RE: Considerations for > 5 kms.

["Vipul Bhatt" <vipul.bhatt@xxxxxxxxxxx>]

Jonathan,

Since I started the topic, I will be happy to present three or four
PowerPoint slides to set the framework for the question and invite
responses from the attendees. Estimate: five minutes for presentation, 15
minutes of open discussion following it.

For the flow control question, someone who participated in the 802.3x
process will be a very useful contributor to the discussion following my
presentation.

Thanks,
Vipul

Vipul Bhatt
Project Manager - Link Extenders
Finisar Corporation
274 Ferguson Drive
Mountain View CA 94043
Phone: (650)691-4000 x113
Fax: (650)691-4010
Email: vipul.bhatt@xxxxxxxxxxx

==============================================


> -----Original Message-----
> From: Jonathan Thatcher [mailto:jonathan@xxxxxxxxxxxxx]
> Sent: Thursday, May 20, 1999 7:07 AM
> To: 'Vipul Bhatt'; stds-802-3-hssg@xxxxxxxx
> Subject: RE: Considerations for > 5 kms.
>
>
> Anyone who feels qualified to put some thoughts together for
> these topics?
>
> jonathan
>
> > -----Original Message-----
> > From: Vipul Bhatt [mailto:vipul.bhatt@xxxxxxxxxxx]
> > Sent: Tuesday, May 18, 1999 7:14 PM
> > To: Jonathan Thatcher; stds-802-3-hssg@xxxxxxxx
> > Subject: Considerations for > 5 kms.
> >
> >
> > Jonathan,
> >
> > I would like to suggest a couple of topics for discussion, in case you
> > haven't already included them in your agenda.
> >
> > 1. Use of WWDM in 1550 nm range for dark fiber, single mode,
> > metropolitan
> > area applications: It seems to have some advantages. A
> > combination of DFB
> > Isolated lasers and low attenuation will permit the link to
> > support useful
> > distances (25 kms.?). If wavelengths are spaced widely enough, use of
> > uncooled lasers will reduce cost and complexity of transmitters. These
> > lasers can be directly modulated. If four wavelengths are
> > selected, each
> > wavelength needs to carry data only at 2.5 Gbps (3.125 Gbaud
> > for 8B10B),
> > which makes jitter issue more manageable compared to the 10
> > Gbps serial
> > option.
> >
> > 2. Flow Control Implications: I am perplexed as to why no one
> > is talking
> > about the impact of extended distances on the buffer size of 10GbE
> > switches. Compared to Gigabit Ethernet, as we consider longer
> > distances and
> > ten times the bit rate, it will take a much larger buffer in
> > a switch to
> > operate properly. This is because a switch must accommodate
> > the greater
> > number of bits that can still be in the pipeline after the 802.3x flow
> > control is invoked. (Propagation delay through one kilometer
> > of fiber is
> > the equivalent of more than 6 kilobytes of data at 10 Gbits/sec.) The
> > longer the distance, the greater the buffer size required, or
> > the switch
> > has to drop the packets. Until now, this hasn't been an issue because
> > Ethernet was not expected to work at long distances so modest
> > buffer size
> > was adequate. If we want 10GbE to work over MAN or even WAN
> > distances, the
> > required increase in buffer size for switches may be so large
> > that at some
> > point, packets have to be dropped. That may well be the basis of a
> > cost-throughput tradeoff, but we should decide if we want to
> > address that
> > tradeoff or leave it to implementers.
> >
> > Thanks,
> > Vipul
> >
> > Vipul Bhatt
> > Finisar Corporation
> > 274 Ferguson Drive
> > Mountain View CA 94043
> > Phone: (650)691-4000 x113
> > Fax: (650)691-4010
> > Email: vipul.bhatt@xxxxxxxxxxx
> >
> > ========================
> >
>