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Author Topic: G.fast - first mile latency?  (Read 1025 times)

boost

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G.fast - first mile latency?
« on: June 29, 2018, 07:53:59 PM »

Anyone on G.fast?
Pings improved at all? :)
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PhilipD

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Re: G.fast - first mile latency?
« Reply #1 on: July 06, 2018, 05:20:16 PM »

Hi

It's not been designed for lower latency, and if anything it's probably worse than VDSL as G.Fast uses Time division multiplexing, this means it's really a half duplex connection (it can't send and receive at the same time), so the line is constantly switching direction, so when you send some data, the modem has to wait for it's turn to talk, then wait for it's turn to receive, adding extra latency.

G.Fast is a rubbish technology really, reach is poor, and it interferes with FM radio so has to have all sorts of power reductions applied over specific frequencies, further reducing reach.

Regards

Phil
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Black Sheep

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Re: G.fast - first mile latency?
« Reply #2 on: July 06, 2018, 05:45:27 PM »

I didn't know about that, PhilipD ..... very educational. Thank you.  :)
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ejs

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Re: G.fast - first mile latency?
« Reply #3 on: July 06, 2018, 05:53:17 PM »

It's not been designed for lower latency

Are you sure about that? What makes you think it wouldn't have been designed for low latency?

https://www.ispreview.co.uk/index.php/2016/09/sckipio-interview-can-expect-bts-g-fast-broadband-tech.html
Quote
Our strategy is to build a copper technology that feels like fibre to the user. This means delivering very low latency, the fewest dead zones, breakthrough stability, very fast recovery times, and very fast training times.
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Sniper

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Re: G.fast - first mile latency?
« Reply #4 on: July 06, 2018, 06:19:03 PM »

I was on 80/20 until 19/3/2018 when g.fast was installed.

I've attached a history of my tests, latest on from today, hope it helps.
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underzone

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Re: G.fast - first mile latency?
« Reply #5 on: July 06, 2018, 06:30:11 PM »

Was VDSL fast path or interleaved? Huawei with g.inp or ECI?
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Sniper

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Re: G.fast - first mile latency?
« Reply #6 on: July 06, 2018, 06:42:35 PM »

I was on ECI with Fast path, pings were usually under 15ms, however when interleaved it was over 15ms. I never got under 10ms until I got g.fast.

The results were similar on unifi controller, its ping value used to stick around 12ms on ADSL and now usually reports 8ms.
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PhilipD

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Re: G.fast - first mile latency?
« Reply #7 on: July 06, 2018, 07:30:23 PM »

Hi

Only a percentage of that amount of ping is related to the time it takes getting from one modem to the other.  It could just be a difference in routing that is making your pings better on G.Fast (better backhaul, faster switches etc), rather than G.Fast itself, it's hard to know for sure.

I've had bigger differences in ping responses because of network routing or different gateways.

The article at Ispreview show their aims, they of course want it to "seem" like fibre, but I think they are really talking about the whole network built for G.Fast.  We've heard all these lofty claims before and it never quite gets delivered.

Latency isn't suddenly going to be improved just because its G.Fast if everything else remains the same, thankfully the extra speeds means new kit and new networks, which will give rise to improvements.

Regards

Phil

 
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Weaver

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Re: G.fast - first mile latency?
« Reply #8 on: July 06, 2018, 11:35:29 PM »

I don't agree at all with the point about TDM. If you are not transmitting simultaneously in the opposite direction then 100% of the bandwidth is available so G.Fast is faster not slower. In ADSL/VDSL2 you are permanently deprived of some of the speed because the, say, upstream bands have taken some of the frequencies away even when no data is being sent upstream, say, at that instant. I do not know what the turnaround time is but I do not see why it needs to be much, perhaps someone will set me straight on this point.

Anyway, the point remains that with G.Fast because it is half duplex you are getting 100% of the link capacity used at all times, there is never one side unused.

Have I missed something?
« Last Edit: July 06, 2018, 11:48:13 PM by burakkucat »
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boost

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Re: G.fast - first mile latency?
« Reply #9 on: July 08, 2018, 03:09:44 PM »

Some great input.

Thanks all :)
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CarlT

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Re: G.fast - first mile latency?
« Reply #10 on: July 09, 2018, 12:21:34 PM »

G.fast is designed to have latency of less than 1ms in each direction, if configured as such. It should improve latency somewhat over VDSL but will still fall slightly short of FTTP with that in mind.

Not a lot of difference in it and, regardless, unless there's an error correction at work that adds a chunk of latency most of the delay will come from the trip from cabinet to wherever you're trying to reach on the Internet, even if that destination is relatively close.
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psychopomp1

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Re: G.fast - first mile latency?
« Reply #11 on: July 09, 2018, 06:43:40 PM »

Going from 80/20 FTTC to 330/30 FTTP, my pings improved by 2 ms...20ms versus 22ms. Which still ain't too bad considering I'm way up north in the Highlands.
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kitz

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Re: G.fast - first mile latency?
« Reply #12 on: July 09, 2018, 11:20:34 PM »

According to my daughter's partner (who is an avid gamer), g.fast hasn't made any noticeable difference to his latency when going from a g.inp (non interleaved) fttc connection.   Obviously speed has improved, but interestingly they report throughput appears to have decreased and speedtests are now at just slightly over 200Mbps.   Whilst I have been over a couple of times, we had more interesting or important r/l things to do rather than me sit inside and play with their connection :/ 
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boost

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Re: G.fast - first mile latency?
« Reply #13 on: July 10, 2018, 03:18:20 PM »

Whilst I have been over a couple of times, we had more interesting or important r/l things to do rather than me sit inside and play with their connection :/

"Can I use your bathroom?"
"Sure!"
*disappears*
*finds PC*
*pings bbc.co.uk*

:D
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Weaver

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Re: G.fast - first mile latency?
« Reply #14 on: July 15, 2018, 08:10:34 AM »

Where abouts are you psychopomp? I am in Skye.
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