How is CDC used by Replicate

Hi

I am looking for information on how CDC is used for Change capture by Replicate when it is reading from a MS Sql Server Source endpoint wih CDC enabled. The Replicate task reads from the Tlogs on the source and I can't see any information on how CDC is actually utilised as a part of that read? I am trying to gain an underatanding on this to better manage our install and investigate issues such as CDC latency on the soure and its imapct on the replication task.

thanks
David