Characterization of Distributed Systems Source: George Colouris, Jean Dollimore, Tim Kinderberg & Gordon Blair (2012). Distributed Systems: Concepts & Design (5th Ed.). Essex: Addison-Wesley

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

2.1 Introduction Networks? Everywhere E.g. : Internet, mobile phone networks, corporate networks, factory networks, campus networks, home networks, in-car networks, etc. What are the differences and similarities of these networks?

2.1 Introduction What are distributed systems? Systems that have hardware or software components located at networked computers Communication and coordination of actions are done by passing messages Networked computers may separated by any distance Separate continents, buildings, rooms OR may be in the same room

2.1 Introduction Features of distributed systems: Concurrency Concurrent program execution No global clock Coordination of actions Independent failures Failure in a machine would not known by other machines Concurrent program execution: parallel execution of multiple programs. Coordination of actions: exchange message between machines in order to access remote resources Failure in a machine would not known by other machines: Terminated programs due to issues in other components of a machine is not immediately made known to the communicated components.

2.1 Introduction Motivation for distributed systems: Resource sharing E.g. hardware components, software entity

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

2.2 Examples of distributed systems Finance and commerce eCommerce e.g. Amazon and eBay, PayPal, online banking and trading The information society Web information and search engines, ebooks, Wikipedia; social networking: Facebook and MySpace. Creative industries and entertainment online gaming, music and film in the home, user-generated content, e.g. YouTube, Flickr Healthcare health informatics, on online patient records, monitoring patients Education e-learning, virtual learning environments; distance learning Transport and logistics GPS in route finding systems, map services: Google Maps, Google Earth Science The Grid as an enabling technology for collaboration between scientists Environmental management sensor technology to monitor earthquakes, floods or tsunamis

2.2 Examples of distributed systems Web search engine An important tool for Internet users Index the www contents (web pages, multimedia sources, e-books, etc. How many pages of pages do the web contain? Over 63 billion 1 trillion unique web addresses

2.2 Examples of distributed systems Massively multiplayer online games (MMOGs) Large number of users interact through the Internet E.g. Sony Ever Quest II, EVE online Fast response time, real-time propagation of event

2.2 Examples of distributed systems Financial trading Real-time access to a wide range of information access (e.g. current share prices and trends, economic and political development) Example, Reuters & Financial Information eXchange (FIX) events

2.2 Examples of distributed systems An example of financial trading systems

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

2.3 Trends in distributed systems Top Technology Trends for 2014 http://www.computer.org/portal/web/membership/Top-10-Tech-Trends-in-2014

2.3 Trends in distributed systems The Fruits of Innovation: Top 10 IT Trends in 2014 http://www.datacenterknowledge.com/archives/2013/12/30/the-fruits-of-innovation-trends-2014/

2.3 Trends in distributed systems Significant changes in current distributed systems: The emergence of pervasive technology The emergence of ubiquitous & mobile computing The increasing demand of multimedia technology The view of distributed systems as a utility

2.3 Trends in distributed systems Pervasive technology Modern Internet – Collection of internetworked devices- wired & wireless Pervasive resources and devices can be connected at any time and in any place

2.3 Trends in distributed systems intranet ISP desktop computer: backbone satellite link server: ☎ network link: - This figure shows a typical portion of the Internet. Computers in the network interact by passing messages. - The Internet Protocol (IP) enables programs running anywhere to address messages to programs anywhere. The Internet is an example of a very large distributed system. The figure also shows collections of Intranets ( a sub-network that operated by organizations) A backbone is a network link with a high transmission capacity, utilizing satellite connections, fibre optics and other high-bandwidth circuits. A typical portion of the Internet

2.3 Trends in distributed systems Mobile & ubiquitous computing Small and portable devices are possible to be used within distributed systems E.g. laptop computers, handheld devices, wearable devices, devices embedded in appliances Mobile computing: portability of the devices and the ability to connect to networks in different places Ubiquitous computing: small computing devices that available everywhere and are easily attached to networks

2.3 Trends in distributed systems This figure shows how a user can access resources at office network via his/her home network Portable & handheld devices in a distributed system

2.3 Trends in distributed systems Distributed multimedia systems The use of multimedia contents in distributed systems Multimedia support Major benefits of multimedia support Distributed multimedia computing can be accessed through desktop or mobile devices. E.g. live tv broadcast, video-on-demand, IP telephony, webcasting, etc.

2.3 Trends in distributed systems Distributed computing as a utility distributed resources as commodity or utility in similar as water and power. Physical and logical service resources are rented rather than owned by the end users. Physical resources: e.g. : storage and processing Logical services: e.g. email, calendars Cloud computing: distributed computing utility. A cloud is a set of internet-based application, storage and computing services sufficient to support most users’ needs

2.3 Trends in distributed systems The aim of cloud computing is to reduce requirement of end-user devices, allowing them to has all the required resources through simple desktop or handheld devices. Cloud computing

2.3 Trends in distributed systems Cloud are implemented on cluster computers to provide the appropriate scale and performance required by such services A cluster computer: a set of interconnected computers that cooperate closely to provide a single integrated high-performance computing capability A blade server: a computer server that has been designed to minimize the use of physical space and energy

2.3 Trends in distributed systems Grid Computing Is a form of cloud computing Authorized users share processing power, memory and data storage Use to support scientific applications

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

2.4 Focus on resource sharing Sharing of high-level resources Disks and processors Sharing of search engines, tools –which servers host these applications? Computer-supported cooperative working (CSCW) A group of users who cooperate directly share resources such as documents in a small closed group.

