RE: [EFM] RE: Relative OSP Costs of PON vs. P2P
>I believe there is a misconception we are locked in regarding P2P networks.
>The thread so far shows a concentration factor of 1:3 (32x1G in, 10G out).
>This is a very hefty number that does not scale well in medium to large
>deployments.
>
>A neighborhood switch serving 1000 customers will have a 300G uplink! While
>a typical CO with 10000 customers will have a 3T uplink. Backbones can't
>handle so much traffic, especially when it is not necessary. A large POP
>will have a 10G uplink, and 40G in the far future, this is a concentration
>factor of 1:1000.
I believe there is a miscalculation here - your neighborhood switch @ CO
would have 300M of bandwith per subscriber. With the 1G PON, 1:32 split
ratio and no any oversubscription, the number is a bit over 30G - and
according to above 1:3 ratio this would be about 10G, which is a very
reasonable number cost wise.
Backbones can handle the capacity, single fiber can carry over terabit/s
NOW, with the equipment commercially available from multiple sources
although the cost is still high. Typical backbone has ~16 ducts, with
four inner ducts a piece, and single innerduct can handle ~800 fibers
(conservatively). Only thing keeping us from low concentration ratios
at a moment is cost and lack of need for such high sustained bandwiths
due to bursty nature of traffic.
The concentration discussion in pt-pt vs. PON context is missing a few
points:
1.) pt-pt systems have virtually unlimited capacity from OSP plant
perspective, and the per subscriber bandwith can be set anywhere system
operator wants, without affecting any other users in the system. Thus
the future upgrades are much easier than in PON (no modifications to
all subscribers required for speed upgrade, no downtime or plant
modifications for WDM upgrades & no differences in customer equipment
for the different wavelengths like in WDM PON). When the concentration
is done in the switch in pt-pt system, the only things that need
to be changed for any bandwith point are affected customers equipment,
and associated CO equipment.
2.) the oversubscription in the access portion (in PONs) requires
careful resource management (especially if anything better than
best effort is required). This adds to cost & management overhead.
3.) aggregates of traffic from large user populations (1000-10000:s
vs 10:s) behave better with respect to burstiness - this suggests that
it might actually help to have the concentration done in switch.
4.) discussion is omitting the operational cost differences, where
pt-pt would have advantage over PONs, although these are hard to
quantify them are important part of the system life time cost.
>Hence, although theoretically EPONs provide lower bandwidths
>due to sharing of the medium, there is no difference what so
>ever in practice between P2P and EPON networks.
This is not true, in P2P the operator can match the access speed
to any point, with the backbone concentration ratio (done in
switch) that satisfies the required QoS constraints with respects
to loss rates, delay, etc. PONs cannot simply do this for higher
bandwith subscribers (or essentially "degrade" to pt-pt system).
Peoples are really doing this in practice for various types of
users and SLAs right now.
PONs definitely have their place, which is for the operators who have
some fiber already installed (most), and in situations where the
services do not (ever) require the high bandwith available in pt-pt
systems.
Pasi