Πρωτόκολλα Διαδικτύου (ΨΣ-326 DS151)

Transcription

1 ΠΑΝΕΠΙΣΤΗΜΙΟ ΠΕΙΡΑΙΩΣ ΤΜΗΜΑ ΨΗΦΙΑΚΩΝ ΣΥΣΤΗΜΑΤΩΝ Πρωτόκολλα Διαδικτύου (ΨΣ-326 DS151) 3 Η ΕΡΓΑΣΤΗΡΙΑΚΗ ΔΙΑΛΕΞΗ (SOCKET PROGRAMMING) Υπεύθυνος καθηγητής: Άγγελος Ρούσκας Βοηθός: Υ.Δ. Ευθύμης Οικονόμου Πέμπτη 30/03/2017

2 Chapter 2 Application Layer A note on the use of these ppt slides: We re making these slides freely available to all (faculty, students, readers). They re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following: If you use these slides (e.g., in a class) that you mention their source (after all, we d like people to use our book!) If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Thanks and enjoy! JFK/KWR Computer Networking: A Top Down Approach 4th, 5th and 6th edition Jim Kurose, Keith Ross Addison-Wesley All material copyright J.F Kurose and K.W. Ross, All Rights Reserved 2

3 Chapter 2: Application layer Principles of network applications Socket programming 3

4 Some network apps web instant messaging remote login P2P file sharing multi-user network games streaming stored video (YouTube, Hulu, Netflix) voice over IP (e.g., Skype) real-time video conferencing social networking search 4

5 Creating a network app write programs that run on (different) end systems communicate over network e.g., web server software communicates with browser software No need to write software for network-core devices* Network-core devices do not run user applications or tamper with packet payloads applications on end systems allows for rapid app development, propagation application transport network data link physical application transport network data link physical application transport network data link physical * Will revisit this statement later when we talk about NAT devices 5

6 Application layer functions Implement desired functionality within application protocols when no underlying transport/network service supports it e.g. Mail, Web, News, P2P, etc. Congestion and flow control (Non-TCP applications) Reliability (Non-TCP applications) underlying transport/network service is inadequate Security (S/MIME, PGP, HTTPS) Delivery semantics (multicast) Naming (DNS, URLs) Routing (overlays) Functionality that is common rolled into libraries and middleware 6

7 Application architectures Client-server Peer-to-peer (P2P) Hybrid of client-server and P2P 7

8 Client-server architecture client/server server: always-on host permanent IP address data centers for scaling clients: communicate with server may be intermittently connected may have dynamic IP addresses do not communicate directly with each other 8

9 Pure P2P architecture no always-on server arbitrary end systems directly communicate peers request service from other peers, provide service in return to other peers peers are intermittently connected and change IP addresses Examples: Gnutella, Skype peer-peer Highly scalable but difficult to manage 9

10 Hybrid of client-server and P2P Skype voice-over-ip P2P application centralized server: finding address of remote party: client-client connection: direct (not through server) Instant messaging Chatting between two users is P2P Presence detection/location centralized in client-server manner: User registers its IP address with central server when it comes online User contacts central server to find IP addresses of buddies 10

11 Processes communicating Process: program running within a host. within same host, two processes communicate using inter-process communication (defined by OS). processes in different hosts communicate by exchanging messages Client process: process that initiates communication Server process: process that waits to be contacted Note: applications with P2P architectures have client processes & server processes 11

12 Sockets process sends/receives messages to/from its socket socket analogous to door sending process shoves message out door sending process relies on transport infrastructure on other side of door which brings message to socket at receiving process host or server process socket TCP with buffers, variables controlled by app developer controlled by OS Internet host or server process socket TCP with buffers, variables API: (1) choice of transport protocol; (2) ability to fix a few parameters (lots more on this later) 12

13 App-layer protocol defines types of messages exchanged, e.g., request, response message syntax: what fields in messages & how fields are delineated message semantics meaning of information in fields rules for when and how processes send & respond to messages open protocols: defined in RFCs allows for interoperability e.g., HTTP, SMTP proprietary protocols: e.g., Skype 12

14 Application layer protocols Types of application protocols Public-domain protocols defined in RFCs allows for interoperability e.g., HTTP, SMTP Proprietary protocols e.g., KaZaA, Skype Your game protocol for your final project Key design characteristic What transport service should the application protocol use? 14

