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Procesy informacyjne w
zarządzaniu
Wykład 8.
Sieciocentrycznosc
procesów informacyjnych
Wykładowca:
McGraw-Hill/Irwin
Prof. Anatoly Sachenko
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2
Lecture frame
 Introduction
 Interprocess
Communication 1 - peer-to-peer model
 Model of Open System Interconnection
 Networks classification and topologies
 Protocols
 Combining networks
 Ethernet
Interprocess
 Distributed
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Communication 2
Systems
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0. Sieć Komputerowa Przedsiębiorstwa


Biznes staje się przedsięwzięciem połączonym
przez sieć komputerową. Poprzez ich stosowanie
(sieci) firmy mogą:

Współpracować bardziej kreatywnie

Kierować ich działaniami biznesowymi i
bogactwami organizacyjnymi bardziej
efektywnie

Pomyślnie konkurować w dzisiejszej, szybko
zmieniającej się gospodarce globalnej
Dziś wiele organizacji nie mogłoby przetrwać bez
różnorodności połączeń sieci komputerowych do
obsługi procesów informacyjnych i potrzeb
komunikacji.
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Introduction




The need to share the
information.
Data exchange and
resource sharing.
From simple systems to
sophiscated wide network
infrastructure.
Network software evolve into
network wide OS.
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Interprocess Communication - peer-to-peer model
 The
peer-to-peer model is also a popular means of sharing files
such as music recordings and motion pictures via the Internet
 You might often read or hear the term peer-to-peer network,
which is an example of how misuse of terminology can evolve
when technical terms are adopted by the nontechnical
community
 The term peer-to-peer refers to a system by which two
processes communicate over a network (or internet)
 A process might use the peer-to-peer model to communicate
with another process and later use the client/server model to
communicate with another process over the same network
 peer-to-peer is base for a model of Open System
Interconnection(OSI) – a standard for Computer Networks
(see next slide)
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Network classification and topologies

Network classification (territory):




Network classification (design):



Local Area Networks
Metropolitan Area Network
Wide Area Network
Open network.
Closed (proprietary) network.
Network Classification (topology):
Star
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Network classification and topologies (cont-d)
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Network classification and topologies (cont-d)
 Today,
the bus topology, having been popularized under the
standards known as Ethernet, is probably the most popular
network topology
 It is common to construct a bus network by running links
from each computer to a central location where they are
connected to a device called a hub
 A point to emphasize is that the connections between machines
in a network do not need to be physical
 Wireless networks, using radio broadcast technology, are
becoming quite common
 In particular, the hub in many of today's bus networks is
essentially a radio relay station
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Protocols

Protocol - rules by which network
activities are conducted.
Protocol examples
TokenRing
example
CSMA/CD
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Protocols (cont-d)
Let’s consider the problem of coordinating the transmission of messages
among computers in a network
 Without rules governing this communication, all the computers might insist
on transmitting messages at the same time or might fail to relay messages
 One approach to solving this problem is the token ring protocol (IBM in the
1970s) and continues to be a popular protocol in the ring topology
 In this protocol, all the machines in the network transmit messages in only
one common direction (see a previous slide and Fig. 5.2 on next slide)
 When a message reaches its destination, the destination machine keeps a
copy of it and forwards a copy on around the ring
 When the forwarded copy reaches the originating computer, that machine
knows that the message must have reached its destination and removes the
message from the ring
 A unique bit pattern, called a token, is passed around the ring
 Possession of this token gives a machine the authority to transmit its own
message
 without the token, a machine is only allowed to forward messages

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Figure 5.2 Communication over a ring
network
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Protocols (cont-d)
Another protocol for coordinating message transmission is used in bus
topology
 networks that are based on the Ethernet protocol collection
 In an Ethernet system, the right to transmit messages is controlled by the
protocol known as Carrier Sense, Multiple Access with Collision Detection
(CSMA/CD)
 This protocol dictates that each message be broadcast to all the machines
on the bus (Fig. 5.3)
 Each machine monitors all the messages but keeps only those addressed to
itself
 To transmit a message, a machine waits until the bus is silent, and at this
time it begins transmitting while continuing to monitor the bus
 If another machine also begins transmitting, both machines detect the clash
and pause for a brief random period of time before trying to transmit again
 The result is a system similar to that used by a small group of people in a
conversation
 If two people start to talk at once, they both stop

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Figure 5.3 Communication over a bus
network
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Combining Networks
 Sometimes
it is necessary to connect existing networks to form
an extended communication system
 This can be done by connecting the networks to form a larger
version of the same "type" of network
 For example, in the case of bus networks based on the
Ethernet protocols, it is often possible to connect the buses to
form a single large bus
 This is done by means of different devices known as repeaters,
bridges, and switches
 the distinctions of which are subtle yet informative
 The simplest of these is the repeater that connects two buses to
form a single long bus (Fig. 5.4a)
 The repeater simply passes signals back and forth between the
two original buses (usually with some form of amplification)
without considering the meaning
of the signals
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Figure 5.4 Building a large bus network
from smaller ones
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Combining Networks
(cont-d)
A
bridge is similar to, but more complex than, a
repeater
 Like a repeater, it connects two buses, but it does not
necessarily pass all messages across the connection
 Instead, it looks at the destination address that
accompanies each message and forwards a message
across the connection only when that message is
destined for a computer on the other side
 Thus, two machines residing on the same side of a
bridge can exchange messages without interfering
with communication taking place on the other side
 A bridge produces a more efficient system than that
produced by a repeater (see examples on next slide)
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Combining networks
Bridges
Bridged network
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Combining Networks
(cont-d)
 It
is important to note that when networks are
connected via repeaters, bridges, and switches, the
result is a single large network (see next two slides)
 Sometimes, however the networks to be connected
have incompatible characteristics
 For instance, the characteristics of a ring network
using the token ring protocol are not readily
compatible with an Ethernet bus network using
CSMA/CD
 In these cases the networks must be connected in a
manner that builds a network of networks, known as
an internet,
 in which the original networks maintain their
individuality and continue to function as
independent networks
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Combining networks
Repeater
Cell phone
repeater
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Radio
repeater
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Combining networks
Switches
Switched network

Repeaters, hubs and switches unites computers into ONE network.

