Artem Barger's questions

I've just some question regarding TCP congestion avoidance algorithm.

1. First of all I'm looking for explanation of, why the part of congestion avoidance algorithm is called "fast recovery"? I mean I cannot find any good reason for it, seems like it doesn't really that fast recovery.
2. I'm reading the book of Douglas E. Comer "Networking with TCP/IP" and there is statement where said that although TCP SACK and New Reno is about the same, still SACK is preferable, but there is no good reasonable explanation why, so I would be appreciated for helping me figuring it out.

I'm trying to figure out the differences(pros/cons) between two routing protocols approach and I would be great-full for any help, advice and explanation. As far I can say that it seems like distance vector is more static and more local based routing, since it doesn't know the network state whereas link state is more aware of current states therefore it seems more natural to use it over distance-vector, but I have a feeling like I'm missing something. And I would be glad to here about more aspects and different issues I have to consider while choosing one of them.

Why is in TCP a 3-way handshake used during establishing a connection? Meaning, why it is not enough to use a 2-way handshake?

Recently I've started to read RFCs of different multicast standards and came out to the question, which is not totally clear for me. I'm trying to compare DVMRP vs PIM-DM routing protocols in order to understand which one is better, which one producing less multicast message while establishing route and during routing process at all. And which one of them is able to produce more sophisticated source tree.

Can you, please help me to figure out the answers for my questions?