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Communication Asynchronous RPC (1) 2-12 a) b) The interconnection between client and server in a traditional RPC The interaction using asynchronous RPC Asynchronous RPC (2) 2-13 A client and server interacting through two asynchronous RPCs Message-Oriented Communication • RPCs and RMIs are not always appropriate – Both assume that receiver is executing when a request is issued – Inherently synchronous • Buffer-based network model – Hosts are connected to communication servers – Message buffers at end hosts and communication servers – Example: Email system Message Oriented Transient Communication -Berkeley Sockets • Interface for transport layer • A communications end point Primitive Meaning Socket Create a new communication endpoint Bind Attach a local address to a socket Listen Announce willingness to accept connections Accept Block caller until a connection request arrives Connect Actively attempt to establish a connection Send Send some data over the connection Receive Receive some data over the connection Close Release the connection Socket primitives for TCP/IP. Berkeley Sockets Connection-oriented communication pattern using sockets. Message-Passing Interface • Multi-computers need low-overhead communication primitives • Sockets are not suitable • Send/Receive primitives are too simple • Not optimized for proprietary protocols • Provides transient asynchronous communication • Local and remote buffers • Identification by (groupID, processID) MPI Primitives Message Oriented Persistent Comm. • Message Queuing Systems or Message-Oriented Middleware (MoM) • Incorporates support for persistent asynchronous communication • Offers intermediate-term storage capacity – Neither sender or receiver need to be active for the entire communication duration Message Queuing Model • Applications communicate through messages stored in queues • Each application has its own (local) queue • Guarantees that the message will be inserted in recipient’s queue – No guarantee about time or whether receiver reads the message • Supports loosely coupled communication Message-Queuing Model (1) 2-26 Four combinations for loosely-coupled communications using queues. Message-Queuing Model (2) Primitive Meaning Put Append a message to a specified queue Get Block until the specified queue is nonempty, and remove the first message Poll Check a specified queue for messages, and remove the first. Never block. Notify Install a handler to be called when a message is put into the specified queue. Basic interface to a queue in a message-queuing system. General Architecture of a Message-Queuing System (1) • • • • Source Queue/Destination Queue Each queue has a unique name Queuing system maps queue names to network address Queue managers and relays General Architecture of a Message-Queuing System (2) 2-29 The general organization of a message-queuing system with routers. Message Brokers • Message brokers convert messages to a format required by destination application 2-30