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+Network Working Group                                    L.P. Deutsch
+RFC # 550                                                PARC-MAXC
+NIC # 17796                                              August 24, 1973
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+                           NIC NCP EXPERIMENT
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+For the past couple of weeks, the NIC NCP has been keeping statistics on
+total incoming messages, incoming host-host control opcodes, and size of
+outgoing messages. The results have been rather enlightening and, I
+think, should be carefully considered by future implementors of NCPs for
+servers. The statistics will be presented in a rather qualitative
+fashion, since they were reset each time the system came up, but they
+represent a total of about 100 hours of uptime, most of it during the
+working day.
+
+The total numbers of incoming and outgoing messages were almost
+identical. There were about 5% more outgoing. There were slightly over
+half as many incoming control opcodes processed as incoming messages; on
+the assumption that no incoming control message had more than one
+opcode, slightly over half the incoming messages were control messages.
+
+The Opcode statistics were somewhat variable. In all cases the ALL
+opcode accounted for the great majority, from a low of about 50% on
+weekends to a high of 98% on a busy weekday.  Almost all of the
+remainder were NOPs. No other opcode ever accounted for more than 5%.
+
+The output message statistics were taken as log2(message size): this
+included 1 word of buffer header, 1 word of IMP header, and l word of
+host header. As might be expected, 95% of all outgoing messages had l to
+4 PDP-10 words (36-bit) of data. However, if one multiplies the count
+for each bucket by the average message site for the bucket, the result
+is that only 75% of all outgoing data was in the smallest message size:
+the remaining data was spread out fairly evenly between the other
+buckets.
+
+I would draw the following conclusions from these statistics. First,
+half the messages on the network appear to be ALLs. This suggests that
+NCPs should give some thought to processing control messages
+efficiently. Second, 95% of the messages are very short. This suggests
+that elaborate buffering and queuing schemes are not likely to be
+valuable, since the hypothetical gain in efficient use of the IMP is
+probably swamped by the overhead within the host. Third, a sufficiently
+large fraction of all data is in large messages (presumably file
+transfers) that it is also necessary to deal with this situation
+efficiently, e.g. a NCP which always sent l-character messages would not
+be satisfactory.
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+Deutsch                                                         [Page 1]
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+RFC 550                    NIC NCP EXPERIMENT                August 1973
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+The ARPANET has been in vigorous operation for a year or two, and many
+NCPs have been written during this time (including a rewrite of the
+TENEX NCP, which probably handles more traffic than all other NCPs
+combined); to my knowledge, no one has bothered to gather these
+statistics before.  The total time invested in putting these
+measurements into the NIC system was about half an hour (10
+instructions).  I find it regrettable that even those of us presumably
+engaged in "computer science" have not found it necessary to confirm our
+hypotheses about network operation by experiment an to improve our
+theories on the basis of evidence.
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+       [ This RFC was put into machine readable form for entry ]
+       [ into the online RFC archives by Alex McKenzie with    ]
+       [ support from GTE, formerly BBN Corp.            10/99 ]
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+Deutsch                                                         [Page 2]
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