When we update the Exchange Server 2003 schema, how much replication traffic will we see?

The amount of replication traffic will vary depending on the number of objects in your Global Catalog (GC) and the size of the corresponding Active Directory (AD) .dit file. When you add new attributes to the Exchange 2003 schema, AD replicates those schema changes to every GC server in the organization because the new attributes change the contents of the partial attribute set stored in the GCs. The partial attribute set is a partial copy of the complete attribute set for each domain in the forest. The mechanics of this replication vary depending on the forest functional level. In a pure Windows 2000 Server forest, changing the partial attribute set membership by adding or removing attributes causes each GC to reset the synchronization watermark counter, thus triggering a wave of replication as AD replicates the entire partial attribute set to all GCs. In a Windows Server 2003 forest, changing the partial attribute set is less disruptive because AD replicates only those partial attribute set elements that changed. Thus, if you update your GC servers and domain controllers (DCs) to Windows 2003 before you update the Exchange 2003 schema, you can deploy the schema update with minimal effect on your network.