Network Working Group Marc Seriff
Request for Comments 308 MIT-DMCG
NIC 9259 13 MARCH 1972
References: RFC 254
ARPANET HOST AVAILABILITY DATA
Several months ago a SURVEY program was implemented on the
MIT-DMCG ITS PDP-10 system to aid in gathering information on the
availability of various HOSTS on the ARPANET. The purpose of this
Request for Comments is threefold:
1. to inform the Network Working Group of the
existence of this information gathering service
and about getting access to it,
2. to present the results of SURVEY for its first
few months, and
3. to correct errors in our data or collection methods.
Briefly, the SURVEY program works as follows: At 15-minute
intervals whenever the MIT-DMCG ITS Time-Sharing system is in normal
operation, a SURVEY is started. The SURVEY program attempts to
establish a connection to the LOGGER (socket 1) of each HOST listed in
its table. The results of each connection attempt are recorded for
future reference. The Initial Connection Protocol is aborted prior to
reading the transmitted socket number so as to cause the minimum
amount of processing at SURVEYed HOSTS. If the LOGGER connection
succeeds, the average request-for connection response time (in
seconds) for the HOST is updated. This information can later be
viewed in several formats using the MIT-DMCG server TELNET "NETWRK" as
Each test results in the assignment of one of the following
1. LOGGER available - connection completed.
2. LOGGER not responding - RFC sent (HOST-HOST OK), but
no response (20 seconds allowed).
3. LOGGER rejecting - CLOSE returned by NCP.
4. NCP not responding - RESET timed out (15 seconds allowed).
5. HOST dead - host-dead status returned by IMP.
There are, in addition, two other shortcomings of which we are
aware. The first is that SURVEY is on a 24-hour basis and does _not_
consider advertised up time. For example, MIT-DMCG will never be
better than 67% on a Tuesday since the machine is always unavailable
from 4 p.m. to midnight. The second shortcoming is the fact that the
Lincoln Lab's TX-2 shows as "never available". This reflects an as
yet undiagnosed problem currently under investigation.
To get availability information from DMCG, you must first follow
the scenario in RFC 254. Once in NETWRK, the DMCG user-TELNET, there
are seven available commands which pertain to SURVEY data:
SUMMARY.OF.SURVEYS - summarizes most recent information.
HISTORY.OF. <host name> - gives a detailed recent history
of the given host. This generates a lot
of output, so use it sparingly.
ACTIVE.HOSTS - lists those hosts who accepted a connection
at least once during the last 24 hours.
BEST.SURVEY - lists the best of the recent surveys.
LONGTERM SUMMARY.OF.SURVEYS - summarizes all past
information. This was used to generate
the table on the next page.
LONGTERM HISTORY.OF <host name> - gives a summary of
past history of the given host. It
does not generate as much output as the
LONGTERM ACTIVE.HOSTS - lists those hosts who accepted a
connection at least once since December 13,
For help in accessing SURVEY data and comments on improving the
admittedly limited SURVEY service, please contact:
M.I.T. - Project MAC
545 Main Street
Cambridge, Mass. 02139
(617) 864-6900 ext. 1458
* Remember that "UP is defined as "Logger Accepting connections."
** Surveyed only since February 18, 1972.
*** MIT-DMCG is actually up about 66% of the time.
[ This RFC was put into machine readable form for entry ]
[ into the online RFC archives by BBN Corp. under the ]
[ direction of Alex McKenzie. 12/96 ]