Contention - What it is, how it works. Or "Why is my Internet slow?"

Contention - What it is, how it works. Or "Why is my Internet slow?"

One of the thing's that I end up posting about most on this forum, is something called Contention. So I thought it would be useful if I put together a rough and ready guide explaining exactly what it is, so that I can link to it rather than having to keep repeating myself.

Note that alot of this, especially the examples, is specifically based around my experiences with the UK Broadband network, but the same rules apply to most broadband networks, and even LAN's.

What is Contention?
The Cambridge Online Dictionary defines the word Contention as "to compete in order to win something". This is actually a fantastic definition, as when sharing a network connection with other people, (be it over the internet, or on a private network) you are competing with them for bandwidth.

Ok, so I'm competing for bandwidth, but what does this actually mean?

Think of your network connection as a motorway (or freeway, autobahn, whatever you call them where your from) and the data you are transferring as the cars. It can only physically take so much traffic. When traffic is light all car's (and data) move at the optimum speed.

This works fine, right up until the point where the number of car's exceeds the number of cars that can travel on the motorway at optimum speed. At this point, everyone is forced to slow down.

The exact same thing happen's to network connections. When traffic is light, everybody get's fast speeds, and everybody is happy. However, as more and more people fill the available bandwidth, the connection is forced to slow down.

In the UK, Home broadband is sold at a contention ratio of 50:1. What this means is that I am sharing my connection with 49 other people. Well actually, that isn't entirely accurate, I am actually sharing it with 200 people, but the pipe can handle 4 times more data than my connection can, so the 50:1 contention ratio still applies.

So for example: I have an 8Mb/s connection. After overheads, and translating bits (which internet speed is measured in) to Bytes (which download speed is measuring) this translates to about 900KB/s (8000Mb/s / 8 = 1000KB/s - 10% for overheads = 900KB/s

So, lets say I start a download from a site, like Nvidia. To start off with, I'm getting all 900KB/s of goodness. However, what happens if my girlfriend decides that she absolutely has to download something? Well then my connection is being split between two machines. There is still 900KB/s of bandwidth available, but now it isn't just going to me, it's being split between us.

50 people sharing 8Mb? That works out to just 160Kb each, how is it that I can download at near full speed most of the time?

The reason this model actually works is because it is highly unlikely that all 50 people you are sharing your connection with will be online at the same time, and using all of their available bandwidth. Something like 70% of Internet use is web browsing and online games, which use very little bandwidth. However, at peak times, such as evening's and weekends, when most people are online generally Internet speeds are slower, simply because more people are online and therefore statistically, more of the "49" are online.

If the connection is being split, and contention is the answer, why do my speeds vary wildly?

Here's the rub. The split isn't even, the connections will fight or contend with each other, trying to get more bandwidth. So in my example above, rather than getting 450KB/s each, it's more likely our download speeds will vary from 300KB/S anything up to 600KB/s as the fight goes back and forth. Obviously downloading is a lot more bandwidth intensive than merely browsing web pages. In that situation the web pages invariably lose out, causing a slowdown or lag while waiting for responses.

What can I do about Contention?

The sad thing is, there is very little you can actually do. You can try to get a different Internet package, which offer's a lower contention ratio, but ultimately, there will still be contention on the line. It is just not cost effective for ISP's to offer each home customer their own dedicated pipe. Merely laying the infrastructure would cost billions that they would never recoup. Your best hope is to try and do heavy internet usage at off-peak times (anything before 6pm on a weekday is usually good, although the quietest times tend to be 12am-5am) and at peak times try to keep it down to web browsing or gaming. It is worth noting though that contention can also affect ping (or server reponse) times, as if the network is saturated then it will take longer for it to get through.

Anyway, I hope that clears things up a little. Hopefully you learned something.

Credits: Plusnet's guide to Contention, some of which I took and modified for my own use. http://usertools.plus.net/tutorials/id/11

Absolutely fabulous! I hope all information would be available like this. Easy to understand, logically told. You really can your stuff.

Must spread around, you know what I mean...

Kari

Great explanation!

(Took care of it, Kari, and well worth it. )

i'm content with this explanation.

+rep

mickey megabyte said:

i'm content with this explanation.

+rep

Click to expand...

~Lordbob

Great post, Marin. I repped you. Good, clear expalnation. Even I can understand it!