1 mcgraw-hill/irwin copyright © 2004, the mcgraw-hill companies, inc. all rights reserved. wykład...

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McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved.

Wykład 8. Sieciocentrycznosc

procesów informacyjnych

Wykładowca:

Prof. Anatoly Sachenko

Procesy informacyjne w zarządzaniu

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Lecture frame

IntroductionInterprocess Communication 1 - peer-to-peer modelModel of Open System InterconnectionNetworks classification and topologies ProtocolsCombining networks EthernetInterprocess Communication 2Distributed 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): Local Area Networks Metropolitan Area Network Wide Area Network

Network classification (design): Open network. Closed (proprietary) network.

Network Classification (topology):

RingBusTreeStar

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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 examplesTokenRing 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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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 characteristicsFor 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

Radio repeater

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Combining networks

SwitchesSwitched network

Repeaters, hubs and switches unites computers into ONE network.

Group of networks is known as internet.

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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

ROUTERS

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 Communication2

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

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 as chess or 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

Examples: Java NetBeans Enterprise Microsoft .Net Framework

Main concept:

One task is separated among multiple PCs

1 mcgraw-hill/irwin copyright © 2004, the mcgraw-hill companies, inc. all rights reserved. wykład...

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