Cache miss #2
Client A sends a HTTP request, it gets to proxy B, which does not have the
relevant document cached, it then sends a ICP request to its siblings (proxy C),
and to its parent (proxy A). Proxies A & C does not have the document either,
and they do not send a ICP reply, after a set period of time, proxy B has a
timeout, and it requests its parent (Proxy A) to retrieve the document. Proxy A
send a HTTP request to the destination server, and gets a HTTP reply, he then
sends the document in a ICP reply to proxy B, which then sends the relevant
document to the client.
