The Great Big NBN Sticky Thread

Discussion in 'Networking, Telephony & Internet' started by Akh-Horus, Dec 21, 2016.

  1. oculi

    oculi Member

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    Just doing some experimenting now, it seems marginally less likely to drop out on ethernet (PC wifi card disabled) than on wifi (ethernet cable disconnected) when i'm running an 8k youtube video at 8k and smashing that speedtest button.

    oddly i'm now getting 30 Mbps over wifi, don't remember that happening before. maybe the wifis are getting transmitted down the unplugged network cable to the modem

    hang on disregard all that, I unplugged a USB cable, not the network cable. More testing is required...
     
    Last edited: Aug 10, 2018
  2. Newbie12

    Newbie12 Member

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    That's right, it was because fibre uses VDSL or something like that....which is supposedly better than ADSL and there was something about why latency will reduce but can't remember if it was because of this change or something else when using fibre to the curb or fibre to the node.....

    Well he did basically say "there's no expectation that an NBN FTTN connection will improve latency" which to me interprets as "It will not improve at all"

    ...well to our houses of course from the ISP, where else?

    Is that once off or per month for a gigabyte(or is that gigabit?) link?
     
  3. oculi

    oculi Member

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    FTTN and DTTC are both VDSL, but one has a short run of copper and the other has a long run of copper with more room for activities like twisting and taping, getting damaged, going through underground rivers and so on. I suspect FTTN has loads of copper pairs feeding into one fibre wheras FTTC has one copper pair feeding into one fibre.

    It really depends how you define "better" my ADSL has been rock solid, speeds as good as one can expect from it and zero dropouts, my FTTN has been a total nightmare since day one.

    I did expect latency to improve, and I still do, but I know it might not.


    More testing is suggesting mine is much less stable on Wi-Fi than wired. Think I'll still switch to TPG though.
     
    Last edited: Aug 10, 2018
  4. sir_bazz

    sir_bazz Team Papparazi

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  5. Sankari

    Sankari Member

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    I am 4km from my local exchange, so in terms of sheer speed, ADSL was killing me. However, my latency was pretty low for some reason.

    I'm not familiar with the mechanics behind latency, so can't speculate about why it dropped even further when I switched to FTTC. But I don't play online games, so it was never an issue for me in the first place.
     
  6. cvidler

    cvidler Member

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    Why waste your money?

    The ISP will have contention, to their wholesaler ISP, which will have contention to their backbone ISP, which will have contention over the submarine cables to Europe/US/Japan etc. then there'll be contention from there to the data centre, then contention from there to the server that holds your precious cat pictures on instabooktube.

    contention is a fact of life for everyone, even the major ISPs and content providers.
     
  7. cvidler

    cvidler Member

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    latency difference between 4km or 4m to your exchange is nothing, and a miniscule nearly unnoticeable part of the end-to-end connection to where ever you want your data to actually go.

    the technology you use has some impact to latency, but since the majority of the latency is on 'the rest of the internet™' rather than the bit of fibre/copper/air between your house and the exchange/node/etc. there's little point worrying about it (you can't do anything about it either).
     
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  8. caspian

    caspian Member

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    yes, that's pretty much right. the difference in latency from changing a couple of hundred metres of copper to fibre approaches zero.

    in the other instance you quoted earlier, a whole bunch of stuff changes, not just the last mile physical access medium. you cannot attribute a change to one out of many factors that were altered without a lot more visibility than you get as an end user.

    I think you need to go back and read a lot more widely before we go on with this one. with all due respect, if our starting point is that "fibre uses VDSL or something", then we're in that place where you don't have the prerequisite knowledge to understand the answer to the question.
     
    Last edited: Aug 10, 2018
  9. Sankari

    Sankari Member

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    Thanks. I was content with my latency on ADSL, so the fact that it's improved with FTTC doesn't change anything for me.
     
