Network Working Group L. Peter Deutsch (PARC-MAXC)
Request for Comments: 567 September 6, 1973
NIC #18970
CROSS-COUNTRY NETWORK BANDWIDTH
- The following computation of cross-country network bandwidth was
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- contributed by Butler Lampson of PARC.
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- Consider what happens when a TIP user on the West Coast, connected to a
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- full-duplex Host on the East Coast, strikes a key on his terminal.
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- The TIP sends a one-character message (1 packet).
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- The destination IMP sends a RFNM (1 packet).
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- The destination Host sends an ALLocate - this seems to be the strategy
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- used by TENEX Hosts, at least (1 packet).
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- Thc TIP sends a RFNM for the ALLocate (1 packet).
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- The same sequence repeats itself, with roles interchanged, for the echo
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- character (4 packets).
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- This constitutes 4 packets or 4OOO bits in each direction. The current
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- cross-country transmission capability of the ARPANET is 3 5OKb phone
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- lines; ergo, it can only support 3*50000/4000=37.5 such characters per
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- second!
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- It may be that RFNMs are transmitted between IMPs more efficiently; at
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- best this can only double the network capacity.
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- This computation may help explain why cross-country TIP users (e.g. the
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- substantial West Coast community of BBN-TENEX users) experience such
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- bad echo response, at least in bursts: the network itself may be
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- experiencing momentary peak loads.
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- If this argument is correct, the proposed remote echoing facilities of
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- the new TELNET protocol could have a major effect on network operation.
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