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Computer network
Computer networks allow interconnected computers to work together. They can be used for business applications using a client-server model, home networking, by mobile users, and raise social issues. The document discusses different types of network hardware including local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), wireless networks, home networks, and internetworks. It also covers network software including protocol hierarchies, connection-oriented vs. connectionless services, service primitives, and the relationship between services and protocols.
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Computer network
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- 2. Computer Networks The oldmodel of a single computer serving all of the organization's computational needs has been replaced by one in which a large number of separate but interconnected computers do the job. These systems are called computer networks.
- 3. Uses of ComputerNetworks • Business Applications • Home Applications • Mobile Users • Social Issues
- 4. Business Applications ofNetworks A network with two clients and one server. This whole arrangement is called the client-server model. It is widely used and forms the basis of much network usage. It is applicable when the client and server are both in the same building (e.g., belong to the same company), but also when they are far apart.
- 5. Business Applications ofNetworks (2) The client-server model involves requests and replies.
- 6. Home Network Applications Someof the more popular uses of the Internet for home users are as follows: 1. Access to remote information. 2. Person-to-person communication. 3. Interactive entertainment. 4. Electronic commerce.
- 7. Home Network Applications(2) In peer-to-peer system there are no fixed clients and servers.
- 8. Mobile Users Mobile computers,such as notebook computers and personal digital assistants (PDAs), are one of the fastest growing segments of the computer industry. Many owners of these computers have desktop machines back at the office and want to be connected to their home base even when away from home
- 9. Mobile Users (2) Combinationsof wireless networks and mobile computing.
- 10. Social Issues The widespreadintroduction of networking has introduced new social, ethical, and political problems. A lot of these problems could be solved if the computer industry took computer security seriously. If all messages were encrypted and authenticated, it would be harder to commit mischief.
- 11. Network Hardware • LocalArea Networks (LANs) • Metropolitan Area Networks (MANs) • Wide Area Networks (WANs) • Wireless Networks • Home Networks • Internetworks
- 12. Broadcast Networks Types oftransmission technology Broadcast links: Broadcast networks have a single communication channel that is shared by all the machines on the network. Point-to-point links: Point-to-point networks consist of many connections between individual pairs of machines.
- 13. Broadcast Networks (2) Classificationof interconnected processors by scale.
- 14. Local Area Networks Two broadcast networks (a) Bus (b) Ring In a bus (i.e., a linear cable) network, at any instant at most one machine is the master and is allowed to transmit. All other machines are required to refrain from sending. In a ring, each bit propagates around on its own, not waiting for the rest of the packet to which it belongs. Typically, each bit circumnavigates the entire ring in the time it takes to transmit a few bits, often before the complete packet has even been transmitted. Local area networks, generally called LANs, are privately-owned networks within a single building or campus of up to a few kilometers in size.
- 15. Metropolitan Area Networks Ametropolitan area network based on cable TV. A metropolitan area network, or MAN, covers a city. The best-known example of a MAN is the cable television network available in many cities.
- 16. Wide Area Networks Relationbetween hosts on LANs and the subnet. A wide area network, or WAN, spans a large geographical area, often a country or continent.
- 17. Wide Area Networks(2) A stream of packets from sender to receiver.
- 18. Wireless Networks Categories ofwireless networks: System interconnection Wireless LANs Wireless WANs
- 19. Wireless Networks (2) (a)Bluetooth configuration (b) Wireless LAN
- 20. Wireless Networks (3) (a)Individual mobile computers (b) A flying LAN
- 21. Home Network Categories Someof the more obvious categories (with examples) are as follows: Computers (desktop PC, PDA, shared peripherals Entertainment (TV, DVD, VCR, camera, stereo, MP3) Telecomm (telephone, cell phone, intercom, fax) Appliances (microwave, fridge, clock, furnace, airco) Telemetry (utility meter, burglar alarm, babycam). The fundamental idea is that in the future most homes will be set up for networking. Every device in the home will be capable of communicating with every other device, and all of them will be accessible over the Internet.
- 22. Network Software Protocol Hierarchies DesignIssues for the Layers Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to Protocols
- 23. Architecture of theInternet Overview of the Internet
- 24. Protocol Hierarchies To reducetheir design complexity, most networks are organized as a stack of layers or levels, each one built upon the one below it. The purpose of each layer is to offer certain services to the higher layers, shielding those layers from the details of how the offered services are actually implemented. A protocol is an agreement between the communicating parties on how communication is to proceed. The interface defines which primitive operations and services the lower layer makes available to the upper one.
- 25. Protocol Hierarchies (2) Layers,protocols, and interfaces.
- 26. Protocol Hierarchies (3) Thephilosopher-translator-secretary architecture.
- 27. Protocol Hierarchies (4) Exampleinformation flow supporting virtual communication in layer 5.
- 28. Protocol Hierarchies (5) Amessage, M, is produced by an application process running in layer 5 and given to layer 4 for transmission. Layer 4 puts a header in front of the message to identify the message and passes the result to layer 3. Layer 3 must break up the incoming messages into smaller units, packets, prepending a layer 3 header to each packet. In this example, M is split into two parts, M1and M2. Layer 3 decides which of the outgoing lines to use and passes the packets to layer 2. Layer 2 adds not only a header to each piece, but also a trailer, and gives the resulting unit to layer 1 for physical transmission. At the receiving machine the message moves upward, from layer to layer, with headers being stripped off as it progresses.
