Physical A/B switching of gigabit ethernet signals - Page 1
Forum section: electronics / beginners

author: danielbriggs
author_rank: Regular Contributor
timestamp: July 30, 2022, 03:54:11 pm
content: Hello EEVBlog-hive-mind,I have a need to physically switch one gigabit ethernet port to *either* laptop A or laptop B, in a main and backup type scenario; for various reasons the two should never and will never be online at the same time. e.g. the ultimate aim is: in the event of an issue, press a button or turn a switch and the ethernet line is physically disconnected from laptop A and connected to laptop B.There appears to be a couple of rough old school switch box solutions out there for cheap, but most look shonky.e.g.orhttps://www.amazon.in/Network-Iseebiz-Selector-Bidirectional-Ethernet/dp/B01EJK8J0YHowever most are 100Mbit.The only gigabit one I can find is:https://www.amazon.com/Gigabit-Ethernet-Network-Splitter-Selector/dp/B077NYH15HThere is another off the shelf solution, that can switch from 4x sources (I only need 2), but it's £2,000 which is a little pricey for me. (I'd like to make 5x of these).So, my question: if I'm to attempt to build a Gigabit literal "switch" I/O to A, OR I/O to B, does anyone know of any suitable switching options they could point me in the right direction of?If it's a traditional relay, are there any multi-pole // 8 way relays that can switch all 8x datalines from one control coil? I'm not sure I like the idea of multiple relays to switch a single port, should any fail or have different switching times etc.Or would a better solution be a solid state option e.g. a bilateral or analog switch?Again, any pointers on what best to use? Should these even be used for ethernet signals?Also, can relays or bilateral switches have bandwidths up to 100MHz Cat5e / 250MHz Cat6 to ensure there's no signficant signal attentuation through these switching elements?I'm aware of impedence matching any PCB traces, but just thought I'd check on people's thoughts on the actual switching element; relay or otherwise.I'm very aware of "just because I can, doesn't mean I should" so any pointers / tips on the best way to acheive this switching goal would be greatly welcomed.Thanks + have a great afternoon,DanEdit: Would something like a MAX4889A potentially work?https://datasheets.maximintegrated.com/en/ds/MAX4888A-MAX4889A.pdf

author: tooki
author_rank: Super Contributor
timestamp: July 30, 2022, 04:55:18 pm
content: Do a careful forum search. I feel like this question was asked and discussed not all that long ago.

author: Bobson
author_rank: Regular Contributor
timestamp: July 30, 2022, 07:44:45 pm
content: Most (not all) GE cards would fall back to 100BaseTX if autonegotiation is enabled (default for 90%+ cases).Some GE cards would run in Gigabit mode on 2-pairs in half-duplex mode, and some would even run Gigabit duplex, if cabling is short and adequate quality.So, 100BaseTX hardware selector would solve your problem, if 100 Megabit/sec speed is OK for you.

author: radiolistener
author_rank: Super Contributor
timestamp: August 01, 2022, 01:36:41 pm
content: Gigabit ethernet is sensitive to line impedance and phase delay, so I think if you use mechanical relay or mechanical switch, your link speed will be reduced due to high error rate.I think the best way is to use gigabit switch.

author: KT88
author_rank: Frequent Contributor
timestamp: August 01, 2022, 02:34:50 pm
content: A mechanical switch must be rated for at least 125MHz and 100Ohms differential characteristic impedance.Except one can be found on E*** for a reasonable price, a 4-port 1000BASE-T switch can be found for less than 20 bucks online...

author: danielbriggs
author_rank: Regular Contributor
timestamp: August 01, 2022, 02:36:29 pm
content: Thanks all.I've found some suitable IC's designed for gigabit mux switching, so will design one of those into it.Thanks again.

author: fordem
author_rank: Regular Contributor
timestamp: August 04, 2022, 01:51:05 pm
content: Quote from: danielbriggs on July 30, 2022, 03:54:11 pmThere are simpler ways to achieve this ...Option 1 - put the two systems side by side and physically move the ethernet cable from one to the other.Option 2 - connect the two systems to an ethernet switch and disable the ethernet port on the system you want off line.Option 3 - connect the two systems to a managed or smart ethernet switch and disable the switch port connected to the system you want off line.None of the three options requires custom hardware, option 3 has the advantage that the switching can be done remotely - options 2 & 3 require the person doing the switching to disable one system before enabling the other.Lastly, "high availability" solutions have been around for at least two decades, two computers can be set up to function as an "active/passive" system in which the second system sits idle, "mirroring" the first system, waiting for it to fail - you wouldn't even need to be around to push the button.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: August 04, 2022, 02:16:59 pm
content: Ignore those switching boxes, they are from the 'olden days' and are a source of pain.So do both of your laptops have the same static IP and Mac address? Very unlikely. Even with a physical XOR switch, the LAN will see each laptop as two different clients.I agree with @fordem. Correct but expensive ($50); use a 5 port managed network switch with a web browser to patch the live device. Or, easy but maybe too simple; just hot plug a single wire.