The basic functionality of the WPN Peer cache is to facillitate the delivery of node data to WPN clients wishing to join the network.

Due to the network being formed of two tiers of client type (network load carrying "primary" clients and lower powered/slower connection type "secondary" clients) facilities have to exist to enable both levels of client to form such connections and we will look at how each client tier is serviced individually, below is a visual representation of the network in an idealised form.

In reality the ratio of primary to secondary clients will vary coniderably and the network will look appreciably different, the theoretical model however is excellent for both explanation and visual comprehension.

http://www.winmxworld.com/tutorials/connecting-to-wpn.html