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Client/Server and OS

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Server program does

Waits for client-initiated requests

Executes many requests at the same time

Takes care of VIP clients first Initiates and runs background-task activity

Keeps running

Grows bigger and fatter

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What Does a Server Need From an

OS?

Base Services

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Base Services

Task Preemption

Task Priority

Semaphores

Interprocess Communications (IPC)

Local/Remote Interprocess Communications

Threads

Intertask Protection

Multiuser High-Performance File System Efficient Memory Management

Dynamically Linked Run-Time Extensions

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What Does a Server Need From an

OS?

Extended Services

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Extended Services

Ubiquitous Communications

Network Operating System Extensions

Binary Large Objects (BLOBs)

Global Directories and Network Yellow Pages

Authentication and Authorization Services

System Management

Network Time

Database and Transaction Services Internet Services

Object-Oriented Services

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Server Scalability

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Multiprocessing Superservers

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clusters

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Client Categories

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Non-GUI Clients

Non-GUI clients that do not need multitasking

Non-GUI clients that need multitasking

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GUI Clients

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Object-Oriented User Interface

(OOUI) Clients

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GUI Versus OOUI

Feature Grapical User Interface (GUI) Object-Oriented User Interface (OOUI)

Application Structure

A graphic application consists of an icon, a primary window with

a menu bar, and one or more secondary windows. The focus is

on the main task. Ancillary tasks are supported by secondary

windows and pop-ups. Users must follow the rigid task structure

(and may get trapped in a task). An application represents a

task.

A graphic application consists of a collection of

cooperating user objects. Everything that you see is an

object. Each object is represented by an icon and has at

least one view. Objects can be reused in many tasks. The

application's boundaries are fuzzy. The user defines

what's an application by assembling a collection of

objects. These objects may come from one or more

programs and are integrated with the desktop objects the

system provides (likes printers and shredders). The users

can innovate and create their own "Lego-like" object

collections.

Icons Icons represent a running application. Icons represent object that may be directly manipulated.

Starting an

ApplicationUsers start application before selecting an object to work with.

Users open the object on the desktop, which causes a

window view of the object to be displayed.

Windows

Users open a primary window and then specify the objects they

want to interact with. The same window can be used to displayother objects.

A window is a view of what's inside an object. There is a

one-to-one relationship between a window and anobject.

MenusMenus provide the primary method for navigating within an

application.

Each object has a context menu. You navigate within an

application or across applications by directly manipulating

objects. The desktop functions as one big menu; icons

represent the objects that you can manipulate.

Active Application

VisualIcons represent minimized windows of active applications.

Icons are augmented with the in-use emphasis to

represent an active object.

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GUI Versus OOUI

Feature Grapical User Interface (GUI)Object-Oriented User Interface

(OOUI)

Direct ManipulationAn application may provide direct manipulation

on an ad hoc basis.

Objects are created, communicated with,

moved, and manipulated through drag-and-drop

manipulation.

Creating New Objects

Objects are created in an application-specific

manner, usually through some form of copy

mechanism or using the menu choices: new or

open.

A templates folder contains a template for every

object type. To create a new instance of an

object, drag its template to where you want the

new object to reside.

ActionsChoose object; then choose action from menu

bar.

In addition to choosing actions from menus, a

user can drag objects to icons to perform

operations; for example, dragging a file to a

printer icon.

ContainersText-based list boxes provide the primary form

of containment.

In addition to list boxes, OOUIs provide

container objects, including folders and

notebooks. These in turn can contain other

objects. Actions performed on container objectsaffect all the objects inside them.

Focus Focus is on the main task. Focus is on active objects and tasks.

Who Is In Control?Control alternates between the user and the

application.

All the applications behave the same and the

user acts as the conductor. Think of the user as

the visual programmer of the desktop.

Product Examples Windows 3.X, Motif, and simple Web pages.

NextStep/Mac OS X, Mac OS, Windows 98, OS/2

Workplace Shell, and Web pages that take

advantage of Java 2 JavaBeans.

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Compound Documents: OOUIs on

Steroids

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Shippable Places

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What Does a Client Need From an OS?

