TCP/IP) can be inefficient using satellite links due to latency created by long transmission path lengths and the noise associated with wireless links. Because geosynchronous satellites are in orbit at 22,300 miles high, there is a very long delay in the up/down link.(on the order of .25 - .50 of a second) Though TCP can be optimized for operation over satellite links to a certain degree, (buffering, proxy, spoofing, etc.) it does not consistently perform well under the full range of varying conditions that are expected to occur when the communications path comprises multiple satellite and terrestrial segments. These conditions include error rates caused by channel noise (not simply network congestion), link asymmetry (different bandwidths in opposing directions), long propagation delays, and interrupted connectivity. TCP was designed to operate in a low-noise environment and, therefore, tends to treat all packet loss as due to network congestion. The normal reaction of the TCP congestion control algorithms to either real congestion or to packet corruption, caused by a high bit error rate on the link, is to throttle back on the packet transmission rate (reduce sliding window).
Also, acknowledgements that are delayed in transmission can force a retransmission of data that has actually been received correctly. Because VPN is an end to end link, as opposed to just say an HTTP best effort connection, it will be slower.
