Distributed Systems
Bina Ramamurthy
5/28/2016
From the CDK text
1
Introduction
Distributed system is the one in which
hardware and software components at
networked computers communicate and
coordinate their activity only by passing
messages.
Examples: Internet, intranet and mobile
computing systems.
5/28/2016
From the CDK text
2
Major Challenges
Heterogeneity of components
Openness


interfacing and
addition and removal of components
Security
Scalability : ability to work well when number
of users increases



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Failure handling
Concurrency
Transparency
From the CDK text
3
Internet
Internet is a very large distributed
system.
Interconnection of a collection of
heterogeneous networks of computers.
Services: world wide web (www), file
transfers (ftp), email, etc.
5/28/2016
From the CDK text
4
A typical portion of the Internet
intranet
%
ISP
%
%
%
backbone
satellite link
desktop computer:
server:
network link:
5/28/2016
From the CDK text
5
A typical intranet
email s erv er
Desktop
computers
print and other servers
Web server
Local area
netw ork
email s erv er
print
File s erv er
other servers
the rest of
the Internet
router/firew all
5/28/2016
From the CDK text
6
Mobile and Ubiquitous
computing
Technological advances in device
miniaturization and wireless networking
have led to integration of small and
portable devices into distributed
systems.

Laptop computers, hand held devices,
wearable devices, appliances such as
washing machines and refrigerators.
What are some of the issues here?
5/28/2016
From the CDK text
7
Portable and handheld devices in a
distributed system
Internet
Host intranet
Wireles s LAN
Mobile
phone
Laptop
Printer
Camera
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WAP
gatew ay
Home intranet
Host site
From the CDK text
8
Client/Server
Server: refers to a process on a networked computer
that accepts requests from other (local or remote)
processes to perform a service and responds
appropriately.
Client: requesting process in the above is referred to
as the client.
Request and response are in the form of messages.
Client is said to invoke an operation on the server.
Many distributed systems today are constructed out
of interacting clients/servers.
5/28/2016
From the CDK text
9
Web servers and web browsers
www.google.com
http://www.google.comlsearch?q=kindberg
Browsers
Web servers
www.cdk3.net
Internet
http://www.cdk3.net/
www.w3c.org
File system of
www.w3c.org
http://www.w3c.org/Protocols/Activity.html
Protocols
Activity.html
Reading assignment: Section 1.3.1
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From the CDK text
10
Computers in the Internet
Date
1979, Dec.
1989, July
1999, July
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Web servers
Computers
188
0
130,000
56,218,000
0
5,560,866
From the CDK text
11
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
location.
•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.
•Performance transparency: allows the system and applications to expand in scale
without change to the system structure or the application algorithms.
5/28/2016
From the CDK text
12