Chapter 13 1

Distributed Processing, Client/Server, and Clusters

Chapter 13

Chapter 13 2

Distributed Data Processing

• Allows processors and data to be dispersed

• Provides a system that is more responsive to a users needs

• Minimize communication costs by comparison with a centralized approach

Chapter 13 3

Distributed Data Processing

• Personal computers• many employees have one• support user-friendly applications such as

word processing , spreadsheet, and presentation graphics

• Mainframe• corporate database• sophisticated software for database

management

Chapter 13 4

TCP/IP Protocol Architecture

• Developed during work on the packet-switched network ARPANET

• Five independent layers• application• hot-to-host• internet• network access• physical

Chapter 13 5

TCP/IP Protocol Architecture

• Physical layer• physical interface between a data

transmission device and a network• deals with signals, data rate, etc.

Chapter 13 6

TCP/IP Protocol Architecture

• Network access layer• concerned with the exchange of data

between and end system and the network

• software used depends on type of network

• concerned with access to and routing data across a network

Chapter 13 7

TCP/IP Protocol Architecture

• Internet layer• used when two devices attached to

different networks• internet protocol (IP) is used to provide

the routing function• routers are used to relay data from one

network to another

Chapter 13 8

TCP/IP Protocol Architecture

• Transport layer• provides logic for assuring that data

exchanged between host is reliably delivered

• protocol at this layer is the transmission control protocol (TCP)

Chapter 13 9

TCP/IP Protocol Architecture

• Application layer• contains protocols for specific user

applications

Chapter 13 10

Operation of TCP and IP

• TCP may break a block into smaller pieces to make it more manageable• TCP appends information to each piece

• destination port• sequence number• checksum

• TCP hands the message down to IP with instructions to send it to a host

Chapter 13 11

Operation of TCP and IP

• IP hands the message down tot he network access layer with instructions to send it to the router

• IP appends a header of control information• now called an IP datagram• destination host address

• Network access layer appends header information to create a packet or frame

Chapter 13 12

Protocol Data Units in the TCP/IP Architecture

TCPHeader

NetworkHeader

IPHeader

User data ApplicationByte Stream

TCPSegment

IPDatagram

Network-LevelPacket

Chapter 13 13

TCP Header

Source Port Destination Port

Sequence Number

Acknowledgement Number

HeaderLength Unused Flags Window

Checksum Urgent Pointer

Options + Padding

Bit: 40 10 16 31

20 O

ctet

s

Chapter 13 14

User Datagram Protocol (UDP)

• Connectionless server

• Does not guarantee delivery

• It adds a port addressing capability to IP

Source Port Destination Port

Segment Length Checksum

Bit: 160 31

8 O

ctet

s

Chapter 13 15

TCP/IP Applications

• Simple Mail Transfer Protocol (SMTP)• provides basic electronic mail facility• provides mechanism for transferring

messages among separate hosts• includes mailing lists, return receipts,

and forwarding

Chapter 13 16

TCP/IP Applications

• File Transfer Protocol (FTP)• used to send files form one system to

another under user commands• allows user IDs and passwords to be

transmitted• allows the user to specify the file and

file actions desired

Chapter 13 17

TCP/IP Applications

• TELNET• provides remote log-on capability, which

enables a user at a terminal or personal computer to log on to a remote computer

• user functions as if directly connected to the computer

• remote terminals appear as local to the application

Chapter 13 18

OSI Protocol Architecture

• Open Systems Interconnection• Developed by the International

Organization for Standardization (ISO)

• Consists of seven layers• Protocols are developed to perform

the functions at each layer

Chapter 13 19

OSI Layers

Application

Presentation

Session

Transport

Network

Data Link

Physical

Chapter 13 20

Client/Server Computing

• Client machines are generally single-user PCs or workstations that provide a highly user-friendly interface to the end user

• Each server provides a set of shared user services to the clients

• The server enables many clients to share access to the same database and enables the use of a high-performance computer system to manage the database

Chapter 13 21

Client/Server Computing

• Involves splitting an application into tasks and putting each task on the platform where it can be handled most efficiently

• Processing for the presentation on the user’s machine

• Data management and storage on a server

• Involves a network

Chapter 13 22

Generic Client/Server Environment

Chapter 13 23

Client/Server Applications

• Platforms and the operating systems of client and server may differ

• These lower-level differences are irrelevant as long as a client and server share the same communications protocols and support the same applications

Chapter 13 24

Client/Server Applications

• Actual functions performed by the application can be split up between client and server

• Optimize platform and network resources• Optimize the ability of users to perform

various tasks• Optimize the ability to cooperate with

one another using shared resources

Chapter 13 25

Database Applications

• The server is a database server• Interaction between client and server

is in the form of transactions• the client makes a database request

and receives a database response

• Server is responsible for maintaining the database

Chapter 13 26

Client/Server Architecture for Database Applications

Client Workstation

Presentation Services

Application Logic

Database Logic

Communications Software

ClientOperating System

Hardware Platform

Server

Database Logic

Communications Software

Database Management System

Server Operating System

Hardware Platform

Request

Response

ProtocolInteraction

Chapter 13 27

Client Server

Presentation Logic

Application Logic

Database Logic

DBMS

Classes of Client/Server Applications

• Host-based processing• not true client/server computing• traditional mainframe environment

