[SI-LIST] Re: Ethernet switch problems: detailed questions
- From: "john lipsius" <johnlipsius@xxxxxxxxx>
- To: <jan.vercammen.jv1@xxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Thu, 12 Sep 2002 17:16:38 -0700
Jan,
See the other two replies before this one for (obviously) the detailed
explanation why the buffer device power supply was insufficient.
I assume the packet loss was measured on the buffer device, which
led you to investigate it first.
But, it seems the repliers didn't notice that the original issue was the
hangup of the *external* ethernet switch. My guess is that you solved
it by fixing the buffer device because it was perhaps sending so many
bad packets, "chattering", or in some other way violating the physical
protocol, that the switch went into a failure mode.
----- Original Message -----
From: "Jan Vercammen" <jan.vercammen.jv1@xxxxxxxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Thursday, September 12, 2002 7:28 AM
Subject: [SI-LIST] Ethernet switch problems: detailed questions
>
> Hello SI-list,
>
>
> about 5 weeks ago a posted questions concerning Ethernet switch problems.
> The old mail is included below
> as a reference. First of all, many thanks for your helpful comments.
>
> I have more details on the switch problem:
> -1- the switch is not physically damaged, however the swich goes into
> hangup and needs a reset (power off/on)
> -2- disconnecting ports (if necessary all of them) does not help
> -2- the problem is repeatable but we do not have an explanation why the
> switch freezes
>
> Here are the details of the switch configuration: it is a small switch fed
> by an AC/DC adaptor (220V). There are two
> 10Mbit ports connected to printers, two 100Mbit ports (connected to input
> devices that generate images for the
> printers) and one 100Mbit port connected to a printer buffer. All cabling
> is unshielded twisted pair. Maximum length
> of the cables is 3-5m. In short: a small test setup for a network in an
> office environment. There is lot's of traffic
> between the printers, input devices and buffer device. The hardware or
> software has not changed on any device,
> except for the buffer (see belwo).
>
> We can reproduce the hangup, here are the details. The culprit device is
> the buffer device. It is the size of a PC
> with a mother board, hard disk, SDRAM modules, power supply and keypad. The
> processor platform is PowerPC
> and the CPU type is selectable: 603 or 740. The problem is apparently
> caused by the voltage regulator module (VRM)
> which generates 2.6V for the core voltage of the MPC740. The VRM uses the
> 5V as input and as a by-product
> contaminates the 5V with a 470kHz ripple.
> The 5V is also used for the Ethernet physical National DP83840 and used
> specifically for the analog power supply
> part of the physical. Here lies the problem: the 5V is filtered by means of
> an RC filter, using a ferrite bead, a small resistor
> and 100nF+1nF decoupling. This design dates from 1996 and was found to work
> OK with a MPC603 which uses
> the 3.3V for its core supply and does not have a VRM.
> Since we switched to MPC740 and the VRM we had a problem with this (a
> single type of) Ethernet switch. We can correct
> the situation as follows: replace the RC filter decoupling 100nF+1nF with a
> single 10uF ceramic capacitor. We have tested
> both versions: 100nF+1nF and 10uF several times and the 10uF is a big
> improvement:
>
> test with 100nF+1nF test with 10uF
> hangup after 24 to 36 hours no hangup after one week of
> testing!!
> TX and RX error packets about 7-10% TX and RX error packets 0%
>
> So the problem is caused by a bad filtering of the analog supply (our fault
> and not of the componenets) of the Ethernet
> physical. This shows by a 7 to 10% error packets on transmit and receive.
> The switch will freeze after about 1 day to 1.5
> days (tested 3 times). The 10uF capacitor produces errorless TX and RX and
> no hangup, even after a week of testing!
>
> I measured, with a spectrum analyser, the analog power supply on the
> physical: 100nF+1nF gives about 50mV
> of noise at 470kHz, with a 10uF cereamic this is only 0.5mV. So the 10uF
> ceramic does a better job on
> providing a clean analog supply.
>
> Although we seem to have solved the problem a nagging question remains: why
> does this bad filtering freezes
> an (external) switch? Any ideas what is going on?? So our machine when it
> provides a badly filtered analog
> supply to the Ethernet physical can freeze an external Ethernet switch.
> Amazing!!
>
>
> Kind regards,
>
> Jan Vercammen
> Agfa-Gevaert
> Belgium
>
> ****************** old mail below *******************
>
>
> 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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