15 What transport service does an app need? Data integrity some apps (e.g., audio) can tolerate some loss other apps (e.g., file transfer, telnet) require 100% reliable data transfer Timing some apps (e.g., Internet telephony, interactive games) require low delay to be effective Throughput some apps (e.g., multimedia) require minimum amount of throughput to be effective other apps ( elastic apps ) make use of whatever throughput they get Security Encryption, data integrity, 15

16 Transport service requirements of common apps Application Data loss Bandwidth Time Sensitive file transfer Web documents real-time audio/video streaming audio/video interactive games instant messaging no loss no loss no loss loss-tolerant loss-tolerant loss-tolerant no loss elastic elastic elastic audio: 5kbps-1Mbps video:10kbps-5mbps same as above few kbps up elastic no no no yes, 100 s msec yes, few secs yes, 100 s msec yes and no 16

17 Internet transport protocols services TCP service: connection-oriented: setup required between client and server processes reliable transport between sending and receiving process flow control: sender won t overwhelm receiver congestion control: throttle sender when network overloaded does not provide: timing, minimum throughput guarantee, security UDP service: unreliable data transfer between sending and receiving process does not provide: connection setup, reliability, flow control, congestion control, timing, or bandwidth guarantee 17

18 Internet apps: application, transport protocols Application remote terminal access Web file transfer streaming multimedia Internet telephony Application layer protocol SMTP [RFC 2821] Telnet [RFC 854] HTTP [RFC 2616] FTP [RFC 959] proprietary (e.g. RealNetworks) proprietary (e.g., Vonage,Dialpad) Underlying transport protocol TCP TCP TCP TCP TCP or UDP typically UDP 18

19 Chapter 2: Application layer Principles of network applications Socket programming 19

20 Programming application protocols Many possible programming interfaces Socket APIs (most common) BSD C Socket API (most common) Java socket API Python socket API Other APIs Client-side Java URLconnections Server-side Java servlets Python urllib Python HTTPServer RPC, CORBA, Java RMI (not covered) 20

21 Socket programming Goal: learn how to build client/server application that communicate using sockets Socket API introduced in BSD4.1 UNIX, 1981 explicitly created, used, released by apps client/server paradigm two types of transport service via socket API: unreliable datagram reliable, byte streamoriented socket a host-local, application-created, OS-controlled interface (a door ) into which application process can both send and receive messages to/from another application process 21

22 Socket-programming using TCP Socket: a door between application process and endend-transport protocol (UCP or TCP) TCP service: reliable transfer of bytes from one process to another controlled by application developer controlled by operating system process socket TCP with buffers, variables internet process socket TCP with buffers, variables controlled by application developer controlled by operating system host or server host or server 22

23 Socket programming using TCP Server setup server process must first be running server must have created a listening socket (door) that welcomes client s contact Client contacts server by: creating client-local TCP socket specifying IP address, port number of server process When client connects a socket: client TCP establishes connection to server TCP When client connects, server TCP creates new socket for server process to communicate with client different than listening socket (allows server to talk with multiple clients) source IP and port numbers used to distinguish clients (more in Chap 3) application viewpoint TCP provides reliable, in-order transfer of bytes ( pipe ) between client and server 23

24 Addressing processes to receive messages, process must have identifier host device has unique 32-bit IP address Q: does IP address of host on which process runs suffice for identifying the process? A: No, many processes can be running on same host identifier includes both IP address and port numbers associated with process on host. Example port numbers: HTTP server: 80 Mail server: 25 to send HTTP message to gaia.cs.umass.edu web server: IP address: Port number: 80 more shortly 24

25 IPs 32-bit identifier Dotted-quad: > Identifies a host interface (not a host) 25

26 Ports Identifying the ultimate destination IP addresses identify hosts Host has many applications Ports (16-bit identifier) 26

27 Ports For many common services, standard port numbers are defined. 27

28 Sockets socket programming interface in relation to the protocol stack 28

29 Sockets Identified by protocol and local/remote address/port Applications may refer to many sockets 29

30 TCP sockets in action *,SIP:80 *,SIP:80 CIP:1099,SIP:80 *,SIP:80 CIP:1099,SIP:80 CIP:1099,SIP:80 30

31 TCP sockets in action CIP:1099,SIP:80 *,SIP:80 CIP:1099,SIP:80 *,SIP:80 CIP:1100,SIP:80 CIP:1099,SIP:80 CIP:1100,SIP:80 CIP:1099,SIP:80 CIP:1100,SIP:80 31

32 Java network programming Java network applications java.net package System-dependent implementations 32

33 Java installation on linuxlab J2SE javac java java compiler java interpreter 33

34 java.net classes Low-level networking classes Sockets and Packets java.net.socket java.net.serversocket java.net.datagramsocket java.net.datagrampacket java.net.inetaddress High-level URL networking classes java.net.url java.net.urlconnection java.net.httpurlconnection java.net.urlencoder 34

35 java.net.socket Constructors Socket(InetAddress, int) Socket(String, int) Socket(InetAddress, int, InetAddress, int) Some methods getinputstream() getoutputstream() getinetaddress() getport() getlocaladdress() getlocalport() get/set individual socket options 35

36 java.net.serversocket Constructors ServerSocket(int) // port specified ServerSocket(int, int) // port, backlog specified ServerSocket(int, int, InetAddress) // port, backlog, IP address Some methods accept() getinetaddress() getlocalport() 36

37 Stream jargon for Java network programming A stream is a sequence of characters that flow into or out of a process. An input stream is attached to some input source for the process, e.g., keyboard or socket. An output stream is attached to an output source, e.g., monitor or socket. 37

38 Socket programming with TCP Example client-server app: 1) client reads line from standard input (infromuser stream), sends to server via socket (outtoserver stream) 2) server reads line from socket 3) server converts line to uppercase, sends back to client 4) client reads, prints modified line from socket (infromserver stream) Client Process process input stream output stream keyboard infromuser outtoserver monitor infromserver client TCP clientsocket socket input stream TCP socket to network from network 38

39 Client/server socket interaction: TCP Server (running on hostid) create socket, port=x, for incoming request: welcomesocket = ServerSocket() wait for incoming connection request connectionsocket = welcomesocket.accept() read request from connectionsocket write reply to connectionsocket close connectionsocket TCP connection setup Client create socket, connect to hostid, port=x clientsocket = Socket() send request using clientsocket read reply from clientsocket close clientsocket 39

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41 TCP communication Communication of 2 pairs via sockets necessitates existence of this 4-tuple: - Local IP address - Local Port# - Foreign IP address - Foreign Port# 41

42 TCP 3-way handshake client state LISTEN SYNSENT ESTAB choose init seq num, x send TCP SYN msg received SYNACK(x) indicates server is live; send ACK for SYNACK; this segment may contain client-to-server data SYNbit=1, Seq=x SYNbit=1, Seq=y ACKbit=1; ACKnum=x+1 ACKbit=1, ACKnum=y+1 choose init seq num, y send TCP SYNACK msg, acking SYN received ACK(y) indicates client is live server state LISTEN SYN RCVD ESTAB 42

43 TCP 3-way handshake 43

44 TCP: closing a connection client state server state ESTAB ESTAB clientsocket.close() FIN_WAIT_1 FIN_WAIT_2 can no longer send but can receive data wait for server close FINbit=1, seq=x ACKbit=1; ACKnum=x+1 can still send data CLOSE_WAIT TIMED_WAIT timed wait for 2*max segment lifetime FINbit=1, seq=y ACKbit=1; ACKnum=y+1 can no longer send data LAST_ACK CLOSED CLOSED 44

45 Application Example: 1. Client reads a line of characters (data) from its keyboard and sends the data to the server. 2. The server receives the data and converts characters to uppercase. 3. The server sends the modified data to the client. 4. The client receives the modified data and displays the line on its screen. 45

46 Example: Java client (TCP) import java.io.*; import java.net.*; class TCPClient { Create input stream Create client socket, connect to server Create output stream attached to socket public static void main(string argv[]) throws Exception { String sentence; String modifiedsentence; BufferedReader infromuser = new BufferedReader(new InputStreamReader(System.in)); Socket clientsocket = new Socket("hostname", 6789); DataOutputStream outtoserver = new DataOutputStream(clientSocket.getOutputStream()); 46

47 Example: Java client (TCP), cont. Create input stream attached to socket Send line to server Read line from server BufferedReader infromserver = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); sentence = infromuser.readline(); outtoserver.writebytes(sentence + '\n'); modifiedsentence = infromserver.readline(); System.out.println("FROM SERVER: " + modifiedsentence); clientsocket.close(); } } 47

48 Example: Java server (TCP) import java.io.*; import java.net.*; class TCPServer { Create welcoming socket at port 6789 Wait, on welcoming socket for contact by client Create input stream, attached to socket public static void main(string argv[]) throws Exception { String clientsentence; String capitalizedsentence; ServerSocket welcomesocket = new ServerSocket(6789); while(true) { Socket connectionsocket = welcomesocket.accept(); BufferedReader infromclient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream())); 48

