ARPANET short blocking feature

This RFC specifies the ARPANET Short Blocking Feature, which will allow ARPANET hosts to optionally shorten the IMP's host blocking timer. This Feature is a replacement of the ARPANET non-blocking host interface, which was never implemented, and will be available to hosts using either the 1822 or 1822L Host Access Protocol. This RFC is also being presented as a solicitation of comments on the Short Blocking Feature, especially from host network software implementers and maintainers.