[SI-LIST] Re: Jitter transfer - urgent
- From: david_instone@xxxxxxxxxxxxxx (David Instone)
- To: a0756869@xxxxxxxxxxxx
- Date: Wed, 05 Sep 2001 15:01:15 +0100
Dear Krishnan,
Fibre Channel does not specify jitter transfer, Only Jitter Output
and Jitter Tolerance. These are numerical values for these two
specified at 6 points (compliance, or interoperability points) in the
link between tx and rx. (Actually this is not quite technically correct,
it is specified at six points between the output of one retimer to the
input of another retimer) The numerical values at each point are
specified for each variant of both speed and interconnect( copper or
optical).
Jitter transfer is not specified in Fibre channel as the jitter
output from a reclocker or repeater depends on the input jitter to it
and its jitter frequency content. From a receivers point of view it
knows only what amount of jitter it can tolerate (jitter tolerance)
Thus if a link is implemented using reclockers rather than retimers it
is up to the implementer to ensure that, what ever input device is used,
the jitter output from the interconnect to the receiver will not exceed
the amount of jitter output specified at that point. The value for
jitter tolerance at any point is always higher than the jitter output at
the point, which ensures that the Rx has a margin to handle external
interference.
For your convenience I have included the official FC definitions of
repeater, retimer and reclocker below.
For the numberical values I would recommend you download the current rev
of FC-PI, which is currently undergoing its public review comment
resolutions.
ftp://ftp.t11.org/t11/pub/fc/pi/01-025v3.pdf
With regard to GBE, they followed the jitter format of the FC standard
so I would suspect they have no specs for jitter transfer either. They
also use less interoperability/compliance points.
3.1.66 repeater: An active circuit designed to modify the (FC) signals
that pass through it by changing any or all of the following parameters
of that signal: amplitude, slew rate, and edge to edge timing. Repeaters
have jitter transfer characteristics. Types of repeaters include
Retimers, Reclockers and amplifiers.
3.1.63 Reclocker: A type of repeater specifically designed to modify
data edge timing such that the data edges have a defined timing relation
with respect to a bit clock recovered from the (FC) data at its input.
3.1.67 Retimer: A type of repeater specifically designed to modify data
edge timing such that the data edges have a defined timing relation with
respect to a bit clock derived from a timingreference other than the
(FC) data at its input. A Retimer shall be capable of inserting and
removing fill words (see FC-FS) from the (FC) data passing through it.
Inserting a retimer into a TxRx Connection creates two TxRx connections.
Retimers provide complete isolation of input wander, and their output
jitter is unrelated to the input jitter. Retimers are further
characterized by their signal properties including their input jitter
tolerance and their jitter output. These input and output properties may
be associated with selected interoperability points dependent on the
application.
Rengarajan S Krishnan wrote:
>
> Si Gurus,
>
> Can someone let me know the Jitter Transfer specs for
> Gigabit Ethernet and FibreChannel.
> Would appreciate if you could give me the same for SONET/SDH too.
>
> Thanks
> Krishnan
>
> -
> R.S.Krishnan, ASIC Product Development Center
> Texas Instruments (India) Ltd, GolfView Homes, Murugeshpalaya
> Bangalore 560017 Ph. +91-80-509-9194
> mailto:krishnan@xxxxxx
>
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--
Regards
Dave Instone. Compliance Engineer
Storage Systems Development, MP24/22
Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK.
Tel: +44 (0)23-92-496862 (direct line)
Fax: +44 (0)23-92-496014
http://www.xyratex.com Tel: +44 (0)23-92-496000
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