49 Example: Java server (TCP), cont Create output stream, attached to socket Read in line from socket DataOutputStream outtoclient = new DataOutputStream(connectionSocket.getOutputStream()); clientsentence = infromclient.readline(); capitalizedsentence = clientsentence.touppercase() + '\n'; Write out line to socket } } } outtoclient.writebytes(capitalizedsentence); End of while loop, loop back and wait for another client connection 49

50 Socket programming using UDP UDP: no connection between client and server no handshaking sender explicitly attaches IP address and port of destination to each packet server must extract IP address, port of sender from received packet application viewpoint UDP provides unreliable transfer of groups of bytes ( datagrams ) between client and server UDP: transmitted data may be received out of order, or lost 50

51 java.net.datagramsocket Constructors DatagramSocket() DatagramSocket(int) // bind to specific port DatagramSocket(int, InetAddress) // specify local address Some methods getlocaladdress() getlocalport() receive(datagrampacket) send(datagrampacket) get/set individual socket options 51

52 java.net.datagrampacket Constructors DatagramPacket(byte[], int) // receiving packets DatagramPacket(byte[], int, InetAddress, int) // sending packets Some methods getaddress() // remote address getport() // remote port getlength() // get packet length getdata() // return data received or to be sent setaddress(inetaddress) // set remote address setdata(byte[]) // set packet data setlength(int) // set packet length setport(int) // set remote port 52

53 Client/server socket interaction: UDP Server (running on hostid) Client create socket, port=x, for incoming request: serversocket = DatagramSocket() read request from serversocket create socket, clientsocket = DatagramSocket() Create, address (hostid, port=x, send datagram request using clientsocket write reply to serversocket specifying client host address, port number read reply from clientsocket close clientsocket 53

54 Example: Java client (UDP) keyboard monitor Output: sends packet (recall that TCP sent byte stream ) Client Process process input stream UDP packet infromuser sendpacket receivepacket client UDP clientsocket socket UDP packet UDP socket Input: receives packet (recall that TCP received byte stream ) to network from network 54

55 Example: Java client (UDP) import java.io.*; import java.net.*; Create input stream Create client socket Translate hostname to IP address using DNS class UDPClient { public static void main(string args[]) throws Exception { BufferedReader infromuser = new BufferedReader(new InputStreamReader(System.in)); DatagramSocket clientsocket = new DatagramSocket(); InetAddress IPAddress = InetAddress.getByName("hostname"); byte[] senddata = new byte[1024]; byte[] receivedata = new byte[1024]; String sentence = infromuser.readline(); senddata = sentence.getbytes(); 55

56 Example: Java client (UDP), cont. Create datagram with data-to-send, length, IP addr, port Send datagram to server Read datagram from server } DatagramPacket sendpacket = new DatagramPacket(sendData, senddata.length, IPAddress, 9876); clientsocket.send(sendpacket); DatagramPacket receivepacket = new DatagramPacket(receiveData, receivedata.length); clientsocket.receive(receivepacket); String modifiedsentence = new String(receivePacket.getData()); System.out.println("FROM SERVER:" + modifiedsentence); clientsocket.close(); } 56

57 Example: Java server (UDP) import java.io.*; import java.net.*; Create datagram socket at port 9876 Create space for received datagram Receive datagram class UDPServer { public static void main(string args[]) throws Exception { DatagramSocket serversocket = new DatagramSocket(9876); byte[] receivedata = new byte[1024]; byte[] senddata = new byte[1024]; while(true) { DatagramPacket receivepacket = new DatagramPacket(receiveData, receivedata.length); serversocket.receive(receivepacket); 57

58 Example: Java server (UDP), cont Get IP addr port #, of sender String sentence = new String(receivePacket.getData()); InetAddress IPAddress = receivepacket.getaddress(); int port = receivepacket.getport(); String capitalizedsentence = sentence.touppercase(); senddata = capitalizedsentence.getbytes(); Create datagram to send to client Write out datagram to socket } } DatagramPacket sendpacket = new DatagramPacket(sendData, senddata.length, IPAddress, port); serversocket.send(sendpacket); } End of while loop, loop back and wait for another datagram 58

59 Python network programming Python network applications Python network packages (socket, URLlib, HTTPServer) System-dependent implementations 59

60 Python network programming Python Scripting language No compilation required Language reference: Provides APIs similar to Java socket Low-level socket interface urllib HTTP client SimpleHTTPServer HTTP server 60

61 Python sockets Similar to C and Java Client import socket host = localhost port = 7 s = socket.socket(socket.af_inet, socket.sock_stream) s.connect((host,port)) s.send( some data to echo ) print s.recv(20) s.close 61

