OT? - Broadband Troubleshooting

[Benjamin Scott]

On Mon, Mar 8, 2010 at 10:48 AM, Greg <greg at kettmann.com> wrote:
> The network setup is pretty standard.  Broadband connection ...

  What type of Internet connection and who is the provider?  For
example, "Comcast cable", "FairPoint DSL", "Verizon FiOS", etc.

> It seems to be an outbound problem (I can hear fine always)
> since the other end can't hear me for just a few seconds.

  Any other traffic happening on the network?  In particular, any kind
of server (HTTP, SMTP, FTP, etc.) or peer-to-peer file sharing
(BitTorrent, eDonkey, etc.)?  Sometimes, the problem will be due to
outbound traffic, with the asymmetric nature of most consumer Internet
feeds able to saturate the outgoing channel long before the incoming
channel fills.  This can confuse some traffic shaping/prioritization
mechanisms, which often assume a symmetric feed.

> 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.

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

  You might also traceroute to whatever gateway ViaTalk is using.
Maybe there's an obvious jump in latency, which, while not conclusive,
might be a clue.

> Bandwidth is good (based on the web based measurement
> tools) ...

  Those tools, while not entirely useless, can be very misleading or
inaccurate.  I am generally very hesitant to draw conclusions from
them.  That said, throughput is rarely the problem with a single VoIP
feed, and I don't suspect it here.  You only need about 50 Kbps for
that.

-- Ben