TCP

In our networking class this week we started discussing transport layer protocols for the internet, namely the different types of TCP (such as Tahoe, Reno, New Reno, and SACK). While we'll go into more detail in later reading (which compares Reno and Vegas), we were mainly looking at the differences between congestion control and performance, but I am more interested in looking at adoption rates (how successful each have been) as well as deployment strategies.

From what I've read so far it seems that introducing new transport protocols on a large scale seems fairly difficult, however, most TCP-based protocols seem to thrive. Is it because the underlying architecture already uses TCP, so changing it slightly won't make a huge difference. Or is modifying the transport protocol easier than I think? Looking at other transport protocols (like BIC, that was used for Linux a while ago) it seems that implementing a transport protocol is not too difficult, but getting widespread acceptance is. The next question I would ask is: do we need new protocols? I guess that depends on how much the underlying architecture changes over time.