Troubleshooting guide

5-20
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 5 Troubleshooting DOCSIS Networks
Troubleshooting Slow Peformance
While the FTP transfer is occurring, it is possible to monitor the progress of the test on the CMTS using
the show interface cable X/Y sid Z counters command where cable X/Y is the cable interface the modem
under test is connected to, and Z is the Service ID (SID) number of the modem under test. This command
shows how many bytes are being transferred from or to a particular cable modem. Let's say that the CPE
you are testing is behind a cable modem with MAC address 0001.9659.4461.
First you need to find the SID number of the modem you're testing by using the show cable modem
command. In this case the SID of the cable modem is 5.
uBR7246-VXR# show cable modem 0001.9659.4461
Interface Prim Online Timing Rec QoS CPE IP address MAC address
Sid State Offset Power
Cable3/0/U0 5 online 1996 0.25 5 2 10.1.1.24 0001.9659.4461
While the download or upload is progressing you clear all the packet counters on the CMTS back to zero
using the clear counters command. At the exact same time as you clear the counters, you start a
stopwatch or timer.
uBR7246-VXR# clear counters ! Reset packet counter to zero.
Clear "show interface" counters on all interfaces [confirm] ! Start the stopwatch when
you hit Enter.
After the stopwatch or time reads exactly one minute execute the show interface cable X/Y sid Z counters
command. You may wish to type the command first and then hit enter at exactly when your timer
indicates one minute. Naturally you can perform the test over a longer or a shorter period. The longer
the test period, the more accurate the result, however make sure that the download or upload does not
finish before your stopwatch timer reaches the specified time otherwise your measurement will be
inaccurate.
uBR7246-VXR# show interface cable 3/0 sid 5 counters ! Hit enter when stopwatch is at
exactly one minute.
Sid Inpackets Inoctets Outpackets Outoctets Ratelimit Ratelimit
BWReqDrop DSPktDrop
5 4019 257216 3368 1921488 0 149
uBR7246-VXR#
In this case you were testing download speed. The output of the show interface cable X/Y sid Z counter
command indicates that over a period of one minute, 1,921,488 bytes were downloaded by the cable
modem. Converting 1,921,488 bytes into bits you get:
8 bits per byte * 1,921,488 bytes = 15,371,904 bits. Then, to find the download rate in bits per second,
you divide this total number of bits downloaded by the time it took to download them in seconds.
15,371,904 bits / 60 seconds = 256 Kbps The download rate in this example is shown to be approximately
256 Kbps, which happens to be the allowed download rate for the cable modem under test.
In order to look at the upload speed using the show interface cable X/Y sid Z counter command, the
Inoctets column should be used to determine the number of bytes sent in the upstream direction from the
cable modem.
See the Cisco Cable Modem Termination System Command Reference for more information about the
show interface cable X/Y sid <Z> counters command.