FTTP - question out of interest

Why is the upload speed for FTTP not symetrical with the download speed?

I can get my head around with FTTC and ADSL the bandwidth is limited by the line characteristics and more bands are possibly assigned to download, which makes sense.

But why would the FTTP not be 330 down / 330 up?

Surely all of the links in the BT network are symetrical so you would expect with the many 1000's of ADSL / FTTC connections there would be a significantly less upload use on the links compared to download use.

So why restrict the upload when on the face of it to me it seems there could be all of this unused capacity in the BT network??

Openreach made the decision to only offer that, one presumes on feedback from BT Wholesale, Sky and TalkTalk.

Handling 330 + 30 Mbps of capacity is very different to handling 330 + 330 Mbps of capacity though in the network. So suspect if they had opted for a more symmetric option it would have been around 180 + 180 Mbps, and actually cost more.

If demand for 330/30 is higher than the 330/20 product then we may see other higher speed uploads too.

PON systems are usually asymmetric as its a Gbit fibre with its capacity divided up by N premises so you can pick and choose.

I did read that the upstream lasers tend to be less lower spec / power and operate in more variable conditions too.

http://www3.alcatel-lucent.com/technology/gpon/

GPON has a downstream capacity of 2.488 Gb/s and an upstream capacity of 1.244 Gbp/s that is shared among users

Note that it's easier for BT to control the effects of congestion on the 2.488 Gb/s downstream (as they can shape before the GPON kit, at a point where they are aware of which traffic came from which providers, and of the priorities of each bit of traffic) than it is on the upstream (where they know which subscribers have traffic, but not necessarily the priority of that traffic).

I believe BT are choosing to use a 32-way split most of the time, which gives them around 39MBit/s/subscriber uncontended upstream. Coincidentally, the fastest FTTP products have 30MBit/s upstream.

http://sites.google.com/site/amitsciscozone/home/gpo... for technical depth

Commercial reasons. 330/30 already supplants some leased lines. Going to 330/100 say will supplant 100Mb leased lines - offices will find it cheaper to take a 330/100 FTTP service or even two of them and a slower, secondary FTTC service rather than a single leased 100/100 line with no back up at all.

In reply to a post by Ignitionnet:

Commercial reasons. 330/30 already supplants some leased lines. Going to 330/100 say will supplant 100Mb leased lines - offices will find it cheaper to take a 330/100 FTTP service or even two of them and a slower, secondary FTTC service rather than a single leased 100/100 line with no back up at all.

That's assuming the cabling even runs near the office. At office we have lots of ADSL lines for specific testing projects. Some would love FTTC speeds but as we are a "business" we won't get this. The projects are small and can't budget for a real leased line/circuit. (Yes, our corporate uses leased lines).