II. Some Requirements Upon the Host-to-Host Software

Simple Use

As with any new facility, there will be a period of very light usage until the community of users experiments with the network and begins to depend upon it. One of our goals must be to stimulate the immediate and easy use by a wide class of users. With this goal, it seems natural to provide the ability to use any remote HOST as if it had been dialed up from a TTY (teletype) terminal. Additionally, we would like some ability to transmit a file in a somewhat different manner perhaps than simulating a teletype.

Deep Use

One of the inherent problems in the network is the fact that all responses from a remote HOST will require on the order of a half-second or so, no matter how simple. For teletype use, we could shift to a half-duplex local-echo arrangement, but this would destroy some of the usefulness of the network. The 940 Systems, for example, have a very specialized echo.

When we consider using graphics stations or other sophisticated terminals under the control of a remote HOST, the problem becomes more severe. We must look for some method which allows us to use our most sophisticated equipment as much as possible as if we were connected directly to the remote computer.

Error Checking

The point is made by Jeff Rulifson at SRI that error checking at major software interfaces is always a good thing. He points to some experience at SRI where it has saved much dispute and wasted effort. On these grounds, we would like to see some HOST to HOST checking. Besides checking the software interface, it would also check the HOST-IMP transmission hardware. (BB&N claims the HOST-IMP hardware will be as reliable as the internal registers of the HOST. We believe them, but we still want the error checking.)