Re: Upstream bandwidth usage

[Brandon Jackson <bjackson () napshome net>]

> > Why would they mandate such a thing? That seems like purely an operator decision.

It wasn't an arbitrary decision. The downstream has a single "talker",
the OLT, so it can use 100% of the "airtime" for itself to talk to
anyone on the port.

The upstream on the other hand has 1-32 or even more talkers that all
have to be syncrozied to talk at specific times even including guard
bands to account for slight differences is time keeping, not only
that, not every ONT is at the same fiber distance so an ONT that is
closer must wait for a signal from an ONT that is farther to "pass"
it.

All of this creates some inefficiencies in the upstream. Now, it has
gotten better with better technology of course but GPON is already
12-19ish years old.


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Brandon Jackson
bjackson () napshome net

On Thu, Jun 9, 2022 at 9:12 PM Mel Beckman <mel () beckman org> wrote:
> I’m not mistaken, it also depends on the optics in the splitter, given that GPON is bidirectional single strand fiber.
>
> -mel via cell
>
> > On Jun 9, 2022, at 5:01 PM, Raymond Burkholder <ray () oneunified net> wrote:
> >
> > 
> >
> > > On 2022-06-09 17:35, Michael Thomas wrote:
> > >
> > > > On 6/9/22 4:31 PM, Mel Beckman wrote:
> > > > Adam,
> > > >
> > > > Your point on asymmetrical technologies is excellent. But you may not be aware that residential optical fiber is 
> > > > also asymmetrical. For example, GPON, the latest ITU specified PON standard, and the most widely deployed, calls 
> > > > for a 2.4 Gbps downstream and a 1.25 Gbps upstream optical line rate.
> > >
> > > Why would they mandate such a thing? That seems like purely an operator decision.
> >
> > There are also vendor issues involved.  I am glad that Mel mentioned 'optical line' rate.  Which becomes a 
> > theoretical thing.  If the line cards aren't set up with buffering properly, then line rate won't be seen.  And I 
> > think the line cards can also be easily over-subscribed.  Oh, and due to the two or three step fan-out of 8/16/32, 
> > upstream becomes even more limited.
> >
> > So, if you have FTTH with 1::1 house::port, then you are cooking with fire.  Else, it is the luck of the draw in 
> > terms of how conservative the ISP is provisioning a GPON infrastructure.  Which, I suppose, depends if it is 1G or 
> > 10G GPON.