In WAN optimization, transparent addressing is a method in which all intermediate node addresses are spoofed, so the client and server see each other's addresses and port configurations as if there were no intermediate nodes.
In a network that employs transparent addressing, all routers make their Quality of Service (QoS) determinations based on the addresses and port configurations of the client and server. This relative simplicity can produce confusion if a router examines packets in detail. Such problems can be resolved by moving the classification of the packet stream to a router on the client side of the nearest intermediate node or by configuring the nearest intermediate node to identify and mark the packets.
Transparent addressing contrasts with correct addressing, in which the client, server and intermediate nodes see the address and port configurations of the nearest appliance in the data stream. Some providers use transparent addressing, while others employ correct addressing. For example, Cisco networks use transparent addressing and most Riverbed Steelhead networks use correct addressing.
Read more about it:
SearchStorage.com compares the Cisco and Riverbed approaches to network transparency.
David Hughes offers a Network Management tip on "Seeing through transparency claims."
Read about WAN optimization in this book chapter.