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HTTP_DNS

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The InternetandHTTP and DNS ExamplesThe Internet and an internetIPIPv4InternetApplications and Layered ArchitecturesTCP/IP Protocol Architecture ModelLayering AdvantagesLayering ExamplesHTTP ExampleRetrieving a document from the WebRetrieving a document from the WebDNS query and responseNetworks: HTTP and DNS 1The InternetThe InternetandandHTTP and DNS ExamplesHTTP and DNS ExamplesNetworks: HTTP and DNS 2The Internet and an internetThe Internet and an internet[LG&W pp.26[LG&W pp.26--28]28]internet :: internet :: involves the involves the interconnectioninterconnectionof multiple of multiple networks into a single large networks.networks into a single large networks.the “Internet” :: the “Internet” :: refers to the successor to ARPANET.refers to the successor to ARPANET.IP (the Internet Protocol) :: IP (the Internet Protocol) :: provides provides connectionless connectionless transfer of packets across an internet. transfer of packets across an internet.Networks: HTTP and DNS 3GGGGGnet 1net 2net 3net 4net 5G = gatewayGAn internetCopyright ©2000 The McGraw Hill CompaniesLeon-Garcia & Widjaja: Communication NetworksFigure 1.18Networks: HTTP and DNS 4IPIP••Currently provides Currently provides bestbest--effort serviceeffort service––packets may be lost (i.e., IP is unreliable).packets may be lost (i.e., IP is unreliable).••General design philosophyGeneral design philosophy––Keep internal operations simple by relegating Keep internal operations simple by relegating complex functions to the edge of the subnet.complex functions to the edge of the subnet.––IP can operate over IP can operate over any any networknetwork––allow IP to scale!!!allow IP to scale!!!––The endThe end--toto--end mechanisms are responsible for end mechanisms are responsible for recovery of packet losses and congestion recovery of packet losses and congestion control.control.Networks: HTTP and DNS 5IPv4IPv4Network ID Host ID4 bytes••Uses Uses hierarchical address spacehierarchical address spacewith with location information embedded in the location information embedded in the structure.structure.••IP address is usually expressed in IP address is usually expressed in dotteddotted--decimal notation decimal notation (e.g., 128.100.11.56)(e.g., 128.100.11.56)..Networks: HTTP and DNS 6InternetInternet••Provides a Provides a name spacename spaceto refer to machines to refer to machines connected to the Internet connected to the Internet (e.g. (e.g. chablis.cs.wpi.educhablis.cs.wpi.edu))..••The name space is hierarchical, but is only The name space is hierarchical, but is only administrative and not used in network routing administrative and not used in network routing operations.operations.••DNS (Domain Name Service) provides automatic DNS (Domain Name Service) provides automatic translation of names to addresses.translation of names to addresses.Networks: HTTP and DNS 7Applications and Layered Applications and Layered ArchitecturesArchitectures[LG&W pp.43[LG&W pp.43--49]49]••In the 1970’s vendor companies (IBM and In the 1970’s vendor companies (IBM and DEC) developed DEC) developed proprietary networksproprietary networkswith with the common feature of grouping the common feature of grouping communication functions into related and communication functions into related and manageable sets called manageable sets called layerslayers..network architecture :: network architecture :: a set of a set of protocolsprotocolsthat that specify how every layer is to function.specify how every layer is to function.Networks: HTTP and DNS 8TCP/IP Protocol Architecture ModelTCP/IP Protocol Architecture ModelDCC 6DCC 6th th Ed., W. Stallings Figure 1.9Ed., W. Stallings Figure 1.9Networks: HTTP and DNS 9Layering AdvantagesLayering Advantages••Simplified the design process.Simplified the design process.••Led to flexibility in modifying and Led to flexibility in modifying and developing the network.developing the network.••Accommodates incremental changes more Accommodates incremental changes more readily.readily.Networks: HTTP and DNS 10Layering ExamplesLayering ExamplesClient/server relationship ::Client/server relationship ::––Server process waits for incoming requests by Server process waits for incoming requests by listening to a listening to a portport..––Client process makes Client process makes requests requests as required.as required.––Server process provides Server process provides responsesresponsesto these to these requests.requests.––The server process usually runs in the The server process usually runs in the background as a background as a daemondaemon(e.g. (e.g. httpdhttpdis the is the server daemon for HTTP)server daemon for HTTP)..Networks: HTTP and DNS 11HTTP ExampleHTTP Example••HTTP (HTTP (HyperTextHyperTextTransfer Protocol) Transfer Protocol) specifies rules by which the client and the specifies rules by which the client and the server interact so as to retrieve a document.server interact so as to retrieve a document.••The protocol assumes the client and the The protocol assumes the client and the server can exchange messages directlyserver can exchange messages directly••The client software needs to set up a twoThe client software needs to set up a two--way connection prior to the HTTP request.way connection prior to the HTTP request.Networks: HTTP and DNS 12HTTP client/server interactionHTTPserverHTTPclientRequestResponseLeon-Garcia & Widjaja: Communication NetworksFigure 2.1Copyright ©2000 The McGraw Hill CompaniesNetworks: HTTP and DNS 13HTTPSMTPRTPTCPUDPIPNetworkInterface 1NetworkInterface 3NetworkInterface 2DNSLeon-Garcia & Widjaja: Communication NetworksFigure 2.12Copyright ©2000 The McGraw Hill CompaniesNetworks: HTTP and DNS 14HTTPserverHTTPclientTCPTCPGET 80, # #, 80 STATUSEphemeralPort #Port 80Figure 2.2Leon-Garcia & Widjaja: Communication NetworksCopyright ©2000 The McGraw Hill CompaniesThe user clicks on a link to indicate which document is to be retrieved.1.The browser must determine the address that contains the document. It does this by sending a query to its local name server.2.Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections.3.4.The browser runs a client version of HTTP, which issues a request specifying both


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