In reply to a post by garethr:

G.FAST isn't FTTDP necessarily.

True. FTTdp is a set of technologies for the node that will host G.Fast. It doesn't have to be located at the DP to be called FTTdp.

Back when the G.fast research started, the design aims were indeed to place these nodes at the DP - and all scaling work has been done predicated on this fact.

As one consequence, in particular, the chipsets are sized at 4, 8, 16 homes. Scaled to be exactly right for a DP.

The results from the research and the first batches of chipsets have emboldened BT - who now think they can lead/push the research to be considerably faster (lower noise floor, more bits per tone, more spectrum, non-linear coding, etc), and to increase the range. The increased range means they need hardware designs for more lines than currently exist.

The battle between short-range aficionados and long-range ones can be glimpsed in the recent Sckipio presentation mentioned here, towards the end:
http://forums.thinkbroadband.com/fibre/4417661-gfast...

Seeing the action going on in the research side, I think BT's initial plans for a G.fast rollout will be something of a holding pattern, in terms of range and capacity, because they really want to be deploying G.Fast-2.

If you're near enough to an existing cabinet you'll likely be able to order G.FAST. Why?

All very true. Whatever a G.fast node turns out to look like, it is a no-brainer to deploy a node at the existing cabinet location ... even if you have to carefully vet the lines which qualify to use it.

due to the fact it has a C-WDM splitter pre-installed unless it was one of the original 2010 cabs then you are SOL.

Didn't know that. Are they retro-fittable?

At 500 you can get 50 Mbps FTTC and 100Mbps G.Fast.
At 400 you can get 63 MBps FTTC and 200Mbps G.Fast.
At 300 you can get 76 Mbps FTTC and 280Mbps G.Fast.
At 200 you can get 80 Mbps FTTC and 300Mbps G.Fast.

Those broadly fit with the speeds being quoted by Sckipio (though theirs is a combined total):
http://gfastnews.com/index.php/90-r/157-suddenly-g-f...

I assume your FTTC figures really relate to unvectored capability. With vectoring, you'd likely get 100Mbps to 400m. Even without vectoring, you can get 80Mbps at 400m initially ... but the dreaded crosstalk will eat away at that.

In my area 100,000 properties 30-40% would get >200 Mbps. Maybe ish.

The Sagentia report gives a nice breakdown of line lengths:
http://postimg.org/image/bp372fcnn/

A design target range of 400m would perhaps capture 50% of lines from the existing cabinet sites; A second ring (using 1, 2 or 3 nodes, depending on shape) sited at 400m would capture the next 35% of lines. A third ring at 800m would target the next 10% of lines.

If the design target has to be dropped to 300m, then deployment would need one additional ring of nodes.

BUT...

Should BT be trying to maximise the range (which minimises the cost)? Probably ... if they think there is a future FTTP rollout needed later.

On the other hand, there is reason to think that brownfield sites will keep that last little chunk of copper for good ... so G.fast will be the last upgrade they'll ever get (unless they pay for it themselves). In that case, siting nodes at the DP makes sense.

all that is required is a new line card.

A new linecard where?

In reply to a post by MrSaffron:

G.fast hardware will also be capable of VDSL2, so existing FTTrN deployments may see hardware swap outs to give g.fast functionality.

I have assumed the same, but my recent reading suggests the opposite: that G.fast nodes will not include VDSL2 capability.

In Swisscom's FTTS project, they intend to swap out their VDSL2 hardware with plug-compatible G.fast hardware - all Alcatel-based. If the new nodes have no VDSL2 fallback, then they'd have to be being placed with line lengths that will function with G.fast.

Our FTTRN deployments could be swapped out in a similar way ... depending on the coverage range.

FTTP is the eventual end goal, but no timetable set, a lot will hinge on whether costs and time to install can be shown to be less in summer trials and then the balance between G.fast and FTTP will be worked out.

Certainly that balance of costs will determine whether G.fast ever gets considered. However, I'm no longer convinced that FTTP is assured to be the end-goal everywhere.

I suspect that the tricky brownfield locations (eg direct-buried cable) may well find themselves with G.fast as a final solution.

For areas with direct buried copper then the cost of the final fibre drop may make FTTH goal difficult to justify in a ten year plan even. Add the landlord who is slow to reply to wayleave requests, or even refuses and many small flats will have copper as final drop for a long time.

While those who work from home are happy to be around for an install visit, the work pressures for many make it difficult to have someone at home for all the FTTH/FTTP stuff. Remember the posts from people desperate to get a Saturday install slot for FTTC.

The decades of the UK loving the detached and semi home are coming back to bite us.

In reply to a post by garethr:

Isn't an FTTC cabinet a GPON endpoint? That was my point.

In reply to a post by garethr:

OK. Maybe I didn't put my point across very well. It's GPON p2p without the splitter.

If there is no splitter, it isn't a PON!

An FTTC cabinet uses one or more NGA P2P distribution fibres from the aggregation node ... which will be spliced onto spine fibre at the AN.

The fibre spine, running out from a master exchange head-end, will be a fibre cable with up to 288 fibres, leading to a chain of aggregation nodes. A proportion of the fibres will terminate in the aggregation node, while the rest will loop through to the next aggregation node.

BT will have dimensioned the cable size carefully, so the right number of fibres terminate in a node - obviously ready for both current and future usage.

It seems like BT classify those fibres in 2 ways:
- "P2P BAU", which I assume is Point-to-point Business As Usual.
- "NGA Spine Fibres" which seem to be intended for PON purposes. The only current PON type is GPON, but XGPON will turn up.

The BT installation manual for an Aggregation node suggests that NGA P2P distribution fibres (ie those from the AN to the FTTC cabinets) actually end up spliced to the "P2P BAU" fibres.

