Chapter 06.

UDP Server/Client

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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

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TCP and UDP (1/3)

• Similarity of TCP and UDP– Addressing based on port number– Checking data error

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TCP and UDP (2/3)

• Differences between TCP and UDPitem

TCP UDP

①connection-oriented protocol- Data comm. after connection setup

Connectionless protocol- Data comm. without connection

② - byte-stream service - Datagram service

③Reliable data transfer- By data retransmission

Unreliable data transfer- No data retransmission

④ unicastUnicast,Broadcast,Multicast

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UDP server/client operation (1/2)

• UDP server/client operation

UDP server UDP server

UDP Client #1

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UDP server/client operation (2/2)

• UDP server/client operation (cont’d)

UDP server

UDP client #1

UDPclient #2

Comm. Comm.

UDP server

UDP client #1

UDP client #n

. . .

. . .

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UDP server/client example

• Code example

UDP client UDP server

fgets() sendto()

printf()

recvfrom() printf()

sendto()recvfrom()

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UDP server/client analysis (1/4)

• UDP/IP Socket requires three components① protocol

• Defined by Socket() system call

② local IP address and port number• Server or client side

③ remote IP address and port number

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UDP server/client analysis (2/4)

• Socket data structure

server

Local IP addrLocal port num

Remote IP addrRemote port num

client

Local IP addrLocal port num

Remote IP addrRemote port num

application

OS

network

• • • • • •

Recvfrom bufferSendto buffer

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UDP server/client analysis (3/4)

• UDP server/client structure ①

socket()

bind()

recvfrom()

sendto()

closesocket()

socket()

sendto()

recvfrom()

closesocket()

UDP server UDP client

network

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UDP server/client analysis (4/4)

• UDP server/client structure ② (Ignore!!)

socket()

bind()

recvfrom()

sendto()

closesocket()

socket()

send()

recv()

closesocket()

UDP server UDP client

network

connect()

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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

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data transfer system call (2/4)

• sendto() example

// initialize socket address structure to receiver addressSOCKADDR_IN serveraddr;...

// declare buffer for sending datachar 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);

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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

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data transfer system call (4/4)

• recvfrom() example

// initialize socket address structure to sender addressSOCKADDR_IN peeraddr;int addrlen;

// declare buffer for received datachar buf[BUFSIZE];

// data receivingaddrlen = sizeof(peeraddr);retval = recvfrom(sock, buf, BUFSIZE, 0, (SOCKADDR *)&peeraddr, &addrlen);if(retval == SOCKET_ERROR) error handling;printf("%d bytes received...\n", retval);

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broadcasting (1/6)

• Communication types

unicasting broadcasting multicasting

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broadcasting (2/6)

• Broadcasting principle

sender

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broadcasting (3/6)

• Procedure to send broadcast data① 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()");

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broadcasting (4/6)

• Procedure to send broadcast data (cont’d)② Sending data to broadcast address// initialize socket address structureSOCKADDR_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 bufferchar 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);

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broadcasting (5/6)

• Broadcast address

host ID

11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

network ID 11 . . . . . . . . . . . . 1 Network-directed broadcast

local broadcast

network ID 11 . . . 1 subnet-directed broadcastsubnet ID

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broadcasting (6/6)

• Broadcast address (cont’d)

• BroadcastSender.cpp, BroadcastReceiver.cpp

router

router

Network-directed broadcast

Local broadcast