IP SEC networks via satellite TDMA services is not an easy story. The Encore approach overcomes the issue of performance degradation normally experienced with standard IPSec VPNs when operated in conjunction with accelerated modems, caused by the encryption of all the data including the TCP headers. Encore has developed a patent pending software mechanism , Selective Layer Encryption (SLE), which uses IPSec type (3DES or AES) encryption for the payload information but leaves the TCP header information unencrypted (but modified) so that the TCP acceleration performed by the modem can still take place. This allows the enhanced performance provided by the modems to be maintained and is transparent to the end user applications. This SLE mechanism requires an Encore appliance at either end of the VPN link which includes the satellite portion. However all Encore routers are standard IPSec compatible and so the terrestrial end unit can terminate the "SLE" portion and switch the data onwards to a standard IPSec VPN gateway. The terminating end Encore unit could be co-located at the customer HQ (close to the customer VPN gateway), at the satellite service provider hub location or some other intermediate point. Multiple remote VSAT connections can be terminated on a single Encore gateway, and this can then establish standard IPSec VPN connection(s) to the the company VPN gateway for onward switching the VPN traffic. level421 has tested this technique successfully with satellite modem products from iDirect and on our satellite capacity The entry level product including SLE support for VPN over satellite is the VSR-30.
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