[LINK] FTTN architecture

Paul Brooks pbrooks-link at layer10.com.au
Thu Feb 4 12:36:31 AEDT 2016


On 4/02/2016 11:52 AM, David Lochrin wrote:
> This thread follows on from "NBN backup service"...
>
> On 2016-02-02 12:14 Paul Brooks wrote:
>
>> No - call routing and handling will be done by the ISP's softswitch, likely to be located in the nearest capital city - I doubt there will be any voice-handling infrastructure in a node or POI, just effectively an Ethernet tunnel between NTU analog port and softswitch through the backhaul-POI-NNI-CVC-AVC-NTU chain.
> My understanding is that an ISP must have a connection to every POI which services an area containing their customers.  A POI services a "connectivity service area" or CSA and all communication within a CSA is done at OSI level-2, with ADSL / VDSL between the nodes & users.
>
> So someone with existing ADSL & VoIP services doesn't need to change anything much when they migrate to an FTTN-based NBN service except that they'd have to configure a properly allocated VoIP telephone number for communication with other telephone users on the national network, and perhaps some other minor configuration changes.
Most probably they'll be replacing their ADSL modem with a VDSL2-capable modem, so
they might need to do some re-working of the config in the new modem, but essentially
correct - the number shouldn't need to change, and however they are connecting to the
VoIP service is likely to be very similar.

>
> But what do traditional POTS users do when the local NBN network is fully cutover and the exchange effectively closes down?  Will they each be issued with an NTU, or do the kerbside nodes contain analogue signal converters?
For FTTN they'll each need to obtain a VDSL2-capable modem, from their RSP or possibly
from a retail store, which complies with/is certified for the NBN infrastructure. Most
of these also include an analogue voice port and VoIP software inside, which
effectively replaces the analogue socket on the wall. Ideally the RSP will program up
the VoIP module in the router to talk to the RSP's softswitch, and the user will just
unplug their analogue handset from the wall, and plug it into the voice port on the
modem/router.

Alternatively they might get a stand-alone VoIP SIP adapter, and plug their handset
into that.

Note also that the ISP need not be the same as the voice RSP - the VoIP call might
pass through the ISP to a different service provider providing the telephone service.
The telephone RSP doesn't need a connection to any POI or the NBN anywhere.


>
> An ISP which doesn't connect to all 121 or so POIs must have a connection to a service provider which can route voice calls to / from users in those CSAs.  So how does an ISP decide how to route a call when the called number may be with them, with a user on a different ISP in the same CSA, or with a user in a different CSA to which the ISP has direct access, or another CSA altogether?
The same way they do now - they have an upstream connection to a voice call provider
who can direct the call onwards - locally, nationally, and globally. If the call is
directed to another number that is not directly with that RSP, the RSP's softswitch
passes it upstream to be handled.

There are two national call routing databases - the ACMA register of which number
ranges have been allocated to which networks/providers, and the ported number register
that holds the exceptions.

Eventually the call gets passed up to a voice network with hooks into the national
call routing databases, which routes the call to the provider servicing the number
being called - which somehow makes the destination phone ring.

See https://www.thenumberingsystem.com.au/#/number-register/search (you can download
the entire range allocation database at bottom right) and look up your own number to
see the original carrier the number was allocated to.


>
> Is there some sort of online directory which maps telephone number, CSA, ISP, and level-2 address?  Who maintains it, NBNCo?
As above - ACMA maintains the directory mapping telephone number to provider/network. 
Its up to each provider to work out the rest of how to direct an incoming call to make
their own customer's handset ring, whether its on NBN, copper, fibre, wireless, or wet
string.

>
> The more I think about this the more questions arise.  For example, the potential for maintenance problems and "finger pointing" seems quite high.  And it may be difficult to define enforceable service standards.
There are already enforcible service and call quality standards, put in place way back
when service/network competition was introduced (think calling from fixed to mobile,
or copper to HFC voice). Adding the NBN into the mix as just one more possible
transport method doesn't change that aspect at all - or the propensity for
finger-pointing, which was already fairly high before the NBN came along!

Paul.



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