Transcript Real time Networked Simulation

Outline
•Socket programming with Windows OS
•C++ UDPSocket class
Socket Programming with
Windows OS
•1982 - Berkeley Software Distributions
introduced sockets as an interface for
communication between local processes
•1986 - Berkeley extended the socket interface
for use over the TCP/IP with UNIX
•Today many applications (FTP, Telnet, etc)
depend on these interfaces
Socket Programming with
Windows OS
Socket
•a programming interface
•a logical, file handle like, construct that an
application uses for communication (everything
in Unix is a file)
•not restricted to TCP/IP
Socket Programming with
Windows OS
Communication protocols
•connection oriented (Transmission Control
Protocol - TCP/IP)
•connectionless (User Datagram Protocol -UDP
and Inter-network Packet Exchange - IPX)
Socket Programming with
Windows OS
•Microsoft proposed an industry wide socket
standard for Windows OS, called as Windows
Socket Interface or WinSock.
•Windows socket based applications use the
WinSock interface to access the default
Windows WinSock implementation, WinSock.dll
or an alternative implementation such as, the
FTP WinSock.dll
Windows Socket, Protocols and Applications
Application
FTP WinSock.dll
WinSock.dll
Remote Access
Service (RAS)
TCP/IP
Modem
Phone Line
IPX
AppleTalk NetBIOS
Network Drivers
LAN
FTP TCP/IP
Differences Between
Berkeley and WinSock
•Socket is an int data type in Berkeley, but a
SOCKET data type in WinSock
•SOCKET_ERROR is produced by all WinSock
functions, but negative one (-1) in Berkeley
•Applications must call WSAStartup() before
calling any WinSock functions, and should call
the WSACleanup() function before terminating
Structures
struct sockaddr {
// socket address information
u_short sa_family;
// address family
char sa_data[14];
// up to 14 bytes of direct address
};
struct in_addr {
u_long s_addr;
};
// internet address
// socket address
Structures
struct sockaddr_in {
// socket address internet
short sin_family;
// 2 bytes
u_short sin_port;
// 2 bytes port number
struct in_addr sin_addr;
// 4 bytes net ID, host ID
char sin_zero[8];
// 8 bytes unused
};
• There are also some functions to convert from and to native types.
• The internet address for a socket-based application composed of two pieces
- two-byte port number (sin_port) > 1023
- four-byte network address (sin_addr)
Creating a Socket
SOCKET PASCAL FAR socket (int af, int type, int protocol)
Actual
Address Family
Type
Protocol
Protocol
AF_INET
SOCK_DGRAM
IPPROTO_UDP
UDP
AF_INET
SOCK_STREAM
IPPROTO_TCP
TCP
A Non-blocking Socket
Not to block on a socket call use a non-blocking socket.
int PASCAL FAR ioctlsocket (SOCKET soc, long command,
u_long FAR * argp)
Command
Argp
State
FIONBIO
non-zero
non-blocking
FIONBIO
zero
blocking
Binding a Socket
•Associating address with a socket
•The socket end point becomes a named entity visible in
the name space
int PASCAL FAR bind (SOCKET soc, const struct
sockaddr FAR * address, int addrlen)
Sending UDP
•Data delivery is not guaranteed
•Data grams are directed towards a specific recipient.
int PASCAL FAR sendto (SOCKET soc, // my socket
const char FAR * buffer, // sending buffer
int len,
int flags,
// data length
// 0
const struct sockaddr FAR * to, // recipient
int tolen)
// recipient’s address length
Receiving UDP
int PASCAL FAR recvfrom (SOCKET soc, // my socket
char FAR * buffer,
// receiving buffer
int len,
// data length
int flags,
// 0
struct sockaddr FAR * from, // this is me
int FAR * fromlen) // my address length
Communicating UDP
UDP is like making a radio communication.
• You just listen
• if somebody calls your call-sign, then you answer the
call, and vice versa
• The difference is callings are made only once, if you
miss a call, you miss the message
• Use non-blocking sockets not to block on socket calls
recvfrom/sendto
SERVER
CLIENT
socket() & bind()
socket() & bind()
recvfrom()
sendto()
sendto()
recvfrom()
close()
close()
C++ UDPSocket Class
•Constructor
• Creates non-blocking a socket with a default or passed port
number
• Initializes the Winsock.dll
• Finds the internet address of the host computer
• Binds the socket to this address
•Destructor takes care of the closing operations
C++ UDPSocket Class
•Sends data to an internet address and port no
•Internet address, pointer to send buffer, port no
(if not default) must be passed
void sendData(IP, char *, port=default_port)
C++ UDPSocket Class
•Receives data into a buffer through listening
port
•Double array is used for my applications
•Parses and puts the received data into buffer
bool receiveData (double *, port = default_port)
References
•Network Programming in Windows NT, Alok K. Sinha
www.aw.com/cseng
(sample code)
•www.ecst.csuchico.edu/~beej/guide/net/