On 11Nov2013 20:21, Bob Goodwin <bobgoodwin@xxxxxxxxxxxx> wrote: [...] > Source: http://arstechnica.com/business/2012/01/how-viasats-exede-makes-satellite-broadband-not-suck/ > > He makes it sound that it's essential to stick with their software, > some parts of which are apparently contained in the modem. As I said > I am quite happy with the service, it normally works well and there > is nothing better available to me. [...] > If anyone understands what they are doing and can explain it to me I > am interested. If it is like the setup in our Gilat satellite modem here, there are two primary things going on. (Based on reading scattered stuff on the net when trying to debug an annoying problem some months ago.) The modem/satellite system does HTTP prefetching; when you fetch a web page the traffic is sniffed and requests for the page content (images etc) are prefetched. This step may happen upstream of the modem (eg in a proxy at the ISP) or it may happen in the modem - this is unclear; that "HTTP acceleration" is a modem-side setting suggests it may be happening in the modem. The other thing the Gilat modems do is "TCP acceleration". I gather a TCP connection is terminated localy at the modem, and the data stream sent with a more efficient protocol over the satellite section of the link and a TCP connection established on the upstream (far side of you->satellite->downstation) to carry the traffic from there to the target server. The TCP handshake takes place in real time - the modem does not falsely complete a connection only to have upstream fail, but past that the traffic is proxied. This may sound ineffectual, but in fact it has throughput benefits. The TCP connection from upstream to the target server can transfer data rapidly across the fast and low latency ground based network. The data beamed to/from the satellite is sent directly using the satellite specific data integrity protocols without the TCP packet tracking protocol, and the data from your host to the modem travels with low round trip latency to/from the modem I'm speaking here of the TCP packet ACK stuff, which is now you<->modem and upstream<->target-server. This results in greater throughput. Cheers, -- Cameron Simpson <cs@xxxxxxxxxx> I took that Reading Dynamics course, and it really works. I read _War and Peace_ in an hour last night. It's about Russia. - W. Allen, ca. 1962 -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Fedora Code of Conduct: http://fedoraproject.org/code-of-conduct Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