62 Socket programming with TCP client must contact server server process must first be running server must have created socket (door) that welcomes client s contact client contacts server by: Creating TCP socket, specifying IP address, port number of server process when client creates socket: client TCP establishes connection to server TCP when contacted by client, server TCP creates new socket for server process to communicate with that particular client allows server to talk with multiple clients source port numbers used to distinguish clients application viewpoint: TCP provides reliable, in-order byte-stream transfer ( pipe ) between client and server 62

63 Client/server socket interaction: TCP server (running on hostid) create socket, port=x, for incoming request: serversocket = socket() client wait for incoming connection request connectionsocket = serversocket.accept() read request from connectionsocket write reply to connectionsocket close connectionsocket TCP connection setup create socket, connect to hostid, port=x clientsocket = socket() send request using clientsocket read reply from clientsocket close clientsocket 63

64 Example app: TCP client create TCP socket for server, remote port No need to attach server name, port Python TCPClient from socket import * servername = servername serverport = clientsocket = socket(af_inet, SOCK_STREAM) clientsocket.connect((servername,serverport)) sentence = raw_input( Input lowercase sentence: ) clientsocket.send(sentence) modifiedsentence = clientsocket.recv(1024) print From Server:, modifiedsentence clientsocket.close() 64

65 Example app: TCP server Python TCPServer create TCP welcoming socket server begins listening for incoming TCP requests loop forever server waits on accept() for incoming requests, new socket created on return from socket import * serverport = serversocket = socket(af_inet,sock_stream) serversocket.bind((,serverport)) serversocket.listen(1) print The server is ready to receive while 1: connectionsocket, addr = serversocket.accept() read bytes from socket (but not address as in UDP) close connection to this client (but not welcoming socket) sentence = connectionsocket.recv(1024) capitalizedsentence = sentence.upper() connectionsocket.send(capitalizedsentence) connectionsocket.close() 65

66 Socket programming with UDP UDP: no connection between client & server no handshaking before sending data sender explicitly attaches IP destination address and port # to each packet rcvr extracts sender IP address and port# from received packet UDP: transmitted data may be lost or received out-of-order Application viewpoint: UDP provides unreliable transfer of groups of bytes ( datagrams ) between client and server 66

67 Client/server socket interaction: UDP server (running on serverip) create socket, port= x: serversocket = socket(af_inet,sock_dgram) read datagram from serversocket write reply to serversocket specifying client address, port number client create socket: clientsocket = socket(af_inet,sock_dgram) Create datagram with server IP and port=x; send datagram via clientsocket read datagram from clientsocket close clientsocket 63

68 Example app: UDP client Python UDPClient include Python s socket library from socket import * servername = hostname serverport = create UDP socket for server get user keyboard input Attach server name, port to message; send into socket read reply characters from socket into string print out received string and close socket clientsocket = socket(socket.af_inet, socket.sock_dgram) message = raw_input( Input lowercase sentence: ) clientsocket.sendto(message,(servername, serverport)) modifiedmessage, serveraddress = clientsocket.recvfrom(2048) print modifiedmessage clientsocket.close() 68

69 Example app: UDP server create UDP socket bind socket to local port number loop forever Read from UDP socket into message, getting client s address (client IP and port) send upper case string back to this client Python UDPServer from socket import * serverport = serversocket = socket(af_inet, SOCK_DGRAM) serversocket.bind(('', serverport)) print The server is ready to receive while 1: message, clientaddress = serversocket.recvfrom(2048) modifiedmessage = message.upper() serversocket.sendto(modifiedmessage, clientaddress) 69

70 Java: Running Socket Programs Set-up IPs and ports in programs Compile both server and client programs to the respective machine (or localhost) javac TCPServer.java javac TCPClient.java If no error TCPServer.class and TCPClient.class are created First run server: java TCPServer Then run client/s: java TCPClient Type your message on client 70

71 Python: Running Socket Programs Open both server and client programs to the respective machine (or localhost) using IDLE Python (2 different IDLE on localhost) UDPServer.py UDPClient.py Set-up IPs and ports in programs First run server Then run client/s Type your message on client 71

72 Packet Capturing: Wireshark packet analyzer packet capture (pcap) copy of all Ethernet frames sent/receive d application (www browser, client) application OS Transport (TCP/UDP) Network (IP) Link (Ethernet) Physical 72

73 Eg: TCPServer Captured packets 73

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77 Eg: UDPServer Captured packets 77

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