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Network Working Group                             L. Peter Deutsch  (PARC-MAXC)Request for Comments: 567                                     September 6, 1973NIC #18970            CROSS-COUNTRY NETWORK BANDWIDTHThe following computation of cross-country network bandwidth wascontributed by Butler Lampson of PARC.Consider what happens when a TIP user on the West Coast, connected to afull-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 strategyused 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 echocharacter (4 packets).This constitutes 4 packets or 4OOO bits in each direction. The currentcross-country transmission capability of the ARPANET is 3 5OKb phonelines; ergo, it can only support 3*50000/4000=37.5 such characters persecond!It may be that RFNMs are transmitted between IMPs more efficiently; atbest this can only double the network capacity.This computation may help explain why cross-country TIP users (e.g. thesubstantial West Coast community of BBN-TENEX users) experience suchbad echo response, at least in bursts: the network itself may beexperiencing momentary peak loads.If this argument is correct, the proposed remote echoing facilities ofthe new TELNET protocol could have a major effect on network operation.