PS4000 Replication physical network question

I know this is going to be a simple answer but I'm having trouble finding it spelled out.  What network does the actual replication on a pair of PS4000's occur on....the iscsi network or the management port network?    We followed the recommendations for setting up a single PS4000 and have 2 Powerconnect 6224 switches and have the iscsi traffic isolated on them...but now we want to set up the 2nd PS4000 for replication at an external site.  The iscsi traffic is isolated so I figured the management port would handle the replication data...but then in another document I saw a reference to replicating the PS4000's on the iscsi network....so I'm confused.   Plus the management network is only 100Mbps so again, I'm confused since the initial replication is going to take a long time over a 100Mbps connection.   So what is the proper physical set up for replication b/w 2 PS4000 SANs?