Download pdf - 02 Distsyst Basic Concepts

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(resource sharing)

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Lost,

iTunes,

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thin client,

SETI@home

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(typesetters), drum scanners, , ..(typesetters), drum scanners, , ..

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server)

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Lost

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Internet

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Laptop

Mobile

PrinterCamera

Host intranet Home intranetWAP Wireless LAN

phone

gateway

Host site

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RFID reader

RFID tag

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(context)

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(omission failure),

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client/server

To :

service: server

server: /

client: / client: /

28

Directory server Print server File server

client client

client/server

(client)

(server)

Client/Server

(proxy servers)

(caching)

(mobile code)

(mobile agents)

(network computers)

() (thin clients)

(fat clients)

30

-

.

,

,

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:

,

.

32

(proxy servers)

(caching)

33

(proxy servers)

(caching)

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(..

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(.. cache ).

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34

(proxy servers)

(caching)

.

, ,

.

,

,

,

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,

,

(..

HTML WAP). 35

(mobile code)

.

Java applets

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,

.

36

(mobile code)

applet

37

O applet

(mobile code)

,

.

(push model)

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,

.

38

(mobile agents)

( )

,

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.

,

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39

(mobile agents)

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)

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40

(network computers)

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(.. )

RAM.

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Java,

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Sun Oracle

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(thin clients)

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42

(thin clients)

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43

,

PDAs

GSM, 3G,

WiFi Bluetooth.

-

.

,

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45

()

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(service discovery)

.

46

3-

client/server 2-

(2-tier architecture).

2-

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DNS Internet DNS Internet

Domain Names .

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(web crawlers)

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3-

client-server 3-

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Web ,

Web Server

DB Server.49

3-

50

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: URL, : URL,

: HTML,

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OpenOffice

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3-

legacy

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55

3-

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multi-tiered

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58

thin client .

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GUI

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Window System Unix , Virtual Network Computer

& Labs, Remote Desktop Protocol Microsoft, ..

screen-

scraping (emulation-based)

(legacy systems) text-

based windows-based .

(dumb

terminals).59

.

thin client .

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.

on-line

transaction , (ftp, telnet,

..) Web Web

browsers.

60

(application logic) .

(.. ).

.

Web

( ) ,

, Java applet.

61

fat-client

PC.

.

(DB2, Oracle, Informix, ..)

client/server

. .

(Network File Systems)

.

(Decision Support System)

,

.

62

.

fat-client

(cache) (cache)

.

(.. NFS)

.

63

(Peer-to-Peer)

(, )

: Napster,

Gnutella, FastTrack, Kontiki,

Osiris, Skype)

64

,

( ).

(.. )

, ,

.

,

, ,

.

,

.

,

, ,

.

65

CLIENT/SERVER

66

header.h

header.h

/* definitions needed by clients and servers.*/

#define MAX_PATH 255 /* maximum length of a file name */

#define BUF_SIZE 1024 /* how much data to transfer at once */

#define FILE_SERVER 243 /* file servers network address */

/* definitions of the allowed operations. */

#define CREATE 1 /* create a new file */

#define READ 2 /* read a piece of a file and return it */

#define WRITE 3 /* write a piece of a file */

#define DELETE 4 /* delete an existing file */

header.h

/* Error codes. */

#define OK 0 /* operation performed correctly */

#define E_BAD_OPCODE 1 /* unknown operation requested */

#define E_BAD_PARAM 2 /* error in a parameter */

#define E_IO 3 /* disk error or other I/O error */

header.h

/* Definition of the message format. */

struct message {

long source; /* senders identity */

long dest; /* receivers identity */

long opcode; /* which operation: CREATE, READ, etc. */

long count; /* how many bytes to transfer */

long offset; /* where in file to start reading or writing */

long extra1; /* extra field */long extra1; /* extra field */

long extra2; /* extra field */

long result; /* result of the operation reported here */

char name[MAX_PATH]; /* name of the file being operated on */

char data[BUF_SIZE]; /* data to be read or written */

};

server

#include

void main(void)

{

struct message m1, m2; /* incoming and outgoing messages */

int r; /* result code */

while (1) { /* server runs forever */

receive(ANY, &m1); /* block waiting for a message */

switch(m1.opcode) { /* dispatch on type of request */switch(m1.opcode) { /* dispatch on type of request */

case CREATE: r = do_create(&m1, &m2); break;

case READ: r = do_read(&m1, &m2); break;

case WRITE: r = do_write(&m1, &m2); break;

case DELETE: r = do_delete(&m1, &m2); break;

default: r = E_BAD_OPCODE;

}

m2.result = r; /* return result to client */

send(m1.source, &m2); /* send reply */

}

}

client

#include

int copy (char *src, char *dst) { /* procedure to copy file using the server */

struct message m1; /* message buffer */

long position; /* current file position */

long client = 110; /* clients address */

initialize(); /* prepare for execution */

position = 0;

client

do { /* get a block of data from the source file. */

m1.opcode = READ; /* operation is a read */

m1.offset = position; /* current position in the file */

strcpy(&m1.name, src); /* copy name of file to be read to message */

send(FILE_SERVER, &m1); /* send the message to the file server */

receive(FILE_SERVER, &m1); /* block waiting for the reply */

/* write the data just received to the destination file. */

m1.opcode = WRITE; /* operation is a write */m1.opcode = WRITE; /* operation is a write */

m1.offset = position; /* current position in the file */

m1.count = m1.result; /* how many bytes to write */

strcpy(&m1.name, dst); /* copy name of file to be written to buf */

send(FILE_SERVER, &m1); /* send the message to the file server */

receive(FILE_SERVER, &m1); /* block waiting for the reply */

position += m1.result; /* m1.result is number of bytes written */

} while (m1.result > 0); /* iterate until done */

return (m1.result >=0 > OK: m1.result); /* return OK or error code */

} /* copy */

:

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()

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.

74

,

,

.

, :

(.., Ethernet, Token Ring, FDDI)

(.., Big Endian, Little Endian)

(.., Unix, MAC OS, MS Windows)

(.., Java,

C++, Python)

75

TCP/IP (

)

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(middleware)

.

,

,

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,

76

:

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(access rights)

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Virtual Private Networks Secure Sockets Layer

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84

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94

.

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(redundancy)

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.

.

(omission failure),

(arbitrary failure),

(arbitrary failure),

(timing failure).

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.

97

:

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()

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98

.

. .

,

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.99

( ).

.

(amount)

( PIN myPIN)

(thread) .

.

1. case CMD_WITHDRAW:

2. Account sessionAcc = getSessionAccount(myPIN); // Account

3. String result = sessionAcc.withdraw(amount); //

4. saveSessionAccount(sessionAcc); //

5. break;

100

To : (1 2)

()

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3000 4000

.

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(race condition) (race condition)

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To

.

101

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102

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104