Computer Networks. The Socket API (Project 1) & Traceroute (HW 1) ( 1.3.4, )

Transcription

1 Computer Networks The Socket API (Project 1) & Traceroute (HW 1) ( 1.3.4, ) Originally By David Wetherall (djw@), Modified By Qian Yan (qiany7@)

2 I m Anir! (Anirban) o 5th year masters student About Me I love low level systems programming and distributed systems This is my 2nd quarter as a TA Interned at CDK Global, Facbeook and VMware in the past Currently doing research in the Systems Lab Computer Networks 2

3 Michael (Chenyang) Q: What do I like? A: Scuba Diving + music About Me Q: What kind of music do you like? A: British ones, like those made by The Stone Roses Q: What song do you listen to recently? A: Step into My World by Hurricane #1 Computer Networks 3

4 Administrivia Projects ( )% Groups up to 3 Any language. Provide build instructions. We can only help with C/Java/Python Homework (10%) Textbook questions + traceroute/wireshark Individual Pop quiz (5%) 5 quizzes. Lowest score dropped Midterm (15%) Final (25%) Computer Networks 4

5 Traceroute Apps talk to other apps with no real idea of what is inside the network This is good! But you may be curious Peeking inside the Network with Traceroute app host??? host app

6 Traceroute Van Jacobson Widely used command-line tool to let hosts peek inside the network On all OSes (tracert on Windows) Developed by Van Jacobson ~1987 Uses a network-network interface (IP) in ways we will explain later : Credit: Wikipedia (public domain) Computer Networks 6

7 Traceroute Probes successive hops to find network path TTL: time-to-live... Local Host Computer Networks 7 Remote Host

8 Traceroute Local Host 1 hop 2 hops... 3 hops N-1 hops N hops Remote Host Computer Networks 8

9 Using Traceroute Computer Networks 9

10 Using Traceroute (2) ISP names and places are educated guesses Home 1 hop tde 3 hops Telefonica 4 hops Level3 6 hops pnw-gigapop 1 hop UW 3 hops ms 180 ms UW >200 ms My computer NYC San Jose Seattle (www1.cac.washington.edu) Computer Networks 10

11 Network-Application Interface Defines how apps use the network Application Layer APIs Lets apps talk to each other hides the other layers of the network app app network Computer Networks host host 11

12 Project 1 Simple Client Send requests to attu server Wait for a reply Extract the information from the reply Continue Simple Server Server handles the Client requests Multi-threaded Computer Networks 12

13 Project 1 This is the basis for many apps! File transfer: send name, get file ( 6.1.4) Web browsing: send URL, get page Echo: send message, get it back Let s see how to write this app Computer Networks 13

14 Socket API (Generalized) Simple application-layer abstractions (APIs) to use the network The network service API used to write all Internet applications Part of all major OSes and languages; originally Berkeley (Unix) ~1983 Two kinds of sockets Streams (TCP): reliably send a stream of bytes Datagrams (UDP): unreliably send separate messages Computer Networks 14

15 Socket API (2) Sockets let apps attach to the local network at different ports Ports are used by OS to distinguish services/apps using internet Socket Port 1 Socket Port 2 Computer Networks 15

16 Socket API (3) Primitive Meaning SOCKET BIND LISTEN Create a new communication endpoint Associate a local address (port) with a socket Announce willingness to accept connections; (give queue size) ACCEPT Passively establish an incoming connection CONNECT Actively attempt to establish a connection SEND Send some data over the connection RECEIVE Receive some data from the connection CLOSE Release the connection Computer Networks

17 Using Sockets Client (host 1) Time Server (host 2) Computer Networks 17

18 Using Sockets (2) Client (host 1) Time Server (host 2) 1 connect 1 2 request 4 reply disconnect 3 4 Computer Networks 18

19 Using Sockets (3) Client (host 1) Time Server (host 2) 1: socket 1: socket 2: (bind) connect 3: (listen) 4: accept* 5: connect* request 6: recv* 7: send 8: recv* reply 9: send disconnect 10: close 10: close *= call blocks Computer Networks 19

20 Client Program (outline) socket() // make socket getaddrinfo() // server and port name // connect() // connect to server [block] send() // send request recv() close() // await reply [block] // do something with data! // done, disconnect Computer Networks 20

21 Server Program (outline) socket() // make socket getaddrinfo() // for port on this host bind() // associate port with socket listen() // prepare to accept connections accept() // wait for a connection [block] recv() // wait for request send() // send the reply close() // eventually disconnect Computer Networks 21

22 Java Examples with Socket & ServerSocket Server ServerSocket listener = new ServerSocket(9090); try { while (true) { Socket socket = listener.accept(); try { socket.getinputstream(); } finally { socket.close(); } } } finally { listener.close(); } Client Socket socket = new Socket(server, 9090); out = new PrintWriter(socket.getOutputStream(), true); socket.close(); es/ working/datagrams/clientserver.html working/sockets/index.html Computer Networks 22

23 END 2013 D. Wetherall Slide material from: TANENBAUM, ANDREW S.; WETHERALL, DAVID J., COMPUTER NETWORKS, 5th Edition, Electronically reproduced by permission of Pearson Education, Inc., Upper Saddle River, New Jersey Computer Networks 23