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Network Working Group John E. Kreznar
RFC-19 SDC
7 October 1969
TWO PROTOCOL SUGGESTIONS TO REDUCE CONGESTION AT SWAP-BOUND NODES
There is a wide variance in swap rates between core and auxiliary store
among the HOST systems to be nodes in the ARPA network. The slower of
these, of which our 360/50 system with 2303 drum swap store is an example,
might improve the utility of the network not only for themselves but for all
nodes if the two protocol suggestions of this note were to be adopted.
l. HOST control of ordering of IMP-to-HOST traffic. IMP-HOST protocol now
calls for delivery of messages from IMP to HOST in the order in which
the IMP received them. This may lead to wasted swapping, if, for example,
the IMP has messages for its HOST's timeshare users A and B, in that
order, at a time when user B is in HOST core. B would have to be swapped
out, A in, and the first message accepted--only to discover that now A
must be swapped out and B back in again. If the HOST could a) read the
IMP's queue of waiting messages and b) accept them in the order it found
most effective, then a new mechanism for improvement of network efficiency
would be at thand. Clearly this change would have an impact on BBN's IMP
software.
2. Core-to-core transfers between HOSTS. At another level, perhaps not
involving HOST-IMP protocol or IMP software changes, is a HOST-HOST
protocol wherein cooperating HOSTS agree to lock appropriate programs
in core for the duration of a multi-message file transfer on an auxiliary
connection. This could greatly reduce the time to transfer such a file
to or from a swap-bound HOST. Unfortunately, the numbers mitigate possible
advantages of this approach to some extent: if we assume a 50 kilobit/sec
line and suppose further that it is dedicated at 100% efficiency to this
transfer (which may require slightly different handling of RFNMs in this
case) this comes out to just over 6 8-kilobit messages per second. It may
be impolitic in a timeshare environment to lock a single program in core
for more than abvout 2 seconds. If this is the case, then the method
would be applicable only for the rather limited range of file sizes of 2-16
messages. Nevertheless, the time to move a large file could be so greatly
enhanced by this approach that I think it deserves consideration.
1. Abhi Bhushan, Proj. MAC 10. Jerry Cole, SDC
2. Steve Crocker, UCLA 11. John Kreznar, "
3. Ron Stoughton, UCSB 12. Dick Linde, "
4. Elmer Shapiro, SRI 13. Bob Long, "
5. Steve Carr, Utah 14. Reg Martin, "
6. John Haefner, RAND 15. Hal Sackman, "
7. Paul Rovner, LL 16. C. Weissman, "
8. Bob Kahn, BB&N 17. Marty Bleier, "
9. Larry Roberts, ARPA