[LINK] Congestion (was Re: NBN to cost 24 times South Korea's faster network, says research body)

[Richard Chirgwin]

George,

On 21/02/11 12:00 AM, George Bray wrote:
> Thanks Richard.
>
> So it's the switches that have knowledge about the MAC addresses to
> send to? How is this managed without the equivalent of SAP for
> discovery?
Eg:
http://www.ciscopress.com/articles/article.asp?p=101367

The switches build a table recording which MAC address is associated 
with which port.

RC
>> My question: is there a reason that multicast is necessary for NBN Co?
>> Couldn't the retail ISPs simply use IP multicast themselves?
> For resources that need to go everywhere in AU, I'd say NBN Co would
> need some sort of multicast.  It would be nice if all of the
> free-to-air TV channels from all over the country were available to
> all users on all RSPs. Seems rather silly for the broadcasters to have
> retransmission agreements with individual providers when a national
> backbone agreement (and appropriate amendments to the act) would serve
> everyone.
>
> George
>
>
> On Sun, Feb 20, 2011 at 4:54 PM, Richard Chirgwin
> <rchirgwin at ozemail.com.au>  wrote:
>> George, I'll pick this up, since it was my poor memory that gave this to
>> IP multicast instead of Ethernet multicast.
>>
>> Simple answer - one happens at layer 2, the other at layer 3.
>>
>> Longer simplified answer.
>>
>> Ethernet multicast is based on MAC addresses - so the same incoming
>> Ethernet frame gets switched to multiple MAC addresses.
>>
>> IP multicast works in routers - the same TCP/IP packet gets routed to
>> multiple IP addresses.
>>
>> It used to be that Ethernet (switching) would handle the same thing
>> faster than IP (routing), but I guess that gap is narrowed somewhat!
>>
>> In the case of the NBN - still sticking to a basic explanation that
>> others can expand upon if they wish - it's because it keeps the roles
>> clearly delineated. NBN Co is not supposed to route traffic; that's the
>> job of the retail ISPs.
>>
>> My question: is there a reason that multicast is necessary for NBN Co?
>> Couldn't the retail ISPs simply use IP multicast themselves?
>>
>> RC
>>
>> On 20/02/11 3:50 PM, George Bray wrote:
>>> On Mon, Feb 14, 2011 at 10:39 AM, Paul Brooks
>>> <pbrooks-link at layer10.com.au>    wrote:
>>>
>>>> Note also that as far as the NBN is concerned, 'multicast' is ethernet multicast, not
>>>> IP multicast (although the two layers might need to be connected), and the multicast
>>>> capability might well be unidirectional - from the PoI towards the user, not from
>>>> user-to-user.
>>>>
>>>> Paul
>>> Paul, what's the difference between ethernet multicast and IP multicast?
>>>
>>> George
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>>
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