NSCET E-LEARNING PRESENTATION NOTES/unit 1/CS8603_DS.pdf · WHAT ? TANENBAUM A distributed system is a collection of independent computers that appears to its users as a single coherent

NSCETE-LEARNING

PRESENTATIONLISTEN … LEARN… LEAD…

Department of CSE NSCETPage 1 of 79

DEPARTMENT OF COMPUTER SCIENCE & ENGINEERING

III YEAR / VIth SEMESTER

CS8603 – DISTRIBUTED SYSTEMS

VIGNESH L S M.E.,AP/CSE

Nadar Saraswathi College of Engineering & Technology,Vadapudupatti, Annanji (po), Theni – 625531.


UNIT 01 - INTRODUCTION


Distributed Systems

CS8603

INTRODUCTION


WHAT ?

TANENBAUM

A distributed system is a collection of independent computers that

appears to its users as a single coherent system.

2 Aspects

DS consists of components (i.e., computers) that are autonomous.

The Second aspect is that users think they are dealing with a single

system. This means that one way or the other the autonomous

components need to collaborate.


Factors to be considered for creating a DS…

Let us discuss about four important goals for building a distributed

system worth the effort

Making Resources Accessible

Distributed Transparency

Openness

Scalability


Making Resources Accessible

As a whole let us consider an example of Bachman Lab and our HOD Room

The HOD has a separate Printer and moreover all the other students of

third cse who are in bachman lab can be able to take their document print

outs from their labs as they will not be provided with the separate

printers

Ex Resources : Printers, computers, storage facilities, data, files, Web

pages, and networks,


Distributed Transparency

A distributed system should look like a single computer systemto the users which is said to be transparent.

Types of Transparency

1. Access - Different OS

2. Location - Downloading

3. Migration - Transferring a data from one end to other

4. Relocation -

5. Replication – Making copies of a file

6. Concurrency - Locks can be used

7. Failure - accessing a site


Types of Transparency


Openness

The openness of DS is determined primarily by the

degree to which new resource-sharing services can be

added and be made available for use by a variety of client

programs.


Scalability

A system is described as scalable if it remains effective when there

is a significant increase in the number of resources and the number of

users.

Challenges:

Controlling the cost of resources or money.

Controlling the performance loss.


Examples of Distributed Systems

Local Area Network and Intranet

Database Management System

Internet/World-Wide Web

Mobile and Ubiquitous Computing


Local Area Network and Intranet

the res t of

em ail server

Web server

Desktopcomputers

File server

router/ firewall

print and other servers

other servers

print

Local area

network

em ail server

the Internet


Database Management Systems


Internet

intranet

ISP

desktop computer:

backbone

satellite link

server:

%

network link:

%

%

%


World Wide Web


Mobile & Ubiquitous Computing

Laptop

Mobile

PrinterCamera

Internet

Host intranet Home intranetGSM/GPRS

Wireless LAN

phone

gateway

Host site


Figure 1.1 (see book for the full text)

Selected application domains and associated networked applications

Finance and commerce eCommerce e.g. Amazon and eBay, PayPal,

online banking and trading

The information society Web information and search engines, ebooks,

Wikipedia; social networking: Facebook and MySpace.

Creative industries and

entertainment

online gaming, music and film in the home, user-

generated content, e.g. YouTube, Flickr

Healthcare health informatics, on online patient records,

monitoring patients

Education e-learning, virtual learning environments;

distance learning

Transport and logistics GPS in route finding systems, map services:

Google Maps, Google Earth

Science The Grid as an enabling technology for

collaboration between scientists

Environmental management sensor technology to monitor earthquakes,

floods or tsunamis


Figure 1.2

An example financial trading system


Instructor’s Guide for Coulouris, Dollimore, Kindberg and Blair, Distributed Systems: Concepts and Design Edn. 5

© Pearson Education 2012

intranet

ISP

desktop computer:

backbone

satellite link

server:

☎

network link:

☎

☎

☎

Figure 1.3

A typical portion of the Internet


Figure 1.4

Portable and handheld devices in a distributed system


Figure 1.5

Cloud computing


Figure 1.6

Growth of the Internet (computers and web servers)

Date Computers Web servers Percentage

1993, July 1,776,000 130 0.008

1995, July 6,642,000 23,500 0.4

1997, July 19,540,000 1,203,096 6

1999, July 56,218,000 6,598,697 12

2001, July 125,888,197 31,299,592 25

42,298,3712003, July

2005, July

~200,000,000

353,284,187 67,571,581

21

19


Section 1.5.7

Transparencies

Access transparency: enables local and remote resources to be accessed using identical

operations.

