sem 7

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sem 7
2013-05-02 12:31:52

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  1. Describe how connectionless communication between a client and a serverproceeds when using sockets.
    Both the client and the server create a socket, but only the server binds thesocket to a local endpoint. The server can then subsequently do a blockingread call in which it waits for incoming data from any client. Likewise, aftercreating the socket, the client simply does a blocking call to write data tothe server. There is no need to close a connection.
  2. Suppose that you could make use of only transient asynchronous communi-cation primitives, including only an asynchronous receive primitive. Howwould you implement primitives for transient synchronous communication?
    Consider a synchronous send primitive. A simple implementation is to send amessage to the server using asynchronous communication, and subsequentlylet the caller continuously poll for an incoming acknowledgment or responsefrom the server. If we assume that the local operating system stores incom-ing messages into a local bu er, then an alternative implementation is toblock the caller until it receives a signal from the operating system that amessage has arrived, after which the caller does an asynchronous receive.
  3. Does it make sense to implement persistent asynchronous communicationby means of RPCs?
    Yes, but only on a hop-to-hop basis in which a process managing a queuepasses a message to a next queue manager by means of an RPC. E ectively,the service o ered by a queue manager to another is the storage of a message.The calling queue manager is o ered a proxy implementation of the interfaceto the remote queue, possibly receiving a status indicating the success orfail- ure of each operation. In this way, even queue managers see only queuesand no further communication.