SOCKET PROGRAMMING IN JAVA Narendran Thangarajan, @naren_live, II Year, BE, CSE, SSN College of Engg, Chennai.
What started it all.. Internet has emerged as a global ubiquitous media for communication It has changed the way we live, learn, enjoy, communicate, interact, engage, etc. To take advantage of this, businesses are ceaselessly trying to offer their services through the internet. So a huge demand for software developers good in creating internet-enabled applications.
Client Server Applications The Web Service is provided by the server and the clients use these services Client Server NetworkClient machine Server machine A client, where sockets and network This is A server, come in !!
Sockets Introduced in BSD 4.1 UNIX 1981. Sockets are the endpoints of any communication over the internet. Sockets are identified by socket addresses. Socket Address = IP Address + Port Number
Why IP Address + Port number? • IP Address is of the form 10.0.0.1 • Port Number can be anything from 0 to 65,535.
Destination Socket = 10.0.0.2 : 80IP Address -> MAC Address – Locate the specific system 10.0.0.1 10.0.0.2
Port Number – Process specificPort 10000 Port 11000 Port 120000
Understanding Ports OutLook AVGGmail YM Express UpdatePort 1 Port 2 Port 3 Port 4 Transport Layer Packet Port num data Network layer
Thus virtually, sockets are a connection between the two processes in different systems. Eg : Let the socket pairs be 10.0.0.1 : 80 and 18.104.22.168 : 2000 192.168.21.10 : 3000 and 192.168.100.1 : 6000
Networking Basics – the larger picture Applications Layer Standard apps HTTP TCP STACK FTP Telnet Application User apps (http,ftp,telnet,…) Transport Layer Transport TCP (TCP, UDP,..) UDP Network Network Layer (IP,..) IP Link Layer Link (device driver,..) Device drivers
Network Basics - Where are these sockets? Applications Layer Standard apps HTTP TCP STACK FTP Telnet Application User apps (http,ftp,telnet,…) Programming Interface: Sockets SOCKETS Transport Transport Layer (TCP, UDP,..) TCP UDP Network (IP,..) Network Layer Link IP Link Layer (device driver,..) Device drivers
Socket Programming with TCP Server starts first.. Server Process must be running first Server must have created a socket which welcomes client’s connection. (Welcoming socket) Client contacts server by.. Creating Client local TCP socket Specify IP Address and port number of server process. When Client socket is created, the connection is established. When connection is established, server creates a new socket (Connection Socket) to communicate with that client and the Welcoming socket is once again waiting for connections for other clients.
Client/Server Socket Interaction inTCP Server create socket, port=x, for incoming request: welcomeSocket = ServerSocket() Client wait for incoming TCP create socket, connection request connection setup connect to hostid, port=x connectionSocket = clientSocket = welcomeSocket.accept() Socket() send request using read request from clientSocket connectionSocket write reply to connectionSocket read reply from connectionSocket close connectionSocket close clientSocket
Step 1 : Connection request port Server ClientStep 2 : port Server port Client port Connection
Types of Sockets in TCP ServerSocket – the socket used by servers Socket – Socket used by clients Create a ServerSocket in the server and make it to wait for connections from Sockets from other clients
The concept of Streams Client output Server input stream stream Client Server socket socket Client input Server output stream stream
Socket Programming with UDP No Connection between client and server. No handshaking The sender has to explicitly mention the IP address and the port of the destination. The server should extract the IP Address of the datagram everytime. Uses DatagramSocket.
Client/server socket interaction:UDP Server Client create socket, create socket, port=x, for clientSocket = incoming request: DatagramSocket() serverSocket = DatagramSocket() Create, address (hostid, port=x), send datagram request using clientSocket read request from serverSocket write reply to serverSocket read reply from specifying client clientSocket host address, port number close clientSocket