HTTP design issues

• How to map URL's to Multicast addresses
  The name space for URL's, the number of HTTP servers, and the number of pages on any one server all vastly exceed the number of multicast addresses. Since the multicast address must be known before the server is contacted, some method of resolving URLs to multicast addresses must be determined. We have implemented a static hash function with the server address as the key. The function will return the multicast address. We also have a static hash function with the page on the server as the key, which returns the port to listen to. Both of these hash functions are shared by all servers and proxies. While this approach would not be practical for real deployment, it satisfies our needs.
• Out of Band messages
  Out of band messages are used to exchange information about requests and ACKs of URLs from proxies. The server is listening for requests from proxies on a well-known UDP port instead of TCP port. The same UDP port is used by the proxy to tell the server that they received all the packets associated with the requested URL. By doing so, the server adds or deletes proxies from the list and can tell the end of connection if every proxy received the requested URL or not. In figure 1, HTTP Req, HTTP ACK and URL ACK belong to out of band messages. The HTTP Req is the URL request from the proxy and the server confirms the request with HTTP ACK. At the end of connection, if the proxy receives packets successfully, it sends URL ACK to the server. Otherwise it is silent, causing the retransmission of the multicast.