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Message 1 of 12

Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

Screenshot 2023-02-23 at 16.48.39.pngI need help - even the Open Reach Engineers didn't have an answer for this - Fibre Broadband (G.fast) Downstream sync speed is 246Mbps vs the actual throughput speed I am getting will never go above 150Mbps... with an ethernet cable plugged directly into the hub...nothing else connected to it! fast.com will always go to 150Mbps and stop. I have tried two BT Smart Hub 2's and a G.fast Zyxel modem/router..... x2 Engineer visits and numerous phone calls to BT, they are stumped! No one can tell me why the throughput is almost 100Mbps slower than the sync rate; and that it always gets to 150Mbps exactly and stops... it never fluctuates... always the 150.....Open Reach Engineer got 270Mbps at the socket on his tester.....

Does anyone have any ideas please?Screenshot 2023-02-23 at 16.37.12.pngScreenshot 2023-02-23 at 16.45.00.png

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Message 2 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

I assume G.FAST capped at a speed band depending what level you pay for? Similar to VDSL (38/68Mb) and FTTP (150, 500, 900Mb).

What level are you paying for?

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Message 3 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

Are you using the same equipment ( laptop /desktop) every time, or is this something you have confirmed on multiple wired devices and always received the same results on different equipment ?.
There was a post on a similar, but slightly more technical in nature , forum , someone complaining that the real world speed they measured was much worse that the speed the ISP said they were getting , it turned out it was the end users setup , the virus checking software running on their  PC was the issue .

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Message 4 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

Hi - I have Fibre 250 with BT Halo 3, Ultrafast speeds, a 250Mb with Stay Fast Guarantee of a minimum of 150Mb

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Message 5 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

Any ethernet device always gives 150Mps.... Laptop, PS4, MAC... other devices on wifi range from 140 to 147Mbps...BT Tech over the phone have tested it numerous times and can never get it about 143Mbps

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Message 6 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

Another box fresh smart hub was tried today, and still the same - I would really appreciate it if anyone has any ideas. 

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Message 7 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

@miata121 Your downstream noise margin is 9.1 and that with short connection times indicates a line fault, the DLM has put you on a lower profile and that's why you are seeing slow speeds.

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Message 8 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

That is interesting because the OpenReach engineer specifically said that he re-set the DLM and that the line showed no faults... 

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Message 9 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

Also (thanks by the way for taking the time to post) If the DLM was restricted would I still be getting a sync rate of 246Mbps? I don't think the DLM has the ability to restrict the throughput rate, it can only restrict what is actually being sent to the socket/property? am I right?

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Message 10 of 12

Re: Fibre Broadband (G.fast) Downstream sync speed 246Mbps vs actual throughput speed 150Mbps

It has nothing to do with DLM. DLM acts at the DSL layer, not the IP layer, your sync speed is ok which is the only speed DLM can control.

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