Requirements From an

OS

Non-GUI Client Simple GUI

ClientOOUI ClientWithout

MultitaskingWith Multitasking

Request/reply mechanism

(preferably with local/remote

transparency)

Yes Yes Yes Yes

File transfer mechanism tomove picture, text, and

database snapshots

Yes Yes Yes Yes

Pre-emptive multitasking No Yes Desirable Yes

Task priorities No Yes Desirable Yes

Inter-process communications No Yes Desirable Yes

Threads for background

communications with server

and receiving callbacks from

servers

No YesYes (unless you like

the hourglass icon)Yes

OS robustness, including

intertask protection and

reentrant OS calls

No Yes Desirable Yes

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Client/Server Hybrids

Clients are becoming more intelligent These "New Age" clients must provide a server lite

function

It should still be able to download shippableplaces, run Java applets, and receive calls from a

server

A server lite implementation does not need tosupport concurrent access to shared resources,

load balancing, or multithreaded communications

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Client OS Trends

The desktop is becoming more fragmented

The universal client is really a Web browser

There will be a huge demand for super-fat PCs There will be a huge demand for ultra-thin PCs

Shippable places will become the new desktops

Embedded clients will be everywhere

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Client OS: Meet the Players

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Server OS Trends

Application vs Mixed Server File/Print Server

Unix 83.00% 17.00%

Windows NT 46.00% 54.00%

OS/2 Warp

Server31.80% 68.20%

NetWare 18.00% 82.00%

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NOS Middleware: The Transparent

Illusion

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What Does Transparency Really

Mean?

Location transparency

Namespace transparency

Logon transparency

Replication transparency

Local/remote access transparency

Distributed time transparency

Failure transparency

Administration transparency

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NOS: Extending the Local OS's Reach

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Global Directory Services

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Federated Directories

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types of synchronization schemes

Immediate replication causes any update to

the master to be immediately shadowed on all

replicas

Skulking causes a periodic propagation (for

example, once a day) to all the replicas of all

changes made on the master

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How Do You Interface to These

Directories?

Directory-specific APIs and class libraries

LDAP and X.500 APIs Java classes

Distributed object interfaces

Meta-directory services and scripts

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Distributed Time Services

It periodically synchronizes the clocks on every

machine in the network

It introduces an inaccuracy component to

compensate for unequal clock drifts that occur

between synchronizations

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Distributed Security Services

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Can We Obtain C2-Level Security on

the Intergalactic Net?

Authentication: Are you who you claim to be?

Authorization: Are you allowed to use this

resource?

Audit Trails: Where have you been?

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Can We Do Better Than C2 on the

Intergalatic Net?

Integrity: Is My In-Transit Data Safe?

- Encryption- Cryptographic checksums

Non-Repudiation: Can You Prove It in Court?-Evidence of message creation

- Evidence of message receipt

- An action timestamp

- The evidence long-term storage facility

- The adjudicator

.

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The Non-Repudiation Framework

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The Internet: In Certificates We Trust

How Do You Like your Keys?

- Shared Private Keys

- Public Keys

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The Shared Private Key Approach to

Encryption

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The Public/Private Key Approach to

Encryption

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Using Public/Private Keys to Send

Signed Documents and Contracts

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So What Exactly Is a Digital

Certificate?

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A Certificate Usage Scenario

Jeri must first obtain a certificate

Jeri applies for a store account

Merchant determines if the certificate is OK

Jeri's certificate is OK

Jeri can now shop, shop, shop

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What a Certificate Authority Does

Today

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Electronic Payments: The SET Protocol

Jeri places an order

Merchant asks bank for authorization

The bank asks the credit card issuer for

authorization The credit card company approves the

transaction

The bank says it's OK

The merchant sends Jeri a receipt and ships goods

Jeri receives her monthly credit card bill

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SET: The Next Electronic Shopping and

Payment Infrastructure

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Network operating system

A 'networking operating system ' is an

operating system that contains components

and programs that allow a computer on a

network to serve requests from othercomputers for data and provide access to

other resources such as printer and file

systems.

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Features

Add, remove and manage users who wish to useresources on the network.

Allow users to access to the data on the network. Thisdata commonly resides on the server.

Allow users to access data found on other networksuch as the internet.

Allow users to access hardware connected to thenetwork.

Protect data and services located on the network. Enables the user to pass documents on the attached

network.

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features may include

basic support for hardware ports security features such as authentication, authorization,

login restrictions, and access control

name services and directory services

file, print, data storage, backup and replication services remote access

system management

network administration and auditing tools with graphic

interfaces clustering capabilities

fault tolerance and high availability

Wh th M t P l St k Fit i th OSI

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Where the Most Popular Stacks Fit in the OSI

Reference Model

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Peer-to-Peer Communications

Sockets

NetWare: IPX/SPX and TLI

NetBIOS and NetBEUI

Named Pipes

Th "N " SNA APPC APPN d

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The "New" SNA: APPC, APPN, and

CPI-C

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Remote Procedure Call (RPC)

An essential problem is that RPCs are not

procedure calls at all; they are truly process

invocations. The invoked program runs across

the wire in a different resource domain

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Remote Procedure Call

(1)

(8)