Location transparency: enables resources to be accessed without knowledge of their physical

or network location (for example, which building or IP address).

Concurrency transparency: enables several processes to operate concurrently using shared

resources without interference between them.

Replication transparency: enables multiple instances of resources to be used to increase

reliability and performance without knowledge of the replicas by users or application

programmers.

Failure transparency: enables the concealment of faults, allowing users and application

programs to complete their tasks despite the failure of hardware or software components.

Mobility transparency: allows the movement of resources and clients within a system

without affecting the operation of users or programs.

Performance transparency: allows the system to be reconfigured to improve performance

as loads vary.

Scaling transparency: allows the system and applications to expand in scale without change

to the system structure or the application algorithms.


Figure 1.7

Web servers and web browsers

Internet

BrowsersWeb servers

www.google.com

www.cdk5.net

www.w3c.org

standards

faq.html

http://www.w3.org/standards/faq.html#conformance

http://www.google.comlsearch?q=obama

http://www.cdk5.net/

File system ofwww.w3c.org


http://www.cdk5.net

http://www.google.comlsearch?q=obama

http://www.cdk5.net

Figure 13.1

Composed naming domains used to access a resource from a URL

http://www.cdk3.net:8888/WebExamples/earth.html

URL

Resource ID (IP number, port number, pathname)

Network address

2:60:8c:2:b0:5afile

Web server

55.55.55.55 WebExamples/earth.html8888

DNS lookup

Socket


2:60:8c:2:b0:5a



Figure 13.2

Iterative navigation

Client1

2

3

A client iteratively contacts name servers NS1–NS3 in order to resolve a name

NS2

NS1

NS3

Nameservers


Figure 13.3

Non-recursive and recursive server-controlled navigation

1

2

3

5

1

2

34

4

A name server NS1 communicates with other name servers on behalf of a client

client client

Recursiveserver-controlled

NS2

NS1

NS3

NS2

NS1

NS3

Non-recursiveserver-controlled


Figure 13.4

DNS name servers

Note: Name server names

are in italics, and the

corresponding domains are in

parentheses.

Arrows denote name

server entries

a.root-servers.net

(root)

ns0.ja.net(ac.uk)

dns0.dcs.qmul.ac.uk(dcs.qmul.ac.uk)

alpha.qmul.ac.uk(qmul.ac.uk)

dns0-doc.ic.ac.uk(ic.ac.uk)

ns.purdue.edu(purdue.edu)

ukpurdue.edu

ic.ac.uk

qmul.ac.uk

dcs.qmul.ac.uk

*.qmul.ac.uk*.ic.ac.uk

*.dcs.qmwul.ac.uk

* .purdue.edu

ns1.nic.uk(uk)

ac.uk

co.uk

yahoo.com


Figure 13.5

DNS resource records

Record type Meaning Main contents

A A computer address IP number

NS An authoritative name server Domain name for server

CNAME The canonical name for an alias Domain name for alias

SOA Marks the start of data for a zone Parameters governing the zone

WKS A well-known service description List of service names and protocols

PTR Domain name pointer (reverselookups)

Domain name

HINFO Host information Machine architecture and operatingsystem

MX Mail exchange List of <preference, host > pairs

TXT Text string Arbitrary text


Figure 13.6

DNS zone data records

domain name time to live class type value

1D IN NS dns0

1D IN NS dns1

1D IN NS cancer.ucs.ed.ac.uk

1D IN MX 1 mail1.qmul.ac.uk

1D IN MX 2 mail2.qmul.ac.uk

domain name time to live class type value

www 1D IN CNAME apricot

apricot 1D IN A 138.37.88.248

dcs 1D IN NS dns0.dcs

dns0.dcs 1D IN A 138.37.88.249

dcs 1D IN NS dns1.dcs

dns1.dcs 1D IN A 138.37.94.248

dcs.qmul.ac.uk

dcs.qmul.ac.uk

dcs.qmul.ac.uk

dcs.qmul.ac.uk

dcs.qmul.ac.uk


Figure 13.7

GNS directory tree and value tree for user Peter.Smith

UK FR

AC

QMWDI: 322

Peter.Smith

passwordmailboxes

DI: 599 (EC)

DI: 574DI: 543

DI: 437

Alpha GammaBeta


Figure 13.8

Merging trees under a new root

EC

UK FR

DI: 599

DI: 574DI: 543

NORTH AMERICA

US

DI: 642

DI: 457DI: 732

#599 = #633/EC#642 = #633/NORTH AMERICA

Well-known directories:

