Tutorial week 3

1. If you don't know already, familiarise yourselves with common network applications such as ping, telnet and ftp.
2. A proxy is used both to act as a cache so that some messages can be answered by the proxy and also to block unwanted messages. When a cache is used the client must know to talk to the cache and to tell it where the server is. How do protocols such as HTTP and FTP deal with caches?
3. How can a connection-oriented protocol such as TCP be built on top of a connectionless protocol such as IP?
4. How can a connectionless protocol such as HTTP be built on top of a connection-oriented protocol such as TCP?
5. What are the meanings of
   • access transparency
   • location transparency
   • migration transparency
   • replication transparency
   • concurrency transparency
   • scalability transparency
   • performance transparency
   • failure transparency
   Which of these are applicable to the Web as a general system. Which are applicable to browsers such as IE ro Firefox? Which are applicable to HTTP servers such as Apache?

6. The IETF controls many of the Internet protocols. The protocols are defined in RFC's (Request for Comments). There is a searchable list maintained at http://www.rfc-editor.org/.

   The documents often contain the phrase "The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [34]"

   Look at the original specification for HTTP 0.1 in 1991 at http://www.w3.org/Protocols/HTTP/AsImplemented.html

   HTTP 1.0 is defined in RFC1945, and is still one of the simpler protocols. Read through this protocol to see a good example of how a protocol is specified, once it becomes an important standard

   If you have a lot of time, compare this to the HTTP 1.1 specification in RFC2068