Advanced UNIX programming

1
Advanced UNIX programming

• Fall 2002
• Instructor Ashok Srinivasan
• Lecture 24

Acknowledgements The syllabus and power point
presentations are modified versions of those by
T. Baker and X. Yuan
2
Announcements

• Reading assignment
• Chapter 8
• Especially sections 8.1 to 8.8
• Chapter 9
• Midterm next Monday

3
Week 9 Topics

• Socket options
• getsockopt, setsockopt
• fcntl
• ioctl
• Introduction to UDP
• TCP vs UDP
• UDP interface

4
TCP vs UDP

• TCP
• Reliable byte stream service
• Connection setup overhead
• UDP
• Unreliable datagram service
• Data may get lost
• Application may need to deal with more details
  in the communication

5
Why UDP

• Applications that do not need 100 reliability
  communication
• Examples
• VoIP, video stream, DNS servers
• Applications that care about performance
• Example
• Some high performance computing applications
• Applications that need multicast or broadcast
• TCP only supports point to point communication

6
UDP interface

• socket, bind, sendto, recvfrom, close

TCP server TCP client socket
socket bind
connect listen accept
read/write
close read/write close

UDP server UDP client socket
socket bind
sendto recvfrom recvfrom sendto
close
7
UDP interface ... continued

• include ltsys/socket.hgt
• ssize_t recvfrom(int sockfd, void buff, size_t
  nbytes, int flags, struct sockaddr from,
  socklen_t addrlen)
• ssize_t sendto(int sockfd, void buff, size_t
  nbytes, int flags, const struct sockaddr to,
  socklen_t addrlen)
• See example1.c and example2.c for communication
  using UDP
• Lost packets in UDP
• How does the error rate vary with size of data?