Hi Hootan,
SpeedFusion WAN Smoothing and SpeedFusion Bonding can’t really be compared.
When you use WAN smoothing you use WAN bonding as well; WAN Smoothing is a feature that can be enabled for the SpeedFusion tunnel.
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SpeedFusion bonding, truly bonds several WANs on a packet level, which is explained here.
All WAN’s can be combined to form one virtual WAN; packets at the local site are sent through each of the WANs and reassembled in the original order at the remote site of the SpeedFusion tunnel.
WAN Smoothing is a different feature that can be enabled for SpeedFusion.
Instead of using 1 packet WAN Smoothing will send packets over 2 or more WAN connections and only the packets that arrive first will be used (other packets get discarded)
Thus, the latency of the SpeedFusion tunnel becomes the latency of the most responsive WAN connection.
This is extremely useful for deployments where improving consistency is more important than improving bandwidth.
WAN Smoothing is only needed if the environment is having problems on for example VOIP or video streaming (packet drop, jitter).
More information on WAN smoothing can be found here.