Author Topic: 100 basetx full duplex? (Read 238 times)

Speed55 · « **on:** May 24, 2007, 11:22:02 AM »

Hi guys. i have a question about the connection speed.

When i check the connection speed it says 100mbps.

I went into advanced settings and changed the speed on the computer to 100base tx full duplex instead of auto.

I did this with the mindset that it is good to match the connection with the computer, although i really have no idea if it really makes a difference or not.

Could someone please explain a little bit about how the speeds work, like full duplex, half duplex, ect. and the benefits or negatives of using them?

Thanks.

Bad31st · « **Reply #1 on:** May 24, 2007, 02:38:52 PM »

You are correct to assume that connection speed and duplex settings should match on the PC and the device you are connecting to. More on this in a moment...

Autonegotiation is the method with which two networked broadcast their capabilities and establish common speed and duplex settings. In many if not most situations multiple speed and duplex settings are supported by an individual card or interface. In these cases the best possible common settings are automatically selected for use in transmission of data.

As far as speeds are concerned it should suffice to simply understand that that speeds or transmission rates are 10Mbps, 100Mbps, and 1000Mbps.

A word on duplex settings

Half Duplex - Think of Half Duplex like a walkie talkie or CB radio - this setting allows for your network card to talk to another network card but only one machine can talk at a time. That being said in order to transmit data, your card must "seize" the line and then transmit. If both machines try to transmit at the same time what's known as a collision occurs and the process must begin again.

Full-Duplex - More like a telephone allows traffic from both machines to flow simultaneously. Full Duplex utilizes seperate conductors or pairs of wire for transmit and recive resulting in a collision free environment.

Now with this basic understanding of autonegotiation and duplex settings there can be negative effects to manually setting your duplex mode. When two connected devices are using different speed and or duplex setting a mismatch occurs causing the link between the two devices to fail or go down.

Speed55 · « **Reply #2 on:** May 24, 2007, 02:47:00 PM »

oh wow. thanks.

You wouldn't happen to work in the communications field by chance?

Vulcan · « **Reply #3 on:** May 25, 2007, 12:46:05 AM »

Quote

Originally posted by Bad31st
When two connected devices are using different speed and or duplex setting a mismatch occurs causing the link between the two devices to fail or go down.

Incorrect.

When two connected devices are using different speed and or duplex bad s**t happens (packet loss, crc errors, all sorts of goodness).

Speed55: you should set both to Auto. Having one set to Auto and one manually set to 100Mbps Full Duplex can result in problems occasionally. If one is set to manual then both should be set to manual.

Speed55 · « **Reply #4 on:** May 25, 2007, 05:52:31 AM »

thanks,

This is what i see. Start---Control Panel----Network Connections---Local Area Connectoin---- Status-----Speed--- 100mbps.

I haven't played ah yet since i changed to full duplex. I'll give it a go later, and if i noticed warps i'll change it back. I haven't noticed any difference doing the usual web browsing stuff.

Auger · « **Reply #5 on:** May 25, 2007, 05:13:47 PM »

Autonegotiation usually just works, so I tend to leave it enabled. The time it usually fails miserably is when you connect a mission critical Sun server to any piece of Cisco networking gear. Then it will fail at about 2 AM on a Saturday when you are on call.

Vulcan · « **Reply #6 on:** May 25, 2007, 06:23:07 PM »

Hahahah you've obviously had the same experiences I've had with cisco's fubar'd autonegotiation code auger