How can I know a Ethernet card (for PLC, computer, etc) is half-duplex or full duplex? and can I connect a card (I don't know it's full-duplex or not) to a repeating hub this time, and at the other time the same card to a switching hub (full-duplex)? Especially for a half-duplex card.

 

This one is simple...

If you are connected to a HUB, then you are going to be in half-duplex mode. If you are connected to a SWITCH or directly to another Ethernet Device (through a cross-over cable) and that device supports full duplex, then you are in full duplex mode.

The above assumes you are connecting to a 100 Megabit Ethernet device from a 100 Megabit Ethernet device connected via CAT-5 cable and RJ-45 type connectors.

Modern Ethernet cards will auto-detect if they are connected to a hub or switch and will switch to the proper duplex mode immediately. With some Ethernet cards, you can through software force the card into a certain mode to some degree - typically to force downgraded operation.

--
Ron Gage - Owner
Linux Network Services
Saginaw, Michigan

 

Unfortunately this isn't all so easy to tell. You must rely on the vendor documentation.

Some rules of thumb: -) If the device is 10M only, assume it is half-duplex only -) If the device is 10/100M and "new", then it probably supports half & full duplex & auto-negotiate properly. -) IT folks prefer to manually fix settings once it is known to work - this avoids these situations where devices negotiates a low-speed link due to some noise or events when they should be running at 100M/FD

Good News: - All HD/FD Enet devices will have (I hope) been tested on old HD hubs, so I would NEVER worry about buying a new 10/100 HD/FD device to use with older half-duplex HUB equipment. - The issue of HD/FD is mainly an issue hidden in the lower physical layers, so it's almost trivial to add to existing products. Often it's little more than using model X chip instead of model Y from the same vendor. The only "work" needed is if vendors need to display to users the current settings and allow manual settings (both are desireable).

Bad News: - There was a short period of time when 100M "switches" cost $2000+ each and supported an all or nothing design. The entire 8/16/32-port switch would assume the setting of the lowest speed device, so one 10M/HD device forced all to this setting. Such switches should be replaced with newer switches for a dozen reasons - mainly to lower troubleshooting and fault recovery costs. Keeping these around is "penny-wise and pound-foolish". - If the device is 10/100M and say 3-5 years old, then it may not auto-negotiate properly - for example may set to 10M if the switch/hub tries 10M first even if both support 100M. This is when the habit of manual settings took hold.

But overall things connect pretty well these days.

- Lynn

 

It is possible to see the mode of transmission of your ethernet card. However, it depends on the operating system where you have your card configured. In case of any Windows version you can see the mode of transmission by selecting the properties of your card, in addition you can select it if you need a specific use.

New ethernet cards can work in any transmission modes and if you are not sure what modes of transmission support your card and other devices on your net, you can select auto-detect in the configuration of you card in the operating system, this option is the easy way to make many devices to work correctly.

if you need any other specific question you can e-mail me [email protected], hope this could help you.

Jose Calzadilla