Is 100Base-TX switch or hub?

I'm not sure I understand your question. 100TX can use either a switch or a hub--with a hub it's half-duplex, with a switch it should be full. Connecting only two computers it doesn't need to use either, just a crossover cable.

It's neither. 100baseTX is an ethernet specification, that may be used with switches, hubs and NICs. It can also be full or half duplex.

Hubs are half duplex and switches can be operated in full duplex.

A "hub" is a device that operates only at the physical (eg electrical) layer - another term for a hub is a multi-port repeater. It does not traffic isolation - basically, it makes things look like every node in the network is on the same piece of wire.

A "switch" is a device that operates at the data-link layer - another term for a switch is a multi-port bridge. A switch can do traffic isolation - learning which MAC addresses are associated with which ports on the switch and then only sending traffic to those MAC addresses on the associated port(s).

rick jones

Thanks for all the replys.

Sorry for the confusion. Yeah, right. I meant for the central device conforming to 100Base-TX spec. I wanted to make sure if it can function as either a hub or switch and if so, when it runs as a hub, the communciation mode must always be in half-duplex, and when it runs as a switch, it must always be in full-duplex.

If I still understand the system incorrect, please let me know.

Thank you so much, everybody.

Min

One more thing, for switch configuration, can the half-duplex mode not be supported? I don't see why not.

Thank you.

Min

No, you have the wrong emphasis.

Any given communications device might be a hub, switch, or router. If it is a hub, then due to the definition of what hubs are, then the device -must- communicate in half duplex. Switches and routers can use full duplex or half duplex independantly for each link.

Putting any given device into half duplex mode will not make it a hub, and these days very few devices that are running in half duplex mode are hubs. (These days, it's mostly printers that run half duplex... since they seldom need to communicate much back towards the hosts.)

The concepts of hubs and switches and routers are independant of

While hubs are always half duplex, switches are generally, but not always full duplex. Also, if you configure your NIC to HD, your connection to the switch will be HD, though it shouldn't affect other ports.

When an ethernet device is connected, it autonegotiates with the device at the other end of the cable to determine optimum configuration. If one device only supports HD, the other has to use it as well.

Thank you all again for the valuable information.

Min

"Never" :) hardcode one side and not the other.

How Autoneg is supposed to work:

When both sides of the link are set to autoneg, they will "negotiate" the duplex setting and select full duplex if both sides can do full-duplex.

If one side is hardcoded and not using autoneg, the autoneg process will "fail" and the side trying to autoneg is required by spec to use half-duplex mode.

If one side is using half-duplex, and the other is using full-duplex, sorrow and woe is the usual result.

So, the following table shows what will happen given various settings on each side:

Auto Half Full

Auto Happiness Lucky Sorrow

Half Lucky Happiness Sorrow

Full Sorrow Sorrow Happiness

Happiness means that there is a good shot of everything going well. Lucky means that things will likely go well, but not because you did anything correctly :) Sorrow means that there _will_ be a duplex mis-match.

When there is a duplex mismatch, on the side running half-duplex you will see various errors and probably a number of late collisions. On the side running full-duplex you will see things like FCS errors. Note that those errors are not necessarily conclusive, they are simply indicators.

How do you "hardcode" an ordinary consumer level switch?

No, it's just a cheap made in China type. There was no mention of such a thing in the docs for it.

BTW, please do not reply via e-mail, unless the message contains something that should not be public.

ROF,L. You've never actually encountered a consumer level switch, have you? There is no http interface, no GUI, no telnet, no configurability at all other than what can be done with switches on the front panel. To get that sort of functionality you need a _managed_ switch, which is far, far more costly than the 40 bucks that you pay for a 5 port gigabit Netgear.

Most switches should at least allow this via a http interface or some gui.

Particular brand?

BernieM

Sounds like it's 'auto' all the way. Sorry about replying via email ... it was a mistake.

bernieM

You're right. I've been spoilt for too long now surrounded by Cisco gear. 'Unmanaged' >= 'Unbearable'

BernieM