[LINK] NBN to cost 24 times South Korea's faster network, says research body

Paul Brooks pbrooks-link at layer10.com.au
Thu Feb 10 16:10:24 AEDT 2011

Thanks for the lead-in Richard...

On 10/02/2011 3:05 PM, Richard Chirgwin wrote:
> <by mistake I replied to Marghanita but not to the list>
> On 10/02/11 12:57 PM, Marghanita da Cruz wrote:
>> Stilgherrian wrote:
>>> On 10/02/2011, at 12:19 PM, Richard Chirgwin wrote:
>>>> Define "aggregate"! :-)
>>> Agreed. It's a bit like asking "Where does the traffic merge on the 
>>> roads?"
>> Well that analogy isn't too bad in this case, as I did mean the data 
>> traffic.

Yes, there will be multiple points of aggregation - and also multiple points of
disaggregation, depending on how the userbase becomes distributed across the
collection of retail providers.
However, this is only relevent if the network operator chooses to overbook the
available capacity, and I understand NBNCo will not be doing this.

1) The GPON fibre access network segment is the first (closest?) - currently that is
an aggregate of 2.4 Gbps downstream, 1.2 Gbps upstream, split up to 32 ways. If you do
the sums, at 3:40pm when all the kids get home from school, that would give around 80
Mbps per house (compared to the 100 Mbps performance limit), except....

 NBNCo, I understand, will not be overbooking the Ethernet virtual circuits between
the houses and service providers. Each customer will subscribe for a certain amount of
bandwidth through their ISP (lets say 50Mbps down, 20 Mbps up, for example), which
will be reflected in a Ethernet tunnel with reserved bandwidth across the GPON
network. NBNCo systems will not allow the aggregate bandwidth of all the tunnels to
exceed the available network capacity - if an ISP tries to provision a new customer
when all the bandwidth is reserved, they'll reject the order, and make moves to split
that network portion into two pieces.
This means each customer should be able to use the full capacity they have subscribed
for at all times, without any congestion between their house and the PoI. It also
means that at most times the GPON network will be virtually idle, and if it spikes to
much more than 10% of capacity I'll be surprised - the burst capacity will definitely
be there.

2) At the PoI, each ISP has the choice of how much capacity they provision on the
aggregated tunnel between the ISP and that PoI. If the ISP dimensions this too small,
then users of that ISP might experience congestion - but users through other ISPs
should not be affected. This is another point of aggregation - under the control of
the ISP, not NBN.

3) There could be points of aggregation within an ISP's backbone network, just as
there can be now.
4) There can be points of aggregation within an ISP's upstream supplier networks -
including international - just as there would be now.

>>> In the NBN, traffic is aggregated in the very first length of fibre, 
>>> because it's a herringbone-shaped GPON back to the exchange, or 
>>> possibly a node a few streets away.
>> The reason I raise this is that congestion/contention only seems to be 
>> raised as an issue with wireless cells. There was extensive discussion 
>> about the capacity of cells and prohibiting roaming between cells.
>> There has to be some point at which congestion/contention becomes an 
>> issue on the fibre.
congestion/contention is only an issue if the aggregate traffic demand is higher than
the aggregate available capacity. If two links each running at 5% are aggregated into
a third single link, which ends up running at 10%, there is no problem - thats good
efficiency. Its only if the two links are each running at 60% that the aggregation
causes a problem. Thats bad network management and poor forecasting.

> Yes and no.
> What do we need to experience congestion? Aggregate user traffic 
> exceeding the upstream capacity at some point.
> a. In the GPON part of the network I would consider severe congestion to 
> be unlikely for most end users (will welcome correction).
Correct - I believe  NBNco will be refusing bandwidth reservations that exceed the
available bandwidth, no overbooking, so no congestion.

> b. After traffic is "handed off" to the Layer 3 provider - either the 
> retail carrier or the intermediate wholesaler - contention is no longer 
> an NBN issue. It's about the provisioning of the retailer's core network.
>> Richard,
>> The example I had in mind was VoD/IPTV, Premium QoS Voice/Interactive 
>> Video, which is ofcourse the compelling killer app, as opposed to 
>> multicast cable TV.
>> ie where did the problem occur with the afore discussed "via 
>> broadband" ABC news reporter picture from Townsville. Was it in the 
>> digitisation of the picture, the transmission capacity at some point, 
>> or in the recording/decompression?

The video signal was being sent 'upstream' on whatever the broadband technology was -
so maximum of 1 Mbps on naked DSL, probably closer to 512kbps or 256 kbps on most
consumer ADSL links.
If it was 3G wireless, then even less upstream capacity available.

A video camera puts out a significantly higher video data rate - in the order of 2 - 4
- 8 Mbps for MPEG2 broadcast quality signal - which this wasn't, I suspect it was
someone's webcam pointed out the window.
The issue is likely to be a combination of the device being low resolution webcam to
begin with, probably compressing the signal inside the PC rather than a dedicated
video camera, but more importantly trying to squeeze the
signal upstream on restricted bandwidth link compared to the capacity the video signal
actually needed.

> However, from other discussions, it seems to me that compression 
> algorithms may have been the problem - the ABC was trying to put the 
> pictures in a skinny pipe, so quality suffered.
Is that a problem with the algorithms, or the skinniness of the pipe?

> I don't see this happening (say) in the NBN for IPTV content.
Nor do I, because:
    1) the cyclone picture was being sent upstream, IPTV will be transmitted
downstream - most plans will have much higher capacity downstream compared to up
    2) IPTV content will be captured with much higher quality cameras, and much higher
capacity MPEG-4/H.264 dedicated compression encoders, so better quality pictures
    3) IPTV over the NBN will be carried over QoS-enabled prioritising networks, not
the dismal excuses of best-efforts no QoS consumer broadband we have today


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