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Standard User mixt
(fountain of knowledge) Sun 20-Jul-14 15:02:04
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Download Speed Mystery


[link to this post]
 
My downstream sync, as reported by Zen, is 62289 kbps.
My downstream BRAS profile, as reported by Zen, is 60293 kbps.

Most times, when I perform a wget on the 100Mb TBB test file, speeds fluctuate (as you would expect) but never exceed precisely 6.89 MB/s = 57797509 b/s = 57.80 Mb/s.

Indeed, a speed test just now ( http://www.speedtest.net/my-result/3636439021 ) matches this number (57.78).

So, why is this figure of 57.80 significantly lower than the BRAS profile of 60.29 ? Nearly a whole 2.5 Mb/s slower than what I believe it should be? Or is there some other traffic overhead at work which I've missed? (I thought it might be TCP but that does not account to where 2.5 Mb/s of speed has vanished to). Or are Zen applying their own limiting to a few % below the BRAS profile?

Zen Unlimited Fibre 2 (60/20Mb FTTC) | IPv6 via HE | » Hourly HTTPx5 TBB Speed Tests «
Previous ISPs » aaisp.net (40/10Mb FTTC) | Virgin Media (50Mb/Cable) | Be* Un Limited (ADSL2+) | Zen (ADSL)
Download Maximiser | BIND GeoDNS | Are you being blÝcked?
Standard User Pipexer
(eat-sleep-adslguide) Sun 20-Jul-14 15:09:52
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Re: Download Speed Mystery


[re: mixt] [link to this post]
 
If it was me I probably wouldn't get hung up about 2.5Mbps at those speeds, but of course you have a valid question. Perhaps Zen do rate limit a few % below the BRAS profile.

The trouble is, I'd be amazed if you get an answer out of Zen, they seem totally secretive nowadays about their whole network. I think they a little bit paranoid that by disclosing details about their broadband network it may somehow affect their reputation/PR with their larger (say large business and enterprise) customers etc.

AAISP Home::1
Standard User Geordish
(learned) Sun 20-Jul-14 16:08:36
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Re: Download Speed Mystery


[re: mixt] [link to this post]
 
4% overhead seems reasonable.
https://learningnetwork.cisco.com/thread/43446


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ISP Representative SkyFire
(isp) Mon 21-Jul-14 09:56:35
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Re: Download Speed Mystery


[re: mixt] [link to this post]
 
Hi,

Geordish shared something, but here's my own contribution which may help explain it:

http://packetpushers.net/tcp-over-ip-bandwidth-overh...

...a smaller MTU value would increase the percentage required for overheads too.

And to confirm - we don'have any limit imposed below BT's BRAS profile. smile

regards,
Phil.

--
Phil Long
ZeN Performance and Process Improvement Manager
The above post has been made by an ISP REPRESENTATIVE (although not necessarily the ISP being discussed in the post).
Standard User mixt
(fountain of knowledge) Mon 21-Jul-14 11:12:16
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Re: Download Speed Mystery


[re: SkyFire] [link to this post]
 
Thanks Phil, and Geordish!

Zen Unlimited Fibre 2 (60/20Mb FTTC) | IPv6 via HE | » Hourly HTTPx5 TBB Speed Tests «
Previous ISPs » aaisp.net (40/10Mb FTTC) | Virgin Media (50Mb/Cable) | Be* Un Limited (ADSL2+) | Zen (ADSL)
Download Maximiser | BIND GeoDNS | Are you being blÝcked?
Standard User ByteTraveller
(newbie) Mon 21-Jul-14 11:58:53
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Re: Download Speed Mystery


[re: mixt] [link to this post]
 
I wouldn't pay too much attention to it either - for reference I just checked my details, I was disconnected overnight so have just resynced - according to the line rate data, up/down is 6264/34913kbit/Sec, however I know via the modem that I'm synced at 5729.12/866.5KB/Sec, and I have been downloading/uploading at a higher rate than the line rate data says.

My upload speed has tanked from 1.1MB/Sec originally to 866KB/Sec (was <800KB/Sec yesterday!) making me think of downgrading the line, but thats another story.

ZeN / Zen Fibre Office Plus (VDSL2)
Standard User mixt
(fountain of knowledge) Mon 21-Jul-14 12:27:00
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Re: Download Speed Mystery


[re: Pipexer] [link to this post]
 
Yeah, I'm not really fussed about the 2.5Mb/s - just trying to understand the reason for it, which I believe has now been answered in the other replies.

Zen Unlimited Fibre 2 (60/20Mb FTTC) | IPv6 via HE | » Hourly HTTPx5 TBB Speed Tests «
Previous ISPs » aaisp.net (40/10Mb FTTC) | Virgin Media (50Mb/Cable) | Be* Un Limited (ADSL2+) | Zen (ADSL)
Download Maximiser | BIND GeoDNS | Are you being blÝcked?
Administrator MrSaffron
(staff) Mon 21-Jul-14 15:02:52
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Re: Download Speed Mystery


[re: mixt] [link to this post]
 
These small overheads due to network stacks have been there all along just that now we have faster connections it is easier to see them.

Hint: If someone posts a Gigabit connection speed test at over 950 Mbps a good chance the figures are wrong.

The author of the above post is a thinkbroadband staff member. It may not constitute an official statement on behalf of thinkbroadband.
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