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

Paul Brooks pbrooks-link at layer10.com.au
Mon Feb 21 13:09:44 AEDT 2011

On 21/02/2011 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?

In a closed network, IGMP Internet Group Management Protocol for IPv4 does this -
however one of the issues with use on a public Internet platform is that IGMP has no
concept of security/permission granted by the server. In an open network with possibly
many multicast sources, it is generally not true that every client is permitted by all
sources to become a client and receive the traffic, and IGMP has no mechanism for the
multicast source to say "no, you aren't authorised to be a customer".

In the NBN, with its enduser-NBN-serviceprovider model, it can be managed simply by
the end-user applying to the service provider to become a customer, and the service
provider then instructing the NBN provisioning system to add the end-user into that
service provider's distribution list within the NBN switches.

>> My question: is there a reason that multicast is necessary for NBN Co?
>> Couldn't the retail ISPs simply use IP multicast themselves?
Not efficiently - the NBN model is to set up a dedicated VLAN tunnel between each
subscriber and their ISP, so if the NBN didn't support multicast within its fabric, 
the ISP would need to send one copy of each multicast IP packet to each subscriber on
each of the its subscribers' tunnels - the ISP would need to do the replication before
injecting the traffic into the NBN, sending a dedicated copy to each customer and many
multiple streams of the same stuff through their interconnect link and through the NBN

> For resources that need to go everywhere in AU, I'd say NBN Co would
> need some sort of multicast.

Yes, NBN Co does need to participate in the multicast replication process, for traffic
that needs it, so the replication can occur at the closest point to the customer.

>   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

One issue is that all NBN services - including a multicast service - ultimately map a
physical port at the end-users site to one particular service provider. For this
free-to-air television scenario to come about, each commercial IPTV pay TV provider
would need to redistribute all the FTA channels within its lineup, and also someone
(probably government) would need to set up a separate FTA-channel-only IPTV service
provider, and a compatible set-top-box distribution system, so that those that choose
not to have a commercial service can access the free one.

I rather suspect that with all the money spent on digital RF transmitters and a
satellite distribution system for those outside the digital RF transmitter footprint,
there won't be a lot of support for setting up a FTA provider over the NBN, since it
can already be received through an RF medium. Of course, I could be wrong.


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