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2. A remedy

This is a suggested modification of the Host-Imp users interface which has been tentatively sketched on diagrams extracted form BBN 1822 report.

2.1 Host to Imp​

The modification consists of adding a counter to 32, enabled as the beginning of a message, and incremented at each bit passed to the IMP; when it reaches 32 it forces a "word complete" signal asking for a new word in the shift register and resetting the word length counter; thus the unused bits in the last word of the leader are not transmitted and the message starts with the next word (see figure 2.1)

   0                                       23
   ------------------------------------------
   |             leader                     |
   |                   ----------------------
   |                   | XXXXXXXXXXXXXXXX   | <- contents of
   |-----------------------------------------    sending Host memory
   |                                        |    (24 bits)
   |            Message                     |
   |                                        |

   Corresponding message in the sending IMP memory

   0                             15
   --------------------------------
   |                              |
   |                              |
   |         leader               |
   |                              |
   --------------------------------
   |                              |
   |   message                    |
   |                              |

Figure 2.1

2.2 Imp to Host​

The modification consists of adding a counter to 32. When 32 bits have entered the shift register form the Imp at the beginning of a new message, the counter allows the register to be shifted up to the point to be full (which is detected by the word length counter) without entering any new bit from the Imp.

Thus, the next bit of the message which is the first bit of text will be entered as the first bit of the next word (see figure 2.2).

Message in receiving IMP memory  Contents of receiving Host memory (35
bits)

0                        15      0                                   35
------------------------------   --------------------------------------
|                            |   |                                    |
|       leader               |   |     leader                  | 0000 |
------------------------------   --------------------------------------
|                            |   |                                    |
| message                    |   | message                            |
|                            |   |                                    |
|                            |   |                                    |

Figure 2.2

Though the accumulated cost of useless marking bits sent over the network plus computation to reshape received texts makes this modification probably whorkwhile being considered, this decision is not of our competence and we merely wanted to suggest a better solution then marking.

Pages 5 and 6 contain a wire Diagram of a "IMP to Host" "Host's special Interface"

Note: This RFC was put into machine readable form for entry into the online RFC archives by Gottfried Janik 2/98.