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Cross Country Network Bandwidth
RFC 567

Document Type RFC - Unknown (September 1973)
Updated by RFC 568
Last updated 2013-03-02
RFC stream Legacy stream
Stream Legacy state (None)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state RFC 567 (Unknown)
Telechat date (None)
Responsible AD (None)
Send notices to (None)
RFC 567
Network Working Group                             L. Peter Deutsch  (PARC-MAXC)
Request for Comments: 567                                     September 6, 1973
NIC #18970


The following computation of cross-country network bandwidth was
contributed by Butler Lampson of PARC.

Consider what happens when a TIP user on the West Coast, connected to a
full-duplex Host on the East Coast, strikes a key on his terminal.

The TIP sends a one-character message (1 packet).

The destination IMP sends a RFNM (1 packet).

The destination Host sends an ALLocate - this seems to be the strategy
used by TENEX Hosts, at least (1 packet).

Thc TIP sends a RFNM for the ALLocate (1 packet).

The same sequence repeats itself, with roles interchanged, for the echo
character (4 packets).

This constitutes 4 packets or 4OOO bits in each direction. The current
cross-country transmission capability of the ARPANET is 3 5OKb phone
lines; ergo, it can only support 3*50000/4000=37.5 such characters per

It may be that RFNMs are transmitted between IMPs more efficiently; at
best this can only double the network capacity.

This computation may help explain why cross-country TIP users (e.g. the
substantial West Coast community of BBN-TENEX users) experience such
bad echo response, at least in bursts: the network itself may be
experiencing momentary peak loads.

If this argument is correct, the proposed remote echoing facilities of
the new TELNET protocol could have a major effect on network operation.