Think Broadband Ping Monitor Results (POST YOURS)
25-01-2015, 16:17
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#4906
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Inactive
Join Date: Oct 2009
Location: Warwickshire
Services: XL TV, Tivo, 152Mb, Phone
Posts: 52
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Re: Think Broadband Ping Monitor Results (POST YOURS)
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28-01-2015, 22:54
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#4907
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cf.geek
Join Date: Apr 2008
Services: V6 with Full-House/Maxit Sports & Movies, 100Mb broadband, Talk Weekends.
Posts: 570
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Re: Think Broadband Ping Monitor Results (POST YOURS)
What sort of speeds are you getting in the evening peak then Tony? My 50Mb is currently only getting anything between 5-12Mb/s at peak times since a few weeks, but the graph is nowhere near that bad.
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02-02-2015, 16:54
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#4908
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cf.geek
Join Date: Dec 2003
Location: Hove East sussex
Age: 73
Posts: 574
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by japitts
What sort of speeds are you getting in the evening peak then Tony? My 50Mb is currently only getting anything between 5-12Mb/s at peak times since a few weeks, but the graph is nowhere near that bad.
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From what I've experienced then TBB is skewed more towards showing upstream utilisation and mine doesn't indicate downstream utilisation to anything like the same extent.
(Since I have Samknows then I have a relatively accurate and consistent benchmark to compare against)
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03-02-2015, 00:24
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#4909
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cf.mega poster
Join Date: Aug 2004
Posts: 11,207
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by horseman
From what I've experienced then TBB is skewed more towards showing upstream utilisation and mine doesn't indicate downstream utilisation to anything like the same extent.
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That's less about the TBB graphs than it is about latency on DOCSIS simply being affected more by upstream utilisation than down.
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03-02-2015, 08:20
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#4910
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Inactive
Join Date: Jun 2008
Location: Leeds, West Yorkshire
Age: 45
Posts: 13,996
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by horseman
From what I've experienced then TBB is skewed more towards showing upstream utilisation and mine doesn't indicate downstream utilisation to anything like the same extent.
(Since I have Samknows then I have a relatively accurate and consistent benchmark to compare against)
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Two issues at play here.
1) DOCSIS upstream is TDMA which is more prone to latency caused by utilisation - there are 2 contention points at play, contending to send your request for a grant and then waiting for the grant time to actually transmit the data.
2) DOCSIS allows large traffic bursts to request more bandwidth as part of a data burst so favours continuous large amounts of upstream traffic over small bursts such as a response to a TBB ping.
Downstream uses a scheduler at the CMTS. The pipe has to max out, with interest, in order to increase latency substantially.
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03-02-2015, 11:03
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#4911
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cf.addict
Join Date: May 2012
Posts: 153
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by Ignitionnet
Two issues at play here.
1) DOCSIS upstream is TDMA which is more prone to latency caused by utilisation - there are 2 contention points at play, contending to send your request for a grant and then waiting for the grant time to actually transmit the data.
2) DOCSIS allows large traffic bursts to request more bandwidth as part of a data burst so favours continuous large amounts of upstream traffic over small bursts such as a response to a TBB ping.
Downstream uses a scheduler at the CMTS. The pipe has to max out, with interest, in order to increase latency substantially.
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Which makes sense but what about the relationship between download speed and latency.
At peak times my download drops to 50% (50Mb/s from 100Ms/s) but the peak latency on the graph does not increase significantly (outside of the test window).
If my download packets cannot be scheduled at the required rate to achieve 100Mb/s and are buffered in the CMTS then surely ICMP packet would be delayed too?
Also, the TBB speed test during peak hours shows a big drop in the x1 speed even before the x6 rate gets reduced. This x1 rate always starts high (close to 100Mb/s) and drops back to 20M/s or so.
To my mind this suggest some packet priority scheme on the downstream based on how close together packets are received by the CMTS for a particular CPE.
So if you're gaming with infrequent bursts these get scheduled immediately but if you are downloading the packets get delayed.
This is my speed test at ~11am
Ian
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03-02-2015, 12:33
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#4912
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cf.mega poster
Join Date: Aug 2004
Posts: 11,207
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by Eeeps
If my download packets cannot be scheduled at the required rate to achieve 100Mb/s and are buffered in the CMTS then surely ICMP packet would be delayed too?
