Communication

Asynchronous RPC (1) a)The interconnection between client and server in a traditional RPC b)The interaction using asynchronous RPC 2-12

Asynchronous RPC (2) A client and server interacting through two asynchronous RPCs 2-13

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: system

Message Oriented Transient Communication -Berkeley Sockets Socket primitives for TCP/IP. PrimitiveMeaning SocketCreate a new communication endpoint BindAttach a local address to a socket ListenAnnounce willingness to accept connections AcceptBlock caller until a connection request arrives ConnectActively attempt to establish a connection SendSend some data over the connection ReceiveReceive some data over the connection CloseRelease the connection Interface for transport layer A communications end point

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) Four combinations for loosely-coupled communications using queues. 2-26

Message-Queuing Model (2) Basic interface to a queue in a message-queuing system. PrimitiveMeaning PutAppend a message to a specified queue GetBlock until the specified queue is nonempty, and remove the first message PollCheck 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.

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) The general organization of a message-queuing system with routers. 2-29

Message Brokers Message brokers convert messages to a format required by destination application 2-30