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PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

Community Veteran
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Registered: 11-08-2007

PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

My broadband has YET AGAIN descended into the depths of unusability because Plusnet, in their lack of wisdom, unilaterally removed traffic prioritization on my 20CN ADSL connection !. Angry

 

The latency plot shown below is WITH the "Pro-Addon" enabled, but that is still not enough to cope with just three people browsing, gaming, and watching Youtube !.

It was even worse without the "Pro Addon" enabled !  Shocked

 

Before full traffic prioritization was removed on 1st July 2017, we had thirteen YEARS without issues of competing traffic demands rendering each others internet usage unusable, as now happens daily.

 

My physical modem connection is as good as ever, and I don't have ANY other network issues.

This is purely my broadband download path being unable to cope without the traffic management in place.

 

PLEASE  PLUSNET  REINSTATE  FULL  TRAFFIC  PRIORITIZATION  ON  ADSL  CONNECTIONS !

 

Screenshot from 2017-11-11 17-46-55.jpg

 

 

11 REPLIES
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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

Why does the minimum latency seem to be about 40ms?

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

Before I requested the "Pro Addon", the minimum latency was about 28ms, mostly down to the interleave depth of 64 - which got set months ago when Openreach were tinkering with the underground cables in order to make new connections for a nearby building site.

On my exchange the interleave depth never goes back down (on it's own) UNLESS I request a full line reset, which makes the interleave switch to FASTPATH and the latency drops to about 12ms with zero errors - and will run happily like that until perhaps a thunderstorm or other major interference.

 

As for being around 40ms now,  as you can see from the TBB plot below, the minimum latency jumped by about 10 to 12ms slower at the exact moment that the "Pro Addon" was enabled !.

 

To be honest, the minimum latency would have been a problem if I was still using VoIP, but I had to abandon that because of the traffic prioritization being removed making VoIP calls impossible,  therefore the high minimum latency is the least of my problems right now.

Right now I'm migrating my line rental and phone calls to a new provider, who has call charges comparable to those found on many VoIP contracts.  If Plusnet don't fix this soon, then I will probably HAVE TO migrate my broadband to another ISP who does a decent job of traffic management (as used to be the case here), because Christmas will be unbearable with my kids wanting to watch Netflix, YouTube, and Steam without the traffic prioritization reinstated.

 

It is the long periods of high packet loss and often greater than 200ms latency that is intolerable.

Today I have had to abandon looking at eBay, because there was simply not enough bandwidth to load the web pages in a reasonable time, which gets extremely frustrating when you are dealing with more than a hundred eBay items.

 

I just need the bloody traffic prioritization putting back to how it was for the last decade !.  Knuppel

 

PlusnetProAddonLatency.jpg

Community Veteran
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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

Last week before the "Pro-Addon" was enabled, just a single PC doing a Steam update (from 9:30 to 11:00) made ANY other internet activities IMPOSSIBLE.

 

Screenshot from 2017-11-11 20-27-45.jpg

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

I don't seem to suffer the same problem without traffic prioritization. Of course heavy usage makes other things slower, but not impossible. I thought pretty much all my traffic ended up being given the same priority anyway.

According to https://www.plus.net/help/broadband/about-traffic-prioritisation/ - on the Pro Add-on, browsing, streaming and software updates (steam?) and all assigned the same Medium priority. So what's the difference between having no prioritisation, and having everything assigned the same priority?

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

I *think* the difference is that the "Pro-Addon" is as you say effectively unprioritized for the traffic types I'm using, BUT does at least appear to limit those equal priority traffic streams to the maximum bandwidth of the modem connection (i.e. the incoming data rate does not exceed the BT line profile rate).

 

Whereas "no prioritization" is not only unprioritized but also appears to be ignoring the Current Line Speed, and therefore by sending more data than can be sent to my modem from the exchange, the associated packet loss causes a large increase in packet resends, which in turn increases latency, and the whole shooting match turns to [-Censored-].

 

For completeness, the previously implemented full traffic prioritization scheme, took into account the available bandwidth (i.e. the Current Line Speed) and then did an excellent job of prioritizing the various traffic types to that available bandwidth, and therefore packet loss and the associated increase in latency due to packet resends was minimised, and gave a very acceptable compromise under heavy loading.

Moderator's note by Mike (Mav): Avoidance of swear filter edited as per Forum rules.

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

But there's no need to inform servers on the Internet how much bandwidth you have, I thought TCP tends to deal with that. How does Plusnet limit the data rate? Surely Plusnet has to either queue up traffic, or because the queues at Plusnet must have a limited size, eventually the discarded packets would be happening at Plusnet.

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection


ejs wrote:

But there's no need to inform servers on the Internet how much bandwidth you have, I thought TCP tends to deal with that.

Yes that is correct.

 


ejs wrote:

How does Plusnet limit the data rate?


Well they used to get updates from the telephone exchange equipment, whenever the BT Line Profile changed (depending on your modem sync rate).  That Line Profile was then taken by Plusnet, reduced by few percent (I can't remember the exact maths now) and stored on your account as the Current Line Speed.  It used to be a requirement of Openreach that an ISP will not send data to the exchange at a rate faster than the BT Line Profile (otherwise uncontrolled packet loss will occur, due to no buffering at the exchange).

 


ejs wrote:

Surely Plusnet has to either queue up traffic, or because the queues at Plusnet must have a limited size, eventually the discarded packets would be happening at Plusnet.


