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Chapter 15: Distributed Communication

This chapter explores the essential concepts of distributed communication in operating systems, focusing on sockets, remote procedure calls (RPC), remote method invocation (RMI), and the Common Object Request Broker Architecture (CORBA). It defines sockets as endpoints for communication and discusses their use in both connection-oriented and connection-less protocols. The chapter elaborates on RPC as a higher-level communication method and contrasts it with RMI, emphasizing the ability to use object-oriented programming. Furthermore, it covers stubs, skeletons, marshalling, and security aspects of remote communication.

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Chapter 15: Distributed Communication

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  1. Chapter 15: Distributed Communication • Sockets • Remote Procedure Calls (RPCs) • Remote Method Invocation (RMI) • CORBA • Object Registration Applied Operating System Concepts

  2. Sockets • Defined as an “endpoint for communcation” • Concatenation of IP Address + Port • All Ports < 1024 are Considered “well-known” - TELNET uses port 23 - FTP uses port 21 - HTTP server uses port 80 Applied Operating System Concepts

  3. Communication Using Sockets Applied Operating System Concepts

  4. Java Sockets • Java Provides: - Connection-Oriented (TCP) Sockets - Connection-less (UDP) Sockets - Multicast Connection-less Socket Applied Operating System Concepts

  5. Time-Of-Day Server/Client • Server uses s = new ServerSocket(5155) To Create the Socket on Port 5155 • To Accept Connections From Clients: Socket client = s.accept() • Connections are Often Serviced in Separate Threads • The Client Connects to the Server Using: Socket s = new Socket(“127.0.0.1”,5155); Using the IP Address of the Server. Applied Operating System Concepts

  6. Remote Procedure Calls (RPC) • Sockets are Considered Low-level. • RPCs Offer a Higher-level Form of Communication • Client Makes Procedure Call to “Remote” Server Using Ordinary Procedure Call Mechanisms. Applied Operating System Concepts

  7. Remote Method Invocation (RMI) • Java’s Version of RPCs • A Thread May Invoke a Method on a Remote Object • An Object is Considered “remote” if it Resides in a Separate Java Virtual Machine. Applied Operating System Concepts

  8. Remote Method Invocation (BMI) Applied Operating System Concepts

  9. RPC versus RMI • RPC’s Support Procedural Programming Style • RMI Supports Object-Oriented Programming Style • Parameters to RPCs are Ordinary Data Structures • Parameters to RMI are Objects Applied Operating System Concepts

  10. Stubs and Skeletons • “Stub” is a Proxy for the Remote Object – Resides on Client. • The Stub “Marshalls” the Parameters and Sends Them to the Server. • “Skeleton” is on Server Side. • Skeleton “Unmarshalls” the Parameters and Delivers Them to the Server. Applied Operating System Concepts

  11. Marshalling Parameters Applied Operating System Concepts

  12. Parameters • Local (Non-Remote) Objects are Passed by Copy using Object Serialization • Remote Objects are Passed by Reference Applied Operating System Concepts

  13. Remote Objects • Remote Objects are Declared by Specifying an interface that extends java.rmi.Remote • Every Method Must Throw java.rmi.RemoteException Applied Operating System Concepts

  14. MessageQueue interface public interface MessageQueue extends java.rmi.Remote { public void send(Object item) throws java.rmi.RemoteException; public Object receive() throws java.rmi.RemoteException; } Applied Operating System Concepts

  15. MessageQueue implementation public class MessageQueueIMPL extends java.rmi.server.UnicastRemoteObject implements MessageQueue { public void send(Object item) throws java.rmi.RemoteException { /* implementation */ } public Object receive() throws java.rmi.RemoteException { /* implementation */ } } Applied Operating System Concepts

  16. The Client • The Client Must (1) Install a Security Manager: System.setSecurityManager( new RMISecurityManager()); (2) Get a Reference to the Remote Object MessageQueue mb; mb = (MessageQueue)Naming. lookup(“rmi://127.0.0.1/MessageServer”) Applied Operating System Concepts

  17. Running the Producer-Consumer Using RMI • Compile All Source Files • Generate Stub and Skeleton rmic MessageQueueImpl • Start the Registry Service rmiregistry • Create the Remote Object java –Djava.security.policy=java.policy MessageQueueImpl • Start the Client java –Djava.security.policy=java.policy Factory Applied Operating System Concepts

  18. Policy File • New with Java 2 grant { permission java.net.SocketPermission "*:1024-65535","connect,accept"; }; Applied Operating System Concepts

  19. CORBA • RMI is Java-to-Java Technology • CORBA is Middleware that Allows Heterogeneous Client and Server Applications to Communicate • Interface Definition Language (IDL) is a Generic Way to Describe an Interface to a Service a Remote Object Provides • Object Request Broker (ORB) Allows Client and Server to Communicate through IDL. • Internet InterORB Protocol (IIOP) is a Protocol Specifying how the ORBs can Communicate. Applied Operating System Concepts

  20. Cobra Model Applied Operating System Concepts

  21. Registration Services • Registration Service Allows Remote Objects to “register” Their Services. • RMI, CORBA Require Registration Services Applied Operating System Concepts

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