Dr. Michael J. Chudobiak wrote:
I looked long and hard at the LAN and it was basically narrowed down
to the
switches. In this smaller install, several cheapo Dlink ($30) switches
de-aggregate a Cisco Catalyst switch. What I noticed was that any phone
plugged direcly into the Catalyst did *not* lock up or reboot. Any phone
plugged into the crap switches experienced the lockup. So now we are
down to
the cheap switches themselves. We are nuking the Dlink switches and
replacing them with 3com workgroup switches, same as what we use in the
large install to good effect, and I fully expect the problem to
dissapear.
So does anyone have any theories as to what the technical difference
between a "good" switch and a "bad" or "cheapo" switch actually is?
Lower latency? Better grounding? More cowbell?
By far, the majority of switches on the market today will work just fine
for VoIP. Past professional experience dictates (in my mind) that a
"managed" switch is the only reasonable approach for any network larger
then a home office.
There are some inexpensive switches being sold that are less then
adequate for business use. For example, Dell rebranded and sold some
switches about two years ago that would reboot if an html packet hit the
manager IP address; didn't even have to be a crafted packet. Cabletron
sold a number of models that would auto reboot at random intervals. HP
had some issues with early firmware that essentially resulted in reboots
(it was fixed in later firmware versions).
Our company conducts professional network performance, security, and
voip readniness assessments, and have worked with corporations and
institutions in over 40 US states in the last 12 years. We constantly
see folks making assumptions about how switches function that are far
less then accurate. One example is leaving switch ports to auto
negotiate duplex settings. Roughly 50% of the time the switch (and/or
device attached to the switch) will get it wrong; one will be full
duplex while the other ends up half duplex. "That" one item will have a
serious impact on voip quality.
The only way to ensure a solid network infrastructure is to use switches
that are "manageable", and there are now lots of inexpensive switches on
the market that are manageable. In "very" general terms, the higher the
cost of the switch, the more functionality one receives.
Also in very general terms, the larger the network, the more
functionality one needs within the switches. In other words, a network
with several hundred switch ports likely requires switches with the
capability of supporting vlans, packet queuing/prioritization, etc.
Small networks (eg, low traffic volumes) in most cases do not need those
same functions.
So, your choice of switches is highly dependent on the size of network
that your working with.
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