LPC Bind req

Recv bind

marshalSend req

Recv

result

unmarsh

return

(5)

(6)

execute

return

recv req

unmarsh

LPC

marshal

send

result

recv req

register

or search

return

client server

Binding server

(8)

(0)

(1)

(7)

(6)

(5)

(4)

(3)

(2)

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Distributed Systems 52

Remote Procedure Call: steps

(0) Remote procedures registration;(1) Client procedure calls client stub in normal way;

(2) Client stub sends a binding request asking for information;

(3) Binding server searches for binding and reply to client stub;

(4) Client stub packs a message (marshalling) and send to server stub;

(5) Server stub unpacks parameters (unmarshalling), invokes LPC;(6) Server procedure executes and returns results to server stub;

(7) Server stub packs results (marshalling) and sends to client stub;

(8) Client stub unpacks results and returns to client procedure.

Call-by-value: parameter is a straight value (int, float, )

Call-by-reference: parameter is a pointer to anything (int,

record, array, pointer, )

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The stub is application-specific code, but it isnot directly generated by the application writer

and therefore appears as a separate layer from

the programmer's point of view.

The function of the stub is to provide

transparency to the programmer-written

application code.

Stubs

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1.On the client side:

The stub handles the interface between the

client's local procedure call and the run-time

system, marshaling and unmarshaling data,

invoking the RPC run-time protocol, and if

requested, carrying out some of the binding steps.

2. On the server side:

The stub provides a similar interface between therun-time system and the local manager

procedures that are executed by the server.

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Issues faces by RPC

How are the server functions located and started

How are parameters defined and passed between

the client and the server

How are failures handled

How is security handled by the RPC

How does the client find its server

How is data representation across systems

handled

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The Mechanics of an RPC Stub Compiler

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Getting a Seat for a Madonna Concert Using RPCs

Messaging And Queuing: The Mom

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Messaging And Queuing: The Mom

Middleware

Every DAD needs a MOM

DAD stands for Distributed Application

Development

MOM stands for Message-Oriented

Middleware

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MOM: Two-way Message Queuing

MOM: Save Your Messages Until You

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MOM: Save Your Messages Until You

Get to a Server

MOM: Many to Many Messaging via

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MOM: Many-to-Many Messaging via

Queues

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Mom Versus RPC

Feature MOM: Messaging and Queuing Remote Procedure Call (RPC)

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Feature MOM: Messaging and Queuing Remote Procedure Call (RPC)

Metaphor Post office-like. Telephone-like.

Client/Server time relationship

Asynchronous. Clients and

servers may operate atdifferent times and speeds.

Synchronous. Clients and

servers must run concurrently.

Servers must keep up withclients.

Client/Server sequencing No fixed sequence.

Servers must first come up

before clients can talk to them.

Style Queued. Call-Return.

Partner needs to be available No. Yes.

Load-balancing

Single queue can be used to

implement FIFO or priority

based policy. Requires a separate TP Monitor.

Transactional support

Yes (some products). Message

queue can participate in the

commit synchronization.

No. Requires a transactional

RPC.

Message filtering Yes. No.

Performance

Slow. An intermediate hop is

required. Fast.

Asynchronous processingYes. Queues and triggers arerequired.

Limited. Requires threads and

tricky code for managingthreads.

Dynamic Data Exchange (DDE)

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Dynamic Data Exchange (DDE)

Dynamic Data Exchange or DDE is a Windows feature that allowsWindows applications to communicate with each other. DDE is

based on the messaging system built into Windows. Two Windows

programs can carry on a DDE "conversation" by posting messages to

each other. These two programs are known as the "server" and the

"client". A DDE server is the program that has access to data that

may be useful to other Windows programs. A DDE client is the

program that obtains this data from the server.

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What is CORBA?

Common Object Request Broker Architecture

Communication infrastructure for distributed

objects

Allows a heterogeneous, distributed collection

of objects to collaborate transparently

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What is CORBA good for?

Developing distributed applications

Locating remote objects on a network

Sending messages to those objects

Common interface for transactions, security,

etc.

CORBA Services (more later)

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Copyright 1998 Purple Technology, Inc.

Why Distributed Applications?

Data is distributed

Administrative and ownership reasons

Heterogeneous systems

Shared by multiple applications

Scalability

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Why Distributed Applications?

Computation is distributed

Scalability: multiprocessing

Take computation to data

Heterogeneous architectures

Users are distributed

Multiple users interacting and communicating via

distributed applications

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Distributed Object Systems

All entities are modeled as objects

Systems support location transparency

Interfaces, not implementations, define

objects

Good distributed object systems are open,

federated systems

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What is the OMG?

