Re: Clock Tolerance and WAN PHY
This is an interesting email chain.
I am wondering if these comments need to be madeand responded to in the
next rev of the draft document.??
Bruce Tolley
Cisco Systems
At 12:03 PM 1/23/01 -0500, Geoffrey Garner wrote:
>James, Tom,
>
>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
>mapping
>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.
>
>Regards,
>
>Geoff Garner
>Lucent Technologies
>101 Crawfords Corner Rd.
>Room 3C-511
>Holmdel, NJ 07733
>USA
>+1 732 949 0374 (voice)
>+1 732 949 3210 (fax)
>gmgarner@xxxxxxxxxx
>
>Tom Alexander wrote:
>
> > James,
> >
> > 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
> >
> > Luigi,
> > 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?
> >
> > James
> >
> > --- 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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