TENEX BANDWIDTH

NIC 11584 (RFC 392) BY G. HICKS AND B. WESSLER AT UTAH RECENTLY DISCUSSED THE COST OF USING THE NETWORK.

   I WOULD LIKE TO TAKE THESE SAME TYPES OF NUMBERS AND LOOK AT THEM
   FROM ANOTHER POINT OF VIEW.  WITHOUT CALCULATING COSTS, LET US
   CONSIDER ULTIMATE PERFORMANCE OF THE HOSTS.  I WROTE A SIMPLE TENEX
   PROGRAM THAT SENT ITSELF STRINGS OVER THE NET.  IT USED BIN/BOUT AND
   THE BUFFERED SEND MODE.   IT COUNTED THINGS, BUT DID NOT PROCESS THE
   STRING.  WITH SAMPLES OF A MILLION BITS, THE FOLLOWING RESULTS WERE
   OBTAINED.
   
   BYTES/SIZE      REAL BAUD       CPU BAUD      CPU NEEDED
   
     50/36          48.8K           291K          16%
    100/36          46.5K           309K          15%
    200/36          52.7K           322K          16%
    400/36          59.3K           267K          22%
    800/36          61.1K           279K          21%
   
     50/8           22.0K           70K           31%
    100/8           26.7K           76K           35%
    200/8           29.0K           79K           36%
    400/8           30.0K           81K           37%
    800/8           31.9K           78K           40%
   1600/8           38.1K           64K           59%
   3200/8           41.8K           59K           70%

THE FOLLOWING WERE OBTAINED BY USING SIN/SOUT WITHOUT THE BUFFERED MODE.

   BYTES/SIZE      REAL BAUD       CPU BAUD      CPU NEEDED
     50/36          36K             95K           38%
    100/36          44K             95K           45%
    200/36          49K             92K           53%
    400/36          54K             90K           60%
   
     50/8           12K             22K           57%
    100/8           16K             21K           75%
    200/8           18K             20K           92%
    400/8           20K             20K           99%

THESE TESTS WERE RUN WITH NO OTHER LOAD ON OUR SYSTEM, AN EARLY VERSION OF 1.29. THE INPUT AND OUTPUT HALVES OF THE TRANSMISSION HAVE BEEN AVERAGED TOGETHER. I.E. THE ABOVE BAUD RATES WERE CALCULATED USING 2 MILLION BITS SINCE THE STRINGS WENT OUT AND IN.

OTHER PIECES OF DATA:

OUR TTY'S AND LPT HAVE ULTIMATE CPU BANDWIDTHS NEAR 15-20 KB. AT 2400 BAUD, A TTY TAKES 15% OF THE CPU. TELNETS NESTED THREE DEEP ARE ALMOST COMPUTE LIMITED WHEN JUST TYPING THINGS OUT ON A 2400 BAUD TERMINAL.

AS A ROUGH CALCULATION, THE BANDWIDTH OF THE TIP TAPE TRANSMISSION FEATURE - USING STEVE BUTTERFIELD'S (OF BBN) NETMAG PROGRAM - IS ABOUT 7 KILOBITS/SEC. ONE TAPE OF ABOUT 6,000 TENEX PAGES TOOK ABOUT 4 HOURS TO TRANSMIT. THIS WAS A FULL TAPE FROM ETAC TO CCA LATE ONE NIGHT WITH NOTHING ELSE RUNNING ON OUR SYSTEM. ABOUT 30% OF THE CPU IS NEEDED TO MAINTAIN THIS BANDWIDTH. AGAIN THIS IS ONLY ABOUT 20KB PER CPU SEC.

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