Chapter 1

Slides for Chapter 1
Introduction to Distributed System and
Computing
From Coulouris, Dollimore and Kindberg
Distributed Systems:
Concepts and Design
Edition 4, © Pearson Education 2005
Reference slides from Distributed Computing Introduction, M. Liu
And Java programming, D. Liang

Distributed system, distributed computing
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 4
© Pearson Education 2005
Early computing was performed on a single
processor. Uni-processor computing can be called
centralized computing.
A distributed system is a collection of independent
computers, interconnected via a network, capable of
collaborating on a task by message passing. It has
three features:
Concurrency
No global clock
Independent failure
Distributed computing is computing performed in a
distributed system.

Examples of Distributed Systems
Web Search: major growth industry in the last decade. 10 billion per
month for global number of searches. Complex task for searching a big
database with 63 billion pages. (e.g. Google distributed infrastructure, file
system, storage, lock service, parallel computing)
Massively multiplayer online games: Large number of people interact
through the Internet with a virtual world. Challenges include fast response
time, real-time propagation of events.
Financial trading: provides real-time access to a wide range of information
sources such as current share prices and trends, economic and political
development news. Challenges include how to deliver events reliably and
in a timely manner to very large numbers of clients.

Trend in Distributed Systems
Pervasive networking and modern Internet: Wifi, WiMax, Bluetooth, the third-
generation of mobile phone networks. The result is that networking has
become a pervasive resource and devices can be connected at any time and
in any place.
Mobile and ubiquitous computing: small and portable computing devices are
integrated into the distributed system such as laptop, handheld
devices( PDA, cell phone, camera etc).
Distributed multimedia systems: it support a range of media types such as
audio, video in a distributed system. So desktop can access live television,
file libraries, music libraries, telephone IP phone (Skype) in distributed
system. QoS issue
Distributed Computing as a utility: A number of companies provide the
computing, storage and application resources as a commodity or utility to
users. So users do not need to maintain local IT. Pay as use. Analogy
between distributed resources and other utilities such a water or electricity.

intranet
ISP
desktop computer:
backbone
satellite link
server:
network link:
Figure 1.1
A typical portion of the Internet

Figure 1.2
A typical intranet
the rest of
email server
Web server
Desktop
computers
File server
router/firewall
print and other servers
other servers
print
Local area
network
email server
the Internet

Figure 1.3
Portable and handheld devices in a distributed system
Laptop
Mobile
Printer
Camera
Internet
Host intranet Home intranet
WAP
Wireless LAN
phone
gateway
Host site

Figure 1.4
Web servers and web browsers
Internet
BrowsersWeb servers
www.google.com
www.cdk3.net
www.w3c.org
Protocols
Activity.html
http://www.w3c.org/Protocols/Activity.html
http://www.google.comlsearch?q=kindberg
http://www.cdk3.net/
File system of
www.w3c.org

Figure 1.5
Computers in the Internet
Date Computers Web servers
1979, Dec. 188 0
1989, July 130,000 0
1999, July 56,218,000 5,560,866
2003, Jan. 171,638,297 35,424,956

Centralized vs. Distributed Computing
m a in f r a m e c o m p u t e r
w o r k s t a t io n
n e t w o r k h o s t
n e t w o r k lin k
t e r m in a l
c e n t r a l i z e d c o m p u t i n g
d i s t r i b u t e d c o m p u t i n g

Evolution of paradigms
Client-server: Socket API, remote method invocation
Distributed objects
Object broker: CORBA
Network service: Jini
Object space: JavaSpaces
Mobile agents
Message oriented middleware (MOM): Java Message
Service
Collaborative applications

Why distributed computing?
Resource sharing/Economics: distributed systems allow
the pooling of resources, including CPU cycles, data
storage, input/output devices, and services.
Scalability: Increasing demands and users can be easily
addressed by adding more resources and the system can
still run effectively.
Reliability: a distributed system allow replication of
resources and/or services, thus reducing service outage
due to failures.
The affordability of computers and availability of network
access: The Internet has become a universal platform for
distributed computing.

