[SI-LIST] Re: Fibre channel interconnect margins

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: David Instone <dave.instone@xxxxxxxxxx>
  • Date: Tue, 04 Jul 2006 03:39:18 -0700


I would just like to make certain that we are talking along the same 
lines here.  The operation of the oscillator, no matter what its 
construction is causal.  So the closest that any two events can occur 
is epsilon.  That means that any single incremental interval can 
never have jitter of more than -(1UI-epsilon).

If on the other hand we want to integrate phase compared to some 
distant fixed timing reference, then a stream can theoretically 
precess total time interval error by an unbounded amount.


At 03:10 AM 7/4/2006, David Instone wrote:
>   I didn't disallow an infinite time between events.  I allow for 
> the time between events to be between 0 and infinity, but not negative.
>Thus if I'm measuring the time between edges and my reference I can 
>measure an infinite time between my reference and a following edge 
>but never more than 1 UI between the last edge and my 
>reference.  That last edge could of course be from a edge that 
>should have occurred an infinite amount of time in the future, but 
>from the point of view of the measurement it's only 1 UI early.
>steve weir wrote:
>>David, I disagree.  It does not change causality.  It changes the 
>>incremental delay between two events.  Imagine for a moment that we 
>>have a simple relaxation oscillator as the basis of our VCO.  In 
>>the presence of an infinitely large noise pulse, which is the limit 
>>for random noise, it takes an infinite amount of time for the ramp 
>>to reach the threshold.  The next cycle will not begin untilt he 
>>current cycle completes.  It may sound like something from Douglas 
>>Adams, but it really is mathematically and physically sound.
>>At 01:50 AM 7/4/2006, David Instone wrote:
>>>Because it makes for a nice simple clean definition.  However, I 
>>>believe you have to take the real world into 
>>>consideration.  Allowing the RJ to be really unbounded means that 
>>>each edge in a bit stream could be advanced or delayed by an 
>>>infinite amount.  Taken to extremes this means that  the order 
>>>of  edges  could be reversed.
>>>This is obviously absurd, the measured time between edges can 
>>>reduce until it is zero, it cannot go negative.  The time between 
>>>edges can of course go to +ve infinity, but that isn't a bit 
>>>error, the system has failed or been switched off.
>>>steve weir wrote:
>>>>RJ really is unbounded by definition.
>>>>At 09:46 AM 7/3/2006, Steven Kan wrote:
>>>>>>Date: Fri, 30 Jun 2006 21:48:56 -0700
>>>>>>From: Alan.Hiltonnickel@xxxxxxx
>>>>>>Subject: [SI-LIST] Re: Fibre channel interconnect margins
>>>>>>In fact, I think that companies DO ship products that toss a random
>>>>>>error approximately every 10e-xx or so. Why? Because the statistical
>>>>>>theory behind those errors is that random/Gaussian noise is, by
>>>>>>definition, unbounded - errors are a fact of life, even if the error
>>>>>>rate is very low.
>>>>>I suppose we're way off in the weeds, here, but is the noise actually
>>>>>unbounded? Or does it just behave in a Gaussian-like manner 
>>>>>within the realm
>>>>>of times/rates that matter for shipping product? I suppose if I sat in my
>>>>>chair for long enough, a truly unbounded system might cause a gold bar to
>>>>>pop into existence on my desk, but my empirical GBR (gold-bar rate) is
>>>>>currently 0.
>>>Dave Instone
>>>Oxford Semiconductor Ltd
>>>25 Milton Park
>>>Oxon ox14 4ea
>>>+44 (0)1235 824963
>Dave Instone
>Oxford Semiconductor Ltd
>25 Milton Park
>Oxon ox14 4ea
>+44 (0)1235 824963

To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:

List technical documents are available at:

List archives are viewable at:     
or at our remote archives:
Old (prior to June 6, 2001) list archives are viewable at:

Other related posts: