|
Items in cart [0] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 327
327
manuscript a list of all objects discussed in the manu-
script (i.e., a key object list in addition to a keyword
list). As mentioned previously, the committee described
in Section V could play a useful role in coordinating
these data-base activities.
VI I I . TELECOMMUNICATIONS.
The Panel investigated the increased access to computa-
tional facilities and data bases that might result from
enhanced telecommunications.
Telecommunications services may be divided into three
regimes depending on the bandwidth of the service. At
the low end are communications over ordinary voice-grade
telephone lines at rates up to 9600 baud. In the mid-
range are services that use a single digital voice chan-
nel at 56 kilobits per second (kbps), and on the high end
are services at 1.544 megabits per second (Mbps) (24
digital voice channels plus control bits) and up. The
cost of the voice-grade line is just the cost of a long-
distance telephone call between the same two endpoints.
At the high end, only dedicated channels are available at
a typical cost of $50 per mile per month. In the mid-
range, packet-switching networks are available. These
networks can route packets (a packet can contain up to
128 characters or 1024 bits) to one or more nodes on the
network, perform code translations, hold packets until
the destination can receive them, and perform other simi
lar services. Costs are based on a fixed connect charge
(typically $2100 per month) and a packet charge (typically
O.OOOS˘ per packet). It is not expected that the costs
of these services will drop dramatically over the next
decade but, rather only at a rate on the order of 10
percent per year in real dollars.
The Panel identified several potential uses for
telecommunications:
1. Remote access to the data archives described
earlier,
2. Remote access to the data bases described earlier
3. Remote access to centralized computational
facilities, and
4. Remote operation of telescopes.
The typical application of remote access to data ar-
chives would be to transfer data from the centralized ar-
-
OCR for page 328
328
chives to the users' local facility for local analysis.
This application does not require high-bandwidth telecom-
munications. The 56-kbps bandwidth is adequate to allow
"overnight delivery" of several large images (202 Mbytes
in 8 h). At 5 X 10-4˘ per packet it is already cheaper
to send an image in this manner than to mail a tape. The
main drawback is the $2100 per month connect charge. This
is far too large to be borne by most astronomy depart-
ments. If it is possible to spread this charge over sev-
eral university departments, then access by remote link
may become a cost-effective method of retrieving data
from archives.
Voice-grade lines are adequate for most accesses of
the data bases described earlier. Terminals and modems
(which provide the interface between terminals or com-
puters and the telephone lines) are proliferating rapidly
among astronomers, so this method of access to data bases
will become a reality when the data bases are upgraded to
support remote access as recommended the previous section.
Remote access to centralized computational facilities
is, of course, already a reality. Access over voice-
grade lines is adequate for analyses of one-dimensional
data or for those theoretical computations that do not
generate a large quantity of output requiring interactive
examination. However, voice grade or even 56-kbps lines
are inadequate for interactive image analysis or for those
theoretical computations that generate large quantities
of output requiring interactive evaluation. mese latter
cases require high-bandwidth communications, and the cost
of such services effectively precludes this mode of opera-
tion. For the foreseeable future, interactive image
analysis and large-volume interactive theoretical compu-
tations require that either the user must travel to the
centralized facility or the computational facilities must
be distributed among the users, as already recommended
here.
Remote operation of instruments is, of course, neces-
sary for all unmanned spacecraft. Remote operation of
ground-based telescopes can be conceived of in two modes.
Telescopes that are at relatively inhospitable or inacces-
sible sites may be operated remotely from a control center
within the observatory headquarters. Also, remote opera-
tions may enable observers to participate in an observing
run (i.e., to examine quick-look data and make decisions
concerning the short-term course of the observing program)
from a terminal at or near their home institutions without
traveling to the observatory site. A 56-kbps line, if
Representative terms from entire chapter:
computational facilities