BT clearly classify the PON and P2P worlds very differently.

What isn't clear to me yet is whether the G.fast boxes will end up physically connected direct to an NGA P2P spine fibre, or as part of an XGPON, or it will be physically connected into an existing FTTC cabinet.

As far as I can make out, the Alcatel system architecture for their current VDSL2 micro-nodes (and therefore the plug-compatible G.fast micro-nodes) means they are managed as sub-elements of a full-size FTTC node. Such management might require a physical interconnection (though not necessarily) and some architectural diagrams show a connection in this way.

I haven't found any indication about how Huawei expect their small nodes (FTTRN or G.fast) to be connected.

wwwombat well what you just posted concerns me, it seems BT want to push the range ultimately to decrease costs, so they dont have push out fiber as far and deploy less nodes, the increased range I imagine would mean more variability in access speeds, which is bad for the end user. Its a bit like choosing to deploy adsl2 upto 4km instead of upto 1km, they can sell the product at 4km in the latter example but wouldnt work anywhere near the marketed speeds.

e.g. if I ordered g.fast and ended up with something like 150mbit sync speeds I would be pretty angry not just disappointed. I would expect more than a doubling of speed on a newer generation product, its a big reason why g.fast doesnt excite me, distance based speeds are getting old, bring on fttp please, until then I will keep vdsl2.

This is also why I said I think they will have a harder time selling g.fast, as I am somewhat of a broadband geek and I dont see myself ordering g.fast if available unless there was no extra price premium over vdsl2.

Edited by Chrysalis (Tue 08-Sep-15 15:30:24)

But, G.Fast at 150Mb/s is still a big improvement for a lot of FTTC customers. Over 3 times my current speed and for some getting the node just a bit closer could make a big difference.

Personally I'm hoping the new FTTPoD will be sensible and if it is then I will invest (assuming they let me).

I'm unsure where you've researched but I can perhaps answer some other points raised here and elsewhere.

FTTC
Vectoring will be deployed very soon.

Vectoring will be deployed on a very tactical basis to hit local authority targets. There has been no indication from BT that such a deployment will be widespread, or that there will be much of it in the commercial areas. It is extremely wise to not assume vectoring is arriving.

I reckon any G.FAST to the distribution point will actually be a later project

BT's trials they are doing right now are with G.fast to distribution points. The deployment as it stands will use nodes in varying depths in the network.

G.FAST can do a very fast resync - unlike FTTC. However, BT use PPP at higher network layers which is slow.

PPP is not slow. Certainly not compared to xDSL sync times. It carries overheads but reconnecting a PPP session takes a second or two, most of that delay waiting on RADIUS.

That explains why they are working with both ECI and HUAWEI

Given ECI have no G.fast hardware and Openreach are working with Huawei and Alcatel on the G.fast side the idea that Openreach are working with ECI and Huawei to upgrade cabinets to G.fast doesn't seem to be supported.

The ECI DSLAMs would need a not inconsiderable amount of work, not just new line cards, to run G.fast.

The cab has power it is also compatible with the FTTP2 2.5Gbps/10Gbps G-PON due to the fact it has a C-WDM splitter pre-installed unless it was one of the original 2010 cabs then you are SOL.

There's no CWDM splitter in the cabinets as far as I'm aware. They run on point to point Ethernet backhaul over a single fibre from what I gather which each connection running on a dedicated fibre, 1000Base BX-10. A CWDM splitter is not required to run GPON and XGPON on the same fibre. To backhaul the cabinets with XGPON requires new line cards as the existing ones do not support it.

The only things using PON are FTTP, which is why to connect FTTP customers providers have to pay for a connection to an entirely separate OLT, while they have to pay for connectivity to a layer 2 switch in the exchange to access the FTTC customer base.

The new FTTPoD trials are largely about testing new deployment methods. BT already know XGPON works having tested it out in Cornwall.

G.fast is not dependent on any iteration of FTTPoD; delivering 300Mb to a even a fairly substantial group of properties does not require 10Gb, a single symmetrical gigabit backhaul would be fine for most streets.

Edited by deleted (Tue 08-Sep-15 15:39:58)

doesnt a single gigabit per street seem a bit low for when a single user can pull 300mbit/sec? that is VM type contention and we have seen what happens there.

For a street where a single user can pull 300mbit/sec. I would consider 3gbit/sec absolute minimum for backhaul following the rule that one user cannot use more than 10% of capacity.

And how many other installations of FTTB across Europe rely on Gigabit backhaul per building, and why even if you look at South Korean speed tests (done in country) people don't max out all the time.

Once you supply Gigabit and start to use it you suddenly discover that many hosting providers have speed limits below your actual connection speed.

In reply to a post by Chrysalis:

doesnt a single gigabit per street seem a bit low for when a single user can pull 300mbit/sec? that is VM type contention and we have seen what happens there.

For a street where a single user can pull 300mbit/sec. I would consider 3gbit/sec absolute minimum for backhaul following the rule that one user cannot use more than 10% of capacity.

What is the equivalent setup for VM and their shared coax?

IIRC, they currently bond 8 Eurodocsis channels, each capable of 55Mbps - giving a grand total of 440Mbps. That bandwidth is shared over a few hundred homes, but they'll sell packages of 152Mbps.

That means 3 users, out of a few hundred, can saturate the downstream. However, only around 10% of users actually choose to buy the top-speed package. Two-thirds are on 50Mbps or less, which is a lot closer to your suggested rule.

However, with the current generation of G.Fast nodes, you are looking at 1Gbps backhaul shared over only 8-16 users. That leads to a better contention ratio than with VM.

If BT roll this equipment out, I wonder if they'll be offering lower-speed packages too - especially at 40 and 80Mbps levels.

Edited by deleted (Tue 08-Sep-15 18:00:33)