Group of networks is known as internet.
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Combining Networks
(cont-d)
 The
connection between two networks to form an internet is
handled by a machine known as a router
 A router is a computer belonging to both networks that
forwards messages in one network into the other network (Fig.
5.5)
 The task of a router is significantly greater than that of
repeaters, bridges, and switches
 because a router must convert between the idiosyncrasies of
the two original networks
 For example, when transferring a message from a network
using the token ring protocol to a network using CSMA/CD,
 a router must receive the message using one protocol and
then transmit it to the other network using another protocol
 Router constructions and router usage are illustrated on a
slide 27
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Figure 5.5 A router connecting a bus
network with a star network to form an
internet
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Combining networks
R
O
U
T
E
R
S
Routers' usage
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Ethernet


Ethernet is a set of standards for implementing a LAN with a bus
topology. Its name is derived from the original Ethernet design in
which machines were connected by a coaxial cable called the ether.
Originally developed in the 1970s and now standardized by IEEE as a
part of the IEEE 802 family of standards, Ethernet is the most common
method of networking PCs.
Today there are actually several versions of Ethernet, reflecting
advances in technology and higher transfer rates. All, however, share
common traits that characterize the Ethernet family. Among these are
the format in which data are packaged for transmission, the use of
Manchester encoding (a method of representing 0s and 1s in which a 0
is represented by a descending signal and a 1 is represented by an
ascending signal) for the actual transmission of bits, and the use of
CSMA/CD for controlling the right to transmit.
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Interprocess Communication
2

Interprocess Communication - communication
between processes that are executing on the different
computers within a network (or even executing on
the same machine via time sharing)
Client/server
architecture
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Peer-to-peer
architecture
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Interprocess Communication 2 (cont-d)
A
popular convention used for interprocess communication is
the client/server model
 This model defines the basic roles played by the processes as
either a client,
 which makes requests of other processes, or a server,
 which satisfies the requests made by clients
 An early application of the client/server model appeared in
networks connecting all the computers in a cluster of offices
 In this situation, a single, high-quality printer was attached to
the network where it was available to all the machines in the
Network
 In this case the printer played the role of a server (often called
a print server), and the other machines were programmed to
play the role of clients that sent print requests to the print
server
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Interprocess Communication 2(cont-d)
 Another
early application of the client/server model
was used to reduce the cost of disk storage while also
removing the need for duplicate copies of records
 Here one machine in a network was equipped with a
high-capacity mass storage system ( a magnetic disk)
that contained all of an organization's records
 Other machines on the network then requested access
to the records as they needed them
 Thus the machine that actually contained the records
played the role of a server (called a file server),
 and the other machines played the role of clients
that requested access to the files that were stored at
the file server
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Interprocess Communication 2 (cont-d)
 Today
the client/server model is used extensively in network
applications
 However, the client/server model is not the only means of
interprocess communication
 Another model is the peer-to-peer (often abbreviated P2P)
model,
 whose properties provide insightful contrasts to the
client/server model
 Whereas the client/server model involves one process (the
server) communicating with numerous others (clients)-Fig.
5.6a,
 the peer-to-peer model involves two processes
communicating as equals -Fig. 5.6b
 For example, applications of the peer-to-peer model include
instant messaging in which two people carryon a written
conversation over the Internet as well as situations in which
people play games such asCopyright
chess© 2004,
or The
checkers
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Figure 5.6 The client/server model
compared to the peer-to-peer model
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Distributed Systems
 With
the success of networking technology, interaction
between computers via networks has become common and
multifaceted
 Many modern SW systems, such as global information
retrieval systems, company-wide accounting and inventory
systems, computer games are designed as distributed systems,
 meaning that they consist of software units that execute as
processes on different computers
 We can envision these processes as guests at the various
machines in which they reside-an analogy that leads to the
computers in a network being called hosts
 That is, a host is a computer at which processes reside or, in a
more dynamic context, might take up residence
 Examples of distributed systems are illustrated on next slide
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Distributed Systems
 With
the success of networking technology, interaction
between computers via networks has become common and
multifaceted
 Many modern SW systems, such as global information
retrieval systems, company-wide accounting and inventory
systems, computer games are designed as distributed systems,
 meaning that they consist of software units that execute as
processes on different computers
 We can envision these processes as guests at the various
machines in which they reside-an analogy that leads to the
computers in a network being called hosts
 That is, a host is a computer at which processes reside or, in a
more dynamic context, might take up residence
 Examples of distributed systems are illustrated on next slide
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Distributed systems

Distributed systems

Main concept:
One task is
separated
among multiple
PCs

Examples:

Java NetBeans Enterprise

Microsoft .Net Framework
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