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ICMP does not require 100Mb/s. There may not be enough capacity left to schedule an additional 100Mb/s while still having 0.01Mb/s required for ICMP.
---------- Post added at 12:33 ---------- Previous post was at 12:28 ----------
Quote:
Originally Posted by Eeeps
To my mind this suggest some packet priority scheme on the downstream based on how close together packets are received by the CMTS for a particular CPE.
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Oh how I wish VM were actually that competent.
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03-02-2015, 13:07
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#4913
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Inactive
Join Date: Jun 2008
Location: Leeds, West Yorkshire
Age: 45
Posts: 13,996
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by Eeeps
Which makes sense but what about the relationship between download speed and latency.
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Easy - the DOCSIS scheduler uses something similar to Weighted Fair Queuing.
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03-02-2015, 15:29
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#4914
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cf.addict
Join Date: May 2012
Posts: 153
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by Ignitionnet
Easy - the DOCSIS scheduler uses something similar to Weighted Fair Queuing.
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Had to look that up but from Wiki...
'...an ill-behaved flow (who has sent larger packets or more packets per second than the others since it became active) will only punish itself and not other sessions' which is kind of what I described (in a less technical way).
Do the Virgin CMTS really implement that? On the upstream too?
Ian
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03-02-2015, 22:22
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#4915
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Inactive
Join Date: Jun 2008
Location: Leeds, West Yorkshire
Age: 45
Posts: 13,996
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Downstream it works that way, upstream doesn't use the DOCSIS scheduler it uses TDMA.
See my earlier post - http://www.cableforum.co.uk/board/35...-post4910.html
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04-02-2015, 12:52
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#4916
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cf.addict
Join Date: May 2012
Posts: 153
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Quote:
Originally Posted by Ignitionnet
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I guess something similar could be implemented on upstream by limiting the rate of the 'grants' for 'ill-behaved' streams.
Thinking about the downstream, this definitely seems to explains why the TBB graph can look quite good even though download speeds have dropped significantly due to congestion; infrequent ICMPs being scheduled in advance of download packets for other CPEs.
I would have thought this constitutes a form of traffic management / priority scheme?
Ian
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04-02-2015, 13:32
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#4917
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Inactive
Join Date: Jun 2008
Location: Leeds, West Yorkshire
Age: 45
Posts: 13,996
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Re: Think Broadband Ping Monitor Results (POST YOURS)
The scheduler isn't a traffic management scheme, it doesn't really have any intelligence to speak of.
I was, perhaps, overly kind when I described the scheduler as being WFQ. It doesn't have the smarts to 'selectively' slow heavy bandwidth flows, it's more that it shares bandwidth between flows and the way it empties buffers.
Essentially smaller packets, such as pings, get through more quickly than larger ones, such as a standard download.
On the upstream you can, certainly, prefer certain traffic, indeed it's needed as part of voice services, however it's of questionable value and is more inefficient in terms of usage of the resource to prefer pings or whatever over normal traffic.
This will be useful in DOCSIS 3.1 though and will I suspect present way more of a benefit than playing with upstream schedulers.
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04-02-2015, 13:59
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#4918
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cf.mega poster
Join Date: Aug 2004
Posts: 11,207
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Well that's a very up-to-date game...
---------- Post added at 13:59 ---------- Previous post was at 13:55 ----------
[Edit]
So basically they've implemented random early detection, a standard, widespread queue management mechanism that's been around since 1993...
... And what about ECN? Why aren't more people using it?
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05-02-2015, 19:13
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#4919
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cf.mega poster
Join Date: Nov 2010
Location: Stafford
Posts: 4,226
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Re: Think Broadband Ping Monitor Results (POST YOURS)
I seem to be getting awful jitter at the moment!
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05-02-2015, 20:39
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#4920
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FORMER Virgin Media Staff
Join Date: Dec 2010
Location: Warrington
Posts: 4,737
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Re: Think Broadband Ping Monitor Results (POST YOURS)
Well as you can see, there's absolutely nothing wrong with my area at the moment.
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