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Mathematical Analysis of Gnutella
jrp2 sent in a paper written by one of Napster's founding engineers. It is
a mathematical evaluation of Gnutella discussing
why the network won't be able to scale up to any reasonable size. I
have been impressed with Gnutella in the past, and have wondered along
these same lines in the past.
As I pointed out last time this was posted, this article is basically 100% FUD. Yes, the amount of traffic goes up. And no, gnutella doesn't scale very well. But the author goes out of his way to make the problem look worse than it actually is. You see, the article only computes the total amount of traffic in the entire network. A number which is both huge and meaningless. You see, by this math, if I send a packet somewhere and it takes 10 hops, well, thats like sending 10 packets!
At the end of the paper, the author coughs up the big scary number of 63GBps of traffic in the Gnutella network when the nodes each have 8 connections and are using a TTL of 8. Wow! That's a lot of traffic. That certainly isn't scaling! Well, what the author never points out is that, by his own math, the network has 7,686,400 users at this point! When we divide up the total traffic among all of those network links, we get a different view. If you do the math you discover that this is a whopping 72Kbps! Oh no! It's the end of the world! Well, no, it's not. True, it's more than a modem can handle. But it's well within the reach of most cable modem connections. Given that your computer is being expected to handle the search requests of over 7 million other people, it's not that much traffic.
Don't get me wrong, I agree that Gnutella doesn't scale all that well. But this paper is just plain FUD. The only number that really matters to users is the total bandwidth load on their pipe. By carefully avoiding that number, which isn't very big and scary at all, the auther is clearly lying by ommision. Given all of the real problems networks like Gnutella encounter, it isn't interesting to read this sort of drivel. Why don't we drag out Mathmatical and model how much bandwidth Napster wastes by transmitting the names of all the files being shared even though most of them will never get searched for. Hmmm. lets assume 7,000,000 users. Let's assume that they each share 1000 files with an average filename length of 32 characters. Why, that's 224 Gigabytes of data, and we haven't even done any searches yet! Cleary, Napster doesn't scale. Ugh. This guy might know how to use Mathematica, but I still suspect he worked in the Marketing department. With the same guys who will tell you about their 200Mbps fast ethernet.