Network Applications and the Web
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1 Network Applications and the Web Antonio Carzaniga Faculty of Informatics Università della Svizzera italiana October 4, 2017
2 Outline General concepts for network applications Client/server architecture The world-wide web Basics of the HTTP protocol
3 Examples of Network Applications
4 The world-wide web Examples of Network Applications
5 Examples of Network Applications The world-wide web Electronic mail
6 Examples of Network Applications The world-wide web Electronic mail Instant messaging
7 Examples of Network Applications The world-wide web Electronic mail Instant messaging Peer-to-peer file sharing
8 Examples of Network Applications The world-wide web Electronic mail Instant messaging Peer-to-peer file sharing Video streaming
9 Examples of Network Applications The world-wide web Electronic mail Instant messaging Peer-to-peer file sharing Video streaming Multi-user networked games
10 Examples of Network Applications The world-wide web Electronic mail Instant messaging Peer-to-peer file sharing Video streaming Multi-user networked games... Remote login...
11 Examples of Network Applications The world-wide web Electronic mail Instant messaging Peer-to-peer file sharing Video streaming Multi-user networked games... Remote login... Remote on-line banking Network telephony...
12 End System Applications Internet applications are end system applications Internet
13 End System Applications Internet applications are end system applications Internet
14 End System Applications Internet applications are end system applications Internet
15 Aprocessisanexecutionofaprogram Processes
16 Processes Aprocessisanexecutionofaprogram A single sequential program i.e.,asinglethread
17 Processes Aprocessisanexecutionofaprogram A single sequential program i.e.,asinglethread Processes may exchange messages obviously, received messages can be considered as input to a process(program)
18 Processes Aprocessisanexecutionofaprogram A single sequential program i.e.,asinglethread Processes may exchange messages obviously, received messages can be considered as input to a process(program) Different processes may be running on different end systems possibly on different computers running different operating systems aprocessmustbeabletoaddressanotherspecificprocess
19 Example while(browsing) { url = read_url(keyboard); page = get_web_page(url); display_web_page(page); } while(serving_pages) { page_name = read_web_request(network); page = read_file(page_name, disk); write_page(page, network); }
20 Example while(chatting) { msg = read_message(keyboard); write_message(msg, network); msg = read_message(network); write_message(msg, screen); } while(chatting) { msg = read_message(network); write_message(msg, screen); msg = read_message(keyboard); write_message(msg, network); }
21 For each pair of communicating processes, we distinguish two roles Clients and Servers
22 Clients and Servers For each pair of communicating processes, we distinguish two roles Client: process that initiates the communication specifically, if the communication is carried over a connection-oriented service, then the client is the process that establishes the connection
23 Clients and Servers For each pair of communicating processes, we distinguish two roles Client: process that initiates the communication specifically, if the communication is carried over a connection-oriented service, then the client is the process that establishes the connection Server: process that waits to be contacted specifically, if the communication is carried over a connection-oriented service, then the server is the process that passively accepts the connection
24 Clients and Servers For each pair of communicating processes, we distinguish two roles Client: process that initiates the communication specifically, if the communication is carried over a connection-oriented service, then the client is the process that establishes the connection Server: process that waits to be contacted specifically, if the communication is carried over a connection-oriented service, then the server is the process that passively accepts the connection Some applications have processes that act both as clients and servers. This is often called peer-to-peer architecture
25 Clients and Servers For each pair of communicating processes, we distinguish two roles Client: process that initiates the communication specifically, if the communication is carried over a connection-oriented service, then the client is the process that establishes the connection Server: process that waits to be contacted specifically, if the communication is carried over a connection-oriented service, then the server is the process that passively accepts the connection Some applications have processes that act both as clients and servers. This is often called peer-to-peer architecture Caveat: this classification is useful, but it is little more than nomenclature. Some applications and protocols mix and confuse those terms(e.g., FTP)
26 An end system(host) may run multiple processes Processes and Hosts
27 Processes and Hosts An end system(host) may run multiple processes process X process Y process Z Network Application Programmer Interface Operating System
