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- 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.
Matthew James Sanders
Wed Dec 2 16:23:52 EST 1998