Others have already answered with the technical details. Let me take a stab at some more, uh, variable items. In a message written on Tue, Apr 19, 2016 at 09:29:12PM -0400, Jean-Francois Mezei wrote:
Also, when you establish a TCP connection, do most stacks have a default window size that gives the sender enough "patience" to wait long enough for the ACK ?
Your question is phrased backwards. All will wait for the ACK, the timeouts are long (30-120 seconds). The issue is that you only get one window of data per RTT, so if the window is too small, it will choke the connection. 90%+ of the stacks deployed will be too small. Modern Unix generally has "autotuning" TCP stacks, but I don't think Windows or OS X has those features yet (but I'd be very happy to be wrong on that point). Regardless of satellite uplink/downlink speeds, boxes generally need to be tuned to get maximum performance on satellite.
What i am trying to get at here is whether 25/1 on satellite, in real life with a few apps exchanging data, would actually be able to make use of the 25 download speed or whether the limited 1mbps upload would choke the downloads ?
With a properly tuned stack what you're describing is not a problem. 1460 byte payloads down, maybe 64 byte acks on the return, and with SACK which is widely deployed an ACK every 2-4 packets. You would see about 2,140 packets/sec downstream (25Mbps/1460), and perhaps send 1070 ACKs back upstream, at 64 bytes each, or about 68Kbps. Well under the 1Mbps upstream bandwidth. -- Leo Bicknell - bicknell@ufp.org PGP keys at http://www.ufp.org/~bicknell/