28 Processes and Hosts An end system(host) may run multiple processes process X process Y process Z Network Application Programmer Interface Operating System Aprocessisaddressed(withinitshost)byitsportnumber
29 The operating system manages the network interfaces Sockets
30 Sockets The operating system manages the network interfaces Applications use the network through sockets
31 Sockets The operating system manages the network interfaces Applications use the network through sockets client host server host
32 Sockets The operating system manages the network interfaces Applications use the network through sockets client host server host
33 Sockets The operating system manages the network interfaces Applications use the network through sockets operating system client host operating system server host
34 Sockets The operating system manages the network interfaces Applications use the network through sockets client application operating system client host server application operating system server host
35 Sockets The operating system manages the network interfaces Applications use the network through sockets client application socket operating system client host server application socket operating system server host
36 Sockets The operating system manages the network interfaces Applications use the network through sockets client application socket operating system client host server application socket operating system server host
37 Client application Application Programs
38 Application Programs Client application 1. create a socket C by connecting to the server application i.e.,connecttohosthonportp
39 Application Programs Client application 1. create a socket C by connecting to the server application i.e.,connecttohosthonportp 2.usesocketCbyreadingandwritingdataintoit thisisthebodyoftheclientapplicationprotocol
40 Application Programs Client application 1. create a socket C by connecting to the server application i.e.,connecttohosthonportp 2.usesocketCbyreadingandwritingdataintoit thisisthebodyoftheclientapplicationprotocol 3. disconnect and destroy C
41 Application Programs Client application 1. create a socket C by connecting to the server application i.e.,connecttohosthonportp 2.usesocketCbyreadingandwritingdataintoit thisisthebodyoftheclientapplicationprotocol 3. disconnect and destroy C Server application(running on host H)
42 Application Programs Client application 1. create a socket C by connecting to the server application i.e.,connecttohosthonportp 2.usesocketCbyreadingandwritingdataintoit thisisthebodyoftheclientapplicationprotocol 3. disconnect and destroy C Server application(running on host H) 1.createasocketSby accepting aconnectiononportp aportisoftencalleda serversocket
43 Application Programs Client application 1. create a socket C by connecting to the server application i.e.,connecttohosthonportp 2.usesocketCbyreadingandwritingdataintoit thisisthebodyoftheclientapplicationprotocol 3. disconnect and destroy C Server application(running on host H) 1.createasocketSby accepting aconnectiononportp aportisoftencalleda serversocket 2.usesocketSbyreadingandwritingdataintoit thisisthebodyoftheserverapplicationprotocol
44 Application Programs Client application 1. create a socket C by connecting to the server application i.e.,connecttohosthonportp 2.usesocketCbyreadingandwritingdataintoit thisisthebodyoftheclientapplicationprotocol 3. disconnect and destroy C Server application(running on host H) 1.createasocketSby accepting aconnectiononportp aportisoftencalleda serversocket 2.usesocketSbyreadingandwritingdataintoit thisisthebodyoftheserverapplicationprotocol 3. disconnect and destroy S
45 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
46 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
47 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
48 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
49 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
50 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
51 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
52 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
53 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
54 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
55 Example 3 (HTTP) while(browsing) { url = read_url(keyboard); socket = open_connection(url); request = compose_http_request(url); write_message(request, socket); reply = read_message(socket); display_web_page(reply); } while(serving_http) { socket = accept_connection(); request = read_message(socket); reply = serve_http_request(request); write_message(reply, socket); }
56 The World-Wide Web
57 The World-Wide Web Developed in the early 1990s Basedontheideaofhypertextandlinks
58 The World-Wide Web Developed in the early 1990s Basedontheideaofhypertextandlinks Extremely successful, even though... the HyperText Transfer Protocol(HTTP) is just a glorified file transfer protocol theideaofhypertextandlinkswasalreadyquiteoldatthetimehttpwas developed
59 The World-Wide Web Developed in the early 1990s Basedontheideaofhypertextandlinks Extremely successful, even though... the HyperText Transfer Protocol(HTTP) is just a glorified file transfer protocol theideaofhypertextandlinkswasalreadyquiteoldatthetimehttpwas developed Success factors simplicity(openness) of the HTML language and simplicity of HTTP(a stateless protocol) low entry barrier for publishers GUI browsers(remember Netscape? Or Mosaic?!), search engines(altavista?!), etc.
