Question : average overhead on a PIX site to site IPSec tunnel

I'm about to deploy a remote server that will be used to offsite replication.  The connection between each site can send/receive right at 3mbps.  Each site will be connected via an IPSec tunnel established with a ASA 5510 on one end and a PIX 506e on the other.  In general is there any way to know how much overhead will exist on a connection like this?  The side where the ASA 5510 is has dual T1's and the side that has the 506e is a DSL.  I have a bandwidth calculator and I'm curious to what the overhead should be...  If even possible to estimate.

Answer : average overhead on a PIX site to site IPSec tunnel

IPSEC can add up to 52 bytes per packet of overhead, but in my opinion, it's a waste of brain cells to try to calculate your exact bandwidth requirements based on this. Whatever bandwidth you can get, the VPN overhead will be least of your worries. I would figure 6-8% overhead for encryption.