understanding networked applications: a first course midterm two review by david g. messerschmitt

Understanding Networked Applications:A First Course

Midterm two review

by

David G. Messerschmitt

Understanding Networked Applications A First Course2

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.


Major topics

• Architecture– decomposition and modularity– granularity and hierarchy– interfaces and data types

• Layering– network, operating system, middleware,

application


Major topics

• Interface vs decomposition

• Protocol and user interface

• Challenges for selling information– Intellectual property– Copy protection– Policy issues


Major topics

• Economics of networked computing– Lock-in– Network effects


Major topics

• Applications and organizations– rationale for networked applications– acquiring applications– application lifecycle


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


Software:

Allows a system to be understood at different granularity

Hierarchy

Organization:Allows a managerto focus on high-levelobjectives, delegatinglow-level detail


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


Example: automobile internal architecture

Steeringwheel

Accelerator Brake

Powersteering

EnginePowerbrakes

Front wheels Rear wheels


Module interaction through interfaces

Client Server

action, parameters

returns

Both subsystems areaffected by the interaction

Data customizing an actionand disclosing its results


Layering

Existing layers

Elaboration or specialization

Layering builds capability incrementally by adding to what exists


Communications Storage

Network equipment Storage peripherals

Network software File system

Distributed objectmanagement

Databasemanagement

Application

Middleware

Operatingsystem

Equipment

Simplified infrastructure layering


Applications

Integrative services

Generic services

Common representations

Processing Storage Connectivity

Application components


The basic idea

Diversity of applications

Diversity of processing, storage, andconnectivity technologies

Common services andrepresentationsand structures forinformation


Layer above is a client of thelayer below

Layer below as as a serverto 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


Web browser

File system

Operatingsystem

File

Network

Message

Collection of packetsFragmentation Assembly

Message

HTML

Screen

Application

Web server

Example


Standardization

• De facto standard

• De jure standard

• Industry standard


Industry structure

• Architecture and industrial organization

• Stovepipes vs layers and implications


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?


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


Intellectual property

• Trademark

• Trade secret

• Patent

• Copyright


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


Complementary measures

TechnologyLicensing and enforcement

Casual copierHobbyistCrackerSmall-scale pirateLarge-scale pirate


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?


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


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.)


Types of network effects

No network: independence

Direct: complementary Indirect : mutual

dependence on some complementary commodity


Copy protection

satellite (encrypted)

Digital Transmission Copy Protection (DTCP)

satellite receiver

High-bandwidthDigital CopyProtection (HDCP)

(DVI)

(IEEE1394)


Reasons to distribute

• Performance– interactivity– scalability

• Specialization– simplify administration

• Compartmentalization– data in the organization that administers it


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


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


Waterfall model: lifecycle of an application

• Conceptualization

• Analysis

• Architecture

• Development

• Integration and testing

• Deployment

• Operations, maintenance and upgrade

understanding networked applications: a first course midterm two review by david g. messerschmitt

Documents

major topics applications

application slide

messerschmitt slide

course midterm

network effects slide

modules reusability

infrastructure layering

hierarchy interfaces