[AusNOG] Looks like the NBN will be a PON variant for sure...

Mark Smith marksmith at adam.com.au
Wed Apr 29 10:12:05 EST 2009

Nick Brown wrote:
> Narelle wrote:
>>     HFC networks are often operated as Layer 3 with customers even being
>>     able to see their neighbours at Layer 2.
>> Only if you do it badly. The older stuff was all bridged and really 
>> poor security wise. All the newer stuff is layer 3 and DOCSIS 
>> separates people nicely via RF encoding.
>> You should really be able to see your neighbours, anyway. Why not use 
>> LANs like they were meant to??
> Because from an ISP operational perspective thats a horrible thought? 
> You lose the ability to shape / count / monitor traffic, in addition to 
> the increased support because Joe next door has been browsing someone 
> else's $c share.

Look up "IPoE" in Google (as silly as the acronym is), all those 
problems have or are being solved (e.g. cable networks use DHCP, and all 
the Ericsson DSLAMs that a lot of ISPs have are (and have been for a 
long time) "IPoE" capable)). Cisco's ISG product can apparently turn 
DHCP leases into RADIUS accounting records for example.

In a "native", not wholesale ADSL environment, the 8 byte per-packet 
overhead and BRAS processing load, MTU issues and hair-pinning of PPPoE 
encapsulated traffic are very expensive, when you consider that the only 
real purpose of converting a multi-access medium like Ethernet into a 
point-to-point virtual link is to be able to authenticate the user. If 
you already know where they live (and DSLAMS can insert that circuit-id 
in DHCP requests), why do you care what username / password they use?

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