Designers of CORBA

Consortium of 700+ companies

Not including Microsoft

Members: platform vendors

database vendors

software tool developers

corporate developers

software application vendors

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Its Just A Spec

Has never been fully implemented

Probably never will be

Industry moves quickly and spec has to keep

up

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Basic CORBA Architecture

Client Server

ORB ORB

requestresponse

Object Bus

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CORBA Objects

Examples

Service

Client

Component Business object

CORBA objects approach universal accessibility

Any Language

Any Host on network

Any Platform

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what CORBA does on the client side

The client IDL stubs

The Dynamic Invocation Interface (DII)

The Interface Repository APIs

The ORB Interface

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what CORBA elements do on the server

The Server IDL Stubs (OMG calls them

skeletons)

The Dynamic Skeleton Interface (DSI)

The Object Adapter

The Implementation Repository

The ORB Interface

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CORBA Elements

1. ORB

2. CORBA Services

3. CORBA Facilities

4. Application Objects

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ORB

Object Request Broker

Object Bus

Handles all communication among objects

Each host (machine) has its own ORB

ORBs know how to talk to each other

ORB also provides basic services to client

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ORB Responsibilities

Find the object implementation for the

request

Prepare the object implementation to receive

the request

Communicate the data making up the request

Retrieve results of request

k f

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Network of ORBs

Theres an ORB on the server too

ORB receives request

ORB Vers s RPC

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ORB Versus RPC

With an RPC, you call a specific function (thedata is separate).

In contrast, with an ORB, you're calling a methodwithin a specific object.

ORB method invocations have "scalpel-like"precision. The call gets to a specific object thatcontrols specific data, and then implements thefunction in its own class-specific way.

RPC calls have no specificityall the functions

with the same name get implemented the sameway. There's no differentiated service here.

O C

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ORB Versus RPC

IIOP

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IIOP

Internet Inter-Orb Protocol

Network or wire protocol

Works across TCP/IP (the Internet protocol)

ORB F

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ORB Features

Method invocations

Static and Dynamic

Remote objects or CORBA services

High-level language bindings

Use your favorite language; ORB translates

Self-describing

Provides metadata for all objects and services

ORB F

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ORB Features

Local or remote

Same API wherever target object lives

Preserves context

Distributed security and transactions

Coexistence with legacy code

Just provide a wrapper object

Wh t i ORB ll ?

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What is an ORB really?

Not a separate process

Library code that executes in-process

Listens to TCP ports for connections

One port per local object

Opens TCP sockets to other objects

N ports per remote machine

IDL

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IDL

Interface Definition Language

Defines protocol to access objects

Like a contract

Well-specified

Language-independent

IDL E l

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IDL Example

module Calc {

interface Adder {

long add(in long x, in long y);

}

} Defines an object called Adder with a method

called add

St b d Sk l t

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Copyright 1997 Alex Chaffee

Stubs and Skeletons

Stub

lives on client

pretends to be remote object

Skeleton

lives on server

receives requests from stub

talks to true remote object

delivers response to stub

St b d Sk l t (Fi )

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Copyright 1997 Alex Chaffee

Stubs and Skeletons (Fig.)

IIOPORB

Client Host Machine

Client Object

ORB

Server Host Machine

Stub

Remote Object

Skeleton

Cli t S

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Client vs. Server

in CORBA, a client is a client relative to aparticular object i.e. an object with a

reference to a server object

A client may also act as a server If it has an IDL and stubs and skeletons

Technically, a CORBA server contains one or

more CORBA objects

Diff t M i f S

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Different Meanings of Server

Host machine

Program running on host machine

CORBA object running inside program

has IDL, stub, skeleton

Sometimes called a Servant

Stubs and Skeletons -> Platform

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Independence

Client code has no knowledge of theimplementation of the object or which ORB is

used to access the implementation.

CORBA Services

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CORBA Services

APIs for low-level, common tasks

Life Cycle Service

creating, copying, moving, removing objects

Naming Service

Register objects with a name

Look up objects by name

CORBA Services

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CORBA Services

Concurrency Control Service

Obtain and release exclusive locks

Transaction Service

Two-phase commit coordination

Supports nested transactions

Persistence Service

Storing objects in a variety of databases

RDBMS, OODBMS, file systems

CORBA Services

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CORBA Services

Security Service

Authentication, ACLs, encryption, etc.

Event Service

Uncoupled notifications

CORBA Services

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CORBA Services

Relationship Externalization

Query

Licensing

Properties

Time

Trader

Collection

and so on

See what I mean about it never beingimplemented?

CORBA Facilities

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CORBA Facilities

Frameworks for specialized applications

Distributed Document Component Facility

OpenDoc

In progress:

Agents

Business Objects

Internationalization

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