[AusNOG] Simon Hackett's presentation from Comms Day yesterday - NBN fibre on copper prices

[Jonathan Thorpe]

While I strongly support the idea of users being able to have their own certified GPON NTD, it does raise an interesting point about the potential for abuse and interference with GPON in general.

What happens if someone directs a laser pointer (at approximately the correct wavelength) down a GPON fibre interface?
What stops people from using WDM equipment or simply an optical transceiver at a different wavelength to "steal" wavelengths that the splitter can distribute between people on the same splitter?

-----Original Message-----
From: AusNOG [mailto:ausnog-bounces at lists.ausnog.net] On Behalf Of Paul Brooks
Sent: Monday, 22 July 2013 12:45 AM
To: ausnog at lists.ausnog.net
Subject: Re: [AusNOG] Simon Hackett's presentation from Comms Day yesterday - NBN fibre on copper prices

On 21/07/2013 1:06 PM, John Edwards wrote:
> I think this argument is a distraction when compared to the costs of a FTTH network.
> Today there are millions of Australian mobile subscribers bringing 
> their own CPE to a data network on a shared medium that has a much 
> greater surface area than 31 neighbours, and everyone seems quite 
> content, even preferring this situation over the certainty of a fixed line.
I'm not sure its comparable - a rogue mobile handset can still only block out a single channel, other handsets in the immediate area will be using slightly different frequencies to transmit and receive on, as allocated by the signalling. if the rogue handset decided to ignore the frequency required by the basestation and used a different channel, its unlikely to affect more than a few handsets/calls in the immediate area. Plus, if it *was* doing a broad-spectrum transmission and blocking a large number of calls, its battery would soon be flat.

> I am pretty sure the OLT can do something about this in 2013.
Nope - upstream on GPON every terminal transmits upstream on precisely the same frequency, and the whole system relies on each one keeping to its timeslot so that only a single terminal's upstream laser is active at any moment. One rogue ONT activating its upstream laser out-of-sequence or on permanently will stomp over all upstream comms from every other terminal on that splitter, blinding the OLT receiver - and there's nothing the OLT can do about it.

The reason certification of ADSL CPE wasn't kept up is that a malfunctioning ADSL modem only affects that customer and its dedicated DSLAM port - if your modem is cactus, it doesn't hurt anyone but yourself, and it can't see anyone else's traffic so there aren't the same security concerns. The security concerns with user-subverted GPON CPE are significantly greater as each CPE sees every packet destined to all the other CPE on the PON.

P.


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