Hi,
On 12/23/2013 08:12 AM, Paride Legovini wrote:
On Mon, Dec 23, 2013 at 04:22:08AM +0100, Carl-Daniel Hailfinger wrote:
Am 22.12.2013 18:10 schrieb Paride Legovini:
I'm working in an Antarctic research station where our connection to the
Internet is a 512kbps satellite link.
Assuming that the satellite link is expensive and has long roundtrip
times, it is probably a wise idea not to throw away any data which has
already been sent over the satellite link.
You're perfectly right here: the link is expensive and the round trip is
700ms at best, but reaches easily 3000ms or even 4000ms when the network
is congested.
Those long RTTs will get even longer if you add shaping of your own.
Most software is written with much shorter RTTs in mind, triggering
retransmits after one to three seconds without acknowledgement or reply.
One example I have seen in packet traces were three DNS replies to the
same request, spaced 1 second apart, but altogether delivered 30 seconds
after the first DNS request. This resulted in two retries of the DNS
request and a subsequent failure, while delivering three full DNS
request and reply pairs.
This kind of behavior can cripple goodput of the satellite link. You
might want to keep this in mind when designing traffic shaping.
Erik
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