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Fernique, P. & Durand, D 2001, in ASP Conf. Ser., Vol. 238, Astronomical Data Analysis Software and Systems X, eds. F. R. Harnden, Jr., F. A. Primini, & H. E. Payne (San Francisco: ASP), 63
AstroRoute
P. Fernique
Centre de Données astronomiques de Strasbourg (CDS), Strasbourg, France
D. Durand
Canadian Astronomical Data Centre (CADC), Victoria, Canada
Abstract:
The Internet is now the most commonly used medium for the exchange of data between data centres. However the quality of this network of
networks is completely outside the astronomical community's control: the routing rules for each country and the technologies deployed
depend on various interests generally far from astronomical concerns.
In order to get actual measurements of the fluctuating network flow rates between some astronomical Web sites, the CDS has developed a
tool called AstroRoute. Its goal is to supply, on an hourly basis, a measurement of the network quality between
astronomical Web sites over the world.
AstroRoute is a system to get measurements about the connectivity and the quality of the
network between astronomical web sites. It is an initiative and a development of the CDS
(Centre de Données astronomiques de Strasbourg) with the help of D. Durand from the
CADC (Canadian Astronomical Data Center). Several other institutes collaborate : the
Observatoire de Paris/Meudon, ISO, ATNF (Sydney), NOAO, STScI, and CFHT. This project
started in June 2000.
There exists a lot of network tools to test network quality, but the main problem is that the tests
are generally done from one single site--the tester's own host machine. In order to obtain more reliable results,
AstroRoute is based on a set of distributed agents which test synchronously a list of targets in
order to measure the network connectivity and the bandwidth between any pair of agent/web
site in the AstroRoute system. So, it becomes possible to know the authority that should be
contacted in case of network problem or bad performances (local, campus, and national
network instance) and to build convincing arguments for future upgrades.
To implement this principle, AstroRoute is based on two elements: a main site and some
agents. The main site controls all agents: it synchronizes their clock reference, sends the list of
astronomical Web sites to be tested and compiles their results. Each agent tests individually
these web sites and sends regularly a report to the main site. The resulting data set can be browsed
on the main site with a classical web interface.
The agent and main site software are written in Perl in order to keep a
good portability. The system is designed to take into account bandwidth
less than 200 kilobytes per second. The reports sent by the agents to
the main site use a simple SMTP mail. By default, the tests are done
hourly, and the reports are sent daily. The result browser is a classical
HTML application. It is also possible to use a more powerful Java applet.
AstroRoute should provide network measurements reproducing a current web usage.
This is why the tests are simple HTTP URLs providing a static file or image.
With these tests AstroRoute records three measurements for each pair agent/web-site:
- The delay required to establish a network connection between the agent and the site. It
means the time required for the DNS address resolution and the time to open an HTTP
TCP session.
- The HTTP flow rate. This measurement requires a test URL providing a file larger than
100 KB.
- The failure frequency.
Table 1:
Excerpt of agents/Web sites pair matrix: time connection, flow rate in kilobytes/sec, and success rate.
 |
AstroRoute has been running for six months, and interesting global trends can be seen:
- Various impact of the peak hours:
The difference between the peak hours and the off-peak hours is very important between
European sites and US sites. The bandwidth can be divided by a factor of two or three at 17hr
GMT. On the other hand, the access quality to Japan (ADAC) or Australia (ATNF) is not
really dependent of time.
Figure 1:
Bandwidth world map.
 |
- Increasing global quality in ``switchback:''
Globally the bandwidth of Internet grows but this longterm tendency results
from alternation of regular decrease and sudden improvements (Figure 2).
Figure 2:
Flow rate evolution.
 |
- Protectionism of routing policy”:
Network agencies seem to keep the bandwidth for local hosts since their network is
loaded. For example, it is easy to reach the ISO Center at Vilspa (Spain) from Strasbourg
(France) even if European network is loaded, but it is very difficult for an American host to
do the same thing at the same time. We can find other examples for the US routing policy
specially concerning the Eastern sites.
The AstroRoute results can be
accessed from CDS via the AstroRoute main page.
The objective is now to extend the set of participating sites to
obtain meaningful world-wide long term statistics, critical to assess the needs for this key infrastructure in the context of rapid
development of interconnection between astronomical on-line resources.
© Copyright 2001 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA
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