[AusNOG] Discussion point: Why aren't the NBNCo tails symmetric in speed?

[David Beveridge]

On Wed, Apr 9, 2014 at 3:22 PM, Greg Anderson <ganderson at raywhite.com> wrote:
> On 9 April 2014 12:08, Lincoln Dale <ltd at aristanetworks.com> wrote:
>> Lincoln Dale | Principal Engineer, Arista Networks Inc. |
>> ltd at aristanetworks.com
>> au did: +61 3 9999 7442 | m: +61 417 457 965 | us did: +1 408 547 5782
>>
>>
>> On Mon, Apr 7, 2014 at 8:52 PM, Skeeve Stevens
>> <skeeve+ausnog at eintellegonetworks.com> wrote:
>>>
>>> - The fibre to the home is symmetric capable
>>
>>
>> Not true.  Its not "symmetric capable" because of the timeslots of how the
>> upstream works.
>>
> Not true.  In fact Lincoln, in my understanding you just mistakenly tried to
> correct Skeeve's statement which was already correct.  I believe the TDM of
> the NBN's PON network has no bearing on its (a)symmetric nature, only the
> maximum potential speeds that may be achieved in either direction.
>
Must understanding of GPON is as follows. The downstream can transmit in
any proportion to any endpoint as it sees fit.  The endpoints can only upload
when they have a time-slot as to avoid a collision with another endpoint.
If an endpoint is not transmitting any real data, then some of it's timeslice
can be reallocated to another busier endpoint.
Therefore there would be some loss of efficiency in upload as the nodes
adjust the timeslices.  I don't know big of an effect this has in practice.