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Author Topic: Anybody on Zen G.fast? Poor single-thread downloads.  (Read 507 times)

re0

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Anybody on Zen G.fast? Poor single-thread downloads.
« on: May 24, 2019, 01:42:23 PM »

Since moving to Zen's G.fast service, I get the full 330/50 sync at about 200m. But one thing that is clear is that single-thread speeds, while not appalling, are pretty poor compared to multi thread.

Just to give some figures, speedtesters are giving 220-280 Mbps and multi-thread downloads seem to be hitting that 300 Mbps mark. However, single-thread downloads are a bit enemic since speedtesters say usually under 100 Mbps and just trying HTTP downloads from different sources seldom reach max speed, and it's not unusual for them to hover around 120-220 Mbps. If they do reach max speed, it can take a while - slow ramp up.

I could be experiencing a situation where the servers I am downloading from do not have sufficent capacity, but given that the fact that speedtests also highlight the same thing I am thinking it is not the issue. Perhaps the slow ramp up may be caused by web server configuration to deal with the load.

I've gone through basically all what Zen have asked me to do, and then some. Stuff like using their supplied router with the Openreach modem. I've done more, such as trying two different modems, three routers, multiple wired and wireless devices, different browsers, getting results no different.

They have recently sent an engineer out who technically did not find a fault at all (which is what I was expecting) but Zen did not want to change backhaul until this had been done. There was a minor balance issue which did not quite meet the fault threshold, but since having that fixed the downstream attainable rate is looking a bit happier.

Before:
Code: [Select]
xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    0
Last initialization procedure status:   0
Max:    Upstream rate = 61552 Kbps, Downstream rate = 338781 Kbps
Bearer: 0, Upstream rate = 50005 Kbps, Downstream rate = 330011 Kbps

Link Power State:       L0
Mode:                   G.fast Annex A
TPS-TC:                 PTM Mode(0x0)
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        3.6             7.5
Attn(dB):        31.0            0.0
Pwr(dBm):        0.0             3.9

After:
Code: [Select]
xdslctl info --stats
xdslctl: ADSL driver and PHY status
Status: Showtime
Last Retrain Reason:    200000
Last initialization procedure status:   0
Max:    Upstream rate = 61789 Kbps, Downstream rate = 344897 Kbps
Bearer: 0, Upstream rate = 50005 Kbps, Downstream rate = 330011 Kbps

Link Power State:       L0
Mode:                   G.fast Annex A
TPS-TC:                 PTM Mode(0x0)
Trellis:                U:ON /D:ON
Line Status:            No Defect
Training Status:        Showtime
                Down            Up
SNR (dB):        4.1             7.6
Attn(dB):        31.0            0.0
Pwr(dBm):        0.0             4.0

Either way, here is one of the TBB speedtests:


Perhaps even if you are not on G.fast but are on Zen with one of their "Fibre" products, you could share you experience of single-thread performance. Would be much appreciated, especially if you were able to resolve the issue if you had one since it is something I wish to do.

I would also like a second opinion on the provided TBB speedtest since I believe it to be indicative of some problem in their network - what do you think? I was under the impression such single-thread performance could mean there is an issue with backhaul.
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Chrysalis

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #1 on: May 24, 2019, 03:59:07 PM »

its been a complaint with zen that comes up every now and then, although in your case the speed isnt terrible at least and should be ok for all streaming services.
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re0

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #2 on: May 24, 2019, 04:46:56 PM »

I've been reading that about Zen. There were quite a few threads on TBB relating to the issue over the past few years and prior.

While I would agree it should be okay for streaming services, it's just a bit annoying when downloading files. I don't consider it to be performing good in that respect.

Another issue with Zen I've had so far is routing - it's annoying that my traffic always gets routed Manchester first then London. Other ISPs in the area have latency ~10ms to London-based servers, but on Zen I seem to be getting an extra 10-15ms.
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Three 4G LTE with Huawei B525 (peak down/up ~75/~27 Mbps, typ. 35-55 Mbps down)

re0

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #3 on: June 05, 2019, 02:58:15 PM »

I consider the problem seemingly resolved after the faults team have routed me to London, which I have been told will remain. Apparently being routed to Manchester in the first place was an "error".



Single-thread speeds have dramatically improved, and multi-thread speeds are more consistent. This is all good news for me.

