RFC 685 (rfc685) - Page 2 of 3

Response time in cross network debugging

Each session lasted about 10 minutes. The terms used below
are:

message -- a single message generated by the PDP-10 portion of X-NET

active command -- a command which involves, actually or virtually,
an interaction with the subject program (e.g., examine, deposit,
start, stop, set breakpoint, etc.)

bytes -- the total of all (8-bit) bytes, both sent and received,
plus any bytes due to receipt of asynchronous replies (e.g.,
breakpoint hit), during processing of the associated message or
active command.

wait -- total elapsed time from handing message to implementation
language (BCPL) network routines, to receipt of the reply from
these routines and through an inferior process in X-NET

The 35 active commands in the scenario are:

1 load program
8 start or proceed program
3 halt program
16 examine contents of memory word
1 deposit new contents in memory word
1 set breakpoint
1 remove breakpoint
1 word search
1 copy program onto disk file
2 network/process management (see user's manual)

The summary statistics are:.

BBN (local) SRI (distant)
AVG STD DEV AVG STD DEV
PER MESSAGE:
BYTES 154 295 164 295
WAIT 1.75 2.04 1.89 0.78 SEC
PER ACTIVE COMMAND:
MSGS 0.91 0.69 0.91 0.69
BYTES 150 331 150 331
WAIT 1.60 2.36 1.73 1.35 SEC

The standard deviation is relatively large partly because of a
small number of samples, but even more because the message size and
the command complexity are bimodal, as shown by the histograms
below. The load and word search commands transferred many bytes, as
did an examine (the first one while the program was halted;
subsequent examines were answerable from the cache; see user s
manual). Other commands needed little or no network transaction.
Those which needed none at all produced a no-delay mode in the
distribution of waiting time per active command.