The Challenges of Distributed Computing
The Challenges of distributed computing:
Heterogeneity: computers and networks are of different
types. Including hardware, network, programming
language, and operating system.
E.g. Two alternatives for byte ordering of integers on different hardware, namely big-
endian and little-endian. Message transfer should take care of it.
E.g. The different types of networks are masked by the fact that all computers
attached to the Internet use the Internet protocols to communicate.
E.g. Different OS may provide the different programming interface for message
exchanges. Like different calls in UNIX and Windows.
E.g. Different programming languages use different representations for characters
and data structures. Difference must be handled if two need to communicate.
E.g. Different programs written by different developers even same language may
use different communication protocols and primitive data items and data structures
in messages.

Failure handling: Failures in a distributed system are partial-
that is, some components fail while others continue to function.
So is particularly difficult.
Detecting failures: some can be detected (checksum) and some may not.
Masking failures: detected and can be hidden or made less severe. a. message
can be retransmitted b. file data can be save on two disks if one fails, the other one
works.
Tolerating failures: not possible to detect all and hide all. Just report the error.
Recovery from failure: software so that the state of permanent data can be
recovered or rolled back after a server crash.
Redundancy: redundant components. a. two routes between two routers. b.
Domain name system, every name table is replicated in at least two servers. c.
database may be replicated in different servers. Redirect client to other servers
The design of effective techniques for keeping replicas of rapidly changing data up-to-
date without excessive loss of performance is challenging.

Concurrency: several clients may attempt to access a
shared resource at the same time. For example, auction bid
data structure by clients
Process manages a shared resource could take one
client request at a time. But that approach limits
throughput. So concurrent threads are usually allowed.
Smith: $122 and Jones: $111. If operations are
interleaved without any control, then they might get
stored as Smith: $1111 and Jones: $122
For data to be safe in a concurrent environment, its
operations must be synchronized in such a way that data
remains consistent such as semaphores.

Scalability: It will remain effective when there is a significant
increase in the number of resources and the number of users.
Controlling the cost of physical resources: as the demand for a
resource grows, it should be possible to extend the system at
reasonable cost.
Controlling the performance loss: Algorithm uses hierarchic structures
O(logN) scale better than those use linear structures O(N).
Preventing software resources running out: IP addresses start with 32
bits. New version 128 bits. Modification to software needed.
Avoiding performance bottleneck: algorithm should be decentralized to
avoid having performance bottleneck.

Security Concerns: In a distributed system, there are
more opportunities for unauthorized attack.
Confidentiality (protecting against disclosure to
unauthorized individuals);
Integrity (protection against alteration or corruption);
Availability (protection against interference with the
means to access the resource);

Transparency: It is a major influence on the design of
the distributed system software
Defined as the concealment from the user and the
application programmer of the separation of
components in a distributed system, so that the
system is perceived as a whole rather than a
collection of independent component.

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.

Operating Systems Basics

Process and program
A process consists of an executing program, its
current values, state information, and the
resources used by the operating system to
manage its execution.
A program is an artifact constructed by a
software developer; a process is a dynamic
entity which exists only when a program is run.

Process State Transition Diagram
S i m p l i f e d f i n i t e s t a t e d i a g r a m f o r a p r o c e s s ' s l i f e t i m e
s t a r t
r e a d y
r u n n i n g
b l o c k e d
t e r m i n a t e d
d is p a t c h
q u e u e d
e v e n t c o m p le t io n w a it in g
f o r e v e n t
e x it

Java processes
There are three types of Java program:
applications, applets, and servlets, all are written as
a class.
A Java application program has a main method, and is
run as an independent(standalone) process.
An applet does not have a main method, and is run
using a browser or the appletviewer.
A servlet does not have a main method, and is run in the
context of a web server.
A Java program is compiled into bytecode, a
universal object code. When run, the bytecode is
interpreted by the Java Virtual Machine (JVM).

Three Types of Java programs
Applications
a program whose byte code can be run on any system
which has a Java Virtual Machine. An application may
be standalone (monolithic) or distributed (if it interacts
with another process).
Applets
A program whose byte code is downloaded from a
remote machine and is run in the browser’s Java Virtual
Machine.
Servlets
A program whose byte code resides on a remote
machine and is run at the request of an HTTP client (a
browser).

