From HTTP channels, transactions connections to TCP sockets - how does this all come together?

Hey.

I've been trying to dig into the Necko source a bit, but I'm having problems understanding the architecture here. I'll just ask what keeps bugging me, any information/pointers at all is uber helpful:

What's the relationship between [HTTP] channels, transactions and connections? E.g. is a connection a collection of transactions (i.e. keep-alive: one connection, many transactions)? Is a transaction a generalization of a connection? The other way around? The fact that other docs around the net seem to use the term "connection" and "transaction" interchangeably is kind of confusing too.

Thanks!