chapter 2- Layered Architectures Based DSs using UDP TCP and Multicast

Overview of Layered Architectures

• Prof. Mourad Elhadef, Ph. D. teaches CSC408 focusing on distributed information systems.

• Chapter 02A covers key topics: UDP (User Datagram Protocol), TCP (Transmission Control Protocol), and Multicast.

• The applications discussed revolve around simple client-server systems and group communication.

Learning Objectives

• Students will learn to develop distributed systems utilizing:

  • UDP Datagram Communication: Implementing systems using UDP.

  • TCP Stream Communication: Implementing systems using TCP.

  • Multicast Group Communication: Exploring communication strategies for groups.

Key Themes

• Introduction: Understand the fundamentals of client-server communication.

• UDP Datagram Communication: Insights into how datagrams are transmitted.

• TCP Stream Communication: Characteristics and strategies for using TCP.

• Group Communication (Multicast): Techniques for utilizing multicast in distributed systems.

Characteristics of Interprocess Communication

Types of Communication

• Synchronous: Processes synchronize for every message.

• Asynchronous: Flexible, with no synchronization between sending and receiving processes.

Operations

• Send/Receive Operations:

  • Synchronous: blocking operations that wait for completion.

  • Asynchronous: non-blocking, allowing processes to continue execution.

Message Characteristics

• Destinations: Messages are sent to secure addresses defined by Internet address and ports.

• Reliability:

  • Integrity: Confirmation that messages are received intact.

  • Validity: Ensuring messages hold necessary content.

  • Ordering: Required for applications needing messages in sequence.

Sockets in Communication

• Sockets: Endpoints for communications, bound to local ports and an Internet address.

• Each protocol (UDP or TCP) correlates to a specific socket, with 216 possible ports available for binding.

Client-Server Communication: Mechanisms

Synchronous Communication

• Client processes wait for server replies; reliability hinges on acknowledgment of requests.

Failure Models

• Types of faults:

  • Omission Faults: Messages may be lost, requiring robust handling strategies like timeouts and idempotent operations.

Request-Reply Protocols

• Variants define how messages (Request, Reply) are sent and acknowledged.

UDP Datagram Communication

Characteristics

• UDP transmits datagrams without acknowledgments or retries, which speeds up communication but lacks delivery guarantees.

• Failure Modes: Messages can be dropped (omission failures) or arrive out of order.

Advantages of UDP

• Efficient performance as it minimizes overheads typically found in guaranteed delivery methods.

Java API for UDP Communication

Key Components

• InetAddress class: Represents Internet addresses for communication.

• DatagramPacket class: For creating packets of data for transmission.

Basic Operations

• Structure includes socket creation and operations to send/receive data, handling various exceptions.

TCP Stream Communication

Characteristics of TCP

• Utilizes streams with guaranteed delivery mechanisms. Handles message sizes, lost messages, flow control, and data integrity.

• Flow matching: TCP servers synchronize their read/write speeds with connected processes.

Java API for TCP Communication

• Socket class: Facilitates connection to servers.

• ServerSocket class: Used for accepting new client connections.

Sample TCP Client and Server Implementation

• Code examples illustrate how a client sends messages and how a server responds, handling potential exceptions during communication.

Multicast Group Communication

Concepts and Infrastructure

• Sends one message to multiple group members, promoting fault tolerance and efficiency through replicated services.

• IP multicast is primarily executed within UDP.

Java API for Multicast

• MulticastSocket Class: Provides functionalities for joining/leaving groups, sending/receiving messages, and setting network interfaces for multicast packets.

Example Multicast Implementation

• Code snippets demonstrate a multicast peer's behavior, including how to send and receive datagrams efficiently.