Do I need a Hub for my application?

I would like to develop an embedded device that has an Ethernet interface connected to a hone or corporate LAN. One potential usage is to bundle several device close together and work as a bunch of "sensors", and pass data to the server at a remote office. For exampe,

3 of them can be connected together one by one with almost no distance in between, then connected to LAN ith just one cable.

Traditionally to connect 3 PCs at one location to LAN, we will need a hub, or a switch. However, my devices will work close together, and Ethernet by its definition support Bus Topology, meaning that all devices or hosts on the network use the same shared communication line. So can I physically use one cable to connect 3 devices to LAN directly without a hub? It will look like a stick, one end is connected to a ethernet jack on the wall (to LAN), the other end is split into 3 tails, connecting to each device. Will it work?

Reply to
Like2Learn
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Of the commonly implemented types of Ethernet, only 10-base-5 and 10- base-2 can be arranged in a physical bus. 10-base-T is simply not electrically compatible with that sort of thing (specifically the TX lines from one side connect to the RX lines on the other, and the sender doesn't disconnect, unlike the coaxial PHYs where the sender is only really driving the (single) bus when it's transmitting a packet).

Reply to
robertwessel2

The twisted-pair Ethernet does not work that way. You'll need hubs or switches.

The original coaxial-cable Ethernet worked that way, if the branching and tapping rules were obeyed.

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Tauno Voipio
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Reply to
Tauno Voipio

Well, my application needs to support both coaxial-cable and twisted- pair, 10-base-2 and 10-base-5 and 10-base-T. I am thinking about integrating a switch into my device, say the broadcom switch for example, then connect the devices by "daisy-chain". Will it work? Do I need to modify the firmware or everthing will be taken care by the switch automatically?

Reply to
Like2Learn

WTF? Are you working on a method of sending this device through a time machine into 1992? If you are asking this type of question, I highly doubt you are building a device to retrofit into legacy military/ banking operations, and I can think of no other first-world entity likely to have such ancient technology in active service.

Reply to
larwe

Not any more it doesn't. Ethernet is logically a shared medium, but hasn't physically been a bus since effectively forever.

No.

No. For that to work, that "stick" must be, for all intents and purposes, a hub. Or something even more unlike a simple cable than that.

Reply to
Hans-Bernhard Bröker

Right. The moon is too high to reach. Well, I am willing to drop off the support for coaxial-cable, let's leave just the twisted-pair here.

Reply to
Like2Learn

Ignoring physical connections for the moments. Your devices still need to have distinct IPs or the very least distinct tcp ports on the same IP.

Probably not, without more work.

Most likely.

Probably not, without DHCP, IP NAT and companies.

Reply to
linnix

Why not use RS-485 sensors and connect the sensors to a RS-485 serial cable and that to some ethernet/RS-485 converter. Of course, there can be only one master (at a time) on the LAN side to poll the sensors one at the time.

Just install an extra double port ethernet interface cards on each PC and use point to point ethernet cables between each machine, with plenty of throughput :-).

Reply to
Paul Keinanen

That depends on how smart the RS485-Ethernet converter is. You can get converters that understand Modbus and will handle multiple masters on the Ethernet side.

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Grant
Reply to
Grant Edwards

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