From: "Rob Janssen" wrote:
Ask Bjørn Hansen wrote:
The "A" in ADSL has minimal or no impact.
The static offset caused by the "A" in ADSL is very small, and it is quite
likely that upstream packets, that experience more delay on the final hop,
are delayed less than downstream packets further in the carrier and/or ISP
network (because that is loaded more in the downstream direction).
However, the "A" in link usage has quite some influence. When you are up-
or downloading large files and saturate the link, the delay in one
direction will really jump up. Normal delay of an ADSL link is only a few
ms in each direction (e.g. 7ms roundtrip for a standard ping packet), but
this will easily increase to 50-100 ms in one direction when a TCP
connection is pushing data.
To avoid this, traffic shaping can be used. This especially helps for
avoiding saturation of the uplink.
Yes, there is a problem when asymmetry changes due to a high load in one
direction because the ntpd response to this change is slow, not shorter than
a poll interval, and a stratum 1 doesn't know about these changes at all.
But with this respect there is no difference between an asymmetric
connection and a symmetric one. If there is any problem with ADSL, it is not
its ratio but the uplink speed itself.
--
Karel Sandler
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