An URI value to be proxied.
Under normal operations a connection created through a BEEP proxy is configured with TUNNEL_IP4 and TUNNEL_PORT values. However, TUNNEL profile also allows requesting to proxy a particular profile, letting the decision to map that "profile" to a particular host location to the BEEP proxy.
How is mapped the "profile" request to a particular host location is a matter of provisioning for each BEEP TUNNEL server.
This value is only allowed to define the remote endpoint to connect to.