Paul Brooks pbrooks-link at layer10.com.au
Thu Apr 9 12:08:13 AEST 2009

George Bray wrote:
> Paul, thanks for your figures and that article link.
> Are FTTP tails generally configured as symmetric pipes in existing
> scenarios (Japan/Korea)? Is a bridged interface by definition
> symmetric?
No, and not really - the bridge itself might be symmetric (a standard 
ethernet port), but the bandwidth back upstream to the network is u 
sually less.

See Chunhwa Telecom's FTTx rates for one point-example of services 
offered in Korea at the moment:

"2. The download/upload speeds for this service are 3M/768K, 10M/2M, 
50M/3M, 100M/5M."

I was a bit disappointed when I saw this - the upstream connection 
should be expected to be greater than this, and there is nothing 
preventing an operator providing symmetric service options - again, in 
the GPON technology I outlined earlier, the downstream link is 2.5 Gbps 
shared, the upstream PON link is half that - 1.25 Gbps or so - so I 
can't see a technical reason why upstream:downstream ratios need to be 
worse than 1:2.
In fact, if half the downstream capacity is tied up with television and 
other one-way traffic (channel-change signals upstream are negligable) 
then 1:1 symmetric links for data should be achievable - it appears to 
be a product marketing issue, not a technical issue that makes these 
plans so asymmetric.

> And do you think we can expect multicast to be enabled across the
> entire net? Is IPv6 multicast in production use these days, or just
> where I've seen it being tested in academia?
I'm sure the operator may use multicast to distribute its own PayTV 
services and thinsg like that, but enabling multicast for the general 
subscriber might be stretch, unless service providers can successfully 
lobby the RuddTelecom engineers that it is required in order to fulfill 
the objective of open-access for all service providers, as the efficient 
method of enabling multiple competing PayTV service providers and 
multimedia education service providers.


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