On this page:
tcp-redirect

17 TCP Redirect: tcp^ via Channels

The net/tcp-redirect library provides a function for directing some TCP port numbers to use buffered channels instead of the TCP support from scheme/tcp.

(tcp-redirect port-numbers)  unit?
  port-numbers : (listof (integer-in 0 65535))
Returns a unit that implements tcp^. For port numbers not listed in port-numbers, the unit’s implementations are the scheme/tcp implementations.

For the port numbers listed in port-numbers and for connections to "127.0.0.1", the unit’s implementation does not use TCP connections, but instead uses internal buffered channels. Such channels behave exactly as TCP listeners and ports.