Three Types of Java programs
c o m p u t e r
J a v a o b j e c t
J a v a V i r t u a l M a c h i n e
A s t a n d a l o n e J a v a a p p l i c a t i o n i s r u n o n a l o c a l m a c h i n e
J a v a o b je c t
J a v a V i r t u a l M a c h i n e
A n a p p l e t i s a n o b j e c t d o w n l o a d e d ( t r a n s f e r r e d ) f r o m a r e m o t e m a c h i n e ,
t h e n r u n o n a l o c a l m a c h i n e .
r e q u e s t
r e s p o n s e
a s e r v l e t
a n a p p l e t
A s e r v l e t i s a n o b je c t t h a t r u n s o n a r e m o t e m a c h i n e a n d
i n t e r a c t s w i t h a l o c a l p r o g r a m u s i n g a r e q u e s t - r e s p o n s e p r o t o c o l
a p r o c e s s

A sample Java application
/ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* A s a m p l e o f a s i m p l e J a v a a p p l i c a t i o n .
* M . L i u 1 / 8 / 0 2
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * /
i m p o r t ja v a . i o . * ;
c l a s s M y P r o g r a m {
p u b l i c s t a t i c v o i d m a i n ( S t r i n g [ ] a r g s )
t h r o w s I O E x c e p t i o n {
B u f f e r e d R e a d e r k e y b o a r d = n e w
B u f f e r e d R e a d e r ( n e w I n p u t S t r e a m R e a d e r ( S y s t e m . i n ) ) ;
S t r i n g t h e N a m e ;
S y s t e m . o u t . p r i n t l n ( " W h a t i s y o u r n a m e ? " ) ;
t h e N a m e = k e y b o a r d . r e a d L i n e ( ) ;
S y s t e m . o u t . p r i n t ( " H e l l o " + t h e N a m e ) ;
S y s t e m . o u t . p r i n t l n ( " - w e l c o m e t o C S C 3 6 9 . n " ) ;
} / / e n d m a i n
} / / e n d c l a s s

A Sample Java Applet
/ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* A s a m p l e o f a s i m p l e a p p l e t .
* M . L i u 1 / 8 / 0 2
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * /
i m p o r t ja v a . a p p l e t . A p p l e t ;
i m p o r t ja v a . a w t . * ;
p u b l i c c l a s s M y A p p l e t e x t e n d s A p p l e t {
p u b l i c v o i d p a i n t ( G r a p h i c s g ) {
s e t B a c k g r o u n d ( C o l o r . b l u e ) ;
F o n t C l a u d e = n e w F o n t ( " A r i a l " , F o n t . B O L D , 4 0 ) ;
g . s e t F o n t ( C l a u d e ) ;
g . s e t C o l o r ( C o l o r . y e l l o w ) ;
g . d r a w S t r i n g ( " H e l l o W o r l d !" , 1 0 0 , 1 0 0 ) ;
} / / e n d p a i n t
} / / e n d c l a s s
< !- - A w e b p a g e w h i c h , w h e n b r o w s e d , w i l l r u n >
< !- - t h e M y A p p l e t a p p l e t >
< !- - M . L i u 1 / 8 / 0 2 >
< t i t l e > S a m p l e A p p l e t < / t i t l e >
< h r >
< a p p l e t c o d e = " M y A p p l e t . c l a s s " w i d t h = 5 0 0 h e i g h t = 5 0 0 >
< / a p p l e t >
< h r >
< a h r e f = " H e l l o . ja v a " > T h e s o u r c e . < / a >

