[SI-LIST] Re: Ethernet switch burnout

  • From: "Ghazzali Majeed" <gmajeed@xxxxxxxxxxxx>
  • To: jan.vercammen.jv1@xxxxxxxxxxxxxxxx, si-list@xxxxxxxxxxxxx
  • Date: Thu, 1 Aug 2002 10:58:11 -0700

Jan,

- A test to do would be to configure the switch and your device in
half-duplex. First send the traffic from switch to the device and see
whether this causes the switch to break. Secondly, send the traffic from
device to the switch and see whether that causes the problem. Atleast, this
way you would know, whether its your device or switch. Its also possible
that you may not see the issue at all in half-duplex mode. You may not be
able to do the test if switch is unmanaged.

- Is the problem speed dependent i.e. does it happen both at 10Mbps and
100Mbps?

- What kind of switch (model/manufacturer) are you using - there are quite
few low cost switches available which are very marginal in meeting ESD
requirements and are poor designs. Try using a switch from a different
vendor.

- You would need to get a *broken* switch in-house and do all basic
debugging to figure out the problem. If its a hard damage, one of the exotic
reasons could be CESD - Cable-sourced electro-static discharge (CESD) is a
phenomenon that occurs when an electrically charged twisted pair RJ45 cable
is plugged into network equipment such as a switch or NIC. CESD is
characterized by higher current, longer discharge time than typical ESD
events, and is caused by a variety of events. The electrical charge on the
cable can build up from dragging a cable across a carpet during install or
proximity to moving equipment (e.g. elevators), air ducts (moving air), or
electrical equipment. The CESD tolerance of any given electronic system
depends on many factors. It should be noted that carefully chosen
isolation-magnetics, layouts and routings, and decouplings of the RJ45(s)
and RJ45 associated circuit paths to the device, are all necessary to get
the most protection against CESD.

If CESD is the cause, I would suspect isolation transformer (magnetics) on
the switch is burnt - you should be able to check for continuity on the
transformer primary and secondary winding. However, if the port is alive
(link up and can transmit/receive traffic) after reset or power recycling
the switch, I would not suspect magnetics to be the cause of the problem.

thanks,
Ghazzali Majeed
Broadcom Corp.




-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Jan Vercammen
Sent: Thursday, August 01, 2002 7:04 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Ethernet switch burnout



Hello SI-list,


I have an urgent question concerning Ethernet twisted pair. We have
received from the field three reports
that one of our products seems to have the capability to physically damage
the port of a switch to which it
is connected.

To be more specific: our device uses a Bob Smith termination. The RJ-45
unused pins are connected with
75ohm to a common-rail, which in turn is capcitively coupled (using 1nF) to
the chassis (=housing of device),
which is also connected to the logic ground of the PCB.
The center taps of both transmit and receive are also connected with 50ohm
to the same common rail.

The other port is a switching hub and I do not know if shielded or
unshielded cable was used.

What seems to happen is that after a while the communication hangs and the
port at the switch does not operate
anymore, not with our device or any other.
For now I cannot confirm that resetting the switch solves the problem and
it looks that there is hard damage.

I have heard of cable sheath discharges (the tubing of the cable charges
and next discharges to the environment,
damaging hardware). However, for now I would like to disregard such exotic
scenario.

So my questions are:
-1- as anyone encountered similar switch burnouts (whether hard or soft)?
-2- if so, what is the possible explanation and fix?


Kind regards,

Jan Vercammen
Agfa-Gevaert, Belgium


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