half duplex versus full duplex

[NikPreviousAcct]

Would I be correct (relatively?) in assuming that a 3mbps internet connection that is half duplex at full bandwidth usage would be passing the same amount of traffic as a 1.5mbps that is full duplex at full bandwidth usage?

Like... if both internet connections were pegged? Would one pass more traffic than the other? Like the 1.5mbps full duplex line could be sending 1.5mbps and receiving 1.5mbps while the 3mbps half duplex line would be either sending or receiving at 3mbps but not both...

Random questions confuse me.

 

[Appledrop]

i dont know the answer to that question.. but totally off topic (but slightly ontopic heh!) i recently changed my nic from full to half duplex and the performance is sooo much better, like, instead of 3 hours to copy far cry.. 10 minutes LOL)

consider this a bump

 

[Cscutch]

Duplex is more a term used for LAN not WAN connections.

In the LAN enviroment Full duplex is double the speed sorta of. It just means it uses two pairs of wires instead, one for transmiting and one for recieving. Half duplex uses the same pair of wires and then useses a software function to control the transmissions to try and prevent collisions.

Chris

 

[ScottMac]

NO, you would not be correct.

The primary difference being how much traffic is passing in either / both directions and when.

Scott

 

[spidey07]

and WAN connections are always full duplex.

 

[Garion]

Originally posted by: Azzy64
i dont know the answer to that question.. but totally off topic (but slightly ontopic heh!) i recently changed my nic from full to half duplex and the performance is sooo much better, like, instead of 3 hours to copy far cry.. 10 minutes LOL)

consider this a bump

a 100Mb/s NIC in full duplex mode will probably be able to handle all the traffic your machine can push out, as there is no interference between the sending and receiving of traffic. In half duplex mode, both send and receive come across the same set of wires. In practice, you'd be lucky to get 40Mb/s half duplex.

If setting your NIC to half duplex made things work better you have other problems - Full duplex should ALWAYS be faster assuming all the devices on the network are working right. You'll have real problems and very slow performance if one side (your NIC) is set to full duplex and the other end (the switch) is set to half.

With most SOHO networking gear, leave everything at autosense - A lot of gear is auto ONLY and if you hard-set your NIC you will just confuse it. This is worst when you force yourself to full duplex, as most auto-sensing gear will default to half.

This kind of goes back to the OP's post..

A full duplex connection can send and receive at the same time. Whenever you are downloading something, you are constantly sending back acknowledgements that you received a chunk of the data. If you are using half duplex, these acknowledgements have to "fight" for bandwidth to get back out, which ends up slowing things down. With full duplex, they can get sent at the same time the data is being received and all flows nicely.

- G

 

[Garion]

Double post

 

[dphantom]

Originally posted by: Azzy64
i dont know the answer to that question.. but totally off topic (but slightly ontopic heh!) i recently changed my nic from full to half duplex and the performance is sooo much better, like, instead of 3 hours to copy far cry.. 10 minutes LOL)

consider this a bump

Copy what and how much??

With that kind of performance difference, I'd look at changing nic to auto-sense first rather than hard-coding at half-duplex. Lose a lot of performance at half-duplex as spidey07 so accuratley points out. Then wiring (maybe) or a port on the switch as possible problems.

I have one building with unreliable wiring (building is being gutted and rebuilt soon) where we have to set a certain 10/100 nic from auto-sense to hard-code 10mbps full duplex to get a network connection.

 

[Kelemvor]

If you set the Lnk Speed to Auto, what does it use to determine whether to use full or half? is there something on the router that you have to set to Full in order for the connects to use full by default?

 

[dphantom]

Originally posted by: FrankyJunior
If you set the Lnk Speed to Auto, what does it use to determine whether to use full or half? is there something on the router that you have to set to Full in order for the connects to use full by default?

The nic and router negotiate to set the connection speed. Or the switch port and router negotiate. asumming both sides agree, auto-sensing will by default set to 100mb full. I use Cisco gear so that is my frame of reference.

That being said, Cisco sometimes has issues properly auto-sensing certain nics. As a standard practice, I set my router FE interface and corresponding Switchport FE interface to 100MB full hard-coded. I have had dropped packets between switch and router at times. I run VoIP as well so dropped packets are unacceptable.

So basically the nic and router or switch will talk at layer 2?? of the OSI model to determine the optimum speed to exchange packets. Since that always does not work because of disparate hardware, we have the option of changing duplex and speed modes.

 

[spidey07]

actualy link negotiation is at layer1. A specially modified link pulse that just advertises the highest capability.

"hey! I can do 100/full"

"Great, so can I"

 

[WiseOldDude]

half duplex - think of a walkie talkie, press to talk, let up to listen cannot talk and listen at the same time
Full duplex - think of a telephone, you can talk and hear the other party at the same time.

broadband - 3 meg download speed, that is how big the pipe is - typically 256K upload (smaller pipe) - full duplex yes, does it divide the 3 meg NO, it is 3 meg down/256K up

 

[dmcowen674]

Originally posted by: WiseOldDude
half duplex - think of a walkie talkie, press to talk, let up to listen cannot talk and listen at the same time
Full duplex - think of a telephone, you can talk and hear the other party at the same time.

broadband - 3 meg download speed, that is how big the pipe is - typically 256K upload (smaller pipe) - full duplex yes, does it divide the 3 meg NO, it is 3 meg down/256K up

Good analogy. I normally use the CB radio analogy.

This is the "cheat" that I tell people to use when they want to limit bandwidth on another PC. It really does work.