A Sample Java Servlet
/ * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* A s a m p l e o f a s i m p l e J a v a s e r v l e t .
* M . L i u 1 / 8 / 0 2
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * /
i m p o r t j a v a . i o . * ;
i m p o r t j a v a . t e x t . * ;
i m p o r t j a v a . u t i l . * ;
i m p o r t j a v a x . s e r v l e t . * ;
i m p o r t j a v a x . s e r v l e t . h t t p . * ;
p u b l i c c l a s s M y S e r v l e t e x t e n d s H t t p S e r v l e t {
p u b l i c v o i d d o G e t ( H t t p S e r v l e t R e q u e s t r e q u e s t ,
H t t p S e r v l e t R e s p o n s e r e s p o n s e )
t h r o w s S e r v l e t E x c e p t i o n , I O E x c e p t i o n {
P r i n t W r i t e r o u t ;
S t r i n g t i t l e = " M y S e r v l e t O u t p u t " ;
/ / s e t c o n t e n t t y p e a n d o t h e r r e s p o n s e h e a d e r
/ / f i e l d s f i r s t
r e s p o n s e . s e t C o n t e n t T y p e ( " t e x t / h t m l " ) ;
/ / t h e n w r i t e t h e d a t a o f t h e r e s p o n s e
o u t = r e s p o n s e . g e t W r i t e r ( ) ;
o u t . p r i n t l n ( " < H T M L > < H E A D > < T I T L E > " ) ;
o u t . p r i n t l n ( t i t l e ) ;
o u t . p r i n t l n ( " < / T I T L E > < / H E A D > < B O D Y > " ) ;
o u t . p r i n t l n ( " < H 1 > " + t i t l e + " < / H 1 > " ) ;
o u t . p r i n t l n ( " < P > H e l l o W o r l d !" ) ;
o u t . p r i n t l n ( " < / B O D Y > < / H T M L > " ) ;
o u t . c l o s e ( ) ;
} / / e n d d o G e t
} / / e n d c l a s s

Concurrent Processing
On modern day operating systems, multiple
processes appear to be executing concurrently
on a machine by timesharing resources.
P r o c e s s e s
t im e
P 1
P 2
P 3
P 4
T im e s h a r in g o f a r e s o u r c e

Concurrent processing within a process
It is often useful for a process to have parallel threads of
execution, each of which timeshare the system
resources in much the same way as concurrent
processes.
p a r e n t p r o c e s s
c h ild p r o c e s s e s
A p a r e n t p r o c e s s m a y s p a w n c h i l d p r o c e s s e s .
a p r o c e s s
m a in t h r e a d
c h ild t h r e a d 1
c h ild t h r e a d 2
A p r o c e s s m a y s p a w n c h i l d t h r e a d s
C o n c u r r e n t p r o c e s s i n g w i t h i n a p r o c e s s

Java threads
The Java Virtual Machine allows an application to have multiple
threads of execution running concurrently.
Java provides a Thread class:
public class Thread
extends Object
implements Runnable
When a Java Virtual Machine starts up, there is usually a single
thread (which typically calls the method named main of some
designated class). The Java Virtual Machine continues to
execute threads until either of the following occurs:
The exit method of class Runtime has been called and the security
manager has permitted the exit operation to take place.
All threads have terminated, either by returning from the call to the
run method or by throwing an exception that propagates beyond
the run method.
Using a subclass of the Thread class
Using a class that implements the Runnable interface

Create a class that is a subclass of the Thread class
i m p o r t S o m e T h r e a d ;
p u b l i c c l a s s R u n T h r e a d s
{
{
S o m e T h r e a d p 1 = n e w S o m e T h r e a d ( 1 ) ;
p 1 . s t a r t ( ) ;
p 2 . s t a r t ( ) ;
p 3 . s t a r t ( ) ;
}
} / / e n d c l a s s R u n T h r e a d s
p u b l i c c l a s s S o m e T h r e a d e x t e n d s T h r e a d {
i n t m y I D ;
S o m e T h r e a d ( i n t i d ) {
t h i s . m y I D = i d ;
}
p u b l i c v o i d r u n ( ) {
i n t i ;
f o r ( i = 1 ; i < 1 1 ; i + + )
S y s t e m . o u t . p r i n t l n ( " T h r e a d " + m y I D + " : " + i ) ;
}
} / / e n d c l a s s S o m e T h r e a d
Declare a class to be a subclass of
Thread. This subclass should
override the run method of class
Thread. An instance of the subclass
can then be allocated and started:

Create a class that implements the Runnable interface
p u b l i c c l a s s R u n T h r e a d s 2
{
{
T h r e a d p 1 = n e w T h r e a d ( n e w S o m e T h r e a d 2 ( 1 ) ) ;
p 1 . s t a r t ( ) ;
p 2 . s t a r t ( ) ;
p 3 . s t a r t ( ) ;
}
}
c l a s s S o m e T h r e a d 2 i m p l e m e n t s R u n n a b l e {
i n t m y I D ;
S o m e T h r e a d 2 ( i n t i d ) {
t h i s . m y I D = i d ;
}
i n t i ;
f o r ( i = 1 ; i < 1 1 ; i + + )
S y s t e m . o u t . p r i n t l n ( " T h r e a d " + m y I D + " : " + i ) ;
}
} / / e n d c l a s s S o m e T h r e a d
The other way to create a thread is to declare a class that
implements the Runnable interface. That class then
implements the run method. An instance of the class can
then be allocated, passed as an argument when creating
Thread, and started.

