RFCs in HTML Format

RFC 0618

Network Working Group                                   Edward Taft (PARC-MAXC)
Request for Comments: 618                                             Feb 1974
NIC #21989

                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
various hosts.

    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. .login 62,# 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 .imp error NCP version 1573.1604 operating statistics 07:29:02 31-JAN-74 NCP (link 0) message errors: Socket not found: 2184 -2-

Improper state: 323 Illegal message type: 2 Last discarded allocation from PARC-MAXC (XEROX) link 12 Timed-out exec ICPs: 3 NCP messages: Type Received Sent NOP 81850 0 RTS 3688 2507 STR 2388 3562 CLS 6055 6059 ALL 183050 101442 GVB 772 0 RET 0 772 INS 109 0 ECO 7472 15426 ERP 15065 7472 ERR 2 0 RST 2782 226 RRP 162 2782 Received NCP error messages: Type Count 4 2 Most recent error: type 4 from UCLA-CCN Data (octal) 4 74 0 10 0 0 74 254 0 200 (decimal) 4 60 0 8 0 0 60 172 0 128 IMP data message faults: Hardware fault: 2 Link not found: 8 Discarded RFNMs: 10 Simulated (timed out) RFNMs: 10 Received IMP messages: Regular 590812 Err w/o id 3 NOP 4 RFNM 490095 Dest dead 366 Inc trans 52 IMP reset 2 Histogram of received data message sizes Bits Count <1 3 <16 146834 <32 39751 -3-

<64 7044 <128 196983 <256 46099 <512 147609 <1024 534 <2048 1820 <4096 1152 <8192 2979 72 free buffers 7% average buffer utilization .kjob/k Job 2, User [62,404000] Logged off TTY25 0729 31-Jan-74 Runtime 0 Min, 03.29 Sec -4-

Back to RFC index






"Every time you tear a leaf off a calendar, you present a new place for new ideas and progress. "