Half-Duplex Question

rewind

A coworker and I got into a discussion about half and full-duplex and couldn't figure something out: 10BaseT can only communicate half-duplex, over a minimum Cat 3 rated cable, so, if 10BaseT uses 2 pairs, (1 and 2 are Transmit positve and negative, and 3 and 6 are Receive pos. and neg) how come 10BaseT can't communicate full-duplex? Or can it? I remember reading somewher that it couldn't, but can't remember where...

Your thoughts?

-Chris

scot_donecker

Hey, I think 10BaseT has multiple modes i.e. half-duplex mode and full-duplex mode.

Hope this helps!

johnnynodough

^

indeed. 10baseT can operate full duplex, as long as it has no other device to contend with on a given segment. i.e. you cant use full duplex on a hub, even if its 100baseT, but you can with a switch, as well as 10baseT with a switch.

Yankee

It ain't whether 10bt supports full duplex because it does. The issue is if the platform supports it, because the support is in the hardware/software. I think I remember issues with the model 2611 routers where the IOS said it supported it (meaning the command was there) but you accumulated errors like it was set to half.

Yankee

rewind

So if I had a crossover ethernet cable going from one router to another, could this segment be full-duplex? I think I tried forcing it in both the interface setting, but when you did a sh int, they came up as Half. also I was getting these imcompatible duplex console messages. does this have to do with what johnnynodough said about the device contending on the same segment?

johnnynodough

^

No, both Yankee and I are right, I missed a big piece that Yankee pointed out though. There is no contention on that segment, but this device may not support full duplex. My 2501's dont support full duplex with IOS 12.3 (may just be the trasnciever), even though the command is there it wont take, whether cabled to a router, a switch, or a host.