CANADA

DI: 633 (WORLD)


Figure 13.9

Restructuring the directory

EC

UK FR

DI: 599

DI: 574DI: 543

NORTH AMERICA

US

DI: 642

DI: 457DI: 732CANADA

DI: 633 (WORLD)

#633/EC/US

US

#599 = #633/EC#642 = #633/NORTH AMERICA

Well-known directories:


Figure 13.10

X.500 service architecture

DSA

DSA

DSA

DSA

DSADSADUA

DUA

DUA


Figure 13.11

Part of the X.500 Directory Information Tree

... France (country) Great Britain (country) Greece (country) ...

BT Plc (organization) University of Gormenghast (organization)... ...

Department of Computer Science (organizationalUnit)

Computing Service (organizationalUnit)

Engineering Department (organizationalUnit)

...

...

X.500 Service (root)

Departmental Staff (organizationalUnit)

Research Students (organizationalUnit)

ely (applicationProcess)

...

...

Alice Flintstone (person) Pat King (person) James Healey (person) ...... Janet Papworth (person)...


Figure 13.12

An X.500 DIB Entry

info

Alice Flintstone, Departmental Staff, Department of Computer Science, University of Gormenghast, GB

commonName

Alice.L.FlintstoneAlice.FlintstoneAlice FlintstoneA. Flintstone

surname

Flintstone

telephoneNumber

+44 986 33 4604

uid

alf

mail

[email protected]

[email protected]

roomNumber

Z42

userClass

Research Fellow


Figure 3.1

Network performance

km


Figure 3.2

Conceptual layering of protocol software

Layer n

Layer 2

Layer 1

Message sent Message received

Communication

medium

Sender Recipient


Figure 3.3

Encapsulation as it is applied in layered protocols

Presentat ion header

Application-layer message

Session header

Transport header

Network header


Figure 3.4

Protocol layers in the ISO Open Systems Interconnection (OSI) model

Application

Presentat ion

Session

Transport

Network

Data link

Physical

Message sent Message received

Sender Rec ipient

Layers

Communicat ion

medium


Figure 3.5

OSI protocol summary

Layer Description Examples

Application Protocols that are designed to meet the communication requirements ofspecific applications, often defining the interface to a service.

HTTP, FTP , SMTP,CORBA IIOP

Presentation Protocols at this level transmit data in a network representation that isindependent of the representations used in individual computers, which maydiffer. Encryption is also performed in this layer, if required.

Secure Sockets(SSL),CORBA DataRep.

Session At this level reliability and adaptation are performed, such as detection offailures and automatic recovery.

Transport This is the lowest level at which messages (rather than packets) are handled.Messages are addressed to communication ports attached to processes,Protocols in this layer may be connection-oriented or connectionless.

TCP, UDP

Network Transfers data packets between computers in a specific network. In a WANor an internetwork this involves the generation of a route passing throughrouters. In a single LAN no routing is required.

IP, ATM virtualcircuits

Data link Responsible for transmission of packets between nodes that are directlyconnected by a physical link. In a WAN transmission is between pairs ofrouters or between routers and hosts. In a LAN it is between any pair of hosts.

Ethernet MAC,ATM cell transfer,PPP

Physical The circuits and hardware that drive the network. It transmits sequences ofbinary data by analogue signalling, using amplitude or frequency modulationof electrical signals (on cable circuits), light signals (on fibre optic circuits)or other electromagnetic signals (on radio and microwave circuits).

Ethernet base- bandsignalling, ISDN


Figure 3.6

Internetwork layers

Underlying network

Application

Network interface

Transport

Internetwork

Internetwork packets

Network-spec ific packets

MessageLayers

Internetworkprotocols

Underlyingnetworkprotocols


Figure 3.7

Routing in a wide area network

HostsLinks

or local

networks

A

D E

B

C

1

2

5

43

6

Routers


Figure 3.8

Routing tables for the network in Figure 3.7

Routings from D Routings from E

To Link Cost To Link Cost

A

B

C

D

E

3

3

6

local

6

1

2

2

0

1

A

B

C

D

E

4

4

5

6

local

2

1

1

1

0

Routings from A Routings from B Routings from C

To Link Cost To Link Cost To Link Cost

A

B

C

D

E

local

1

1

3

1

0

1

2

1

2

A

B

C

D

E

1

local

2

1

4

1

0

1

2

1

A

B

C

D

E

2

2

local

5

5

2

1

0

2

1


Figure 3.9

Pseudo-code for RIP routing algorithm

Send: Each t seconds or when Tl changes, send Tl on each non-faulty outgoing link.

