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Re: Link Status thoughts and other status signals


For those of us that are unfamiliar with Fibre Channel optics, could you 
explain what the "Rate Select" function is?

Thank you,
Roy Bynum

At 04:42 PM 10/28/00 -0700, schelto.vandoorn@xxxxxxxxxxxx wrote:

>In the same sense as Rich did, I would like to throw in my 10 cents.
>Just as the link status needs to be defined, I see also the need to define 
>two additional signals in the other direction.  Namely transmit disable 
>and rate select.
>Transmit Disable
>laser transmitters are designed to always transmit light at a predefined 
>average level.  So even if the transmitter gets all zeroes at the input, 
>after a certain amount of time it will start transmitting static light. 
 >From the fiber Channel the experience has been, that in some instances 
>the cross talk from neighboring transmitters could be modulated onto this 
>static light signal.
>The receiver on the other side has gone into maximum amplification, 
>because it is not receiving a signal, and the outputs are "chattering" on 
>the input noise. If the input noise, to the receiver, contains some valid 
>signals, the signals might be interpreted by the upper layers as valid 
>signals, and the system will oscillate between initialization and shutoff.
>To avoid this, the new transceivers have a transmit disable pin, that will 
>shutoff the light coming out of the transceiver.  This signal has to be 
>provided by the upper layer.
>Rate Select
>This is also a new single on transceivers and in 10 GbE will be 
>optional.  But I can see for some implementations that this signal could 
>be useful to switch between different receive filters for different data 
>rates, or different PMD's,  if they are implemented.
>I strongly believe that we should also define these signals.
>Have fun