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