Receive: Whenever a routing table Tr is received on link n:

for all rows Rr in Tr {

if (Rr.link | n) {

Rr.cost = Rr.cost + 1;

Rr.link = n;

if (Rr.destination is not in Tl) add Rr to Tl;

// add new destination to Tl

else for all rows Rl in Tl {

if (Rr.destination = Rl.destination and

(Rr.cost < Rl.cost or Rl.link = n)) Rl = Rr;

// Rr.cost < Rl.cost : remote node has better route

// Rl.link = n : remote node is more authoritative

}

}

}


Figure 3.10

Simplified view of part of a university campus network

file

compute

dialup

hammer

henry

hotpoint

138.37.88.230

138.37.88.162

bruno138.37.88.249

router/sickle

138.37.95.241138.37.95.240/29

138.37.95.249

copper138.37.88.248

firewall

web

138.37.95.248/29

server

desktop computers 138.37.88.xx

subnet

subnet

Eswitch

138.37.88

server

server

server

138.37.88.251

custard138.37.94.246

desktop computers

Eswitch

138.37.94

hubhub

Student subnetStaff subnet

otherservers

router/firewall

138.37.94.251

☎

1000 Mbps Ethernet

Eswitch: Ethernet switch

100 Mbps Ethernet

file server/gateway

printers

Campusrouter

Campusrouter

138.37.94.xx


Figure 3.11

Tunnelling for IPv6 migration

A BIPv6 IPv6

IPv6 encapsulated in IPv4 packets

Encapsulators

IPv4 network


Figure 3.12

TCP/IP layers

Messages (UDP) or Streams (TCP)

Application

Transport

Internet

UDP or TCP packets

IP datagrams

Network-specific frames

MessageLayers

Underlying network

Network interface


Figure 3.13

Encapsulation in a message transmitted via TCP over an Ethernet

Application message

TCP header

IP header

Ethernet header

Ethernet frame

port

TCP

IP


Figure 3.14

The programmer's conceptual view of a TCP/IP Internet

IP

Application Application

TCP UDP


Figure 3.15

Internet address structure, showing field sizes in bits

7 24

Class A: 0 Network ID Host ID

14 16

Class B: 1 0 Network ID Host ID

21 8

Class C: 1 1 0 Network ID Host ID

28

Class D (mult icast): 1 1 1 0 Mult icast address

27

Class E (reserved): 1 1 1 1 unused0

28


Figure 3.16

Decimal representation of Internet addresses

octet 1 octet 2 octet 3

Class A: 1 to 127

0 to 255 0 to 255 1 to 254

Class B: 128 to 191

Class C: 192 to 223

224 to 239 Class D (multicast):

Network ID

Network ID

Network ID

Host ID

Host ID

Host ID

Multicast address

0 to 255 0 to 255 1 to 254

0 to 255 0 to 255 0 to 255

0 to 255 0 to 255 0 to 255

0 to 255 0 to 255 1 to 254240 to 255 Class E (reserved):

1.0.0.0 to 127.255.255.255

128.0.0.0 to 191.255.255.255

192.0.0.0 to 223.255.255.255

224.0.0.0 to 239.255.255.255

240.0.0.0 to 255.255.255.255

Range of addresses


Figure 3.17

IP packet layout

dataIP address of destinationIP address of source

header

up to 64 kilobytes


Figure 3.18

A typical NAT-based home network


Figure 3.19

IPv6 header layout

Source

address(128

bits)

Destination

address(128

bits)

Version (4

bits)

Traffic class (8

bits)

Flow label (20

bits)Payload length (16

bits)

Hop limit (8

bits)

Next header (8

bits)


