On 11/09/14 22:11, Rob wrote:
mike cook <[email protected]> wrote:
Le 11 sept. 2014 à 21:08, Paul a écrit :
On Thu, Sep 11, 2014 at 2:08 PM, mike cook <[email protected]> wrote:
Did I miss something?
On Tue, Sep 9, 2014 at 3:17 PM, Rich Wales <[email protected]> wrote:
My home LAN is connected to my school's network via a cable modem.
If we make the (safe) assumption of a common cable ISP/FiOS in the
Palo Alto area the path is asymmetric.
Yup, AsymmetricDSL does have different up/down bit rates. What I really
meant was that the difference would not explain his issue.
ex: with a 12Mbps down rate and 1.3Mbps up rate, the ratio is around 40usec
to 300usec transfer of a 48byte NTP packet.
Bitrate is not the only modem parameter.
The baud rate is 4kHz (approx). That means that the absolute minimum
packet time is 125 microseconds. As packets probably don't align with
signalling units, there is a good chance that you will need to add
another 125 microseconds. There is also going to be a delay of, on
average, 63 microseconds waiting for the start of a signalling unit.
To this you need to allow for any expansion due to FEC coding, and the
likely use of interleaving, which, to be effective, would need to spread
adjacent bits over quite a lot of signalling units. I can't find a
figure at the moment, but my guess is that it pushes the minimum delay
into the milliseconds range.
(Gamers tend to turn off interleaving, if they can, as they want low
latency at all costs. Businesses are most likely to want it on.)
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