It used to be the case that there were buffered queues within Plusnet. The point being that as you said the TCP protocol deals with handshaking, but that handshake works much better interacting with a high speed controlled buffer (at Plusnet), rather than uncontrolled packet loss (at the telephone exchange).

If there are resulting discarded packets, it is more efficient (for overall throughput) for that loss to occur at the Plusnet server queues, because the packet resends are both faster and much shorter latency, rather than having to travel all the way through the BT network, via your slow modem connection, and the resend request being generated by your router or PC, and then travelling all the way back across the internet.

 

However since Plusnet have changed to their NEW NETWORK, I'm not sure that anyone understands what gets buffered where, and the architecture must have been screwed up. My understanding is that the reason that the VMBU is no longer accurate, is that not all customer traffic now passes through Plusnet servers, and therefore can't be accounted for.  If there is data which can no longer be accounted for, then the traffic prioritization is likely to be broken, because the throughput can't be limited to the Current Line Speed. If the download bandwidth is no longer controlled, then who knows how any of this is supposed to work with old unbuffered 20CN ADSL exchanges like mine.

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection


Nibiru wrote:


It used to be the case that there were buffered queues within Plusnet. The point being that as you said the TCP protocol deals with handshaking, but that handshake works much better interacting with a high speed controlled buffer (at Plusnet), rather than uncontrolled packet loss (at the telephone exchange).

If there are resulting discarded packets, it is more efficient (for overall throughput) for that loss to occur at the Plusnet server queues, because the packet resends are both faster and much shorter latency, rather than having to travel all the way through the BT network, via your slow modem connection, and the resend request being generated by your router or PC, and then travelling all the way back across the internet.

I think this is not in any way how it works. TCP is an end to end connection between the server on the Internet and your computer. Your computer does not do any handshaking with any "server queues" at Plusnet. I don't think any packet queues at Plusnet will be sending any TCP acknowledgements back to the servers on the Internet, nor somehow arranging for packets they've discarded to be resent. All the ACKs will originate from your computer, and all the sent or re-sent packets will be from the server on the Internet. Any buffer at any point in between can only forward, temporarily store, or discard a packet.

Your explanation sounds good and would make logical sense if it were true, I just don't think it's grounded on how things actually work! I'm not trying to deny the effects you've experience on your connection, I just don't think your explanation is quite right.

The idea of Plusnet's traffic management is that Plusnet could choose to discard lower priority packets from say software updates or P2P protocols first. If everything's got the same priority, Plusnet will have to discard packets evenly or randomly somehow.

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

I was generalizing, and not wishing to expend time with a detailed explanation of how the traffic management used to work.

 

Where I said -

that handshake works much better interacting with a high speed controlled buffer (at Plusnet), rather than uncontrolled packet loss (at the telephone exchange

change "that handshake" to mean -

    "... the handshake mechanism of the underlying ethernet frames containing the TCP payload ...",

and yes, the TCP handshaking is end-to-end.

 

The purpose of this thread is for Plusnet to reconsider their decision to remove the previously working traffic management, and reapply it to ALL ADSL connections, as what they have now is unfit for purpose.

 

There isn't much point trying to second guess or hypothesise the current traffic management architecture, as Plusnet have consistently not answered pertinent questions about that on this forum.

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

Our ADSL connection is just fine without the traffic prioritization. All I used to get from the traffic management was an extra 0.1Mb knocked off the total speed, although that disappeared after the switch to WBMC Dedicated.

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Re: PLEASE re-enable full traffic prioritization on my 20CN ADSL connection

I do wonder whether there are other factors which come into play, such as the manufacturer/model of equipment at the exchange, that explain why some people are affected and others aren't.

 

For example a long time ago @jelv highlighted (from memory) that there was a known issue with the ADSL connection dropping for a particular exchange equipment type when the the phone rang, but only if the line characteristics had been set to "Max Premium".

 

I have always had a weird exchange problem where (on standard modem settings) my SNR margin increases about 0.1dB per week (but is otherwise ultra stable), this keeps going until somewhere about 21dB my (otherwise full) sync speed starts dropping proportionally to the increasing margin.  This can only be cleared (to give full sync again) by requesting a line reset.  However, I discovered that by using modems with SNRM tweaking to attempt to pull the target margin lower by about 9dB, then the 0.1dB degradation can be halted at around 14dB and therefore I can maintain full sync speeds indefinitely. And no it's not a modem fault as I've repeated this with at least four completely different designs of modem.  I think that the part of the DLM algorithm that reduces the signal level on each telephone line (to minimise crosstalk in the multistrand cables) can't cope with my line being at nearly zero errors, and therefore it attempts to reduce the signal level on my line until is starts seeing errors (but never does) - but the algorithm appears to not take into account that is eventually reducing my sync rate.  My normal "maximum attainable rate" is about 12Mbps, and normal "sync rate" is 8128Kbps, but when the margin rises to the low twenties then the max attainable stays the same, but the actual sync has gone as low as 6Mbps before I've requested a line reset - before I discovered how to control it.

 

I'm guessing that being on a 20CN exchange probably designed twenty years go, it's handling of unprioritized traffic and excess incoming data packets, will not be as good as current implementations, and is probably not compatible with Plusnet's NEW NETWORK.

I would also suggest that as you say your exchange is on "WBMC Dedicated" which is only available on 21CN exchanges, then there is a good chance that your exchange will have much better traffic handling than my 20CN exchange, so it will not be a surprise that your experience is different.