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USC Upstate SIMS 415 - NetworkSoftware

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Network SoftwareOverviewProtocol Hierarchies - layerProtocol Hierarchies - protocolProtocol Hierarchies - peersProtocol HierarchiesProtocol Hierarchies - interfaceSlide 8Protocol Hierarchies - analogyPowerPoint PresentationSlide 11Protocol Hierarchies - ExampleSlide 13Slide 14Slide 15Design Issues for the LayersSlide 17Slide 18Slide 19Slide 20Connection-Oriented and Connectionless ServicesSlide 22Slide 23Slide 24Slide 25Network SoftwareNetwork Software22OverviewOverviewProtocol HierarchiesProtocol HierarchiesDesign Issues for the LayersDesign Issues for the LayersConnection-Oriented and Connectionless Connection-Oriented and Connectionless ServicesServices33Protocol Hierarchies - layerProtocol Hierarchies - layerTo reduce their design complexity, most networks To reduce their design complexity, most networks are organized as series of are organized as series of layerslayers or or levelslevels, each , each one built upon the one below it. one built upon the one below it. The number of layers, the name of each layer, the The number of layers, the name of each layer, the contents of each layer, and the function of each contents of each layer, and the function of each layer differ from network to network. layer differ from network to network. However, in all networks, the purpose of each layer However, in all networks, the purpose of each layer is to offer certain services to the higher layers, is to offer certain services to the higher layers, shielding those layers from the details of how the shielding those layers from the details of how the offered services are actually implemented.offered services are actually implemented.44Protocol Hierarchies - protocolProtocol Hierarchies - protocolLayer Layer nn on one machine on one machine carries on a carries on a conversationconversation with with layer layer nn on another machine on another machine. . The rules and conventions used in this conversation are The rules and conventions used in this conversation are collectively known as the layer collectively known as the layer nn protocolprotocol. . Basically, a protocol is an agreement between the Basically, a protocol is an agreement between the communicating parties on how communication is to proceed. communicating parties on how communication is to proceed. As an analogy, when a woman is introduced to a man, she As an analogy, when a woman is introduced to a man, she may choose to stick out her hand. He, in turn, may decide to may choose to stick out her hand. He, in turn, may decide to either shake it or kiss it, depending, for example, on whether either shake it or kiss it, depending, for example, on whether she is an American lawyer at a business meeting or a she is an American lawyer at a business meeting or a European princess at a formal ball. Violating the protocol will European princess at a formal ball. Violating the protocol will make communication more difficult, if not impossible.make communication more difficult, if not impossible.55Protocol Hierarchies - peersProtocol Hierarchies - peersA five-layer A five-layer network is network is illustrated in illustrated in Fig. 1. The Fig. 1. The entities entities comprising the comprising the corresponding corresponding layers on layers on different different machines are machines are called called peerspeers. In . In other words, it other words, it is the peers that is the peers that communicate communicate using the using the protocol.protocol.Fig. 1. Layers, protocols, and interfaces66Protocol HierarchiesProtocol HierarchiesIn reality, no data are actually transferred from In reality, no data are actually transferred from layer layer nn on one machine to layer on one machine to layer nn on another on another machine. Instead, machine. Instead, each layer passes dataeach layer passes data and and control information control information to the layer immediately to the layer immediately below itbelow it, until the lowest layer is reached., until the lowest layer is reached.Below layer 1 is the physical medium through Below layer 1 is the physical medium through which actual communication occurs. In Fig. 1. which actual communication occurs. In Fig. 1. virtual communication is shown by dotted lines virtual communication is shown by dotted lines and physical communication by solid lines. and physical communication by solid lines.77Protocol Hierarchies - interfaceProtocol Hierarchies - interfaceBetween each pair of adjacent layers there is an Between each pair of adjacent layers there is an interfaceinterface. . The interface defines which primitive operations and The interface defines which primitive operations and services the lower layer offers to the upper one. services the lower layer offers to the upper one. When network designers decide how many layers to include When network designers decide how many layers to include in a network and what each one should do, one of the most in a network and what each one should do, one of the most important considerations is defining clean interfaces important considerations is defining clean interfaces between the layers. (each layer performs a specific between the layers. (each layer performs a specific collection of well-understood functions)collection of well-understood functions)In addition, clean-cut interfaces also make it simpler to In addition, clean-cut interfaces also make it simpler to replace the implementation of one layer with a completely replace the implementation of one layer with a completely different implementation without disrupting the rest of the different implementation without disrupting the rest of the layers. (ex. all the telephone lines are replaced by satellite layers. (ex. all the telephone lines are replaced by satellite channels) as all that is required of the implementation is that channels) as all that is required of the implementation is that it offers the exact same set of services to its upstairs it offers the exact same set of services to its upstairs neighbor layer as the old implementation did. neighbor layer as the old implementation did.88Protocol HierarchiesProtocol HierarchiesA set of layers and protocols is called a A set of layers and protocols is called a network network architecturearchitecture. . The specification of an architecture must contain enough The specification of an architecture must contain enough information to allow an implementer to write the program information to allow an implementer to write the program (or build


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