Download speed vs sync.

Is there a formula or calculator to work out download speed from sync. I currently have a sync of 19,627 kbps and achieve 17.4 mbps download. Last week my sync was lower at about 18.9 mbps and I was getting 17.6 mbps download speed. What gives?

there's the ATM tax of 5 bytes per 48 bytes of cargo for starters, see http://blog.ioshints.info/2009/03/adsl-overhead.html

85.8% is mentioned in the comments to the above, so 85.8% of 18.9 = 16.2

Edited by yarwell (Wed 04-Apr-12 20:41:35)

Thanks Yarwell that article says 16% of overhead which would give my current sync speed of 19627 kbps a download of 16,486 kbps but I'm getting 17,817 kbps. Weird thing is my sync gone up but download gone down, not much I know but puzzling.

I did it manually to and came out with a smaller number than your speedtest result, maybe that says something about the tester.

What sort of connection is it / which ISP ? there may be small protocol differences. I've always assumed a max of 1900 per 2272 sync or 6900 for 8128 none of which get you to 17 let alone higher.

Edit: Applying your ratio to a MaxDSL 8128 sync would give a data rate of 7378 which is above the 7150 TCP/IP rate so not possible on an ATM encapsulated DSL link.

Edited by yarwell (Wed 04-Apr-12 21:10:57)

In reply to a post by Banger:

Thanks Yarwell that article says 16% of overhead which would give my current sync speed of 19627 kbps a download of 16,486 kbps but I'm getting 17,817 kbps. Weird thing is my sync gone up but download gone down, not much I know but puzzling.

I've always gone by -12% of sync rate best case then factor in traffic management.

In reply to a post by yarwell:

I did it manually to and came out with a smaller number than your speedtest result, maybe that says something about the tester.

What sort of connection is it / which ISP ? there may be small protocol differences. I've always assumed a max of 1900 per 2272 sync or 6900 for 8128 none of which get you to 17 let alone higher.

LLU connection on O-bit/Vivaciti and testing with JD's Auto speed tester. DU meter says 17.56 mbps when the test is running. 12% gets me nearer.

12% would get you from ATM to IP rate not to useful data.

2272 - 12% = 2000
8128 - 12% = 7150

54 - 12% = 48 ie it's the ATM overhead.

88% * 1460/1500 = 85.7 so I'm nearer 14.3% discount

If it's any help, Tim, I get 5-5.5 MB from a 6 MB sync and 5.5-6 MB from a 7 MB sync (the fastest my modem will sync at).

On the default SNR of 6, I've never seen my sync rate go below 5.5 MB with the Billion 7800 router (this gives me a speed of around 4.8 MB).

Edited by paul_liverpoolfc (Thu 05-Apr-12 10:40:33)