How does it really work?
 

first i have to say sorry for my really bad english, as you see i'm not a´native speaker and i never learnd it well.

I read a lot about gnutella and the new technique and i read the informations provided on this page, but there is still a few questions that i have:

when i'm going online i connect to the server of my internet provider and my computer get's an ip-adress for the time i'm online (i hope this is correct).

Now i start the gnutella programme/protocoll (what is the difference?) and this programme works like a server and it searches for other users, who are running gnutella?

Does it work like an search engine? How does it find other users?

Now i enter a question and this question runs through the gnutella network or my horizon as it is called, but how far is my horizon, what determines my horizon?

Thanks very much for your answers.

First Topic: Getting Connected

There are to ways to get connected to the Gnutella Network: Using AutoConnect Servers (like Gnutellahosts.com, router.limewire.com and gnutella.hostscache.com) or using "Discovered Hosts". Most modern Servents use the first approach by default, but do still have the second one implemented.

Using an AutoConnect server, your servent simply sends a message to that server and gets the IP adresses of other users as results. Note that you do not actually connect to the server, it just tells you where to connect. This method will certainly get you connected as long as the autoconnect server is online (and not shut down by greedy associations, i'm sure that earlier or later they will be trying to do this).

While you are connected, a part of your servent called the "Host Catcher" will catch IP adresses of other users. When you got disconnected and try to connect again some time later, the servent can try to reconnect to all of these "Discovered Hosts" and that really works - there will be lots of it who are still connected (or again, if their IP is static). Of course this approach can fail if you were not connected for weeks or months and all of your "Discoverd Hosts" IP addresses are out of date.

Second Topic: The Network Horizon

You know how the Gnutella Network is build: You are connected to, lets say, five hosts. Each of this hosts is connected to five hosts as well and so on ad infinitum. Now when you send a search request, it passes the first five hosts. Having done this, it will be forwarded to the hosts they are connected to (5x5=25), and then they will be forwarded again (5x5x5=125 hosts). Each step your message makes is called a "Hop". Now each of your messages has a "Time to Live (TTL)" which is about 7 by most servents, but there are also servents who let you choose your TTL (LimeWire). After a hop the TTL is decreased by one, that means, your request will pass about seven levels of forwarding (also called "broadcasting"). The servents that your request is able to reach before it dies (that means its TTL has reached 0) is called your "Network Horizon". It depends on your TTL and the number of connections that you and each of your peers have.