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Broadband sync speed compared to throughput

jonnybennett
Grafter
Posts: 74
Registered: 28-11-2007

Broadband sync speed compared to throughput

Hi,
  my internet now seems to be running very smoothly and speeds are back up, noise margin has dropped to 10.5(downstream) from about 20 ish something and i'm assigned a 4500 BT Profile. Also my router is syncing at 5376.
The only thing i'm wondering is, when I run a BT speed test the actual throughput is something in the region of 2700kbps ish. I was expecting it to be a little higher.
Just wondering thats all. Anyone?. Thanks
6 REPLIES
jonnybennett
Grafter
Posts: 74
Registered: 28-11-2007

Re: Broadband sync speed compared to throughput

actually router sync is now down to 4032 and noise is 15db(downstream).
Seems to go up and down like a yoyo still lol. Ohwell.
Laser
Grafter
Posts: 206
Registered: 23-09-2007

Re: Broadband sync speed compared to throughput

There is about 10% overhead on the sync speed compared to the actual throughput. So 2.7Mb throughput is a bit slow for a 4Mb connection.
You can try a high capacity speed test server like www.speedtest.bbmax.co.uk rather than the usual overloaded ones. At peak times you may well not get much more than 2-3Mb due to exchange contention and/or PlusNet capacity. Off peak you should get about 3.5Mb on a 4Mb sync.
If that still seems to be slow at 1am or something, you might want to play about with MTU/RWIN values and suchlike as discussed here.
jonnybennett
Grafter
Posts: 74
Registered: 28-11-2007

Re: Broadband sync speed compared to throughput

I will have a look into that, no big deal as long as my connection remains at a stable ish speed and is good enough for my needs.
Just get a little worried with things going up and down.
Thanks for taking the time to reply.
Update
----------
Just tried that speedtest.bbmax and got the following:
download speed: 3328
upload speed: 377
So I suppose thats nearly at the speed I should expect, I will have to have a look into MTU/RWIN.
jonnybennett
Grafter
Posts: 74
Registered: 28-11-2007

Re: Broadband sync speed compared to throughput

hmm now thats confusing. Just tried tinkering with the MTU settings. The maximum I was able to achieve was 1405 with the following command:
ping -f -l 1405 [www.bbc.co.uk]
However my router currently shows the MTU as 1432. By using 1432 in cmd I get the packet needs to be fragmented but DF set, which from my understanding means its to high?
thanks
Laser
Grafter
Posts: 206
Registered: 23-09-2007

Re: Broadband sync speed compared to throughput

Yes, you have to add 28 to the size to get the MTU value.
1405+28 = 1433.
Not sure if it is allowable to have odd-numbered packet sizes.
Anyway, it sort of indicates that your router may be fragmenting the packets. Set it to MTU of 1500 temporarily, then do the test again to see what other things cause a fragmentation that is outside your control. You can then set your router and PC to match. You can then boost your RWIN value.
None of this will provide dramatic speed increases, just maximise what you have.
mcgurka
Grafter
Posts: 764
Registered: 09-10-2007

Re: Broadband sync speed compared to throughput

True, an MTU reconfigure could maximise what you have. Im not too sure about odd packet sizes.. need to do some more reading on this one..
On a side note, how long would you expect an IP profile to take to remap before reporting it as stuck? ( I have 1 you see, sync of 8128, profile of 2k)