SSO Multi-Site Replication

I have a quick question.  I was surprised that I was not able to find this info.

What port does replication occur between the SSO sites?  I am looking at doing a Geographically disbursted upgrade to vSphere from 5.0 to 5.5.  We are going to have a singleSSO instances on each site and want to know what port needs to be opened inbetween site for SSO replicaiton to occur?

Thanks