Contention Question

DriveSkill

Hi,

Apologies if this has been covered before but I did a search and couldnt find the answer.

Basically I understand what contention is in terms of 1:48 or 1:24 etc. My question is just to confirm does it only impact you if the other people are actively downloading at the same time ? I assume yes but not certain.

For example if its a 1M link and a contention of 1:10 to make it easy. If the 10 people are connected but lets say they are not doing anything, then person 1 starts to download a file..does he get the full available 1M (or close to it) ? I'm assuming yes. Then if person 2 starts a download they each get 500kbps etc so it would only be if all 10 people were to download at the same time it would drop to 100kps for each. Does that make sense ?

I'm trying to figure out whats up with my connection, explanation is contention ratio from ISP but if my understand is correct then I should be seeing variations in my download speed at different times. As it is for the last 6 hours its been with a few 10s of bits each time and 6Mbps below what its supposed to be

I've configured a speed test to run overnight each hour so I'm hoping to see some improvement....

Thanks,
Declan.

watty

yes you are basically correct, you should see speed vary at different times.

There are 3 types of "contention":

1) Engineering / planning contention. The sum of users packages divided by system bandwidth. This is the 48:1 or 24:1 etc the provider quotes.
2) Actual contention. The sum of actual instantanous traffic divided by system speed. Because of handshaking and gaps in transmission, staring at page, page rendering time etc, it's possible to get negative contention, i.e. on 10Mbps circuit, more than 10 people can "seem" to have 1Mbps. Obviously if you could max out the connection simultanously for 20 x 1Mbps users on 10Mbps you would see 0.5Mbps = 1:2 Contention. Only P2P is able to achieve this in both directions. UDP (i.e. Video) is next worse, but only one way. FTP can't as it stops and acknowledges each part. Web pages is most "friendly" for contention. VOIP is very solid, but only up to 100Kbps. If you had a soft PABX with 5 calls that could do a solid 480k both ways (it's UDP after call connects, and symmetrical traffic). FTP, Web, Video and Email is all non-symmetrical, basically mostly download (up to 90%, email more like 70/30, but not simulaneously). Email has more download than upload due to spam and more images in non-personal emails (i.e. Ebay notices, newsletters etc).

3) Resource contention:
More complex. Some systems can't scale past a certain point (3G Mobile is one). In this case beyond a point you contend to get connected at all. On ordinary voice calls the exchange might have been designed at 1000:1 contention or higher. If the exchange was maxed out you would get engaged tone on some systems. 3.6Mbps HSDPA has a connection limit of about 24 users. A Cable, DSL or Metro system might have 200 to 2000 connected users depending on capacity with a 24:1 or 48:1 contention. Contention in sense (1) as on DSL, Cable, Fibre, Metro, Satellite and other high capacity system is thus Meaningless on GSM/GPRS/EDGE/3G/HSDPA Mobile "Broadband" (really Mobile Internet).



At off peak times you should see full speed and at peak times 1/2th to 1/3rd speed. If it goes a lot lower or never gets to full speed then you share resource with a load of P2P users and the ISP is not doing any quota/Cap (rolling 30 days works better than start of month reset) which would spread out their usage across time and reduce actual contention by 1/3rd or more.

DriveSkill

Thanks Watty,

At the moment is seems like I get at best 20% of the stated bandwidth even off-peak. I ran speed tests every hour throughout the night and best I got was around 1.5Mbps on a supposed 7.6Mbps download.

www.speedtest.net is reading around 1.6Mbps this morning as is www.speedtest.ie but last night before midnight the www.speedtest.net was reading in the 300kbps range even though www.speedtest.ie was always around 1.5/1.6Mbps.

How do you know which one is accurate ??? www.irishisptest.com was always giving a really low speed also!

To me it looks like I have a 1.6Mbps link!!

Thanks,
Declan.

watty

What kind of Broadband is it?

See if the Modem /Router has a stats page and post the signal levels etc.. It could be if your line is DSL and too poor or too far from exchange or something on your home wiring on wrong side of dsl filter or bad dsl filter that is why speed is low.

DriveSkill

Hi,

I think I discovered the problem....Sky box not plugged in through a DSL filter! Stupid mistake, I thought it was as I never had any problems with my old broadband.

Anyway when I un-plug the phone connection from Sky my modem 'syncs' at 5120kbps which is much better. Results from www.speedtest.net are now around 4Mbps which I guess would be about expected.

Thanks for the help....

Must get back on to Vodafone now and cancel my tech support request! They tried to explain it away as pure contention and that it was to be expected! Still the fault was mine at the end of the day.

Declan

watty

It's nice that the real contention is not as bad as they think it is