SeaNET update

			  November 11, 1996
		     Andy Maffei and Dale Chayes

	The SeaNet Communications Node (SCN)/INMARSAT-B system which
has been on the R/V Thompson was moved to the Ocean Drilling Program
drillship Joides Resolution ( formerly the SEDCO/BP-471) during a
regularly scheduled port stop in San Diego at the end of October. This
move would not have been possible without the able assistance of Mike
Realander who handled the removal and packing on the Thompson end and
the SEDCO crew who managed to find time to assist with the
installation in the middle of replacing both of their radars.

	The installation on the Resolution was done to allow wire line
logging data to be transferred ashore for analysis with the results to
be sent back out to the onboard science party during the drilling leg
170. The Borehole Research Group which leads the wireline logging
effort on the Resolution has been using a VSAT system courtesy of
Schlumberger to do this for some time. The SCN/INMARSAT-B system was
installed for the current leg because the drilling site was expected
to be beyond the reach of the existing VSAT capability.

	As with all INMARSAT A installations, there are still problems
with antenna masts (and the drill rig!) blocking the view of the
satellite on certain headings. This problem is somewhat lessened by
SEDCO-471 remaining stationary for much of the time during a
cruise. High Speed connections to shore need to be coordinated for a
time when the ship is pointed towards the equator (more or less). We
are working on a software module that calculates good headings based
on a ship's above deck profile and the predicted azimuth and elevation
to an INMARSAT satellite. Careful planning of the antenna location can
reduce the impact of obstructions. One of the things we have learned
about INMARSAT B is that voice connections are more robust in the face
of obstructions than for INMARSAT A. However, HSD connections require
a clear line of site to the satellite. For shipboard applications
where continuous HSD service is critical and a single location can't
be found, consideration of two antennas might be an alternative.

	We are now getting ready to help with some periodic transfers
of wireline logging data from the SEDCO-471 after the first hole is
finished and logged which we expect within the next week. There are
some ISDN problems to be worked out and some software to be tweaked in
support of their efforts to transmit some fairly large seismic files
over the INMARSAT-B SeaNet system installed on the Resolution.

	It is likely that we will see on the order of half a dozen
large (multi-megabyte) file transfers during this leg and we expect to
be able to monitor the transfer characteristics and hope to be able to
improve the throughput over time while providing a useful service to
the science community at the same time.

	When it became clear that the our INMARSAT B system with High
Speed Data (HSD) was going to be installed to support the wireline
logging effort, TAMU expressed interest in using the link to transfer
their cc:Mail messages between ship and shore. We are working with
them to develop and implement a test plan. One of the problems is that
the ship is currently using a network number that is already in use on
the TAMU campus. A "simple" TCP/IP routing scenario is not an
option. A lesson to be learned from this is that even for ships (or
remote sites) that do not anticipate a direct Internet connection, now
is the time to allocate legitimate network addresses.

	Our hope is that when (if) UNOLS vessels move to using
INMARSAT-B more then we will have an attractive communications hub for
them to use for various Internet type tasks. We should have some hard
numbers to report by the end of the year concerning optimal file
transfer rates and costs. We are also hoping to port the software to a
Linux platform soon and make it available as a development platform
for other shipboard applications.