Temporary hosts may be available only from time to time. Whilst they may store state information in the protocol for their own purposes over long time periods, it is unwise for another node to require anything of the persistence of that state information. Documents Documents are stored originally on permanent nodes. The document is identified by a URL which contains the name of the node. Some documents are virtual documents, in that their state is defined by a function and many vary depending on many things.
Some documents change very slowly.
Each document contains links to a number of other documents. The task is to define a protocol between permanent and temporary nodes to allow copies of documents to be moved around such that when at any node a document is requested, it will be available within a short time with high probability. The program making the request is known as the client. It can start simultaneous processing of requests in which case the number of concurrent requests advresly affects the time for the requet to be completed. There is no fixed cost function for document access delay and this may vary from request to request.