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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