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Latency comparison - g.fast vs vdsl

oakserver — Sat, 06 Mar 2021 00:02:05 GMT

I would be interested to know how latency compares on a BT G.fast line compared with VDSL, in particular whether the latency differences I experience between my BT and Vodafone lines is due to the service provider or the g.fast vs vdsl technology.

Pinging www.google.co.uk on my BT g.fast line I get the following result:

round-trip min/avg/max/stddev = 7.773/13.524/21.244/4.648 ms

Pinging google from my Vodafone VDSL line I get the follow result:

round-trip min/avg/max/stddev = 21.842/24.326/30.325/3.541 ms

It seems that BT G.fast latency is almost half that of Vodafone VDSL.

Would anyone be so good as to ping www.google.co.uk from a BT VDSL line and post here so I can compare?

PS I should add that my Vodafone VDSL is Fast path (no interleaving) so if possible a comparison with the similar type of connection with no interleaving.

Thanks 😀

Re: Latency comparison - g.fast vs vdsl

pippincp — Sat, 06 Mar 2021 01:53:57 GMT

There's no point in anyone doing that for you. BT and Vodaphone are 2 different networks, just do a tracert on both and you'll see totally different paths to google.

Re: Latency comparison - g.fast vs vdsl

oakserver — Sat, 06 Mar 2021 09:11:13 GMT

Yes, I did do exactly as you see and no surprise to see two different paths which is why I wanted a ping or trace route will be even better 🙂

Either I didn’t explain what I’m trying to achieve or you completely missed my point.

I would like to know if a BT VDSL line can match a BT g.fast line in terms of latency and without a BT VDSL line I have nothing to compare. It would also be good to see how Vodafone's routing affects latency compared with BT routing. I know this isn't a scientific test - but without a BT VDSL line I have nothing to compare at all.

So there is a little bit of a point to it and hopefully a cooperative individual will be able to help me out (not someone with line problems and bad latency though!)

Re: Latency comparison - g.fast vs vdsl

oakserver — Sat, 06 Mar 2021 08:28:07 GMT

And from the results so far, if you are interested in latency you can see that Vodafone VDSL compared to BT g.fast latency is almost half. Great for gamers.

You’re welcome.

Re: Latency comparison - g.fast vs vdsl

bkehoe — Sat, 06 Mar 2021 10:15:48 GMT

In principle, G.fast will give latency similar to FTTP, the protocol is designed to deliver low latency like this even on poorer lines, and so will always be better than VDSL (especially when potential things like interleaving are considered). Mine dropped from the high teens/low 20 region with VDSL on a short (under 150m line) to the 9/10ms region with G.fast to London. I only saved line stats of when I had VDSL, nothing with pings though.

Unless its in the same location and same service provider to the same physical server (not google.co.uk where two different people could be routed to 2 different data centres) then a comparison like you're asking for here is very hard to form. EG A FTTP user in Scotland/NI will have approx 15ms to London. Even yours is approx 1ms less than mine so I presume you're further south than Manchester. 😉

Re: Latency comparison - g.fast vs vdsl

oakserver — Sat, 06 Mar 2021 10:50:45 GMT

Thanks for your reply

I can see what you mean that your proximity to the servers and the routes to those servers will make a substantial difference.

Im in the South East, close to London.

So let’s get down to facts - the latency on my BT G.fast line in my area is almost half that of my vodafone VDSL line at least to the destination I was pinging. It would be better to pick a server that is know to be fed from only one data centre to rule out responses from different locations.

So I think I’ve narrowed it down a little to get the best results. Anyone connected to Cabinet 9 in my area willing to give me an indicator of ping to any up address of your choosing to be honest as long as I can ping the same. Trace route even better to be sure we are taking the same routes 🙂

Re: Latency comparison - g.fast vs vdsl

iniltous — Sat, 06 Mar 2021 12:13:47 GMT

What is that you are trying to establish , that Gfast has better latency than VDSL , or that your VF VDSL should perform better and you are going to try and convince VF that your VDSL should have better latency and be the same as Gfast ?, if you have both why does it matter, if you have both , just use Gfast .

