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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