1. Chapter 06.
UDP Server/Client

2. Understanding the basic structure and principle of UDP server/client
Goal
Understanding the basic structure and principle of UDP server/client
Learning socket system calls for UDP application
Understanding broadcasting concept and UDP based implementation

3. Similarity of TCP and UDP
Addressing based on port number
Checking data error

4. Differences between TCP and UDP
item
TCP
UDP ①
connection-oriented protocol
- Data comm. after connection setup
Connectionless protocol
- Data comm. without connection ②
- byte-stream service
- Datagram service ③
Reliable data transfer
- By data retransmission
Unreliable data transfer
- No data retransmission ④
unicast
Unicast,
Broadcast,
Multicast

5. UDP server/client operation (1/2)

6. UDP server/client operation (2/2)
UDP server/client operation (cont’d)
UDP server
UDP server
. . .
Comm.
Comm.
UDP
client #1
UDP
client #2
UDP
client #1
. . .
UDP
client #n

7. UDP server/client example
Code example
UDP client
UDP server
fgets()
sendto()
printf()
recvfrom()

8. UDP server/client analysis (1/4)
UDP/IP Socket requires three components
① protocol
Defined by Socket() system call
② local IP address and port number
Server or client side
③ remote IP address and port number

9. UDP server/client analysis (2/4)
Socket data structure
server
Local IP addr
Local port num
Remote IP addr
Remote port num
client
application OS
network
• • •
Recvfrom buffer
Sendto buffer

10. UDP server/client analysis (3/4)
UDP server/client structure ①
socket()
bind()
recvfrom()
sendto()
closesocket()
UDP server
UDP client
network

11. UDP server/client analysis (4/4)
UDP server/client structure ② (Ignore!!)
socket()
bind()
recvfrom()
sendto()
closesocket()
send()
recv()
UDP server
UDP client
network
connect()

12. data transfer system call (1/4)
sendto()
send application data to peer side
int sendto (
SOCKET s,
const char* buf,
int len,
int flags,
const struct sockaddr* to,
int tolen
) ;
success: num. of bytes sent, fail: SOCKET_ERROR

13. data transfer system call (2/4)
sendto() example
// initialize socket address structure to receiver address
SOCKADDR_IN serveraddr;
...
// declare buffer for sending data
char buf[BUFSIZE];
// store sending data to buffer
// data sending.
retval = sendto(sock, buf, strlen(buf), 0,
(SOCKADDR *)&serveraddr, sizeof(serveraddr));
if(retval == SOCKET_ERROR) error handling;
printf("%d bytes sent...\n", retval);

14. data transfer system call (3/4)
recvfrom()
Data receving from peer side
int recvfrom (
SOCKET s,
char* buf,
int len,
int flags,
struct sockaddr* from,
int* fromlen
) ;
success: num. of bytes sent, fail: SOCKET_ERROR

15. data transfer system call (4/4)
recvfrom() example
// initialize socket address structure to sender address
SOCKADDR_IN peeraddr;
int addrlen;
// declare buffer for received data
char buf[BUFSIZE];
// data receiving
addrlen = sizeof(peeraddr);
retval = recvfrom(sock, buf, BUFSIZE, 0,
(SOCKADDR *)&peeraddr, &addrlen);
if(retval == SOCKET_ERROR) error handling;
printf("%d bytes received...\n", retval);

16. Communication types broadcasting (1/6) unicasting broadcasting
multicasting

17. Broadcasting principle
sender

18. Procedure to send broadcast data
broadcasting (3/6)
Procedure to send broadcast data
① Enable broadcast option for a socket
BOOL bEnable = TRUE;
retval = setsockopt(sock, SOL_SOCKET, SO_BROADCAST,
(char *)&bEnable, sizeof(bEnable));
if(retval == SOCKET_ERROR) err_quit("setsockopt()");

19. Procedure to send broadcast data (cont’d)
broadcasting (4/6)
Procedure to send broadcast data (cont’d)
② Sending data to broadcast address
// initialize socket address structure
SOCKADDR_IN remoteaddr;
ZeroMemory(&remoteaddr, sizeof(remoteaddr));
remoteaddr.sin_family = AF_INET;
remoteaddr.sin_port = htons(9000);
remoteaddr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
// store data to buffer
char buf[BUFSIZE];
...
// sending data.
retval = sendto(sock, buf, strlen(buf), 0,
(SOCKADDR *)&remoteaddr, sizeof(remoteaddr));
if(retval == SOCKET_ERROR) error handling;
printf("%d bytes sent….\n", retval);

20. Broadcast address broadcasting (5/6) host ID
network ID
Network-directed broadcast
local broadcast
subnet-directed broadcast
subnet ID

21. Network-directed broadcast
broadcasting (6/6)
Broadcast address (cont’d)
BroadcastSender.cpp, BroadcastReceiver.cpp
router
Network-directed broadcast
router
Local broadcast