[LINK] NBN Broadband Plan

[Tom Worthington]

David Lochrin wrote:
> I don't fully understand what layered services NBN Co. is proposing 
> for the NBN.  Can anyone clarify this point? ...

The NBN architecture document is reasonably clear: 
<http://www.nbnco.com.au/content/upload/files/NBN001_concept_paper_final.pdf>

My summary is at: 
<http://www.tomw.net.au/blog/2009/12/nbn-broadband-plan.html>

> A GPON network is lit fibre but not much more, as I understand it.

GPON (ITU-T G.984) is a passive optical fibre network. One signal is 
physically split and sent to between a dozen and one hundred homes. GPON 
gives a choice of layer 2 protocols to share the optical signal on the 
cable.

> Ethernet at layer-2 is also fine, assuming it's just a standard for 
> local interfaces  ...

My understanding is that NBN plans to provide a similar physical 
interface for home users as current ADSL modems. That is there will be 
an RJ-45 socket for a copper cable Ethernet connection. The home user 
will not have an optical connection to the network. The protocols to be 
used are less clear.

> But all the other services mentioned need layer-3 services... QoS ...

Yes, NBN Co. are planning four levels of QoS. But keep in mind that the 
layers are just an abstraction, they are not necessarily hard and fast 
boundaries in real services. Providing something like telephony or IPTV 
is likely to require specifications at all layers.

I think NBN are taking the right approach by not trying to do too much 
specifying too soon. It is not clear at present what customers will use 
the network for (assuming they want it at all). So there is no point 
wasting effort on complex specifications for services which may never be 
used.

> And in Tom's point-5,NBN Co. agree that IPTV will need layer-3. ...

IPTV has implications down to the hardware layer. Multicast can be
implemented in hardware on a passive optical network, as the one optical
signal is split and delivered to several homes. However, the protocol
used over this many not permit multicast, for example PPPoE. It would be
a shame if most of the network was filled with millions of copies of old
episodes of "I Dream of Genie" being sent by some pay TV company to
subscribers.

More at: 
<http://www.tomw.net.au/blog/2009/12/nbn-passive-optical-network.html>.


-- 
Tom Worthington FACS HLM, TomW Communications Pty Ltd. t: 0419496150
PO Box 13, Belconnen ACT 2617, Australia  http://www.tomw.net.au
Adjunct Lecturer, The Australian National University t: 02 61255694
Computer Science http://cs.anu.edu.au/people.php?StaffID=140274