I did a search and either didn't find the answer or the answer was vague.

1) Why are the majority of connections with LW users and never with other Phex users?

2) I know a peer is a user and an ultrapeer is a user with a broadband connection but what is a leaf and ultraleaf?

3) When attempting to DL a file it may show 20 possible candidates but only 1 or 2 will actually be available. Why? (by available I mean the "Available" column shows blue.

Thanks!

1 )
Compared to Limewire the Phex user base is much smaller, additionally Phex has no vendor preferencing algorithem that preferes Phex instances over others, like LW does.

2)
They are all basically the same. Before ultrapeers exists peers connected to other peers without preference. But with UPs peers/leafs only connect to UPs and not to other peers/leafs.

3)
Phex can only report how much of a file a candidate has available, when the candidate reports this. That means Phex had to at least connected once to that candidate and the candidate had to report the its availability information of the file. Not all candidates are doing this and not all connections work.

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Ok, that all makes sense...but ya never said what a leaf is. After some thinking I came up with it's someone who I can actually get downloads from? Is that right?

Every peer thats not an ultrapeer is a leaf... nowadays a leaf is the same as a peer.

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Here's a short part about the UP-Leaf model (copied from http://gnufu.net ):

===Network model: Change who calls whom: Ultrapeers and Leafs===
====UPs really short====

You'll surely have friends who know very many other people, and whom you can ask, and be sure they'll know exactly the person who can give you the answer. These are called Ultrapeers in Gnutella. An Ultrapeer doesn't have to know much himself/herself, he/she just needs to know who knows it. In Gnutella that means that a good Ultrapeer doesn't need to have many files to benefit the network. If you're afraid to share much, you should become an Ultrapeer in Gnutella.

====Ultrapeers and Leafs more detailed====

In the Computer World, as in the Real World, there are contacts who can cope with more calls, and those who can't phone often (or can't afford the bills). In the Real World this is because they have more free time. Whereas, in the Computer World, it is because they have faster connections (Like DSL, Cable, T1, T3 or similar broadband).
Upon realizing this, the developers decided to change the topologiy, that means how the network looks from the outside when you draw it. Now you don't just call any of your friends, but only those whom you know have the time to take your call and to send it on to others. To save you from too many calls, they then ask you which kinds of informations you have or, to express it in a more human way, what your speciality is. In the Computer World that means your computer sends a list of all its files to the Ultrapeer, which is how we call these kinds of contacts. That list contains summaries (Hash-Strings) of all your shared files (those you decide to let others download) by which the downloader can verify that they are, indeed, the files he or she wants. Whenever a call reaches the Ultrapeer, it checks if you could know an answer and calls you only in that case.

These Ultrapeers have many connections to others, which means they have a really big address book. Normally they stay in contact with 16 other Ultrapeers whom they have in their address book and to whom they send questions, and who send them to 16 more, each. Also they have about 16 leafs, who can't or don't want to phone that much, from which they accept calls, and whose files or, for the human world, specialities they know.

This may seem like a foul bargain for the Ultrapeers, who devote far more resources to keeping the network intact than leafs, but in fact it isn't. While the Ultrapeer (UP) uses much of her time for keeping the network running, the leafs specialize on gathering and delivering information. So, when anyone, Ultrapeer or Leaf, wants to know something, he or she simply starts a call and a leaf specialist can explain it to them. That way people specialize to get more for all.

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Wow! That makes much more sense! I like the analogy as well. So let me see if I have one more thing straight, all of the connections that I have which are Leaf connections, those are the primary file sharers who are connecting to me and using me as their "hub" into the network because I'm a UP?

Exactly.

And when you are Leaf, you are using other UPs as hub into the network.

Also you might want to look at the QRP and Dynamic Querying, which are further optimizations of Gnutella (both supported by Phex):

===Network model: Intra-ultrapeer QRP===
While with Ultrapeers not everyone needs to participate in sending questions to others, and people can specialize in sharing their information instead, the Ultrapeers would still send every question to everyone, without ever taking into account if that UP even has leaves, who have the files. This sounds normal, for how can an Ultrapeer know which files the other Ultrapeers have? The answer comes, again, from real life. A normal person knows her friends, and knows who of them might know the answer to a specific question, and who most surely will not. In Real Life this is mostly done through friendly chatting.

Now, computers normally don't chat idly, so they don't exchange this information by the way. Thus the Query Routing Protocol was developed. There each Leaf tells its Ultrapeers which files it has, but instead of taking the names, which would consume too much space, each word which is part of the name of a file is saved as numbers (these are computers after all). You can imagine this process like a game of dumping ships (the numbers form the board with two coordinates). An Ultrapeer doesn't send all questions to a leaf, but only those which it might be able to answer (which hit a ship), and so Leafs get far less needless calls.

Now when this takes so much pressure off the leaves, why not extend it? Exactly that was done. Now all Ultrapeers send their boards to their direct neighbors. They send only those searches, which have one more step to go, to other Ultrapeers on whose board they score a hit. That means, the last two steps of a search will only be taken when there is a chance that they give results. You can see quite simply why this heavily reduces the bandwidth usage: imagine a tree, a normal tree, not one of those mathematical constructs. If you try to count the leaves, you have almost no chance. But if you take the leaves away and count only the branches, you have far less work to do. If you now take away all those tiny branches, you can really begin to count them. QRP doesn't take all leaves and all tiny branches away, but it removes those of them who couldn't give you an answer. Since every part through which a question has to travel consumes bandwidth, and there are far more leaves than branches, taking away, in many cases, many of the last two steps (that means many of the leaves and the tiny branches) reduces the number of questions the computers have to send on (there are far more leaves, than branches). The example doesn't work for all of Gnutella, but here it fits nicely.
The people of LimeWire talk about 70-80% savings alone through this.


===Network model: Change Searching: Dynamic Querying===
Now, while the Ultrapeer model and QRP partly solve the problem that you don't have the time to explain something properly to someone else, or to get it explained, because the phone rings endlessly for questions to which you know no answer (or in Tech-Speech: because the network-traffic exceeds your connection-speed), there is still another problem which might normally not even be visible, if you look at it. In the Real World, an Ultrapeer will ask for a specialist who can give you the info until he/she finds one, and then stops. In the Computer-World, the question is sent on and on, to as many contacts as possible, without looking if there already are answers.

With dynamic Querying that changes. Now the Ultrapeers ask one other Ultrapeer at a time, and wait a bit, to see if they get answers. When they have enough answers to be satisfied, they stop asking for more. It sounds pretty natural, but was quite a big step for Gnutella because it saves resources which were wasted on very popular questions. I'll take the example of the of the head of university again: now, if you ask for the head of university, your Ultrapeers will first see if they know someone directly who can answer your question. Then they will simply give you some numbers of people they know who live on the campus. You will still get more than one answer because they will give you more than one number, as they can't be sure that you'll reach every number they gave you. But you won't get thousands of phone-numbers (one from every student on the campus), first because the Ultrapeers would waste their time with that on something which doesn't give you additional benefit, second, because you couldn't ever call all those people, and third, because then you might not reach your Ultrapeers anymore, because they would be so busy getting return calls from others who tell them numbers, and sending your question to other Ultrapeers.

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