full-duplex and half-duplex

full-duplex and half-duplex

Post by Yuan Zhon » Mon, 31 May 2004 23:08:28



Hi, Can someone please help me understand full-duplex and half-duplex.

I understand that you may use ndd to set a ethernet interfac to 10/100M
full/half duplex. What I don't understand is how you can achieve
full-duplex.

Since ethernet is based on CSMA/CD, if the ethernet card send and receive
a packet at the same time, doesn't it collide?

If full-duplex is achieved, can someone explain the physics behind the
scene, like what voltage is used for sending out packets and what voltage
is used for receiving packets.

Thank you and you all have a good memorial weekend.

 
 
 

full-duplex and half-duplex

Post by Rev. Don Koo » Tue, 01 Jun 2004 22:40:29




>>Hi, Can someone please help me understand full-duplex and half-duplex.

>>I understand that you may use ndd to set a ethernet interfac to 10/100M
>>full/half duplex. What I don't understand is how you can achieve
>>full-duplex.

>>Since ethernet is based on CSMA/CD, if the ethernet card send and receive
>>a packet at the same time, doesn't it collide?

> Not on a twisted pair network, no. Send and receive are on different pairs.

>>If full-duplex is achieved, can someone explain the physics behind the
>>scene, like what voltage is used for sending out packets and what voltage
>>is used for receiving packets.

>>Thank you and you all have a good memorial weekend.

> Whatever that might be. Not all the world is the USA, you know.

        Only the part that matters.

                Hope this helps,
                     Don

--
***************************   Q: How many frenchmen does it take
* Rev. Don McDonald, SCNA *      to defend Paris?
* Baltimore, MD           *   A: No one knows, it's never been tried.
***************************

 
 
 

full-duplex and half-duplex

Post by jschmidt40.. » Tue, 01 Jun 2004 23:04:51





>>>Hi, Can someone please help me understand full-duplex and half-duplex.

>>>I understand that you may use ndd to set a ethernet interfac to 10/100M
>>>full/half duplex. What I don't understand is how you can achieve
>>>full-duplex.

>>>Since ethernet is based on CSMA/CD, if the ethernet card send and receive
>>>a packet at the same time, doesn't it collide?

>> Not on a twisted pair network, no. Send and receive are on different pairs.

>>>If full-duplex is achieved, can someone explain the physics behind the
>>>scene, like what voltage is used for sending out packets and what voltage
>>>is used for receiving packets.

>>>Thank you and you all have a good memorial weekend.

>> Whatever that might be. Not all the world is the USA, you know.

>    Only the part that matters.

>            Hope this helps,
>                 Don

Welcome back, Don.  Glad to see you posting again.
 
 
 

full-duplex and half-duplex

Post by Rev. Don Koo » Tue, 01 Jun 2004 23:11:25






>>>>Hi, Can someone please help me understand full-duplex and half-duplex.

>>>>I understand that you may use ndd to set a ethernet interfac to 10/100M
>>>>full/half duplex. What I don't understand is how you can achieve
>>>>full-duplex.

>>>>Since ethernet is based on CSMA/CD, if the ethernet card send and receive
>>>>a packet at the same time, doesn't it collide?

>>>Not on a twisted pair network, no. Send and receive are on different pairs.

>>>>If full-duplex is achieved, can someone explain the physics behind the
>>>>scene, like what voltage is used for sending out packets and what voltage
>>>>is used for receiving packets.

>>>>Thank you and you all have a good memorial weekend.

>>>Whatever that might be. Not all the world is the USA, you know.

>>        Only the part that matters.
> Welcome back, Don.  Glad to see you posting again.

        Thank you.

                        Don

--
***************************   Q: How many frenchmen does it take
* Rev. Don McDonald, SCNA *      to defend Paris?
* Baltimore, MD           *   A: No one knows, it's never been tried.
***************************

 
 
 

full-duplex and half-duplex

Post by ps » Wed, 02 Jun 2004 01:50:21



on 5/30/04 7:58 AM:

Quote:>> Thank you and you all have a good memorial weekend.

> Whatever that might be. Not all the world is the USA, you know.

Memorial Day is a day of rememberance for those who died in the service of
our country. A simple Google search would have told you that.
 
 
 

full-duplex and half-duplex

Post by Darren Dunha » Thu, 03 Jun 2004 01:46:38



> Hi, Can someone please help me understand full-duplex and half-duplex.
> I understand that you may use ndd to set a ethernet interfac to 10/100M
> full/half duplex. What I don't understand is how you can achieve
> full-duplex.
> Since ethernet is based on CSMA/CD, if the ethernet card send and receive
> a packet at the same time, doesn't it collide?

Full-duplex is only supported on networks where collision detection can
be disabled.  You can't do that with the traditional coax cables or
hardware ethenet hubs.  

However switches connected with twisted pair are capable of it because
the packet from each side is sent over independent media, and no other
equipment will see the signals.

In such a configuration, true collisions are impossible and CD (along
with the standard avoidance algorithms) can be disabled.

Quote:> If full-duplex is achieved, can someone explain the physics behind the
> scene, like what voltage is used for sending out packets and what voltage
> is used for receiving packets.

Same voltage, different wires.

--

Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >

 
 
 

full-duplex and half-duplex

Post by Rev. Don Koo » Fri, 11 Jun 2004 13:38:18




> Oh crap.

> I'm going to need to expand my disk array, just to make room for my killfile.

        Your fear is truly sad, my child.  :-(

                Yours in Christ,
                      Don
--
***************************   Q: How many frenchmen does it take
* Rev. Don McDonald, SCNA *      to defend Paris?
* Baltimore, MD           *   A: No one knows, it's never been tried.
***************************

 
 
 

full-duplex and half-duplex

Post by Jay Lesse » Sat, 12 Jun 2004 03:32:40



> Hi, Can someone please help me understand full-duplex and half-duplex.

> I understand that you may use ndd to set a ethernet interfac to 10/100M
> full/half duplex. What I don't understand is how you can achieve
> full-duplex.

http://www.ethermanage.com/ethernet/ethernet.html
 
 
 

1. full-duplex / half-duplex switching, why?

i have rh 8.0 router with iptables and two nic's
eth0 is for local and eth1 for public network.

i can notice in messages something like this:
kernel: eth1: Setting half-duplex on MII #1 link partner capatibility
of 000
kernel: eth1: Setting full-duplex on MII #1 link partner capatibility
of 41e1

it happens more times per day, switching to half-duplex and then back
to full-duplex few minutes later.
why is that?

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