I get that some may want to optimise their broadband and probably know more about the system than the customer service reps of the retail company that supply it , but ultimately it’s a domestic service , that the user pays a domestic rate for...personally I think sometimes the consumer is expecting far too much from a service that is aimed at people who just want plug and play...if you want an ISP that will endlessly tweak , whatever they can tweak to try and squeeze whatever you want from the ‘system’ then using a mass market ISP isn’t likely to provide what you want.

Re: Latency comparison - g.fast vs vdsl

Stu_H — Sat, 06 Mar 2021 12:33:51 GMT

Are you testing latency under load?

it’s all nice when you look at a quiet network but I would try saturating your connection and then see how it’s performing.

Re: Latency comparison - g.fast vs vdsl

oakserver — Sat, 06 Mar 2021 12:41:29 GMT

Goodness me, is it really so difficult. I don’t have to explain to you why it matters to me but it does otherwise I wouldn’t be asking the damn question!

OK so my g.fast line drops two or three times a day. This is a pain in the **bleep** when you are in the middle of a teams call at work. The Vodafone line is completely stable.

I don’t want to pay for an unstable G.fast line, but my sons appreciate the low latency for the gaming pc and Xbox.

So, how do I decide whether to keep the gfast line or downgrade it to VDSL which brings slightly better stability. If the BT VDSL is going to be worse than the Vodafone line then cancel my BT services completely?

Without some figures I can’t tell if it is worth recontracting with BT for a VDSL line for a further 2 years.

Can anyone tell me how best to determine this if it’s not asking for someone to help me compare?

Re: Latency comparison - g.fast vs vdsl

oakserver — Sat, 06 Mar 2021 12:44:11 GMT

I’ve tried both.

@bkehoe has explained though the location and route is probably the biggest factor at play here so hard to compare like for like unless I had two BT lines in my home!

Re: Latency comparison - g.fast vs vdsl

licquorice — Sat, 06 Mar 2021 12:50:31 GMT

Even if you had 2 BT lines to your house they wouldn't be identical. Even the physical location of a pair within a multi-pair cable can make a huge difference. Every line is unique, you can't compare apples and oranges.

Re: Latency comparison - g.fast vs vdsl

Stu_H — Sat, 06 Mar 2021 12:59:25 GMT

It’s really hard to answer that but I game fine on a VDSL line using a HG612 modem and a number of routers aimed at controlling latency for better networking.

normally it’s the isp equipment that offers very little help to refine your network and a base pin means little if your network is the core of the latency and packet loss.

So for example I have a modest 55 down and a 13 up. My base ping is around 6ms. If I run PingPlotter and I’m using a Ubiquiti Dream Machine at the moment and turn off the QoS I get packet loss and spikes into and above 150ms. I turn on the QoS which is FQ Codel based, I limit the connection by 20% on both down and up and then test again my highest latency is just 8ms.

so I would strongly consider looking into another router to control your network as the chances are it’s your equipment rather than the line that’s the issue. If you change your isp the issues will follow you till you start looking at your own network.

Re: Latency comparison - g.fast vs vdsl

oakserver — Sat, 06 Mar 2021 13:07:00 GMT

@Stu_H That’s great and along the lines of what I was looking for. It proves to me that a ping of 6ms is possible from a VDSL line provided by BT and that gfast isn’t the only reason I see great latency with BT.

Although you did make an assumption that my kit was standard 😛 . I do use a Ubiquiti Edgerouter 4 now and the ping results were from the same router so that rules hardware differences out from my end 🙂

Re: Latency comparison - g.fast vs vdsl

Stu_H — Sat, 06 Mar 2021 13:22:19 GMT

So you are still dropping packets and seeing an increase in latency with the edge?

Install PingPlotter and test, don’t go by the sites that offer test like DSLreports but watch carefully using PingPlotter.

Record when you see the spikes or packet loss and see what was occurring on your network at that time ie was someone streaming or downloading or a video call.

Make sure the QoS is working as intended on the edge. I’ve noticed a bug on mine which has remained regardless of firmware or resets where altering the network channels causes the QoS on the upload to set at a different rate than my input. A reboot is required to correct this.

Try PingPlotter and see how you get on, if you saturate your connection and see dropped packets look at the graph to see it’s from your network.

Also look at your modem, I recently tried the Vigor 166 out and that created no end of latency so double check your modem as well.