RFC415 - Tenex bandwidth

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　　Network Working Group H. Murray
Request for Comments: 415 Stanford Research Institute
NIC: 392 29 November 1972

TENEX BANDWIDTH

NIC 11584 (RFC392) 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.

[This RFCwas put into machine readable form for entry]
[into the online RFCarchives by Helene Morin, Via Genie 12/99]

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