After many tests we concluded that Planet Lab landmarks, and to a lesser extent the PingER landmarks, are unpredictable in terms of availability. The TULIP Landmarks Map identifies the landmarks that are currently in use and those that have been disabled since they are not responding. If the landmark is not available the TULIP thread has to time out and this can dramatically extend the measurement duration and insert unnecessary traffic on the Internet. Thus, ideally, requests for pings should not be sent to such landmarks, i.e. they need to be removed from the list of active landmarks. The purpose of this web page is to indicate how we accomplish this.
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