Overview of Network Programming Sockets EE450 Introduction to Computer Networks Professor A Zahid EE450 USC Zahid 1 Application Programming Interface The services provided by the operating system that provide the interface between application and the TCP IP Protocol Suite Application Network API Protocol A Protocol B EE450 USC Zahid Protocol C 2 API Sockets TCP IP does not include an API definition There are a variety of APIs for use with TCP IP UNIX Sockets Winsock Windows Sockets A socket is an abstract representation of a communication endpoint A socket allows the application to plug in to the network and communicate with other applications A socket is uniquely identified by the IP address Port number and the underlying transport layer protocol EE450 USC Zahid 3 Socket Types EE450 USC Zahid 4 Socket Structure EE450 USC Zahid 5 Socket Descriptor Data Structure Descriptor Table 0 1 2 3 Family PF INET Service SOCK STREAM Local IP 111 22 3 4 Remote IP 123 45 6 78 Local Port 2249 Remote Port 3726 4 EE450 USC Zahid 6 Basic Sockets API Clients and Servers differ in some aspects of their use of API and they are the same in other aspects Both client and server programs begin by asking the NOS to create a socket The function to accomplish that is Socket int socket int protocol family int type int protocol Protocol family PF INET Type SOCK STREAM SOCK DGRAM Protocol TCP UDP Return value of Socket is a non negative integer called Socket Descriptor or 1 if errors EE450 USC Zahid 7 TCP Server Create a TCP socket using Socket Assign a port number to the socket using Bind int bind int socket local address address length Local address is the IP address and the port number of the server It is this address that the client and the server need to agree on to communicate Neither one need to know the client address Address length is length of address structure If successful Bind returns a 0 otherwise it returns 1 If successful the socket at server side is associated to the local IP address and the local port number Listen to connections from clients using Listen int listen int socket int queue limit Queue limit is an upper bound on of clients that can be waiting If successful Listen returns a 0 otherwise it returns 1 EE450 USC Zahid 8 TCP Server Continued The socket that has been bounded to a port and marked for listening is never actually used for sending and receiving The socket known as the welcoming socket or the parent socket Child sockets are created for each client It is this socket that is actually used for sending and receiving Server gets a socket for an incoming client connection by calling Accept int accept int socket client address address length If successful accept returns a descriptor for the new socket otherwise it returns 1 EE450 USC Zahid 9 TCP Server Continued Once the child socket is created communications send and receive can take place int send int socket message message length int recv int socket recv buffer buffer length When the application is done with the socket it needs to close it The child socket not the parent socket which is passively open to welcome new clients This is done by calling Close int close int socket EE450 USC Zahid 10 TCP Client Create a TCP socket using Socket Establish a connection to the server using Connect Communications using Send and Recv int connect int socket foreign address address length Foreign address is the address of the server and the port number of the server The well known port number int send int socket message message length int recv int socket recv buffer buffer length Close the socket using Close int close int socket EE450 USC Zahid 11 Connection less Iterative Server EE450 USC Zahid 12 Flow Chart Socket Interface for Connection Less Iterative Server EE450 USC Zahid 13 Connection oriented Concurrent Server EE450 USC Zahid 14 Flow Chart Socket Interface for Connection Oriented Concurrent Server EE450 USC Zahid 15