This document serves as an introduction to distributed systems, covering their concepts, design, and applications across various fields such as finance, healthcare, and education. It discusses key features like transparency, fault tolerance, and scalability, alongside trends exemplified by the Internet and the World Wide Web. The document further includes case studies, technical illustrations, and the architecture of distributed systems like Google's infrastructure.

1. CS6601 DISTRIBUTED SYSTEMS
UNIT – I
Dr.A.Kathirvel, Professor, Computer Science and Engg.
M N M Jain Engineering College, Chennai

2. Unit - I
INTRODUCTION
Examples of Distributed Systems–Trends
in Distributed Systems – Focus on
resource sharing – Challenges. Case
study: World Wide Web.
Coulouris, Dollimore, Kindberg and Blair
Distributed Systems:Concepts and Design Edition 5, Addison-Wesley 2012

3. Applications
Most people know about the Internet (a computer
network) through applications
World Wide Web
Email
Online Social Network
Streaming Audio Video
File Sharing
Instant Messaging
…
3

4. 4
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

5. Fig1.2 : An example financial trading
system
5

6. intranet
ISP
desktop computer:
backbone
satellite link
server:
☎
network link:
☎
☎
☎
Fig1.3: A typical portion of the Internet
6

7. Fig1.4: Portable and handheld devices
in a distributed system
7

8. 8
Fig1.5: Cloud computing
8

9. Fig1.6: 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
9

10. 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.
10

11. Fig1.7: 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 of
www.w3c.org
11

12. Fig2.1:Generations of DS
12

13. Fig2.2:Communicating entities and
communication paradigms
13

14. Fig2.3:Clients invoke individual servers
Server
Client
Client
invocation
result
Serverinvocation
result
Process:
Key:
Computer:
14

15. Fig2.4a:Peer-to-peer architecture
15

16. Fig2.4b: A service provided by multiple
servers
Server
Server
Server
Service
Client
Client
16

17. Fig2.5:Web proxy server
Client
Proxy
Web
server
Web
server
server
Client
17

18. Fig2.6: Web applets
a)client request results in the downloading of applet code
Web
server
Client
Web
serverApplet
Applet code
Client
b)client interacts with the applet
18

19. Fig2.7:Software and hardware
service layers in distributed Systems
Applications,services
Computer and network hardware
Platform
Operating system
Middleware
19

20. Fig2.8:Two-tier & three-tier architectures
20

21. Fig2.9:AJAX example: soccer score
updates
new Ajax.Request('scores.php? game=Arsenal:Liverpool’,
{onSuccess: updateScore});
function updateScore(request) {
.....
( request contains the state of the Ajax request including the
returned result.
The result is parsed to obtain some text giving the score, which
is used to update the relevant portion of the current page.)
....
}
21

22. Fig2.10:Thin clients and compute
servers
Thin
Client
Application
Process
Network computer or PC
Compute server
network
22

23. Fig2.11:The web service architectural
pattern
23

24. Fig2.12: Categories of middleware
24

25. Fig2.13:Real-time ordering of events
send
receive
send
receive
m1 m2
2
1
3
4
X
Y
Z
Physical
time
A
m3
receive receive
send
receive receive receive
t1 t2 t3
receive
receive
m2
m1
25

26. Fig2.14:Processes and channels
processp process q
Communication channel
send
Outgoing message buffer Incoming message buffer
receivem
26

27. Fig2.15: Omission and arbitrary failures
Class of failure Affects Description
Fail-stop Process Process halts and remains halted. Other processes may
detect this state.
Crash Process Process halts and remains halted. Other processes may
not be able to detect this state.
Omission Channel A message inserted in an outgoing message buffer neve
arrives at the other end’s incoming message buffer.
Send-omission Process A process completes asend,but the message is not put
in its outgoing message buffer.
Receive-omissionProcess A message is put in a process’s incoming message
buffer, but that process does not receive it.
Arbitrary
(Byzantine)
Process or
channel
Process/channel exhibits arbitrary behaviour: it may
send/transmit arbitrary messages at arbitrary times,
commit omissions; a process may stop or take an
incorrect step.
27

28. Fig2.11:Timing failures
Class of FailureAffects Description
Clock Process Process’s local clock exceeds the bounds on its
rate of drift from real time.
Performance Process Process exceeds the bounds on the interval
between two steps.
Performance Channel A message’s transmission takes longer than the
stated bound.
28

29. Fig2.17:Objects and principals
Network
invocation
result
Client
Server
Principal (user) Principal (server)
ObjectAccess rights
29

30. Fig2.18: The enemy
Communication channel
Copy of m
Process p Process qm
The enemy
m’
30

31. Fig2.19: Secure channels
Principal A
Secure channelProcess p Process q
Principal B
31

32. Fig3.1:Network performance
km
32

33. Fig3.2: Conceptual layering of
protocol software
Layer n
Layer 2
Layer 1
Message sent Message received
Communication
medium
Sender Recipient
33

34. Fig3.3: Encapsulation as it is applied
in layered protocols
Presentation header
Application-layer message
Session header
Transport header
Network header
34

35. Fig3.4:Protocol layers in the ISO Open
Systems Interconnection (OSI) model
Application
Presentation
Session
Transport
Network
Data link
Physical
Message sent Message received
Sender Recipient
Layers
Communication
medium
35