Thread-safe Programming
When two threads independently access and
update the same data object, such as a
counter, as part of their code, the updating
needs to be synchronized. (See next slide.)
Because the threads are executed concurrently,
it is possible for one of the updates to be
overwritten by the other due to the sequencing
of the two sets of machine instructions
executed on behalf of the two threads.
To protect against the possibility, a
synchronized method can be used to provide
mutual exclusion.

Race Condition
fe tc h v a lu e in c o u n te r a n d lo a d in to a r e g is te r
in c r e m e n t v a lu e in r e g is te r
s to r e v a lu e in r e g is te r to c o u n te r
tim e
s to r e v a lu e in re g is te r to c o u n te r
in s tr u c tio n e x e c u te d in c o n c u r r e n t p r o c e s s o r th r e a d 1
in s t r u c t io n e x e c u te d in c o n c u r r e n t p r o c e s s o r th r e a d 2
T h i s e x e c u t i o n r e s u l t s i n t h e
v a l u e 2 i n t h e c o u n t e r
T h i s e x e c u t i o n r e s u l t s i n t h e
v a l u e 1 i n t h e c o u n t e r

Synchronized method in a thread
c l a s s S o m e T h r e a d 3 i m p l e m e n t s R u n n a b l e {
s t a t i c i n t c o u n t = 0 ;
S o m e T h r e a d 3 ( ) {
s u p e r ( ) ;
}
u p d a t e ( ) ;
}
s t a t i c p u b l i c s y n c h r o n i z e d v o i d u p d a t e ( ) {
i n t m y C o u n t = c o u n t ;
m y C o u n t + + ;
c o u n t = m y C o u n t ;
S y s t e m . o u t . p r i n t l n ( " c o u n t = " + c o u n t +
" ; t h r e a d c o u n t = " + T h r e a d . a c t i v e C o u n t ( ) ) ;
}
}

Network Basics

Network resources
Network resources are resources available to
the participants of a distributed computing
community.
Network resources include hardware such as
computers and equipment, and software such
as processes, email mailboxes, files, web
documents.
An important class of network resources is
network services such as the World Wide Web
and file transfer (FTP), which are provided by
specific processes running on computers.

Network standards and protocols
On public networks such as the Internet, it is
necessary for a common set of rules to be
specified for the exchange of data.
Such rules, called protocols, specify such
matters as the formatting and semantics of
data, flow control, error correction.
Software can share data over the network using
network software which supports a common set
of protocols.

Protocols
 In the context of communications, a protocol is a set of
rules that must be observed by the participants.
 In communications involving computers, protocols must
be formally defined and precisely implemented. For
each protocol, there must be rules that specify the
followings:
 How is the data exchanged encoded?
 How are events (sending , receiving) synchronized
so that the participants can send and receive in a
coordinated order?
 The specification of a protocol does not dictate how the
rules are to be implemented.

The network architecture
Network hardware transfers electronic
signals,which represent a bit stream, between two
devices.
Modern day network applications require an
application programming interface (API) which
masks the underlying complexities of data
transmission.
A layered network architecture allows the
functionalities needed to mask the complexities to
be provided incrementally, layer by layer.
Actual implementation of the functionalities may
not be clearly divided by layer.

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

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

Figure 3.12
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
The Transmission Control Protocol/Internet Protocol suite is a set of
network protocols which supports a four-layer network
architecture.
The Internet layer implements the Internet Protocol, which provides the
functionalities for allowing data to be transmitted between any two hosts
on the Internet.
The Transport layer delivers the transmitted data to a specific process
running on an Internet host.
The Application layer supports the programming interface used for building a
program.

Figure 3.14
The programmer's conceptual view of a TCP/IP Internet
IP
Application Application
TCP UDP
Socket programming in UDP and
TCP.

