Comment by apitman

> TCP-over-TCP

> It lowers the throughput due to more overhead and increases the latency. On connections with packet loss or high latencies (e.x. satellite) it can cause a TCP meltdown.

This actually isn't a problem with SSH tunnels unless you're using TAP/TUN, because It unpacks and forwards the TCP streams. But you can still get reduced performance with multiple channels due to head of line blocking.