faults on the physical layer (either the upstream or downstream).
- Significant upstream
signal error, distortion, or amplitude errors, often resulting in frequent
power adjustments (which are shown in the cable flap list).
- A non-DOCSIS compliant
upstream carrier-to-noise power ratio (C/N) that is between 14 and 21 dB, along
with a mixed modulation profile, such as ranging request/response messages
being sent in QPSK mode and short and long data grants in 16-QAM mode.
Note |
The
ping
docsis
command is a DOCSIS-compliant process that can be used with any
two-way DOCSIS-compliant CM; the CM does not require any special features or
code. The
ping
docsis command cannot be used with telco-return
CMs.
|
Note |
In Cisco IOS
Release 12.2(33)SCA, the
show
cable
modem
domain-name command must be run first on the route
processor (RP) of the CMTS router before any domain name can be used as part of
a cable command.
|
The table below
explains the different characters that can appear in the output for the
ping
docsis command:
Table 2 ping docsis
Command Output Characters
Output
Character
|
Description
|
!
|
Indicates that a successful response was received from the ping request. This
indicates that the CM is reachable from the CMTS and can respond to CMTS
requests at the DOCSIS MAC layer.
|
.
|
Indicates that a DOCSIS ping request was sent out but that the ping request
timed out without receiving a response. This indicates that the CM is having
difficulties maintaining DOCSIS MAC layer connectivity to the CMTS.
Note
| If
the
ping
docsis command displays a number of periods (.)
along with exclamation points (!), it strongly indicates the presence of RF
noise or physical cable and plant issues that is causing a loss of MAC layer
connectivity.
|
|
a
|
Indicates that a response was received but that an adjustment of frequency,
power, or timing was also made in the response. This indicates that, although
the upstream channel is functional, some sort of problem is forcing power
averaging and other misreads of the upstream received power signals.
|
f
|
Indicates that the CMTS failed to send the DOCSIS ping request because the CM
is offline, and therefore MAC-layer communication is not possible. This
indicates that the CM had previously registered with the CMTS, but that at some
point it stopped responding to the DOCSIS station maintenance messages and that
the CMTS eventually marked the CM as offline. The CM might have lost power or
might have been disconnected from the coaxial cable.
Tip
|
Use
the
show
cable
modem command with the same MAC or IP address as
you used with the
ping
docsis command to show the current status of this
CM.
|
|
Note |
If a CM is
already in the flap list, the
ping
docsis command increments the hit, miss, and
power-adjustment fields for it in the cable flap list.
|
Examples
Note |
The
following example shows a default
ping
docsis command that sends five packets to the CM
with the MAC address of 00d0.ba77.7595, with a response being received for
each:
|
Router# ping docsis 00d0.ba77.7595
Queueing 5 MAC-layer station maintenance intervals, timeout is 25 msec:
!!!!!
Success rate is 100 percent (5/5)
Router#
The following
example shows the verbose output for the same command:
Router# ping docsis 00d0.ba77.7595 verbose
Queueing 5 MAC-layer station maintenance intervals, timeout is 25 msec:
Reply from 00d0.ba77.7595: 2 ms, tadj=-1, padj=0.50, fadj=0
Reply from 00d0.ba77.7595: 2 ms, tadj=-1, padj=0.50, fadj=0
Reply from 00d0.ba77.7595: 2 ms, tadj=-1, padj=0.50, fadj=0
Reply from 00d0.ba77.7595: 98 ms, tadj=-1, padj=0.25, fadj=0
Reply from 00d0.ba77.7595: 2 ms, tadj=-1, padj=0.25, fadj=0
Success rate is 100 percent (5/5)
Router#
The following
example shows that the CM at 192.168.100.10 is connected to the network and is
operational, but that one ping packet was lost and that several power
adjustments were made during the ping process:
router# ping docsis 192.168.100.10
Queueing 100 MAC-layer station maintenance intervals, timeout is 25 msec:
!!!!!a!!!!!!!a!a!!!!!!!!!!!!!!!!!!!!!aa!!!!!!!!!!a!!!a!a!!!aa!!!!!!.!!a!!!a!
a!a!!!!!!!!aa!!!!!!!aa!a
Success rate is 99 percent (99/100)
A CM that
displays output such as that above (a higher percentage of successful pings but
with a number of power-adjustment readings) is most likely experiencing a
problem that is not bad enough to force the modem offline but that should be
addressed.
If this problem
is consistent for just a small number of CMs on an upstream receiver (such as a
fiber node within a combining group), then the problem is likely related to
in-home wiring at those modem locations. It could also be due to a cable TV
network element that is on the same HFC segment.
If the problem
occurs for all CMs on a single fiber node, then changing the upstream frequency
or reducing the number of homes passed per combining group might improve
conditions. If this does not help the situation, the problem could be due to a
faulty cable drop, dirty optical connector on the node, or other physical plant
problem.
The
ping
docsis command cannot be used with a CM that has
not yet registered with the CMTS. The following example shows the responses for
a CM that has not yet registered with the CMTS.
Router# ping docsis 192.168.100.111
Cable modem with IP address 192.168.100.111 not registered.
Please try using MAC address instead.
Router# ping docsis 0123.4567.89ab
Cable modem with MAC address 0123.4567.89ab not registered.
router#
The following example shows the output of the ping docsis
command with the repeat
keyword:
Router# ping docsis 192.168.100.10 repeat 22
Queueing 22 MAC-layer station maintenance intervals, timeout is 25 msec:
!!!!!!!!!!!!!!!!!!!!!!
Success rate is 100 percent (22/22)