60 Web Terminology
61 document a web page is also called a document Web Terminology
62 Web Terminology document a web page is also called a document objects a document may contain several objects(images, applets, etc.). An objectissimplyafile
63 Web Terminology document a web page is also called a document objects a document may contain several objects(images, applets, etc.). An objectissimplyafile URL or Uniform Resource Locator specifies the address of an object
64 Web Terminology document a web page is also called a document objects a document may contain several objects(images, applets, etc.). An objectissimplyafile URL or Uniform Resource Locator specifies the address of an object browser also called user agent is the program that users run to get and display documents
65 Web Terminology document a web page is also called a document objects a document may contain several objects(images, applets, etc.). An objectissimplyafile URL or Uniform Resource Locator specifies the address of an object browser also called user agent is the program that users run to get and display documents Web server is an application that houses objects, and makes them available through the HTTP protocol
66 Overview HTTP
67 ThemainpurposeofHTTPistoprovideaccesstoWebobjects Overview HTTP
68 Overview HTTP ThemainpurposeofHTTPistoprovideaccesstoWebobjects Uses a connection-oriented transport mechanism(i.e., TCP) alhoughitcanalsoworkonudp
69 Overview HTTP ThemainpurposeofHTTPistoprovideaccesstoWebobjects Uses a connection-oriented transport mechanism(i.e., TCP) alhoughitcanalsoworkonudp Consists of a sequence of requests issued by the client, and responses issued bytheserver,eachoneinresponsetoasinglerequest
70 Overview HTTP ThemainpurposeofHTTPistoprovideaccesstoWebobjects Uses a connection-oriented transport mechanism(i.e., TCP) alhoughitcanalsoworkonudp Consists of a sequence of requests issued by the client, and responses issued bytheserver,eachoneinresponsetoasinglerequest HTTP is stateless
71 Overview HTTP ThemainpurposeofHTTPistoprovideaccesstoWebobjects Uses a connection-oriented transport mechanism(i.e., TCP) alhoughitcanalsoworkonudp Consists of a sequence of requests issued by the client, and responses issued bytheserver,eachoneinresponsetoasinglerequest HTTP is stateless thebehavior(semantics)ofanhttprequestdoesnotdependonanyprevious request
72 Example: Request
73 Example: Request Client request GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it
74 Example: Reply
75 Example: Reply Server reply HTTP/ OK Connection: close Date: Tue, 15 Mar :00:01 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Tue, 8 Mar :44:00 GMT Content-Length: 2557 Content-Type: text/html <!DOCTYPE HTML PUBLIC "-/W3C//DTD HTML 4.01//EN"...
76 Protocol Features
77 Protocol Features Request protocol version URL specification connection attributes content/feature negotiation
78 Protocol Features Request protocol version URL specification connection attributes content/feature negotiation Reply protocol version reply status/value connection attributes object attributes content specification(type, length) content
79 Protocol Version GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it HTTP/ OK Connection: close Date: Tue, 15 Mar :00:01 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Tue, 8 Mar :44:00 GMT Content-Length: 2557 Content-Type: text/html <!DOCTYPE HTML PUBLIC "-/W3C//DTD HTML 4.01//EN"...
80 Protocol Version GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it HTTP/ OK Connection: close Date: Tue, 15 Mar :00:01 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Tue, 8 Mar :44:00 GMT Content-Length: 2557 Content-Type: text/html <!DOCTYPE HTML PUBLIC "-/W3C//DTD HTML 4.01//EN"...
81 Protocol Version
82 Protocol Version Principle: a protocol should always include a version number usually in the very first bits of the protocol(negotiation messages)
83 Protocol Version Principle: a protocol should always include a version number usually in the very first bits of the protocol(negotiation messages) A mechanism to negotiate the protocol version allows the protocol design to change design for change
84 URL GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it HTTP/ OK Connection: close Date: Tue, 15 Mar :00:01 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Tue, 8 Mar :44:00 GMT Content-Length: 2557 Content-Type: text/html <!DOCTYPE HTML PUBLIC "-/W3C//DTD HTML 4.01//EN"...
85 URL GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it HTTP/ OK Connection: close Date: Tue, 15 Mar :00:01 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Tue, 8 Mar :44:00 GMT Content-Length: 2557 Content-Type: text/html <!DOCTYPE HTML PUBLIC "-/W3C//DTD HTML 4.01//EN"...
