Our site-to-site WAN optimization is based on the ability of our solutions to balance traffic between tunnels. We also perform data compression on the traffic; however compression only works on traffic that is not already pre-compressed.
The balancing is based on sessions, not packets. Packet balancing has major issues with certain applications and thus we have chosen to use session based balancing.
To improve download speeds, the use of session spliting applications like SpeedBit are able to properly balance FTP and other downloads between multiple links and/or tunnels.