You are oversimplifying it. REQ/REP is not the same as TCP, unlike TCP it works with multiple requesters and multiple repliers. Same with other patterns. The m

You are oversimplifying it. REQ/REP is not the same as TCP, unlike TCP it works with multiple requesters and multiple repliers. Same with other patterns. The main distinction between L4 and scalability layer is that L4 works between 2 nodes, scalability between arbitrary number of nodes. There's the special case of UDP multicast, but the multicast itself feels more like a hack rather than a real L4 protocol.