Chapter 13 28

Client Server

Presentation Logic

Application Logic

Database Logic

DBMS

Classes of Client/Server Applications

• Server-based processing• server does all the processing• user workstation provides a user-

friendly interface

Chapter 13 29

Client Server

Presentation Logic

Database Logic

DBMS

Application Logic

Database Logic

Classes of Client/Server Applications

• Client-based processing• all application processing may be done

at the client• data validation routines and other

database logic function are done at the server

Chapter 13 30

Client Server

Presentation Logic

Application Logic

Database Logic

DBMS

Application Logic

Classes of Client/Server Applications

• Cooperative processing• application processing is performed in

an optimized fashion• complex to set up and maintain

Chapter 13 31

File Cache Consistency

• File caches hold recently accessed file records

• Caches are consistent when they contain exact copies for remote data

• File-locking prevents simultaneous access to a file• writing causes the server cached to be

updated

Chapter 13 32

Middleware

• Set of tools that provide a uniform means and style of access to system resources across all platforms

• Enable programmers to build applications that look and feel the same

• Enable programmers to use the same method to access data

Chapter 13 33

Middleware

• Use of a standard programming interface and protocols

• There is both a client and server component to middleware

• Provides uniform access to different systems

Chapter 13 34

The Role of Middleware in Client/Server Architecture

Client Workstation

Presentation Services

Application Logic

Middleware

Communications Software

ClientOperating System

Hardware Platform

Server

Middleware

Communications Software

Application Services

Server Operating System

Hardware Platform

ProtocolInteraction

Middleware Interaction

Chapter 13 35

Logical View of Middleware

Platform: OS Hardware

Application Application

Platform: OS Hardware

Middleware(distributed system services)

APIs

Platform Interfaces

Chapter 13 36

Distributed Message Passing

• Message passed used to communicate among processes

• Send and receive messages as used in a single system OR

• Remote procedure calls

Chapter 13 37

Basic Message-Passing Primitives

Message-passingModule

SendingProcess

ReceivingProcess

Message-passingModule

ProcessID Message

Chapter 13 38

Message-oriented Middleware

Client Server

Application-specificmessages

Ap

pli

cati

on

Ap

pli

cati

on

Mes

sage

-ori

ente

dM

idd

lew

are

Mes

sage

-ori

ente

dM

idd

lew

are

Tra

nsp

ort

Tra

nsp

ort

Net

wor

k

Net

wor

k

Chapter 13 39

Remote Procedure Calls

• Allow programs on different machines to interact using simple procedure call/return semantics

• Widely accepted• Standardized

• client and server modules can be moved among computers and operating systems easily

Chapter 13 40

Remote Procedure Call Mechanism

ClientApplication

ClientApplication

Remote ServerApplication

Remote ServerApplication

Local Applicationor

Operating System

Local Applicationor

Operating System

Local StubLocal Stub

RPCMechanism

RPCMechanism

Local StubLocal Stub

RPCMechanism

RPCMechanism

Remote Procedure Call

LocalResponse

LocalResponse

LocalResponse

LocalProcedure

Call

LocalProcedure

Calls

Remote Procedure Call

Chapter 13 41

Client/Server Binding

• Binding specifies the relationship between remote procedure and calling program

• Nonpersistent binding• logical connection established during

remote procedure call

• Persistent binding• connection is sustained after the procedure

returns

Chapter 13 42

Remote Procedure Calls

Client Server

Application-specificProcedure Invocations

and Returns

Tra

nsp

ort

Tra

nsp

ort

Net

wor

k

Net

wor

kApplication

RPCStub

Program

Application

RPCStub

Program

Chapter 13 43

Object Request Broker

Client Server

Tra

nsp

ort

Tra

nsp

ort

Net

wor

k

Net

wor

kApplication

RPCStub

Program

ObjectServer

Object Requestsand Responses

Object Requestsand Responses

ObjectRequestBroker

Transport

Network

Chapter 13 44

Clusters

• Alternative to symmetric multiprocessing (SMP)

• Group of interconnected, whole computers working together as a unified computing resource• illusion is one machine• system can run on its own

Chapter 13 45

Clusters

• Separate server• each computer is a separate server• no shared disks• need management or scheduling

software• data must be constantly copied among

systems so each is current

Chapter 13 46

Clusters

Standby Server with No Shared Disk

High-Speed Message LinkI/O

P

I/OI/O I/OM M

P PP

Chapter 13 47

Clusters

• Shared nothing• reduces communication overhead• servers connected to common disks• disks partitioned into volumes• each volume owned by a computer• if computer fails another computer gets

ownership of the volume

Chapter 13 48

Clusters

Shared Disk

High-Speed Message Link

I/O

P

I/OI/O I/OM M

P PPI/O I/O

RAID

Chapter 13 49

Clusters

• Shared disk• multiple computers share the same

disks at the same time• each computer has access to all of the

volumes on all of the disks

Chapter 13 50

Windows NT Wolfpack

• Wolfpack is code name for clustering technology

• Shared-nothing cluster• Groups combine resources that are

easily managed• Resources are implemented as

dynamically linked libraries (DLLs)

Chapter 13 51

Windows NT Wolfpack

PhysicalResource

DLL

LogicalResource

DLL

AppResource

DLL

AppResource

DLL

Cluster API DLL

Cluster Management Tools

Cluster-awareApp

DatabaseManager

Global UpdateManager

EventProcessor

CommunicationManager

NodeManager

Non-awareapp

Resource MonitorsResourceManagementInterface

ClusterService

RPC

OtherNodes

Failover MgrResource Mgr

Chapter 13 52

Solaris MC

• Prototype distributed operating system built as a set of extensions to Solaris UNIX

• Provides cluster with a single-system image

Chapter 13 - 53 pages 53

Solaris MC Structure

Other NodesOther Nodes

Network

File System Process

C++ Object Framework

Existing Solaris 2.5 Kernel

Applications

Object InvocationsSolaris MC

System Call Interface