Introduction To Distributed Systems 4/26/2019 Distributed Systems

Introduction Computer revolution started from the year 1945 (modern era) During the year 1985 large and expensive computers were available As time progressed new developments took place and two new technologies were developed. They are 1. Powerful microprocessor (8 bit, 16 bit, 32 bit, 64 bit) 2. High speed networks (100 Gbits/sec LAN – , 10 Gbits/sec WAN) The result of above two technologies were; 1. flexibility 2. easy to access and put together all the computing systems connected together with high speed network. The above result leads to distributed systems…. Than previous centralized systems. 4/26/2019 Distributed Systems

Definition of a Distributed System (1) A distributed system is: A collection of independent(autonomous ) computers that appears to its users as a single coherent system. 4/26/2019 Distributed Systems

Definition of a Distributed System (2) 1.1 A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. 4/26/2019 Distributed Systems

Definition means.. 1. distributed systems consists of components (computers) that are autonomous (independent, self-directing) 2. users they are dealing with single system i.e all the autonomous computers need to collaborate with each others through passing messages. when autonomous computers are collaborated we get distributed systems. 4/26/2019 Distributed Systems

Characteristic of distributed systems 1 Characteristic of distributed systems 1. Resource sharing (h/w, s/w, data, files, should have resource manger) 2. Openness 3. Concurrency 4. Scalability 5. Fault Tolerance 6. Transparency 4/26/2019 Distributed Systems

1. Resources Sharing Access resources and share them in a controlled and efficient way. Printers, computers, storage facilities, data, files, Web pages, and networks, … Connecting users and resources also makes it easier to collaborate and exchange information. Internet for exchanging files, mail, documents, audio, and video Security is becoming increasingly important Little protection against eavesdropping or intrusion on communication Tracking communication to build up a preference profile of a specific user 4/26/2019 Distributed Systems

2. Openness Goal: Open distributed system -- able to interact with services from other open systems, irrespective of the underlying environment: System should conform to well-defined interface Systems should support portability of applications Systems should easily interoperate Achieving openness: At least make the distributed system independent from heterogeneity of the underlying environment: Hardware Platforms Languages 4/26/2019 Distributed Systems

3. Concurrency Concurrency refers when the two or more transaction are executed simultaneously. Ex. Multiprogramming/Parallel programming and Multiprocessing.. Parallel executions in distributed systems 1. Many users using the same resources, application interactions 2. Many servers responding to client requests 4/26/2019 Distributed Systems

4. Scalability Scalability: At least three components: How the system handles growth The current Internet is an example of scalable system Scalability: At least three components: Number of users and/or processes (size scalability) Maximum distance between nodes (geographical scalability) Number of administrative domains (administrative scalability)– (it can still be easy to manage even if it spans many independent administrative organizations.) 4/26/2019 Distributed Systems

5. Fault Tolerance Hardware, Software, network may fail at any point of time. Fault tolerance can be achieved by…. Hardware redundancy Software recovery scheme (i.e. Self Healing S/W) 4/26/2019 Distributed Systems

6. Transparency It is an important goal of the distributed system to hide the fact that its processes and resources are distributed across the multiple computers. A distributed system that is able to present itself to user and application as if it were only a single computer system is said to be transparent. 4/26/2019 Distributed Systems

Transparency in a Distributed System Description Access Hide differences in data representation and how a resource is accessed Location Hide where a resource is located Migration Hide that a resource may move to another location Relocation Hide that a resource may be moved to another location while in use Replication Hide that a resource may be shared by several competitive users Concurrency Failure Hide the failure and recovery of a resource Persistence Hide whether a (software) resource is in memory or on disk Different forms of transparency in a distributed system. 4/26/2019 Distributed Systems

Advantages of Distributed Systems Performance: very often a collection of processors can provide higher performance (and better price/performance ratio) than a centralized computer. Distribution: many applications involve, by their nature, spatially separated machines (banking, commercial, automotive system). 3. Reliability (fault tolerance): if some of the machines crash, the system can survive. Incremental growth: as requirements on processing power grow, new machines can be added incrementally. 5. Sharing of data/resources: shared data is essential to many applications (banking, computer supported cooperative work, reservation systems); other resources can be also shared (e.g. expensive printers). 6. Communication: facilitates human-to-human communication. 4/26/2019 Distributed Systems

Disadvantages of Distributed Systems Difficulties of developing distributed software: how should operating systems, programming languages and applications look like? Networking problems: several problems are created by the network infrastructure, which have to be dealt with: loss of messages, overloading, ... Security problems: sharing generates the problem of data security. 4/26/2019 Distributed Systems

References 1.www.csc.villanova.edu/~schragge/CSC8530/Intro.html – 2. www0.cs.ucl.ac.uk/staff/ucacwxe/lectures/ds98-99/dsee3.pdf 3. www.ida.liu.se/~TDDD25/lecture-notes/lect1.frm.pdf 4. Distributed Systems, Principles and Paradigms, 2nd edition, by Andrew S. Tanenbaum and Maarten Van Steen 4/26/2019 Distributed Systems