Identification of Network Resources
One of the key challenges in distributed
computing is the unique identification of
resources available on the network, such as e-
mail mailboxes, and web documents.
Addressing an Internet Host
Addressing a process running on a host
Email Addresses
Addressing web contents: URL

The Internet Topology
The internet consists of an hierarchy of
networks, interconnected via a network
backbone.
Each network has a unique network address.
Computers, or hosts, are connected to a
network. Each host has a unique ID within its
network.
Each process running on a host is associated
with zero or more ports. A port is a logical
entity for data transmission.

Network Basics
1. Addressing an Internet Host

Figure 3.15
Internet address structure, showing field sizes in bits
7 24
Class A: 0 NetworkID Host ID
14 16
Class B: 1 0 NetworkID Host ID
21 8
Class C: 1 1 0 NetworkID Host ID
28
Class D (multicast): 1 1 1 0 Multicast address
27
Class E (reserved): 1 1 1 1 unused0
Internet routing scheme developed in the 1970s. Class A addresses are the
largest, but there are few of them. Class Cs are the smallest, but they are
numerous. Classes D and E are also defined, but not used in normal
operation.

Figure 3.16
Decimal representation of Internet addresses
octet 1 octet 2 octet 3
Class A: 1 to 126
(0, 127
reserved)
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
Multicast address
0 to 255 0 to 255 1 to 254240 to 255Class E (reserved):
1.0.0.0 to
126.255.255.255
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

The Internet addressing scheme
1 0 n e t w o r k a d d r e s s h o s t p o r t io n
b y t e 0 b y t e 1 b y t e 2 b y t e 3
c l a s s B a d d r e s s
s u b n e t a d d r e s s lo c a l h o s t a d d r e s s
S u b d i v i d i n g t h e h o s t p o r t i o n o f a n I n t e r n e t a d d r e s s :
A c l a s s A / C a d d r e s s s p a c e c a n
a l s o b e s i m i l a r l y s u b d i v i d e d ..
W h i c h p o r t i o n o f t h e h o s t a d d r e s s
i s u s e d f o r t h e s u b n e t i d e n t i f i c a t i o n
i s d e t e r m i n e d b y a s u b n e t m a s k .

Example
Example:
Suppose the dotted-decimal notation for a particular Internet address
is129.65.24.50. The 32-bit binary expansion of the notation is as
follows:
Since the leading bit sequence is 10, the address is a Class B
address. Within the class, the network portion is identified by the
remaining bits in the first two bytes, that is, 1000000101000001,
and the host portion is the values in the last two bytes, or
0001100000110010. so that we would say that this particular
address is at network 129.65 and then at host address 24.50 on
that network.
1 2 9 . 6 5 . 2 4 . 5 0
1 0 0 0 0 0 0 1
0 1 0 0 0 0 0 1
0 0 0 1 1 0 0 0
0 0 1 1 0 0 1 0

The Internet Address Scheme
For human readability, Internet addresses are
written in a dotted decimal notation:
nnn.nnn.nnn.nnn, where each nnn group is a decimal
value in the range of 0 through 255
# Internet host table (found in /etc/hosts file)
127.0.0.1 localhost
129.65.242.5 falcon.csc.calpoly.edu falcon loghost
129.65.241.9 falcon-srv.csc.calpoly.edu falcon-srv
129.65.242.4 hornet.csc.calpoly.edu hornet
129.65.241.8 hornet-srv.csc.calpoly.edu hornet-srv
129.65.54.9 onion.csc.calpoly.edu onion
129.65.241.3 hercules.csc.calpoly.edu hercules

The Domain Name System (DNS)
For user friendliness, each Internet address is
mapped to a symbolic name, using the DNS, in the
format of:
<computer-name>.<subdomain hierarchy>.<organization>.<sector name>{.<country code>}
e.g., www.csc.calpoly.edu.us
05/13/14 54
r o o t
c o m
e d u g o v n e t o r g m i l
o r g a n i z a t i o n
...
...
h o s t n a m e
t o p - l e v e l d o m a i n
s u b d o m a i n
i n t h e U . S .
T o p - l e v e l d o m a i n n a m e h a s t o b e a p p l i e d f o r .
S u b d o m a i n h i e r a c h y a n d n a m e s a r e a s s i g n e d
b y t h e o r g a n i z a t i o n .
c o u n t r y c o d e

The Domain Name System
For network applications, a domain name
must be mapped to its corresponding Internet
address.
Processes known as domain name system
servers provide the mapping service, based
on a distributed database of the mapping
scheme.
The mapping service is offered by thousands
of DNS servers on the Internet, each
responsible for a portion of the name space,
called a zone. The servers that have access
to the DNS information (zone file) for a zone is
said to have authority for that zone.

