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Halting the ethernet signaling

Started by Klaus Kragelund April 9, 2022
Hi

I am working on a product that connects to an access point via ethernet 100 Base TX
I am having some problems with common mode noise on the ethernet cable, and have been trying all sorts of tricks, nothing help as of now

So staring at the signals on the cable, there is a lot of traffic even though we just use it for sub kB/s traffic. The reason for the traffic is the MLT-3 encoding, so even with nothing to transfer, the line is busy as xxxx

So it occurred to me, why not just disable the line, and send a preamble with some data, and shut down the line again to remove this EMC issue. It seems there is a low power mode, that could be used.

Anyone tried something like this?

We are using DP83822

:https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467



--
Klaus
09.04.22 10:59, Klaus Kragelund   wrote:
>Hi > >I am working on a product that connects to an access point via ethernet 100 Base TX >I am having some problems with common mode noise on the ethernet cable, and have been trying all sorts of tricks, nothing help as of now > >So staring at the signals on the cable, there is a lot of traffic even though we just use it for sub kB/s traffic. The reason for the traffic is the MLT-3 encoding, so even with nothing to transfer, the line is busy as xxxx > >So it occurred to me, why not just disable the line, and send a preamble with some data, and shut down the line again to remove this EMC issue. It seems there is a low power mode, that could be used. > >Anyone tried something like this? > >We are using DP83822 > >:https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 > >
The chip supports EEE mode https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet-switches/topics/topic-map/switches-interface-eee.html#:~:text=EEE%20uses%20a%20signaling%20protocol,when%20there%20is%20no%20traffic.
>
-- Klaus
On Saturday, April 9, 2022 at 1:59:15 AM UTC-7, Klaus Kragelund wrote:
> Hi > > I am working on a product that connects to an access point via ethernet 100 Base TX > I am having some problems with common mode noise on the ethernet cable,...
Huh? 100baseTX is transformer-coupled, why would common mode be important? Are you doing power-over-Ethernet and having noisy power?
On 4/9/2022 1:59 AM, Klaus Kragelund wrote:
> I am working on a product that connects to an access point via ethernet 100 > Base TX
Most "access points" are *wireless* devices acting as gateways onto a wired network. Are you trying to connect to the wired port of the AP?
> I am having some problems with common mode noise on the ethernet cable, and > have been trying all sorts of tricks, nothing help as of now > > So staring at the signals on the cable, there is a lot of traffic even though > we just use it for sub kB/s traffic. The reason for the traffic is the MLT-3 > encoding, so even with nothing to transfer, the line is busy as xxxx
Unless you have a point-to-point link, there will almost always be "traffic" on the line as many protocols rely on the switch to replicate the traffic on all ports for other protocols to function properly. E.g., during a DHCP/BOOTP client request, the client *broadcasts* a message to locate any potential DHCP/BOOTP servers on the network. The switch must replicate this message on all of its ports to ensure all hosts in the network get a chance to see it (because the *intended* destination isn't known to the sender) Because the client doesn't (yet) have an IP address, any server(s) receiving it's "discovery" broadcast will *broadcast* a reply, *offering* a lease to that client -- indicating a "server ID" for THAT server (multiple servers can attempt to "offer"). The client will then *broadcast* a "request" -- including an extra ARP to see if any other node has the same (offered) IP address. etc. [You can run something like tcpdump/wireshark (even on a wired network) to examine the actual traffic on your network.]
> So it occurred to me, why not just disable the line, and send a preamble with > some data, and shut down the line again to remove this EMC issue. It seems > there is a low power mode, that could be used.
So, you're saying the "idle traffic" is the problem that you want to eliminate? Is it's quantity or "frequency" the issue? Do you have complete control over the network and the hosts on it? E.g., if your node is "deaf" because the connection is "shut off", then you have to ensure that it's configuration is baked into the network's design; so the IP address it is using (while "shut off") won't be delegated to some other node while your node "isn't watching". Otherwise, each time you "reconnect" to the network, you will have to make sure your presence is known.
> Anyone tried something like this? > > We are using DP83822 > > :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467
On 09-Apr-22 7:12 pm, Klaus Kragelund wrote:
> 09.04.22 10:59, Klaus Kragelund   wrote: >> Hi >> >> I am working on a product that connects to an access point via >> ethernet 100 Base TX >> I am having some problems with common mode noise on the ethernet >> cable, and have been trying all sorts of tricks, nothing help as of now >> >> So staring at the signals on the cable, there is a lot of traffic even >> though we just use it for sub kB/s traffic. The reason for the traffic >> is the MLT-3 encoding, so even with nothing to transfer, the line is >> busy as xxxx >> >> So it occurred to me, why not just disable the line, and send a >> preamble with some data, and shut down the line again to remove this >> EMC issue. It seems there is a low power mode, that could be used. >> >> Anyone tried something like this? >> >> We are using DP83822 >> >> :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 >> >> >> > The chip supports EEE mode > https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet-switches/topics/topic-map/switches-interface-eee.html#:~:text=EEE%20uses%20a%20signaling%20protocol,when%20there%20is%20no%20traffic. > > >> > > > -- > Klaus
How is the common mode noise causing you a problem? Sylvia.
On 09/04/2022 09:59, Klaus Kragelund wrote:
> Hi > > I am working on a product that connects to an access point via ethernet > 100 Base TX > I am having some problems with common mode noise on the ethernet cable, > and have been trying all sorts of tricks, nothing help as of now > > So staring at the signals on the cable, there is a lot of traffic even > though we just use it for sub kB/s traffic. The reason for the traffic > is the MLT-3 encoding, so even with nothing to transfer, the line is > busy as xxxx > > So it occurred to me, why not just disable the line, and send a preamble > with some data, and shut down the line again to remove this EMC issue. > It seems there is a low power mode, that could be used. > > Anyone tried something like this? > > We are using DP83822 > > :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 > > > > > -- > Klaus
Ethernet is normally transformer coupled so any common mode noise may be down to the transformer interwinding capacity and easily dealt with by the traditional ferrite ring over the cable? We recently heard of ferrite beads able to work at 50Hz :) piglet
On 9.4.22 11.59, Klaus Kragelund wrote:
> Hi > > I am working on a product that connects to an access point via ethernet > 100 Base TX > I am having some problems with common mode noise on the ethernet cable, > and have been trying all sorts of tricks, nothing help as of now > > So staring at the signals on the cable, there is a lot of traffic even > though we just use it for sub kB/s traffic. The reason for the traffic > is the MLT-3 encoding, so even with nothing to transfer, the line is > busy as xxxx > > So it occurred to me, why not just disable the line, and send a preamble > with some data, and shut down the line again to remove this EMC issue. > It seems there is a low power mode, that could be used. > > Anyone tried something like this? > > We are using DP83822 > > :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 > > > > > -- > Klaus
100BaseTX sends idle signals all the time when there is nothing else to send. If you have access to the switch at the other end of the link or the configuration of the DP83822, force the link to 10BaseT to stop the idles. There will still be link pulses, but less often. -- -TV
On a sunny day (Sat, 09 Apr 2022 10:59:07 +0200) it happened Klaus Kragelund 
<klauskvik@hotmail.com> wrote in <tscheppe.1ui5uq8q91brg@nntp.aioe.org>:

