Telematics: Distributed Systems Concepts

• The text appears to be study notes for a telematics course, covering topics such as distributed systems, system models, networking, remote method invocation, component-oriented middleware, web services, peer-to-peer systems, name services, cloud computing, and indirect communication.

Basic Concepts of Distributed Systems

• A distributed system comprises interconnected computers working together as a single system, dividing tasks across nodes that communicate over networks.
• In centralized systems, all resources are in one place, decisions are made from a single point, and access is uniform; they are simpler to manage but less scalable and fault-tolerant.
• Distributed systems have resources spread across nodes, distributed decision-making, and more complex management, but offer better scalability and fault tolerance.
• Non-functional requirements for distributed system include scalability, heterogeneity, resource sharing and fault tolerance.
• Transparency in distributed systems means the system hides complexity of the network and implementation, offering access, location, migration, and replication transparency.
• Scalability is the ability of a system to function properly under increased user or resource load, while openness is the capacity for extending and reimplementing applications.
• Heterogeneity refers to the variety of programming languages, operating systems, hardware platforms, and network protocols in a system.
• Resource sharing enables different components and users of the distributed system to access hardware, software, data, and services.
• Fault tolerance is the system's ability to continue operating despite failures of one or more components.
• Concurrency is the system's ability to handle multiple processes or tasks simultaneously
• Middleware is a software layer between operating systems and applications the simplifies communication and data exchange, resolving heterogeneity and distributing transparency.

System Models

• Physical models describe hardware composition and network interconnection.
• A baseline physical model views distributed systems as extensible sets of interconnected computers for message passing.
• Architectural models focus on system structure in terms of specified components and their interactions, with a three-stage approach of core elements, composite patterns, and middleware platforms.
• From a system perspective, communicating entities in a distributed system are processes, or sometimes nodes in sensor networks, often complemented by threads.
• Programmatically, object-oriented approaches use interacting objects as natural decomposition units with interfaces defined by an interface definition language (IDL).
• Threads allow for asynchronous and parallel code execution within a process, sharing global data but with independent control flows.
• Components offer a more complete system construction contact through explicit interfaces and dependencies, fostering third-party development and promoting pure composition.
• Web services are based on objects and components, encapsulating behavior and access via interfaces, and integrating with the World Wide Web.

Communicating Paradigms

• Interprocess communication: Allows processes in a distributed system to communicate and share info, using mechanisms such as message-passing primitives (for message queues) and socket programming (communication over a network using protocols).
• Remote invocation: Involves two-way exchange between communicating entities (emitter and receiver), utilizing request-reply protocols and remote procedure calls (RPCs).
• Indirect communication: Communication between processes/components happens through an intermediary, using group communication and publish-subscribe systems.

Roles and Responsibilities

• Processes assume specific roles, which are fundamental for establishing the general architecture.
• Client-server: Utilizes more and widely used architecture.
• Peer-to-peer: All processes related to task/activity make same roll.

Architectural Patterns

• Architectural patterns provide recurrent composed structures that have demonstrated strong performance in specific circumstances, guiding the designer toward a solution for a certain problem.
• Layering helps organize complex systems by dividing them into different layers.

Tiered Architecture

• It is used to organize the functionality of a layer and place this functionality in appropriate servers.

Middleware Solutions

• Middleware aims to provide high-level programming abstractions for distributed systems.

Networking and Interprocess Communication

• Networking connects devices for communication; internetworking connects networks for larger communication.
• Key networking issues include performance, scalability, reliability, and security.
• Network principles are build the communication, including communication protocols and protocol layers.
• Encapsulation is the process of wrapping data with a header before passing it to the layer below.
• Protocol suites are are a group of protocols that work together to provide a network service
• OSI: Open Systems Interconnection model is a reference model for open communication

Internet Protocols (TCP/IP)

• TCP/IP Suite: Surged from ARPANET, with TCP and IP protocols.
• TCP and UDP protocols : extends the service of the network layer providing a logical communication between processes in different hosts.

Internet Transport Protocols

• TCP: a connection-oriented, reliable protocol that provides in-order delivery of data with error checking and guarantees delivery but can have higher overhead.
• UDP: a connectionless, unreliable protocol that is faster and more efficient but does not guarantee delivery or order.
• Port: Of Protocol. Used by processes to communicate.
• Assigning Ports: Ports ranges go from 0 - 65535

Interprocess Communication

• The API for the Internet Protocols offers processes on different machines the capability to send and receive messages.

Sockets

• Sockets are programming interfaces that enable interprocess communication with features such as being a endpoint of a bi-directional communication and point of access to the transport service.

External Data Representation

• It's created to deal with data representation problems such as different order an data structure alignments.
• The solution is to convert the values to an acorded external data representation.

Marshalling

• It's the process to convert the data representation from the app to a transmittable over-the-network data formt.

Remote Method Invocation

• Remote object references allows the invocation of methods of an object on another remote server,

Component Oriented Middleware

• Component Oriented Middleware is composed applications with interfaces specified with contracts that are independent and reuseble.

Web Services

• Web services enables composition for fast application building, using autonomic entities, offered over the internet.
• XML is a option for representation and marshalling of messages interchanged.
• SOAP establece the rules to use for messages and combines a pair of messages to produce a pattern of recuest/reply.
• REST (REpresentational State Transfer): Is an architectural style for web applications

P2P (Peer-to-Peer)

• P2P Systems consist of scalability, which systems grow depending of resources assigned by his users.
• Challenges in these systems include search and distribution of content
• Overlary Network allows virtual network formed by nodes and virtual links.

Chord System

• A distributed system that allows each resource to a assigned node.

Name services

• Naming Service: is an indepent service used for client process to obrain atributes.
• Zone: part of the domain namespace

CDN (Content Delivery Network)

• Provide a response time with less data from origin server.

Indirect Communication

• Communication between entities of system trough a intermediary process
• Provides benefits as desconection and fault tolerance

Group Communication

• Send to a group and delivered to all group members.

Publish-Subscribe

• System with edits and publishes events using suscripitions.

Message Queue

• Service point to point using a indiection mesaage collection.

Shared Memory

• Distributed Shared Memory (DSM): Share date between ordinetors.

Distributed File Systems

• File systems are responsible to organize, storage and share files.