86 TheHost Header GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it
87 TheHost Header GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it ThehostnameintheURLdetermineswheretherequestgoes hostnamemapstoanetworkaddress
88 TheHost Header GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it ThehostnameintheURLdetermineswheretherequestgoes hostnamemapstoanetworkaddress Thehostnameisalsopassedasaparameterwithintherequest,sothatthe server knows the full URL
89 TheHost Header GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it ThehostnameintheURLdetermineswheretherequestgoes hostnamemapstoanetworkaddress Thehostnameisalsopassedasaparameterwithintherequest,sothatthe server knows the full URL this is to allow a single server to serve multiple virtual sites(e.g., atelier.inf.usi.ch and
90 Connection GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it HTTP/ OK Connection: close Date: Tue, 15 Mar :00:01 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Tue, 8 Mar :44:00 GMT Content-Length: 2557 Content-Type: text/html <!DOCTYPE HTML PUBLIC "-/W3C//DTD HTML 4.01//EN"...
91 Connection GET /carzaniga/index.html HTTP/1.1 Host: Connection: close User-agent: Mozilla/4.0 Accept-Language: it HTTP/ OK Connection: close Date: Tue, 15 Mar :00:01 GMT Server: Apache/1.3.0 (Unix) Last-Modified: Tue, 8 Mar :44:00 GMT Content-Length: 2557 Content-Type: text/html <!DOCTYPE HTML PUBLIC "-/W3C//DTD HTML 4.01//EN"...
92 How HTTP Uses (TCP) Connections
93 How HTTP Uses (TCP) Connections The first version of HTTP used one(tcp) connection per object inefficientuseofthenetwork inefficient use of the operating system
94 How HTTP Uses (TCP) Connections The first version of HTTP used one(tcp) connection per object inefficientuseofthenetwork inefficient use of the operating system HTTP/1.1 introduces persistent connections thesame(tcp)connectioncanbeusedbytheclienttoissuemultiplerequest,and by the server to return multiple replies, and possibly multiple objects
95 How HTTP Uses (TCP) Connections The first version of HTTP used one(tcp) connection per object inefficientuseofthenetwork inefficient use of the operating system HTTP/1.1 introduces persistent connections thesame(tcp)connectioncanbeusedbytheclienttoissuemultiplerequest,and by the server to return multiple replies, and possibly multiple objects the default behavior is to use persistent connections
96 How HTTP Uses (TCP) Connections The first version of HTTP used one(tcp) connection per object inefficientuseofthenetwork inefficient use of the operating system HTTP/1.1 introduces persistent connections thesame(tcp)connectioncanbeusedbytheclienttoissuemultiplerequest,and by the server to return multiple replies, and possibly multiple objects the default behavior is to use persistent connections Connection: close in the request and response indicates the intention, of the client and server, respectively, to not use a persistent connection
97 How HTTP Uses Persistent Connections Apersistentconnectioncanbeusedtorequestandtransfertwoormore objects
98 How HTTP Uses Persistent Connections Apersistentconnectioncanbeusedtorequestandtransfertwoormore objects client request 1 server
99 How HTTP Uses Persistent Connections Apersistentconnectioncanbeusedtorequestandtransfertwoormore objects client request 1 server reply 1
100 How HTTP Uses Persistent Connections Apersistentconnectioncanbeusedtorequestandtransfertwoormore objects client request 1 server reply 1 request 2
101 How HTTP Uses Persistent Connections Apersistentconnectioncanbeusedtorequestandtransfertwoormore objects client request 1 server reply 1 request 2 reply 2
102 How HTTP Uses Persistent Connections Apersistentconnectioncanbeusedtorequestandtransfertwoormore objects client request 1 server reply 1 request 2 reply 2 request 3
103 How HTTP Uses Persistent Connections Apersistentconnectioncanbeusedtorequestandtransfertwoormore objects client request 1 server reply 1 request 2 reply 2 request 3 reply 3
104 Persistent Connections With Pipelining Amoreefficientuseofaconnectionisbypipeliningrequests
105 Persistent Connections With Pipelining Amoreefficientuseofaconnectionisbypipeliningrequests client request 1 server
106 Persistent Connections With Pipelining Amoreefficientuseofaconnectionisbypipeliningrequests client request 1 request 2 server
107 Persistent Connections With Pipelining Amoreefficientuseofaconnectionisbypipeliningrequests client request 1 request 2 request 3 server
108 Persistent Connections With Pipelining Amoreefficientuseofaconnectionisbypipeliningrequests client request 1 request 2 request 3 server
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