Re: Clock Tolerance and WAN PHY
I want to clarify Luigi's email; his point concerns the Optical Transport Network
(OTN) defined in
G.709; it does not concern the SONET network. I think this may have gotten lost
in the discussion.
Mappings have been defined in
G.709 to map constant bit rate (CBR) client signals into the OTN. One of
these mappings is for a 9.95328 Gbit/s nominal frequency client signal. The
requires that the CBR client
have a frequency that is within +/- 20 ppm of the nominal frequency.
The 9.95328 Gbit/s signal could be an OC-192 or STM-64 or, if desired, a
10 Gbe WAN signal.
If there is a desire that it be possible for the 10 Gbe WAN signal to be
carried by the OTN, then it would have to have a +/- 20 ppm frequency
tolerance (this is based on the way the mapping is defined).
Note that this is independent of the SONET network and whether or not
there is an ELTE at the other end of the WAN PHY link; rather, it is related
to whether it will be possible for
the WAN PHY to be carried over the OTN.
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Tom Alexander wrote:
> There is no intent or support for directly interfacing the WAN PHY to standard
> SONET gear, especially in outside plant applications. Off hand, I can think of
> the following obstacles, even if you did match the clocks:
> - The optics are completely different
> - Most of the overhead bytes are not supported (for instance, it
> would not be possible to provision the ring)
> - Much of the defects and alarm reporting is missing
> While it is certainly possible for someone to put back the missing overhead
> and defects and also use SONET optics rather than Ethernet optics, all this
> is totally outside the scope of the 802.3ae standard.
> Best regards,
> - Tom
> -----Original Message-----
> From: James Colin [mailto:james_colin_j@xxxxxxxxx]
> Sent: Sunday, January 21, 2001 12:54 AM
> To: Luigi.Ronchetti@xxxxxxxxxxxxxxxx; tripathi@xxxxxxxxxxxx
> Cc: stds-802-3-hssg@xxxxxxxx
> Subject: Clock Tolerance and WAN PHY
> I think that the motto in the WAN PHY standard is the
> introduction of a new framing scheme (As opposed to
> POS), rather than being gluelessly connectable to the
> SONET network. The WAN PHY is supposed to be connected
> to a SONET LTE (ELTE) that is doing clock drift and
> jitter adjustments.
> Even if the WAN PHY Clock requirements were identical
> to those of SONET, I'm not sure if the ELTE is still
> needed or the WAN PHY can be directly interface to the
> SONET ring. Can anybody comment on that?
> --- Luigi.Ronchetti@xxxxxxxxxxxxxxxx wrote:
> > Hi Devendra and all,
> > I think that is not enough to reduce the clock
> > tolerance to 50ppm.
> > As far as I know, ITU-T is going to approve
> > (February 2001) a new
> > recommendation (G.709) that defines OTN (Optical
> > Transport Network).
> > Future optical backbones over long distances will
> > likely to be realized
> > using G.709 and this will happen before 10 GbE final
> > approval.
> > In G.709, among the others, a CBR10G client signal
> > is defined as "a
> > constant bit rate signal of 9953280 kbit/s +/-20
> > ppm" (for example an
> > OC-192/STM-64 signal and then, in principle, also a
> > 10 GbE WAN signal).
> > So, in my opinion, at least for a 10 GbE WAN signal,
> > the clock
> > tolerance should be 20ppm.
> > Best regards,
> > Luigi
> > __
> > \/ Luigi Ronchetti
> > A L C A T E L via Trento, 30 - 20059 Vimercate (MI)
> > Italy
> > TND R&D phone: +39-039-686.4793 (Alcanet
> > 2-210-(3)4793)
> > fax: +39-039-686.3590 (Alcanet
> > 2-210-(3)3590)
> > mailto:luigi.ronchetti@xxxxxxxxxxxxxxxx
> > > -----Original Message-----
> > > From: tripathi@xxxxxxxxxxxx
> > [mailto:tripathi@xxxxxxxxxxxx]
> > > Sent: Tuesday, January 09, 2001 10:50 PM
> > > To: stds-802-3-hssg@xxxxxxxx
> > > Cc: tripathi@xxxxxxxxxxxx
> > > Subject: Clock tolerance
> > >
> > >
> > >
> > > Hi,
> > >
> > > Right now we are specifying the clock tolerance of
> > 100 ppm. Currently
> > > in-expensive
> > > oscillators are available with tolerance value
> > less than 50
> > > ppm. Just like
> > > we are moving
> > > voltage levels, it is time we revise the tolerance
> > value too.
> > > The elastic
> > > buffer
> > > requirements get simplified by this assumption. I
> > propose
> > > that we reduce it
> > > to 50 ppm.
> > >
> > > Regards,
> > > Devendra Tripathi
> > > VidyaWeb, Inc
> > >
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