  10. TheWedgie

    TheWedgie Salty

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    So I've renamed and stickied this thread to keep the NBN technical discussion in the one place, as we've had the same questions asked a few times.
    I have also merged a few of the other NBN threads in, hopefully it doesn't break too much.

    Will be looking to work on a FAQ and rules/guidelines for this thread at some point so if you regular mob can make some notes for ideas that would be great.
     
  11. oculi

    oculi Member

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    Great idea, I consider myself a late adopter of NBN and I am surprised by the lack of knowledge out there. A quick explanation of all of the systems would be great, plus troubleshooting etc.

    No doubt you guys who actually work in IT will know about this, but to track what your connection is doing (if you can't look at the blinkenlights on your modem) type "ping -t 8.8.8.8" into the command prompt, it will report your latency every second or so and tell you when the connection has dropped out.
     
  12. caspian

    caspian Member

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    the predominant latency difference between ADSL2+ and FTTC would be based on the impulsive noise control error correction method in the copper segment of the connection.

    ADSL2+ uses a fibre link to a DSLAM, generally in a phone exchange, or maybe in a streetside cabinet if the DSLAM is Telstra's. you then have your garden variety copper twisted pair connection to your premises which goes into your modem. in the copper segment, we are using ADSL2+ modulation to put data onto the physical bearer.

    most forms of DSL are actually an analogue signalling method ("business grade" forms like SHDSL are a rarity) so their performance is highly subject to signal to noise ratio (SNR). the better the SNR, the more payload (bitrate, or line speed) you get. line noise is not a constant, because it is impacted by many sources - external electromagnetically coupled sources like mains power, street lighting etc, and a lot of it comes from crosstalk from other lines in the same cable sheath. every neighbour's DSL service in your cable running down the street increases noise, plus all of the repetitive noise from sources like electronics with noisy power supplies (TVs, computers, device chargers) and impulsive noise from electrical devices powering up and down - in-premises lighting, fridge and freezer motors, modems being powered up etc. so we have to deal with the fact that SNR is not a constant, it will vary. changes in SNR mean we run the risk of running higher line errors, which are initially a drop in usable bandwidth, and quickly progress to a trigger for line resyncs, both of which are undesirable. ADSL2+ is more impacted by errors than anything that came before, because as part of driving for higher speeds it runs at generally lower SNRs (more susceptible to impulsive noise), higher frequencies (which means lower SNRs as an inevitable consequence of physics), and also uses superframing to increase data modulation efficiency (more throughput for the same layer 1 line speed), but at the expense that an error damages more data.

    so we need a method of dealing with noise changes, and ADSL2+ has several, the biggest ones being forward error correction (FEC) and interleaving. FEC uses an algebraic method of data corruption detection which is kinda like an advanced checksum. when data is put onto the the line, a computed "check" value is included with it, when the data is received at the far end a comparison check is run and if the result does not match the original, the packet is regarded as corrupt. there's a certain amount of error correction capability built into this method which can recover minimally damaged data, but it's not very good. the biggest problem with FEC is that it's inefficient - it consumes about 8% of payload for the check-and-repair data to be transmitted. that means 8% decreased throughput, 100% of the time, even if errors are not actually occurring. of more impact to latency is interleaving. this is an FDM-based data transmission method that relies on the assumption of SNR drops being "bursty" in nature, and leveraging the error repair capability of FEC. there's some good graphics on this page that I won't recreate that explain the concept pretty well. https://kitz.co.uk/adsl/interleaving.htm the downside to interleaving is that because a packet is "smeared" out onto the line over an extended period of time, depending on the depth of interleaving configured on the DSLAM, latency will increase. if the interleaving is dynamic, you also now get a frame delay variation (latency jitter) problem, which hurts streaming data applications.