>Hi > >I am working on a product that connects to an access point via ethernet 100 Base TX >I am having some problems with common mode noise on the ethernet cable, and have been trying all sorts of tricks, nothing help >as of now > >So staring at the signals on the cable, there is a lot of traffic even though we just use it for sub kB/s traffic. The reason >for the traffic is the MLT-3 encoding, so even with nothing to transfer, the line is busy as xxxx > >So it occurred to me, why not just disable the line, and send a preamble with some data, and shut down the line again to remove >this EMC issue. It seems there is a low power mode, that could be used. > >Anyone tried something like this? > >We are using DP83822 > >:https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467
In the eighties we had a similar problem in a large industrial plant with PLCs connected to a computer Decided to go optical, worked perfectly. Like this (have not tried that one): https://www.amazon.com/Tripp-Lite-N784-001-ST-Multimode-Converter/dp/B000IAOL84/ref=sr_1_10?keywords=fiber%2Bto%2Bethernet%2Bconverter&qid=1649502290&sr=8-10&th=1erface tings you can buy.
> >-- >Klaus >
09.04.22 11:32, Sylvia Else  wrote:
>On 09-Apr-22 7:12 pm, Klaus Kragelund wrote: >> 09.04.22 10:59, Klaus Kragelund&#2013266080;&#2013266080; wrote: >>> Hi >>> >>> I am working on a product that connects to an access point via >>> ethernet 100 Base TX >>> I am having some problems with common mode noise on the ethernet >>> cable, and have been trying all sorts of tricks, nothing help as of now >>> >>> So staring at the signals on the cable, there is a lot of traffic even >>> though we just use it for sub kB/s traffic. The reason for the traffic >>> is the MLT-3 encoding, so even with nothing to transfer, the line is >>> busy as xxxx >>> >>> So it occurred to me, why not just disable the line, and send a >>> preamble with some data, and shut down the line again to remove this >>> EMC issue. It seems there is a low power mode, that could be used. >>> >>> Anyone tried something like this? >>> >>> We are using DP83822 >>> >>> :https://www.ti.com/document-viewer/DP83822I/datasheet/GUID-024DD3DE-0EAA-4F18-9EF3-9C0B37F9613C#TITLE-SNLS505SNLS5058467 >>> >>> >>> >> The chip supports EEE mode >> https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet-switches/topics/topic-map/switches-interface-eee.html#:~:text=EEE%20uses%20a%20signaling%20protocol,when%20there%20is%20no%20traffic. >> >> >>> >> >> >> -- >> Klaus > >How is the common mode noise causing you a problem? >
I am seeing assymetric waveforms on TD+ and TD-, so the resultant addition if the signals results in a non zero voltage on the line. Ethernet compliance allows for 50mV, and I am seeking a lot of noise above 10MHz in the conducted ethernet tesrs . It is possible that the cause is poor layout and or non optimal cable shield I could spend more time on testing and interate the PCB, but a SW mod is a little eas -- Klaus
09.04.22 11:29, whit3rd  wrote:
>On Saturday, April 9, 2022 at 1:59:15 AM UTC-7, Klaus Kragelund wrote: >> Hi >> >> I am working on a product that connects to an access point via ethernet 100 Base TX >> I am having some problems with common mode noise on the ethernet cable,... > >Huh? 100baseTX is transformer-coupled, why would common mode be important? >Are you doing power-over-Ethernet and having noisy power?
It is transformer coupled including a CM transformer, but assymetry of the MDI signal priduces common node noise -- Klaus