CSE 489/589 Recitation TCP Socket & Synchronous I/O Multiplexing

Transcription

1 Recitation TCP Socket & Synchronous I/O Multiplexing Wenjun Jiang Computer Sciences and Engineering University at Buffalo

2 Information Instructor: Dr. Lu Su Office: 321 Davis Hall lusu [at] buffalo.edu Office Hours: Mon. and Wen. 2:00 to 3:00 PM TA: Wenjun Jiang, Hengtong Zhang Course website Piazza 2

3 Office Hours Wenjun Jiang Office: 301C Davis Hall/300 Davis Hall Student Lounge Office Hours: Thur. 1:30 to 2:30 PM wenjunji [at] buffalo.edu Hengtong Zhang Office: 301C Davis Hall/300 Davis Hall Student Lounge Office Hours: Tue. 2:30 to 3:30 PM hengtong [at] buffalo.edu 3

4 Recitation Time and classroom TA Wednesday 3:00-3:50 PM (Baldy 112) Hengtong and Wenjun take turns Content Projects Demos Homework Q & A 4

5 Announcements Project 1 Posted on 9/14, due on 10/14 Homework 1 Post on 9/16, due on 9/23 Wireshark Lab 1 Post on 9/16, not be graded Policy You must test your project on CSE servers! No cheating! Don t copy codes from your friends or from senior students. 5

6 Project 1 Description Develop a simple application for message exchange (489) or file sharing (589) among remote hosts. timberlake Server embankment underground Clients highgate euston 6

7 Project 1 Description Develop a simple application for message exchange (489) or file sharing (589) among remote hosts. timberlake Server embankment underground Clients highgate connect the nodes euston 7

8 Project 1 Description Develop a simple application for message exchange (489) or file sharing (589) among remote hosts. timberlake Server embankment underground Clients highgate connect the nodes take user s input euston 8

9 Outline Part1: Introduction to TCP Socket Programming Part2: Introduction to Synchronous I/O Multiplexing 9

10 Protocol Stack application layer: supporting network applications HTTP, SMTP transport layer: process-process data transfer TCP, UDP network layer: routing of datagrams from source to destination IP, routing protocols link layer: data transfer between neighboring network elements Ethernet, MAC addresses physical layer: bits on the wire application transport network link physical 10

11 TCP Overview Establish connection 3-way handshake Data transmission Reliable (retransmission with timer) In-order delivery (reorder packets if necessary) Support flow control (fast sender vs. slow receiver) Full-duplex (data transferred both ways) Close connection 11

12 About Sockets Socket: a door between application process and endend-transport protocol (TCP or UDP) IP Address + Port Number 12

13 TCP Socket Overview I TCP Connection Establishment Server gets ready (socket, bind, listen) Client gets ready (socket) Client requests connection (connect) 13

14 TCP Socket Overview II Socket structure You need to fill all the values listed in the structure 14

15 TCP Socket Overview II 15

16 Example: Server gets ready 16

17 TCP Socket Overview III TCP Connection Termination A performs active close, sends FIN B performs passive close & acknowledges B closes its socket and sends FIN A acknowledges the FIN 17

18 TCP Socket Summarization 18

19 Synchronous I/O Multiplexing We want to listen for incoming connections, new data from the connections we already have and input from command line at the same time. How can we do it (if do not use multi-threading)? Block at accept ()? receive()? stdin? If you block at any one of them, you miss the other two! Polling? Continuously check their state one by one. Heavy CPU consumption Select ()! Block when none of them is activated Return activated ones when any of them is activated 19

20 Definition File descriptors Def: An abstract handle used to access a file or I/O resources Eg. Socket descriptors, 0 for standard input Select () monitors sets of file descriptors readfds, writefds, exceptfds 20

21 Definition numfds Specify the range of file descriptors to be tested. readfds Specify the file descriptors to be checked for being ready to read. Indicate which file descriptors are ready to read. writefds Specify the file descriptors to be checked for being ready to write. Indicate which file descriptors are ready to write. 21

22 Operations We use these 4 functions to manipulate file descriptor sets. 22

23 Exercise 1 Assume that node A is listening to socket sd1 to accept connection, keeping a connection with node B through socket sd2, keeping a TCP connection with node C through socket sd3, and listening to command line input. How should node A set its readfds and writefds? Answer: readfds={0, sd1, sd2, sd3} writefds={} 23

24 Exercise 2 Assume that node A is listening to socket sd1 to accept connection, transmitting a big file to node B through socket sd2, and listening to command line input. How should node A set its readfds and writefds? Answer: readfds={0, sd1, sd2} writefds={sd2} because when we are transmitting a big file, we can only successfully send part of it because of flow control. Before we continue to send the rest, we must make sure the socket is ready to write. 24

25 Useful links Select() function asp Beej s guide to network programming dex.html Chapter 5, 9 is important, Chapter 6 is the background, Chapter 7 introduces select() 25

26 Acknowledgements These slides contain material developed and copyrighted by Li Sun (SUNY Buffalo). 26