A frequently occurring idea for IP tunneling applications is to run a protocol like PPP, which encapsulates IP packets in a format suited for a stream transport (like a modem line), over a TCP-based connection. This would be an easy solution for encrypting tunnels […] and also an easy way to compress arbitrary IP traffic, while datagram based compression has hard to overcome efficiency limits.
Unfortunately, it doesn’t work well. Long delays and frequent connection aborts are to be expected. Here is why.