OT? - Broadband Troubleshooting

[Ben Eisenbraun]

On Mon, Mar 08, 2010 at 02:12:50PM -0500, Benjamin Scott wrote:
> On Mon, Mar 8, 2010 at 10:48 AM, Greg <greg at kettmann.com> wrote:
> > What's the best approach to isolating or identifying the details of this
> > problem?  One obvious solution is to log some pings for a day or two.
> 
>   This is tricky because what you're looking for is not throughput,
> and not even latency (Round Trip Time), but rather, Packet Delay
> Variation, AKA jitter.  That is, you don't care how long it takes a
> packet to transit, but you need to characterize *variation* in how
> long it takes a packet to transit.

He could also be experiencing just plain ol' packet loss.  If you have RF
ingress or failing RF equipment on your cable segment, you can see patterns 
where the cable modem works fine for a few minutes and then loses lock for
a few seconds, repeat ad infinitum.

People using POP mail clients or browsing the web don't always notice a
problem like that, since its impact on those protocols can be attributed to
general "Internet hiccups" or some such.  It's bleeding obvious if you're
using SSH though.  :P

If you have a decent cable modem, you may be able to use SNMP or at least
do some screen scraping off its internal web server to graph SNR levels,
track if it loses lock, etc.  Googling the model number can frequently
turn up some additional info besides what is in the manufacturer's
manual.

>   I've seen SmokePing recommended in this sort of scenario before,
> although I've never gotten around to trying it out myself.

Two thumbs up for SmokePing.  I used the SmokePing graphs to poke at the
RCN cable ops guys until they fixed some local issues.  Try to find the
interfaces on the routers along your outbound path to ping: inside router
interface, external router interface, cable modem IP address, default route
IP address, a likely look router IP address at your ISP headend, your VOIP 
providers server, etc.

-ben

--
oh, you hate your job? why didn't you say so? there's a support group for
that. it's called EVERYBODY, and they meet at the bar.       <drew carey>