Furthermore, good has also come out of this for the latency since it's now dropped by 10ms, so London is 12ms now and servers further afield have reduced latency for me. It's not quite 10ms as I had previously, but I'll take it. ;D
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Zen Unlimited Fibre 4 G.fast (330/50 Mbps sync, 352/60 Mbps attainable) @ ~200m - Zyxel XMG3927-B50A
Three 4G LTE with Huawei B525 (peak down/up ~75/~27 Mbps, typ. 35-55 Mbps down)

kitz

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #4 on: June 06, 2019, 11:17:11 AM »

Quote
but Zen did not want to change backhaul until this had been done.

afaik they use BTw's Shared WBMC for their g.fast backhaul services - even if they have an 'LLU' presence in the exchange for ADSL & FTTC.   
It will obviously enter one of their gateways at some point ie Manchester or London... so it depends on how much capacity they have on their gateway host link which will be taking feeds from multiple g.fast connections around the UK.
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kitz

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #5 on: June 06, 2019, 11:31:45 AM »

Quote
Furthermore, good has also come out of this for the latency since it's now dropped by 10ms

Glad that swapping the gateway improved things for you. :) 
Totally unsure how many g.fast connections that Zen have, but at a guess I bet that the majority of them are coming off at Manchester as most (if not all) of their trialists were around the Manchester area.
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re0

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #6 on: June 06, 2019, 12:02:23 PM »

I don't think Zen has unbundled my exchange anyway. To my knowledge, it's only Talk talk and Sky who have LLU presence (which is not unusual to see).

It was just frustrating that the support initially told me that I would have to keep getting a new PPP session until I got London, which never happened when I tried. I don't know if that implied that I was bound to Manchester.

I can't really speculate about that since all I know is that it was just an error that they routed my connection to Manchester. As long as it stays with London, I have no issue.
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GeorginaWC

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #7 on: June 07, 2019, 01:25:28 PM »

Your speeds look like you lucked out a bit. I've seen far worse.
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kitz

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #8 on: June 07, 2019, 02:14:13 PM »

Quote
It was just frustrating that the support initially told me that I would have to keep getting a new PPP session until I got London, which never happened when I tried. I don't know if that implied that I was bound to Manchester.

That's the way things worked historically for their WMBC adsl services. You just kept trying to get a new PPP session on a London PoP. 

Not sure about their unbundled exchanges and g.fast though. 
Reading between the lines they purchased a brand new host link for their g.fast trialists - of which all were based around the Manchester area -  so I suppose it is possible that by default those were bound to their Manchester PoP.
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kitz

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #9 on: June 07, 2019, 02:23:59 PM »

Quote
I don't think Zen has unbundled my exchange anyway.

Just a note - It is the headend not local exchange when it comes to FTTC and g.fast.   
I do have a partial but not complete list of which exchanges they had unbundled up to about a year ago.
I believe they were aiming to unbundle most of the headend exchanges in England - although saying that, my headend exchange is not on the list I have.
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re0

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #10 on: June 07, 2019, 03:46:25 PM »

Your speeds look like you lucked out a bit. I've seen far worse.
Possibly. I don't expect perfection, but with single-thread speeds are attaining 1/4 in speedtests consistently then you know something is up. Now it's closer to 4/5 most of the time, which is good enough.

That's the way things worked historically for their WMBC adsl services. You just kept trying to get a new PPP session on a London PoP. 

Not sure about their unbundled exchanges and g.fast though. 
Reading between the lines they purchased a brand new host link for their g.fast trialists - of which all were based around the Manchester area -  so I suppose it is possible that by default those were bound to their Manchester PoP.
On Plusnet (WBMC) I don't recall having anything above about 14ms to London - unless DLM shoved interleaving on on ADSLx. That seems to indicate that it was likely always connecting to London PoP(s). Perhaps the route may have deviated slightly. Though this was some years ago, so I don't remember exactly - and I don't remember if it was shared or dedicated WBMC at the time.

Just a note - It is the headend not local exchange when it comes to FTTC and g.fast.   
I do have a partial but not complete list of which exchanges they had unbundled up to about a year ago.
I believe they were aiming to unbundle most of the headend exchanges in England - although saying that, my headend exchange is not on the list I have.
Same for the presumed headend - no Zen.
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kitz

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #11 on: June 07, 2019, 07:02:04 PM »

Quote
On Plusnet (WBMC) I don't recall having anything above about 14ms to London

All of Plusnet's PoPs are in London.
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re0

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #12 on: June 07, 2019, 10:29:22 PM »

Ah that would make sense then. :) To be honest, I don't remember the details.

Anyway, I think the problem is resolved here with the issues of speed, and latency is better as well. Any deviation in latency on each PPP session is just slight changes in routing.
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Three 4G LTE with Huawei B525 (peak down/up ~75/~27 Mbps, typ. 35-55 Mbps down)

CarlT

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #13 on: June 10, 2019, 06:27:36 PM »

Zen plan to unbundled every exchange with an NGA headend.

They have at least 400 exchanges unbundled covering 55% of NGA premises and are currently unbundling another 50 to provide 65% coverage. Will be at 700 exchanges and 80% by 2021.

They are also modifying their network so that entitling doesn't have to go through London or Manchester.
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re0

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Re: Anybody on Zen G.fast? Poor single-thread downloads.
« Reply #14 on: June 10, 2019, 07:16:56 PM »

I have read about this. I think my geographical location is set to be covered in(?) Q2.

Anyway, routing to London is good enough for me to be quite honest.
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