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Speed tests and other BT info on GEA and VDSL

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On my travels through the net, I found this interesting document, which includes a section on actual transmission speed, which explains just why speed test results can never be as fast as the sync speed.
It also stipulates that the customer modem must support g.vector, g.inp and aelem, which I found very interesting (my cabinet runs ITFN (ECI) equipment, and does not support vectoring, but g.inp seems to be on downstream).
Sadly, it does not mention support for 30a, which is a shame (having said that, the attainable rate on my 80/20 line is indeed over 100Mbit/s).

"...For example, if the reported downstream VDSL2 data rate is 40,000 kbit/s and the IP packet size is 1500 bytes (i.e. Ethernet frame size at End User LAN is 1514 bytes) the maximum throughput achievable is actually 39,178 kbit/s (when measured at the EU LAN i.e. no VLAN header, but including Ethernet header). Alternatively, if the IP packet size is 64 bytes the maximum throughput achievable is further reduced to 35,721 kbit/s. This overhead is particularly important to consider in respect to the downstream shaper setting on the CP’s BRAS. CPs are advised to understand and account for the method that their BRAS uses to implement traffic shaping."
 
The mention of g.vector, g.inp and so forth is all just about future proofing, although BT has no control over third-party modems and routers so it's more about informing ISPs to ensure they have such support in their bundled kit for the future. Vectoring is currently in trial and G.INP is already being rolled out to VDSL / FTTC lines.
 
Of course it is about future-proofing, which is why it is sad not to see 30a mentioned.
Obviously they have no plans to deploy 30a in the foreseeable future.
 
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Sad but understandable, not all the necessary hardware supports 30a (both commercially and in their exchange/cabinets), plus there may be performance issues with coexistence via future tech like G.fast that could cause problems.

I also recall some of the 30a line cards not being able to support as many users and there may have been some issues with mixing 17a and 30a line cards in the same DSLAM (partly interference related, but there were other issues too).

In the end 30a just creates too many problems, so it’s easier to upgrade via Vectoring and then skip to G.fast than spend on a tedious approach via 30a. IMO.
 
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