Network Working Group Edward Taft (PARC-MAXC)
Request for Comments: 618 Feb 1974
A Few Observations on NCP Statistics
The NCP in use at HARV-10, CMU-10A, and CMU-10B collects a number of
operating and error statistics, which may be typed out on demand by
any user by means of the 'IMP ERROR' command, as shown on the sample
The figures shown cover the period since the system was last
restarted. They are not logged or recorded in any more permanent
form due to extremely limited on-line storage at HARV-10. where
the software was implemented. However, due to the small size of
the system and infrequent monitor development work, HARV-10 tends
to stay up for periods approaching the interval between hardware
maintenance, which is one week. The attached output was obtained
after 168 hours system uptime.
There are a few things I would like to point out that may be of
interest to NCP implementers.
First, note that the number of discarded (unexpected) RFNMs is equal
to the number of simulated (timed out) RFNMs. This has been the case
almost every time I have looked at these statistics. It suggests
that the RFNMs are not being lost but are rather delayed beyond the
NCP timeout interval, which I believe is 30 seconds.
I have heard talk among a few people in the Network community
about "lost RFNMs", and would like to suggest this as a possible
alternative explanation. Perhaps longer timeouts are in order.
Second, the observed ratio of received allocates to transmitted
allocates (on the order of two to one) is also fairly typical. I
believe this reflects differences in allocation strategies among
Many hosts appear to send out an allocate for every data message
received. While this is reasonable for connections such as FTP
data transfer connections, it imposes considerable extra traffic
in the case of the single character messages that seem to be the
most common on the network.
The strategy used by the Harvard NCP is to assign a "desired level
of allocation" figure to each socket (typically quite small for
Telnet connections and large for FTP data connections; it is a
user program settable parameter). When the actual allocation for
the socket falls below 50% of this level, enough additional
allocation is sent to bring it up to the full "desired level".
The effect of this strategy is to significantly reduce the number
of allocates returned for a given number of small messages
received. This reduces both network traffic and control message
overhead at the other end. The strategy has no effect on FTP data
messages, since each message is usually large enough to reduce
outstanding allocation by at least half at a single blow.
Finally, I should remark on the appallingly large number of NOPs
received (typically 25% of all control messages). Most of these seem
to be piggy-backed onto other control messages, so the situation is
not as awful as the figures would indicate. Nevertheless, I am
forced to wonder why anyone would want to send so many.
TELNET typescript file started at THU 31 JAN 74 428:05
#harv-10 (settings loaded) is complete.#
Harvard 5.06A-18 7:28:38
Type "HELP" if you need it.
JOB 2 Harvard 5.06A-18 TTY25
Your name please (last name first): Taft
You are logged in as 62,404000
0728 31-Jan-74 Thur
SCHEDULED PM ON THURSDAYS, 0830-1200 EOT
NCP version 1573.1604 operating statistics
NCP (link 0) message errors:
Socket not found: 2184