CSC 423 LEC 1,2: Distributed Systems Intro

• Distributed and Parallel Computer Systems course code is CSC 423.
• The lecture is LEC 1,2
• The topic is Distributed Systems Introduction.

Characterization of Distributed Systems

• A distributed system can be defined as a collection of autonomous computers interconnected by a network.
• These computers are equipped with distributed system software, forming an integrated computing facility.
• The software enables computers to coordinate activities and share hardware, software, and data resources.
• The text references Distributed Systems: Concepts and Design, Edition 5, Addison-Wesley 2012, by Coulouris, Dollimore, Kindberg, and Blair.

Classification of Computer Systems

• Multiprocessors have multiple CPUs sharing memory, with memory access delays in nanoseconds.
• Multicomputers consist of multiple computers, each with its own CPU and memory, connected by a high-speed interconnect.
• Distributed systems are loosely coupled and connected over a Local Area Network (LAN) or long-haul networks like the internet, with delays that can be unpredictable.

Distributed Systems: Main Features

• Distributed systems involve the geographical distribution of computers.
• Communication occurs through cable, fiber optics, wireless, or other connections.
• Distributed systems facilitate interaction, cooperation, and resource sharing.
• Benefits include reduced costs and improved availability and performance.

Distributed Systems: Characteristics

• Distributed systems involve concurrency of components.
• They lack a global clock.
• They have independent failures of components.
• Processes are executed concurrently and interact to cooperate toward a common goal.
• The coordination of activities and information exchange occurs through messages transferred over a communication network.
• Distributed computer systems are critical for the functioning of many organizations, including banks, transport, and telecommunications.

DS Examples

• Distributed Systems are based on familiar and used computer networks such as the Internet, and Intranets, Wireless networks
• Example DS is the World Wide Web
• Other examples of DS applications include data centers and clouds, wide area storage systems, banking systems, Facebook, and Skype

Intranet Characteristics

• Intranets are private networks used by organizations to help users communicate securely.
• Intranets allow users to store information and collaborate.
• They also allow users to share organizational updates and increase productivity.
• Intranets enable information flow within an organization via electronic data and documents.
• They provide services such as file and print servers.
• Intranets are often connected to the Internet via a router.

Internet Characteristics

• The Internet is a global network of interconnected computers communicating through IP protocols.
• It interconnects various networks using routers and gateways.
• Packets are copied as they are transmitted across different networks.
• The Internet is very large and heterogeneous.
• The Internet enables email, file transfer, multimedia communications, and access to the WWW.
• The Internet is open-ended, meaning it does not have a planned ending.
• It connects intranets via backbones and connects home users via modems and ISPs.

Portable and Handheld Devices

• Mobile and ubiquitous computing networking allows devices to connect at any time and place.
• Wireless LANs (WLANs) use WAP (Wireless Applications Protocol).
• Portable devices can connect, including laptops, PDAs, video/digital cameras, and printers.
• Wearable devices (smart watches, glasses) are also able to connect.
• Home intranets comprise devices embedded in home appliances.

Distributed Systems Application Domains

• Finance and Commerce: eCommerce, online banking and trading, ATM machines, airline reservation systems.
• Information Society: web information and search engines, ebooks, Wikipedia, social networking.
• Creative Industries and Entertainment: online gaming, film in the home, user-generated content like YouTube and Flickr.
• Healthcare: health informatics, online patient records, monitoring patients
• Education: e-learning, virtual learning environments, distance learning
• Transport and Logistics: GPS in route finding systems, like Google Maps and Google Earth
• Science: The Grid as an enabling technology for collaboration between scientists.
• Environmental management: Sensor technology to monitor earthquakes, floods, and tsunamis.

Quality of Service (QoS)

• Main nonfunctional properties of systems that affect Quality of Service.
• Reliability, security, and performance are important factors.

Distributed System Challenges

• Key challenges in constructing distributed systems include heterogeneity, openness, security, scalability, failure handling, concurrency, and transparency.

Heterogeneity in Distributed Systems

• Heterogeneity involves varying software and hardware in networks, computer hardware, operating systems, programming languages, and implementations.
• Standards like protocols and middleware are needed.
• Middleware is a software layer that masks heterogeneity of underlying networks, hardware, and operating systems.

Openness in Distributed Systems

• An open distributed system allows new resource-sharing services to be added and made available.
• It also allows components to be added or replaced.
• An open distributed system has a uniform communication mechanism and published interfaces to shared resources.
• Open distributed systems involve heterogeneous hardware and software, but each component's conformance to published standards must be verified.

Security in Distributed Systems

• Security considerations include confidentiality, protecting against unauthorized disclosure.
• Integrity, protecting against alteration and interference, especially for financial data, is another security consideration.
• Availability is also a consideration, referring to protection against denial of services attacks.
• Encryption and knowledge of identity are needed.

Scalability in Distributed Systems

• Scalability is the ability to work well when the system load or the number of users increases.
• Challenges include controlling the cost of physical resources and performance loss.
• Other challenges include avoiding performance bottlenecks.
• Caching and replication is a remedy to avoid bottlenecks

Failure Handling

• Failure handling is the ability to continue computation in the presence of failures.
• Techniques for dealing with failures include detecting, masking, and recovering from failures.
• Redundancy involves using redundant components, such as replicating a database in several servers.
• High availability is the main goal, measuring the proportion of time that the system is available for use.

Concurrency

• Concurrency refers to processes executing simultaneously and sharing resources.
• Objects with shared resources must operate correctly in a concurrent environment.
• Synchronization and inter-process communication is needed.

Transparency

• Transparency conceals the separation of components in a distributed system.
• The transparency allows the distributed system to be perceived as a whole rather than a collection of independent components
• Access transparency hides differences in data representation and resource access.
• Location transparency hides where a resource is located.
• Concurrency transparency hides that a resource may be shared.
• Replication transparency hides that a resource may be replicated.
• Failure transparency involves fault concealment and recovery.
• Scaling transparency enables systems to scale up without requiring system architecture changes.
• Mobility transparency enables the movement of resources/clients within a system.