    FTTC changes that. it still uses fibre to the node, which is much the same as a DSLAM, just with optical line cards, not electrical. it then runs fibre all the way to the pit outside your house, replacing electrical cabling, but the difference in transmission latency over the couple of kilometres of cable that ADSL2+ used is very, very little. (in fact, light in conventional glass fibre is actually slower than an electromagnetic signal can be propagated over copper, because of the wavelength that the fibre signal uses.) the copper link then uses VDSL2, which does away with the permanent overhead of FEC altogether, and discards interleaving too. it uses a new form of error control called RTX (or G.INP, or G.998.4 depending on what terminology you use, they all describe the same thing) that uses layer 1 retransmission to correct errors, based on a far more efficient embedded form of Reed-Solomon coding which the original FEC also crudely leveraged. the result is twofold - error correction now only occurs while errors are occurring, and when it does, it is far more efficient (i.e less payload loss). the downside is that if RTX correction is occurring then packets have to be resent, incurring a jitter spike, so the RTX buffer depth has to be limited to something that is a happy medium between correcting most errors, but not blowing out jitter too far when it occurs. the other downside of VDSL2 is that superframing is pushed even further than what ADSL2+ used, so an unrepairable error is more damaging to usable throughput again.

    FTTN uses exactly the same VDSL2 modulation and error control. there's just a bit more copper between your premises and where a transceiver converts that signal to an optical signal. if you want an idea of how little this actually means in real life, do some maths. electrical signal propagates over copper at close enough to 280,000km/s. light in fibre is more like 206850km/s. so light is actually slower by 73150km/s, but not by much over maybe 5km of cable at most, and then the error correction of VDSL2 pretty much balances that out.

    where any real, observable change in latency between ADSL2+ and FTTC (or FTTN, or FTTP for that matter) comes about is that your service provider probably routes your traffic in a very different way than for a legacy connection, but since it's all layer 2 forwarding, you can't see it, or measure which sub-component of the literally dozens that make up the connection to that speedtest or Fortnite server are the cause of any latency change, unless they show up in a layer 3 traceroute.
     
    banshee, DoCsIs, cvidler and 4 others like this.
  13. shmity

    shmity Member

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    Did you ever get any more clarity or progress Frag ? Im in the same situation.
     
  14. caspian

    caspian Member

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    it will be physical copper work required.
     
  15. darknebula

    darknebula Member

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    We are scheduled for FTTC in April - June next year, just wondering how the rollout is going and are the many issues or delays with it?
     
  16. caspian

    caspian Member

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    nope, going fine.
     
  17. oculi

    oculi Member

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    just got off the phone to TPG, connection with them is on the way. Called flip and flipped them off. Went for the 18 month no setup fee option, hope I don't regret that. Should be fine.

    TPG don't have a Cheaper BYO modem option so guess I can fault find modems at some stage too. Now I'll have 4 modems including the ADSL ones.

    The TPG plan comes with a 3 month free @20 gig simm card, might be useful.
     
  18. banshee

    banshee Member

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    I don't know what's happening with your area, but here I was due for FTTN April-June 2019. Then it changed to FTTC April-June 2018. Yay! Then it was July-August 2018... Currently October-December 2018...

    Yeah, They went from FTTN to FTTC because of very old & crap copper in the whole area. It seems it just cannot handle the VDSL over the distance to the Node. Thanks, Caspian for that description. It explains well why the area has had so many issues with FTTN.

    Now they are finding all the remedial work they have to do before the fibre can be installed. New pits, new conduits. Now I think it is a matter of wait for the fibre guys schedule to clear a space to come back, after the other delays are dealt with...
     
    Last edited: Aug 15, 2018 at 9:37 AM
  19. oculi

    oculi Member

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    righto up and running on TPG, got the conenction email and tried a few times to connect with my billion modem, then the TP-link one arrived, plugged it in and "it just works"

    first speedtest (this is over wifi)

    [​IMG]

    think i'll monitor with this modem for a while then work out the login details and try the billion again.
     
  20. Renegade40D

    Renegade40D Member

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    What login details do you need to work out? If its FTTN you just plug a compatible modem in and thats it, it shouldnt need login details to connect to the internet.
     

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