Hi, I am not sure what you mean NTP refresh, if the test was using the system clock than you would expect in XP that it will be updated every tick which is 10 or 15 msec which can account for the error. NTP is used in RTP (RFC 3550) for synchronization and the RTP time is using the system clock which may add skew but it is not because of NTP.
Roni Even From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Das, Saumitra Sent: Wednesday, November 12, 2008 11:31 AM To: [EMAIL PROTECTED] Cc: ietf@ietf.org Subject: Re: [P2PSIP] P2PSIP diagnostics: PING discussion Hi Song, Even in the planetlab testbed, the following paper at PAM 2008 ( http://pam2008.cs.wpi.edu/slides/pathak.ppt ) shows that more than 40% of nodes have more than 20ms NTP error. In a general overlay we are likely to find a larger fraction of nodes with error in their NTP time (since the planetlab testbed is managed by the people who own the machines while general overlay nodes are unlikely to be that well maintained). Unless NTP refresh is made mandatory within a p2psip implementation, relying on ntp would be unlikely to be helpful to diagnostics Thanks Saumitra www.saumitra.info =============== Dear all, In P2PSIP base protocol, Ping is used to test connectivity along a path. However, connectivity quality can not be measured well without some useful information, such as the timestamp and HopCounter. In p2psip diagnostics draft version 03 http://tools.ietf.org/id/draft-zheng-p2psip-diagnose-03.txt we extend the Ping message payloads with a few kinds of useful information for connectivity quality check purposes. The initiator node receiving the Ping response should compute the overlay hops to the destination peer for the statistics of connectivity quality from the perspective of overlay hops. About the Timestamp, we are not sure if the NTP time is a good candidate for it, or we have other ways to describe it, or we don't need the timestamp at all. But if NTP time is used in the overlay, then it is a good choice, because every peer along the message path will know when the message is generated, and it is easy for the peer along the path to calculate the message latency. However many overlays may not be synchronized with the NTP time. Any comments? Best Regards, Song Haibin Email: melodysong at huawei.com Skype: alexsonghw
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