Top-level Domain Names
.com: For commercial entities, which anyone, anywhere in the
world, can register.
.net : Originally designated for organizations directly involved
in Internet operations. It is increasingly being used by
businesses when the desired name under "com" is already
registered by another organization. Today anyone can register
a name in the Net domain.
.org: For miscellaneous organizations, including non-profits.
.edu: For four-year accredited institutions of higher learning.
.gov: For US Federal Government entities
.mil: For US military
Country Codes :For individual countries based on the
International Standards Organization. For example, ca for
Canada, and jp for Japan.

Example
Another example:
Given the address 224.0.0.1, one can expand it as
follows:
The binary prefix of 1110 signifies that this is class D, or
multicast, address. Data packets sent to this
address should therefore be delivered to the
multicast group 0000000000000000000000000001.
2 2 4 . 0 . 0 . 1
1 1 1 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1

Network Basics
2. Addressing a process running on a host

Addressing a process running on a host
...
p r o c e s s
p o r t
...h o s t A
h o s t B
T h e I n t e r n e t
E a c h h o s t h a s 6 5 5 3 6 p o r t s .

Well Known Ports
Each Internet host has 216
(65,535) logical ports.
Each port is identified by a number between 1
and 65535, and can be allocated to a particular
process.
Port numbers beween 1 and 1023 are reserved
for processes which provide well-known services
such as finger, FTP, HTTP, and email.

Well Known Ports
P r o t o c o l P o r t S e r v ic e
e c h o 7 IP C te s tin g
d a y tim e 1 3 p r o v id e s th e c u r r e n t d a te a n d tim e
ftp 2 1 file tr a n s fe r p r o to c o l
te ln e t 2 3 r e m o te , c o m m a n d - lin e te r m in a l s e s s io n
s m tp 2 5 s im p le m a il tr a n s fe r p r o to c o l
tim e 3 7 p r o v id e s a s ta n d a r d tim e
fin g e r 7 9 p r o v id e s in fo r m a tio n a b o u t a u s e r
h ttp 8 0 w e b s e r v e r
R M I R e g is tr y 1 0 9 9 re g is tr y fo r R e m o te M e th o d In v o c a tio n
s p e c ia l w e b s e r v e r 8 0 8 0
w e b s e r v e r w h ic h s u p p o r ts
s e r v le ts , J S P , o r A S P
A s s ig n m e n t o f s o m e w e ll- k n o w n p o r t s

Choose a port
For our programming exercises: when a port is
needed, choose a random number above the
well known ports: 1,024- 65,535.
If you are providing a network service for the
community, then arrange to have a port
assigned to and reserved for your service.

Network Basics
3. Addressing a Web
Document

The Uniform Resource Identifier (URI)
Resources to be shared on a network need to be
uniquely identifiable.
On the Internet, a URI is a character string which allows
a resource to be located.
There are two types of URIs:
URL (Uniform Resource Locator) points to a specific resource
at a specific location
URN (Uniform Resource Name) points to a specific resource at
a nonspecific location.
“A URN is like a person's name, while a URL is like their street
address. The URN defines something's identity, while the URL
provides a method for finding something. Essentially, "what" vs.
"where".” (from Wiki)

URL
A URL has the format of:
protocol://host address[:port]/directory path/file name#section
A s a m p l e U R L :
h t t p :/ / w w w . c s c . c a lp o ly . e d u :8 0 8 0 / ~ m liu / C S C 3 6 9 / h w . h t m l # h w 1
p r o t o c o l o f s e r v e r
h o s t n a m e
p o r t n u m b e r o f s e r v e r p r o c e s s
d ir e c t o r y p a t h
f ile n a m e
s e c t io n n a m e
O t h e r p r o t o c o l s t h a t c a n a p p e a r i n a U R L a r e :
f i l e
f t p
g o p h e r
n e w s
t e l n e t
W A I S

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