!00B-FX :Ethernet over Fiber Question

!00B-FX :Ethernet over Fiber Question

Post by Kot » Fri, 11 Jul 2003 20:58:09



Hello -

I have two 100B-Fx ports(Port1 and Port 2)connected . If I pull out
the Receive on  port1, , there is packet loss(as expected).What I want
to know is that why is there no one-way  data traffic ( i.e from Port
1 Tx to Port 2 Rx)?
Any explanation on this would be appreciated.

thanks
kott

 
 
 

!00B-FX :Ethernet over Fiber Question

Post by Fester Ranci » Sat, 12 Jul 2003 05:34:42


This is not an Ethernet question, but a protocol stack question. I'll not
give the answer, but a clue would be to look at how stacks like TCP/IP use
acknowledgements.

FR
--
There is nothing more frightening than ignorance in action. - Goethe


Quote:> Hello -

> I have two 100B-Fx ports(Port1 and Port 2)connected . If I pull out
> the Receive on  port1, , there is packet loss(as expected).What I want
> to know is that why is there no one-way  data traffic ( i.e from Port
> 1 Tx to Port 2 Rx)?
> Any explanation on this would be appreciated.

> thanks
> kott


 
 
 

!00B-FX :Ethernet over Fiber Question

Post by Geo » Sat, 12 Jul 2003 07:40:18


Well, it seems like an ethernet question to me, so I'll hazard a thought or
two from what you've indicated.

If an otherwise working full duplex 100FX link has one of its pairs dropped,
then it doesn't automatically try to arrange itself for half-duplex mode.
In this mode, it would still be bi directional, even over one fiber strand.
At 100FX, the half duplex length limit is decreased from the max of 2Km to
412meters.    This may not allow the half duplex mode to be established if
your length is over 412 meters.     In any case, you can't establish  "one
way" traffic, even though you would be able to establish  "two way" traffic
with collisions on one fiber strand.

Is this an academic situational question or are you interested in
troubleshooting a real connection?

George Johnston
Logical Solutions for Integration
Clarity in an Unclear World

> This is not an Ethernet question, but a protocol stack question. I'll not
> give the answer, but a clue would be to look at how stacks like TCP/IP use
> acknowledgements.

> FR
> --
> There is nothing more frightening than ignorance in action. - Goethe



> > Hello -

> > I have two 100B-Fx ports(Port1 and Port 2)connected . If I pull out
> > the Receive on  port1, , there is packet loss(as expected).What I want
> > to know is that why is there no one-way  data traffic ( i.e from Port
> > 1 Tx to Port 2 Rx)?
> > Any explanation on this would be appreciated.

> > thanks
> > kott

 
 
 

!00B-FX :Ethernet over Fiber Question

Post by Geo » Sat, 12 Jul 2003 07:49:50


Even though it's bad form to reply to yourself, I am doing so, since I
realized my "brain cramp" along the use of a single strand producing half
duplex capabilities.    You would still require the dual fiber pair cross
over.   The limits of 100FX at half duplex is 412meters, but this is
relevant for fiber connections to a repeater.   This was not your case.

The simpler answer to your simpler question is that the fiber interface is
expecting to see both paths partner transmit beam to keep the link status
active.   So, if either side of the TX-RX pairs are not functioning, the
whole link is down.

Sorry for the confusion, and the dual reply!

George Johnston
Logical Solutions for Integration
Clarity in an Unclear World

> Well, it seems like an ethernet question to me, so I'll hazard a thought
or
> two from what you've indicated.

> If an otherwise working full duplex 100FX link has one of its pairs
dropped,
> then it doesn't automatically try to arrange itself for half-duplex mode.
> In this mode, it would still be bi directional, even over one fiber
strand.
> At 100FX, the half duplex length limit is decreased from the max of 2Km to
> 412meters.    This may not allow the half duplex mode to be established if
> your length is over 412 meters.     In any case, you can't establish  "one
> way" traffic, even though you would be able to establish  "two way"
traffic
> with collisions on one fiber strand.

> Is this an academic situational question or are you interested in
> troubleshooting a real connection?

> George Johnston
> Logical Solutions for Integration
> Clarity in an Unclear World


> > This is not an Ethernet question, but a protocol stack question. I'll
not
> > give the answer, but a clue would be to look at how stacks like TCP/IP
use
> > acknowledgements.

> > FR
> > --
> > There is nothing more frightening than ignorance in action. - Goethe



> > > Hello -

> > > I have two 100B-Fx ports(Port1 and Port 2)connected . If I pull out
> > > the Receive on  port1, , there is packet loss(as expected).What I want
> > > to know is that why is there no one-way  data traffic ( i.e from Port
> > > 1 Tx to Port 2 Rx)?
> > > Any explanation on this would be appreciated.

> > > thanks
> > > kott

 
 
 

!00B-FX :Ethernet over Fiber Question

Post by shop » Sat, 12 Jul 2003 17:09:57



Quote:> Hello -

> I have two 100B-Fx ports(Port1 and Port 2)connected . If I pull out
> the Receive on  port1, , there is packet loss(as expected).What I want
> to know is that why is there no one-way  data traffic ( i.e from Port
> 1 Tx to Port 2 Rx)?
> Any explanation on this would be appreciated.

Some 100 Base-FX devices implement a function called "far end recieve
failure" or similar

The ports only come up if the device can see keepalives at layer 1 from the
far end

This was invented to fix the 1 way link problem, since fibre links tend to
be in backbones, which is where resilience is most used, and a 1 way link
can lead to spanning tree loops and kill an entire layer 2 set of switches
and hubs.

Quote:

> thanks
> kott

--
Regards

Stephen Hope - remove xx from email to reply

 
 
 

!00B-FX :Ethernet over Fiber Question

Post by Kot » Wed, 16 Jul 2003 16:17:04


Hello -
Thanks for the answers. I am doing some lab tests  on these and what I
saw was all 11111(84 1s ) on the line, when the Rx on Port 1 is
removed.

thanks
Kott




> > Hello -

> > I have two 100B-Fx ports(Port1 and Port 2)connected . If I pull out
> > the Receive on  port1, , there is packet loss(as expected).What I want
> > to know is that why is there no one-way  data traffic ( i.e from Port
> > 1 Tx to Port 2 Rx)?
> > Any explanation on this would be appreciated.

> Some 100 Base-FX devices implement a function called "far end recieve
> failure" or similar

> The ports only come up if the device can see keepalives at layer 1 from the
> far end

> This was invented to fix the 1 way link problem, since fibre links tend to
> be in backbones, which is where resilience is most used, and a 1 way link
> can lead to spanning tree loops and kill an entire layer 2 set of switches
> and hubs.

> > thanks
> > kott

 
 
 

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