Figure 3.20

The MobileIP routing mechanism

Sender

Home

Mobile host MH

Foreign agent FA

Internet

agent

First IP packet

addressed to MH

Address of FA

returned to sender

First IP packet

tunnelled to FA

Subsequent IP packets

tunnelled to FA




Figure 3.21

Firewall configurations

Internet

Router/Protected intranet

a) Filtering router

Internet

b) Filtering router and bas tion

filter

Internet

R/filterc) Screened subnet for bast ion R/filter Bastion

R/filter Bastion

web/ftpserver

web/ftpserver

web/ftpserver




Figure 3.22

IEEE 802 network standards

IEEE No. Name Title Reference

802.3 Ethernet CSMA/CD Networks (Ethernet) [IEEE 1985a]

802.4 Token Bus Networks [IEEE 1985b]

802.5 Token Ring Networks [IEEE 1985c]

802.6 Metropolitan Area Networks [IEEE 1994]

802.11 WiFi Wireless Local Area Networks [IEEE 1999]

802.15.1 Bluetooth Wireless Personal Area Networks [IEEE 2002]

802.15.4 ZigBee Wireless Sensor Networks [IEEE 2003]

802.16 WiMAX Wireless Metropolitan Area Networks [IEEE 2004a]




Figure 3.23

Ethernet ranges and speeds

10Base5 10BaseT 100BaseT 1000BaseT

Data rate 10 Mbps 10 Mbps 100 Mbps 1000 Mbps

Max. segment lengths:

Twisted wire (UTP) 100 m 100 m 100 m 25 m

Coaxial cable (STP) 500 m 500 m 500 m 25 m

Multi-mode fibre 2000 m 2000 m 500 m 500 m

Mono-mode fibre 25000 m 25000 m 20000 m 2000 m




Figure 3.24

Wireless LAN configuration

LAN

Server

WirelessLAN

Laptops

Base stat ion/access point

Palmtop

radio obs truct ion

A B C

DE




Figure 3.25

Bluetooth frame structure

SCO packets (e.g. for voice data) have a 240-bit payload containing 80 bits

of data triplicated, filling exactly one timeslot.

bits: 72 18 18 18 0 - 2744

Access code Headercopy 1

Header

copy 2

Headercopy 3

Data for transmission

bits: 3 1 1 1 4 8

Destination Flow Ack Seq Type Header checksum

Address withinPiconet

= ACL, SCO,poll, null

Header




Figure 14.1

Skew between computer clocks in a distributed system




Figure 14.2

Clock synchronization using a time server

mr

m t

p Time server,S




Figure 14.3

An example synchronization subnet in an NTP implementation

1

2

3

2

3 3

Note: Arrows denote synchronization control, numbers denote

strata.




Figure 14.4

Messages exchanged between a pair of NTP peers

Ti

Ti-1Ti-2

Ti- 3

Server B

Server A

Time

m m'

Time




Figure 14.5

Events occurring at three processes




Figure 14.6

Lamport timestamps for the events shown in Figure 14.5




Figure 14.7

Vector timestamps for the events shown in Figure 14.5




Figure 14.8

Detecting global properties




Figure 14.9

Cuts

m1 m2

p1

p2Physical

time

e1

0

Consistent cut

Inconsistent cut

e 1

1e 1

2e 1

3

e 20

e 21

e 22




Figure 14.10

Chandy and Lamport’s ‘snapshot’ algorithm

Marker receiving rule for process pi

On pi’s receipt of a marker message over channel c:

if (pi has not yet recorded its state) it

records its process state now;

records the state of c as the empty set;

turns on recording of messages arriving over other incoming channels;

else

pi records the state of c as the set of messages it has received over c

since it saved its state.

end if

Marker sending rule for process pi

After pi has recorded its state, for each outgoing channel c:

pi sends one marker message over c

(before it sends any other message over c).




Figure 14.11

Two processes and their initial states




Figure 14.12

The execution of the processes in Figure 14.11




Figure 14.13

Reachability between states in the snapshot algorithm

Sinit Sfinal

Ssnap

actual execution e0,e1,...

recording recording begins ends

pre-snap: e'0,e '1,...e'R-1 post-snap: e 'R,e 'R+1,...

'




Figure 14.14

Vector timestamps and variable values for the execution of Figure 14.9

m1 m2

p1

p2Physical

time

Cut C1

(1,0) (2,0) (4,3)

(2,1) (2,2) (2,3)

(3,0)

x1= 1 x1= 100 x1= 105

x2= 100 x2= 95 x2= 90

x1= 90

Cut C 2




Figure 14.15

The lattice of global states for the execution of Figure 14.14

Sij = global state after i events at process 1and j events at process 2

S00

S10

S20

S21S30

S31

S32

S22

S23

S33

S43

Level 0

1

2

3

4

5

6

7




Figure 14.16

Algorithms to evaluate possibly and definitely


Figure 14.17

Evaluating definitely


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NSCET E-LEARNING PRESENTATION NOTES/unit 1/CS8603_DS.pdf · WHAT ? TANENBAUM A distributed system is a collection of independent computers that appears to its users as a single coherent