Http overview Http: hypertext transfer protocol o Web's application layer PC running A Http request protocol Exple o client/server model e o client: browser that requests, receives Se erver displays"Web objects running o server: Web server Apache Web server sends ob jects in response to requests Mac running g Http 1.0: Rfc 1945 Navigator 0 Http 11: rfc 2068 2: Application Layer 16
2: Application Layer 16 HTTP overview HTTP: hypertext transfer protocol Web’s application layer protocol client/server model client: browser that requests, receives, “displays” Web objects server: Web server sends objects in response to requests HTTP 1.0: RFC 1945 HTTP 1.1: RFC 2068 PC running Explorer Server running Apache Web server Mac running Navigator
Http overview(continued Uses tcp: Http is"stateless o client initiates TCP o server maintains no connection(creates socket) information about to server, port 80 past client requests 口 server accepts TCP connection from client aside Protocols that maintain o htTp messagesapplication state"are complex layer profocol messages exchanged between browser o past history(state)must be maintained (htTp client)and Web server(httpserver o if server/client crashes 了 TCP connection c|osed their views of state "may be inconsistent must be reconcile d 2: Application Layer 17
2: Application Layer 17 HTTP overview (continued) Uses TCP: client initiates TCP connection (creates socket) to server, port 80 server accepts TCP connection from client HTTP messages (applicationlayer protocol messages) exchanged between browser (HTTP client) and Web server (HTTP server) TCP connection closed HTTP is “stateless” server maintains no information about past client requests Protocols that maintain “state” are complex! past history (state) must be maintained if server/client crashes, their views of “state” may be inconsistent, must be reconciled aside
Http connections Nonpersistent Http Persistent Http D At most one object is o Multiple objects can sent over a tcp be sent over single connection TCP connection 0 Http/1.0 uses between client and nonpersistenthttp server 口HTTP/11uses persistent connections in default mode 2: Application Layer 18
2: Application Layer 18 HTTP connections Nonpersistent HTTP At most one object is sent over a TCP connection. HTTP/1.0 uses nonpersistent HTTP Persistent HTTP Multiple objects can be sent over single TCP connection between client and server. HTTP/1.1 uses persistent connections in default mode
Nonpersistenthttp contains text Suppose user enters URL references to 10 Www.SomeSchool. edu/some Department/home. index jpeg images 1a.httpclientinitiatesTcp connectiontohttpserver 1b. Http server at host rocess)at www.someschool.eduonport80 www.someschool.eduwaiting for tCp connection at port 80 accepts"connection, notifying client 2. Http client sends htTp request message(containing URL into TCP connection 3. Http server receives request socket Message indicates message forms response that client wants object message containing requested someDepartment/home. index object and sends message nto its socket time 2: Application Layer 19
2: Application Layer 19 Nonpersistent HTTP Suppose user enters URL www.someSchool.edu/someDepartment/home.index 1a. HTTP client initiates TCP connection to HTTP server (process) at www.someSchool.edu on port 80 2. HTTP client sends HTTP request message (containing URL) into TCP connection socket. Message indicates that client wants object someDepartment/home.index 1b. HTTP server at host www.someSchool.edu waiting for TCP connection at port 80. “accepts” connection, notifying client 3. HTTP server receives request message, forms response message containing requested object, and sends message into its socket time (contains text, references to 10 jpeg images)
Nonpersistent Http(cOnt. ) 4. Http server closes Tcp connection 5.httpclientreceivesresponse message containing html file displays html. parsing htm file, finds 10 referenced jpeg obiects time 6 Steps 1-5 re peated for each of 10 jpeg objects 2: Application Layer 20
2: Application Layer 20 Nonpersistent HTTP (cont.) 5. HTTP client receives response message containing html file, displays html. Parsing html file, finds 10 referenced jpeg objects 6. Steps 1-5 repeated for each of 10 jpeg objects 4. HTTP server closes TCP connection. time