RFC 47 (rfc47) - Page 2 of 4
BBN's Comments on NWG/RFC #33
Alternative Format: Original Text Document
RFC 47 BBN's Comments on NWG/RFC #33 April 1970 I found two substantial errors in the Host Protocol Paper, which was otherwise an excellent paper. Both concern a misunderstanding of the nature of the IMP as a communications device, and in particular the nature of buffering an IMP must do. The authors consider the network as a device into which one pushes a message which travels around some, waits in buffers for substantial lengths of times, and then emerges at the destination. In fact a better model would be that the message pops out again an instant after it is inserted. While it is true there is a delay, it is imposed by phone line hardware for the most part. The IMP buffering is minimal, and devoted to error control and momentary traffic surges. Since we cannot force a Host to take a message, we have built an elab- orate RFNM mechanism to suspend new input until he does. This mech- anism is an imperfect attempt to solve a very hard communications problem. The desire is to regulate traffic in such a way that as the Host takes its message from the IMP the next message is arriving on the phone line, and no buffering occurs at all. In fact we cannot achieve this, and therefore have included buffering to handle traffic surges. These buffers are useless for their intended purpose unless they are empty. Only empty buffers are available to soak up a traffic surge. The two specific errors occur on pages 5 and 23. On page 5 the authors say "Implicit in this purpose is the assumption that a user does not use multiple links to achieve a wide band." In fact one of the primary purposes of links is to achieve a wider band.