2.4 Focus on resource sharing Service: a distinct part of a computer system that manages a collection of related resources and presents their functionality to users and applications. E.g. File service, printing service, payment service Service restricts resource access. A program is required to handle resource access for effective sharing .

2.4 Focus on resource sharing Client-server computing: Server: A running program (a process) that accepts requests from programs running on other computers Client: The requesting process Client invokes an operation – client send a request for an operation to be performed Remote invocation – complete interaction between a client and a server

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

2.5 Challenges As distributed systems are getting complex, developers face a number of challenges: Heterogeneity Openness Security Scalability Failure handling Concurrency Transparency Quality of service

2.5 Challenges Heterogeneity Users access services and run applications on a heterogeneous collection of computers and networks in the Internet Heterogeneity in the context of – networks; computer hardware, OS, programming languages, implementations by different developers Internet protocols are used by these different entities to communicate to each other

2.5 Challenges Heterogeneity A standard that allows different entities to communicate efficiently Middleware : a software layer that provides a programming abstraction and masking the heterogeneity of the underlying networks, hardware, OS and programming languages. E.g.– CORBA, RMI Mobile code : a program code that can be transferred from one computer to another and run at the destination. E.g. Java Applet, Javascript

2.5 Challenges Openness Openness- can the system be extended and re-implemented in different ways? Key to openness  availability of software specification and documentation Examples of specifications – Request for Comment (RFC)  provides technical specification and documentation about the systems Open distributed systems – distributed systems that support resource sharing and extensible

2.5 Challenges Security The security components of information resources Confidentiality – protection against disclosure to unauthorized individuals Integrity – protection against alteration or corruption Availability - protection against interference with the means to access the resources Examples of security challenges: Denial of service attacks Security of mobile code

2.5 Challenges Scalability How effective the system works when there is an increase number of users or increase number of resource access The challenges of designing scalable distributed systems: Controlling the cost of physical resources Controlling the performance loss Preventing software resources running out Avoiding performance bottleneck

Growth of the Internet (computers and web servers) 2.5 Challenges Date Computers Web servers Percentage 1993, July 1,776,000 130 0.008 1995, July 6,642,000 23,500 0.4 1997, July 19,540,000 1,203,096 6 1999, July 56,218,000 6,598,697 12 2001, July 125,888,197 31,299,592 25 42,298,371 2003, July 2005, July ~200,000,000 353,284,187 67,571,581 21 19 Growth of the Internet (computers and web servers)

2.5 Challenges http://news.netcraft.com/archives/2014/01/03/january-2014-web-server-survey.html Number of Websites: 630 million web sites in January 2013 861 million in January 2014 (+37%)

2.5 Challenges Failure handling Distributed system failures are partial- some parts fail while others not Dealing with failures in distributed systems: Detecting failures – known/unknown failures Masking failures – hide the failure from become severe. E.g. retransmit messages, backup of file data Tolerating failures – clients can be designed to tolerate failures – e.g. inform users of failure and ask them to try later Recovery from failures - recover and rollback data after a server has crashed Redundancy- the way to tolerate failures – replication of services and data in multiple servers

2.5 Challenges Concurrency Access to a single service simultaneously/concurrently by multiple clients services and applications must be designed to support concurrent access and work consistently

2.5 Challenges Transparency Concealment of services and applications, so that they can be seen as a whole system rather than a collection of independent objects or components 8 forms of transparency: Access transparency – access to local an remote resources using identical operations Location transparency – access to resources without knowing the physical location of the machine

2.5 Challenges 8 forms of transparency: Concurrency transparency – several processes operate concurrently without interfering each other Replication transparency – replication of resources in multiple servers. Users are not aware of the replication Failure transparency – concealment of faults, allows users to complete their tasks without knowing of the failures Mobility transparency – movement of resources and clients within a system without affecting users operations Performance transparency – systems can be reconfigured to improve performance by considering their loads Scaling transparency – systems and applications can be expanded without changing the structure or the application algorithms

2.5 Challenges Access and location transparency are the two most important – also known as network transparency Web resource names or URLs are location-transparent. The names refer to a computer name (web server) in a domain rather than to Internet addresses. However, they are not mobility transparent. Web pages can be moved to other server in the domain. Links are points to the original page.

2.5 Challenges Quality of service The main nonfunctional properties of distributed systems that affect the quality of service experienced by users or clients are: reliability, security, performance, adaptability. Reliability? Security? Performance ? Adaptability?

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

2.6 Case Study: The World Wide Web History & background www (web) & the Internet CERN (European Center for Nuclear Research), Switzerland Document exchange Technological components of web: HTML URL HTTP Advances in web – dynamic pages, web services

2.6 Case Study: The World Wide Web Internet Browsers Web servers www.google.com www.cdk5.net www.w3c.org standards faq.html http://www.google.comlsearch?q=obama http://www.cdk5.net/ File system of

Contents 2.1 Introduction 2.2 Examples of distributed systems 2.3 Trends in distributed systems 2.4 Focus on resource sharing 2.5 Challenges 2.6 Case Study: The World Wide Web 2.7 Summary

2.7 Summary Important points we have discussed: Resource sharing Challenges in developing distributed systems www

Group discussion Select TWO(2) popular web search engines Compare how many web pages and documents are indexed by the selected search engines. How long it takes to search for the following phrases and how many related web documents are found? Distributed systems Distributed systems projects distributed systems projects and assignments What is your conclusion?

Further information Top 15 Most Popular Search Engines in March 2014 http://www.ebizmba.com/articles/search-engines Google Platform & how it works http://en.wikipedia.org/wiki/Google_platform http://computer.howstuffworks.com/internet/basics/google1.htm http://www.datacenterknowledge.com/archives/2011/08/01/report-google-uses-about-900000-servers/

Thank you…