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1 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Wykład 8. Sieciocentrycznosc procesów informacyjnych Wykładowca:

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Presentation on theme: "1 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Wykład 8. Sieciocentrycznosc procesów informacyjnych Wykładowca:"— Presentation transcript:

1 1 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

2 2 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Lecture frame  Introduction  Interprocess Communication 1 - peer-to-peer model  Model of Open System Interconnection  Networks classification and topologies  Protocols  Combining networks  Ethernet  Interprocess Communication 2  Distributed Systems

3 3 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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.

4 4 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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.

5 5 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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)

6 6 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved.

7 7 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved.

8 8 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved.

9 9 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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): RingBus Tree Star

10 10 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Network classification and topologies (cont-d)

11 11 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

12 12 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Protocols Protocol - rules by which network activities are conducted. Protocol examples TokenRing example CSMA/CD

13 13 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

14 14 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Figure 5.2 Communication over a ring network

15 15 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

16 16 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Figure 5.3 Communication over a bus network

17 17 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

18 18 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Figure 5.4 Building a large bus network from smaller ones

19 19 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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)

20 20 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Combining networks Bridges Bridged network

21 21 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

22 22 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Combining networks Repeater Cell phone repeater Radio repeater

23 23 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Combining networks Switches Switched network Repeaters, hubs and switches unites computers into ONE network. Group of networks is known as internet.

24 24 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

25 25 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Figure 5.5 A router connecting a bus network with a star network to form an internet

26 26 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Combining networks ROUTERSROUTERS Routers' usage

27 27 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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.

28 28 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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 Peer-to-peer architecture

29 29 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

30 30 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

31 31 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

32 32 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Figure 5.6 The client/server model compared to the peer-to-peer model

33 33 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

34 34 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. 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

35 35 McGraw-Hill/Irwin Copyright © 2004, The McGraw-Hill Companies, Inc. All rights reserved. Distributed systems Examples:  Java NetBeans Enterprise  Microsoft.Net Framework Main concept: One task is separated among multiple PCs


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