1. Understanding Networked Applications: A First Course Midterm two review by David G. Messerschmitt

2. Understanding Networked Applications A First Course 2 Copyright notice ©Copyright David G. Messerschmitt, 2000. This material may be used, copied, and distributed freely for educational purposes as long as this copyright notice remains attached. It cannot be used for any commercial purpose without the written permission of the author.

3. Understanding Networked Applications A First Course 3 Major topics Architecture –decomposition and modularity –granularity and hierarchy –interfaces and data types Layering –network, operating system, middleware, application

4. Understanding Networked Applications A First Course 4 Major topics Architecture –decomposition and modularity –granularity and hierarchy –interfaces and data types Layering –network, operating system, middleware, application

5. Understanding Networked Applications A First Course 5 Major topics Interface vs decomposition Protocol and user interface Challenges for selling information –Intellectual property –Copy protection –Policy issues

6. Understanding Networked Applications A First Course 6 Major topics Economics of networked computing –Lock-in –Network effects

7. Understanding Networked Applications A First Course 7 Major topics Applications and organizations –rationale for networked applications –acquiring applications –application lifecycle

8. Understanding Networked Applications A First Course 8 Modularity A system is modular when it is divided into subsystems (called modules) with “good” properties –Modules embody distinct functional groupings –Hierarchy supports views at different granularity and scale –Separation of concerns among modules –Reusability

9. Understanding Networked Applications A First Course 9 Software: Allows a system to be understood at different granularity Hierarchy Organization: Allows a manager to focus on high-level objectives, delegating low-level detail

10. Understanding Networked Applications A First Course 10 Interfaces Focus of module interaction and interoperability Two purposes: –informs other modules how to interact –informs implementer as to what has been promised to other modules

11. Understanding Networked Applications A First Course 11 Example: automobile internal architecture Steering wheel AcceleratorBrake Power steering Engine Power brakes Front wheelsRear wheels

12. Understanding Networked Applications A First Course 12 Module interaction through interfaces Client Server action, parameters returns Both subsystems are affected by the interaction Data customizing an action and disclosing its results

13. Understanding Networked Applications A First Course 13 Layering Existing layers Elaboration or specialization   Layering builds capability incrementally by adding to what exists

14. Understanding Networked Applications A First Course 14 CommunicationsStorage Network equipmentStorage peripherals Network softwareFile system Distributed object management Database management Application Middleware Operating system Equipment Simplified infrastructure layering

15. Understanding Networked Applications A First Course 15 Applications Integrative services Generic services Common representations ProcessingStorageConnectivity Application components

16. Understanding Networked Applications A First Course 16 The basic idea Diversity of applications Diversity of processing, storage, and connectivity technologies Common services and representations and structures for information

17. Understanding Networked Applications A First Course 17 Layer above is a client of the layer below Layer below as as a server to the layer above ….by utilizing the services of the layer below and adding capability Each layer provides services to the layer above…. Interaction of layers

18. Understanding Networked Applications A First Course 18 Web browser File system Operating system File Network Message Collection of packets FragmentationAssembly Message HTML Screen Application Web server Example

19. Understanding Networked Applications A First Course 19 Standardization De facto standard De jure standard Industry standard

20. Understanding Networked Applications A First Course 20 Industry structure Architecture and industrial organization Stovepipes vs layers and implications

21. Understanding Networked Applications A First Course 21 Selling information Information is the commodity of networked applications (and information technology more generally) Information has very different properties from other economic goods What are the implications to how information is bought and sold?

22. Understanding Networked Applications A First Course 22 Some economic properties Extreme supply economies of scale –high creation cost, low replication cost –new models of payment (like free trials, advertising, and versioning) –unlike other goods, pricing cannot be based on marginal cost Non-rival: –unlike physical goods, you can give away or sell and still retain

23. Understanding Networked Applications A First Course 23 Intellectual property Trademark Trade secret Patent Copyright

24. Understanding Networked Applications A First Course 24 Limitations to copyright Fair use: –quote or review –make limited copies for purposes such as teaching a class or using different players for the same licensee Second-use: –right to convey rights to a third party Limited to expression of facts or ideas –does not prevent others from creating independent works based on the same facts or ideas Does extend to “derivative” works

25. Understanding Networked Applications A First Course 25 Complementary measures Technology Licensing and enforcement Casual copier Hobbyist Cracker Small-scale pirate Large-scale pirate

26. Understanding Networked Applications A First Course 26 Lock-in Often there are switching costs associated with moving from one supplier or application to another (beyond just the direct price charged for the new solution) What are some examples of these costs?

27. Understanding Networked Applications A First Course 27 Takeaway sound bite When the new supplier offers a direct substitute product and has identical costs… The asset value of a locked-in customer is equal to that customer’s switching cost Lesson for suppliers: encourage switching cost for your customers Lesson for customers: beware of switching costs

28. Understanding Networked Applications A First Course 28 Wish list As an information technology supplier, you want: 1.Lots of complementary products (to increase the value of your product) 2.Lots of competitors for each complementary product (grab more of the value for yourself) 3.No direct competition for your product, or… 4.High switching costs for your product (which may mean for complementary products, which runs counter to 2.)

29. Understanding Networked Applications A First Course 29 Types of network effects No network: independence Direct: complementary Indirect : mutual dependence on some complementary commodity

30. Understanding Networked Applications A First Course 30 Copy protection satellite (encrypted) Digital Transmission Copy Protection (DTCP) satellite receiver High-bandwidth Digital Copy Protection (HDCP) (DVI) (IEEE 1394)

31. Understanding Networked Applications A First Course 31 Reasons to distribute Performance –interactivity –scalability Specialization –simplify administration Compartmentalization –data in the organization that administers it

32. Understanding Networked Applications A First Course 32 Reasons to distribute (con’t) Locality –data near source, presentation near user Sharing –maintain in one place, access from many Security –access control, selective sharing Availability –redundancy

33. Understanding Networked Applications A First Course 33 Acquisition options To operate it yourself –License “as is” –Outsource its development and license –Develop it internally Outsource deployment and operations –ASP: subscribe to the application over the network

34. Understanding Networked Applications A First Course 34 Waterfall model: lifecycle of an application Conceptualization Analysis Architecture Development Integration and testing Deployment Operations, maintenance and upgrade