- 29. Design Issues forthe Layers Addressing consequence of having multiple destinations Error Control The receiver should be able to inform sender which data was received correctly Flow Control Keep sender from swamping slow receiver with data Keep the sender from swamping with data slow networks Multiplexing Use same communication channel for multiple, unrelated conversations Routing When multiple paths between source and destination, one path must be chosen
- 30. Connection-Oriented and Connectionless Services Connection-oriented Connection-orientedservices includes the steps of setting up a call from one computer to another, transmitting/receiving data, and then releasing the call, just like a voice phone call. However, the network connecting the computers is a packet switched network, unlike the phone system's circuit switched network. Connection-oriented communication is done in one of two ways over a packet switched network: with and without virtual circuits. Connectionless: Connectionless services is just packet switching where no call establishment and release occur. A message is broken into packets, and each packet is transferred separately. Moreover, the packets can travel different route to the destination since there is no connection. Connectionless service is typically provided by the UDP (User Datagram Protocol), which we will examine later. The packets transferred using UDP are also called data grams. With Virtual circuit: A virtual circuit is one which appears to the user as equivalent to a dedicated point-point service but is maintained by computers. Without virtual circuits: This is what TCP does in the Internet. The only two machines in the Internet that are aware a connection is established are the two computers at the endpoints. The Internet itself--its routers and links--have no information about the presence of a connection between the two computers.
- 31. Difference: Connection-Oriented andConnectionless Services Feature Connectionless Connection-oriented How is data sent? one packet at a time as continuous stream of packets Do packets follow same route? no virtual circuit: yes without virtual circuit: no Are resources reserved in network? no virtual circuit: yes without virtual circuit: no Is connection establishment done? no yes Is state information stored at network nodes? no virtual circuit: yes without virtual circuit: no What is impact of node/switch crash? only packets at node are lost all virtual circuits through node fail What addressing information is needed on each packet? full source and destination address virtual circuit: a virtual circuit number without virtual circuit: full source and destination address
- 32. Service Primitives Five serviceprimitives for implementing a simple connection- oriented service.
- 33. Service Primitives (2) Packetssent in a simple client-server interaction on a connection- oriented network.
- 34. Services to ProtocolsRelationship The relationship between a service and a protocol A protocol, in contrast, is a set of rules governing the format and meaning of the packets, or messages that are exchanged by the peer entities within a layer. A service is like an abstract data type or an object in an object-oriented language. It defines operations that can be performed on an object but does not specify how these operations are implemented. A protocol relates to the implementation of the service and as such is not visible to the user of the service.
- 35. Reference Models The OSIReference Model The TCP/IP Reference Model A Comparison of OSI and TCP/IP A Critique of the OSI Model and Protocols A Critique of the TCP/IP Reference Model
- 36. The OSI ReferenceModel
- 37. The TCP/IP referencemodel.
- 38. The TCP/IP referencemodel (2) Protocols and networks in the TCP/IP model initially. On top of the transport layer is the application layer. It contains all the higher-level protocols. The early ones included virtual terminal (TELNET), file transfer (FTP), and electronic mail
- 39. Comparison between OSIand TCP/IP Reference Models OSI 1)It has 7 layers 2)Transport layer guarantees delivery of packets 3)Separate presentation layer 4)Separate session layer 5)Network layer provides both connectionless and connection oriented services 6)It defines the services, interfaces and protocols very clearly and makes a clear distinction between them 7)It has a problem of protocol filtering into a model TCP/IP 1)Has 4 layers 2)Transport layer does not guarantees delivery of packets 3)No presentation layer, characteristics are provided by application layer 4)No session layer, characteristics are provided by transport layer 5)Network layer provides only connection less services 6)It does not clearly distinguishes between service interface and protocols 7)The model does not fit any protocol stack.
- 40. A Critique ofthe OSI Model and Protocols Why OSI did not take over the world: Bad timing Bad technology Bad implementations Bad politics
- 41. A Critique ofthe TCP/IP Reference Model Problems: Service, interface, and protocol not distinguished Not a general model Host-to-network “layer” not really a layer No mention of physical and data link layers Minor protocols deeply entrenched, hard to replace
- 42. EXAMPLE NETWORKS: Internet The ARPANET NFSNET Connection-OrientedNetwork X.25 ATM Ethernet Wireless LANs: 802.11
- 43. ATM (Asynchronous TransferMode) ATM virtual circuits ATM virtual circuits
- 44. ATM Virtual Circuits(2) An ATM cell
- 45. The ATM ReferenceModel The ATM reference model
- 46. The ATM ReferenceModel (2) The ATM layers and sublayers and their functions.
- 47. References Computer Networks,Tanenbaum, 4thEdition. Data Communications and Networking, Behrouz A. Forouzan, 4th Edition. Computer Networks, A Systems Approach, Larry L. Peterson & Bruce S. Davie, 4th Edition.