36. Fig3.5: OSI protocol summary
Layer Description Examples
Application Protocols that are designed to meet the communication requirements of
specific 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 is
independent of the representations used in individual computers, which may
differ. Encryption is also performed in this layer, if required.
Secure Sockets
(SSL),CORBA Data
Rep.
Session At this level reliability and adaptation are performed, such as detection of
failures 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 WAN
or an internetwork this involves the generation of a route passing through
routers. In a single LAN no routing is required.
IP, ATM virtual
circuits
Data link Responsible for transmission of packets between nodes that are directly
connected by a physical link. In a WAN transmission is between pairs of
routers 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 of
binary data by analogue signalling, using amplitude or frequency modulation
of electrical signals (on cable circuits), light signals (on fibre optic circuits)
or other electromagnetic signals (on radio and microwave circuits).
Ethernet base- band
signalling, ISDN
36

37. Fig3.6:Internetwork layers
Underlying network
Application
Network interface
Transport
Internetwork
Internetwork packets
Network-specific packets
Message
Layers
Internetwork
protocols
Underlying
network
protocols
37

38. Fig3.7:Routing in a wide area network
Hosts
Links
or local
networks
A
D E
B
C
1
2
5
43
6
Routers
38

39. Fig3.8:Routing tables for the network
in Fig3.7
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
39

40. Fig3.9: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
}}}
40

41. Fig3.10: Simplified view of part of a
university campus network
file
compute
dialup
hammer
henry
hotpoint
138.37.88.230
138.37.88.162
bruno
138.37.88.249
router/
sickle
138.37.95.241138.37.95.240/29
138.37.95.249
copper
138.37.88.248
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
custard
138.37.94.246
desktop computers
Eswitch
138.37.94
hubhub
Student subnetStaff subnet
other
servers
router/
firewall
138.37.94.251
☎
1000 Mbps Ethernet
Eswitch: Ethernet switch
100 Mbps Ethernet
file server/
gateway
printers
Campus
router
Campus
router
138.37.94.xx
41

42. Fig3.11:Tunnelling for IPv6 migration
A B
IPv6 IPv6
IPv6 encapsulated in IPv4 packets
Encapsulators
IPv4 network
42

43. Fig3.12: TCP/IP layers
Messages (UDP) or Streams (TCP)
Application
Transport
Internet
UDP or TCP packets
IP datagrams
Network-specific frames
Message
Layers
Underlying network
Network interface
43

44. Fig3.13:Encapsulation in a message
transmitted via TCP over an Ethernet
Application message
TCP header
IP header
Ethernet header
Ethernet frame
port
TCP
IP
44

45. Fig3.14:The programmer's conceptual
view of a TCP/IP Internet
IP
Application Application
TCP UDP
45

46. Fig3.15: 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 (multicast): 1 1 1 0 Multicast address
27
Class E (reserved): 1 1 1 1 unused0
28
46

47. Fig3.16: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 239Class 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 255Class 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
47

48. Fig3.17:IP packet layout
dataIPaddress of destinationIPaddress of source
header
upto 64kilobytes
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)
48

49. Fig3.18:A typical NAT-based home
network
49

50. Fig3.20: 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
50

51. Fig3.21:Firewall configurations
Internet
Router/
Protected intraneta) Filtering router
Internet
b) Filtering router and bastion
filter
Internet
R/filterc) Screened subnet for bastion R/filter Bastion
R/filter Bastion
web/ftp
server
web/ftp
server
web/ftp
server
51

52. Fig3.22: 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]
52

53. Fig3.23: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
53

54. Fig3.24: Wireless LAN configuration
LAN
Server
Wireless
LAN
Laptops
Base station/
access point
Palmtop
radio obstruction
A B C
D
E
54

55. Fig3.25: 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 Header
copy 1
Header
copy 2
Header
copy 3
Data for transmission
bits: 3 1 1 1 4 8
Destination Flow Ack Seq Type Header checksum
Address within
Piconet
= ACL, SCO,
poll, null
Header
55

56. Designing Distributed Systems
Google Case Study
56

57. Fig21.1:Outline architecture of the
original Google search engine
57

58. Fig21.2: Example Google applications
58

59. Fig21.3:Organization of the Google
physical infrastructure
(To avoid
clutter the
Ethernet
connection
s are
shown
from only
one of the
clusters to
the
external
links)
59

60. Fig21.4:The scalability problem-Google
60

61. Fig21.5:The overall Google systems
architecture
61

62. Fig21.6: Google infrastructure
62

63. Fig21.7: Protocol buffers example
63

64. Fig21.8a:Summary of design choices
related to communication-paradigmspart
64

65. Fig21.8b:Summary of design choices
related to communication paradigms-part2
65

66. Fig21.9:Overall architecture of GFS
66

67. Fig21.10:Chubby API
67

68. Fig21.11:Overall architecture of Chubby
68

69. Fig21.12: Message exchanges in
Paxos (in absence of failures) - step 1
69

70. Fig21.12:Message exchanges in Paxos
(in absence of failures) - step 2
70

71. Fig21.12:Message exchanges in
Paxos (in absence of failures)-step 3
71

72. Fig21.13:The table abstraction in Bigtable
72

73. Fig21.14:Overall architecture of Bigtable
73

74. Fig21.15:The storage architecture-Bigtable
74

75. Fig21.16:The hierarchical indexing
scheme adopted by Bigtable
75

76. Fig21.17:Summary of design choices
related to data storage and coordination

77. Fig21.18:Examples of the use of MapReduce
77

78. Fig21.19:The overall execution of a
MapReduce program
78

79. Fig21.20:The overall execution of a
Sawzall program
79

80. Fig21.21:Summary of design choices
related to distributed computation
80

81. Questions?