1. 1 CS4550 Computer Networks II Socket Interface Ref: Feit Chap 21 Tanenbaum Chap 6

2. Socket interface Application TCP UDP raw IP Data link physical Application TCP UDP raw IP Data link physical

3. Sockets API - based on Unix Berkeley Software Distribution BSD (release 4.3) A socket is a communication endpoint — an object through which a Windows Sockets application sends or receives packets of data across a network. Sockets Abstractions supports many network protocols including Transmission Control Protocol/Internet Protocol (TCP/IP), Xerox® Network System (XNS), Digital Equipment Corporation's DECNet™ protocol, Novell® Corporation's Internet Packet Exchange/Sequenced Packed Exchange (IPX/SPX), and others. Stream sockets -guaranteed to be delivered and to be correctly sequenced and unduplicated. Datagram sockets - Not guaranteed to be delivered and to be correctly sequenced and unduplicated. GENERAL

4. TCP/IP - Sidnei Feit Chapter 21 Unix Network- W. Richard Stevens Programming Win 32 Network - Ralph DavisProgramming References

5. Uses for Sockets Client/Server models Peer-to-peer scenarios, such as chat applications Making remote procedure calls (RPC) by having the receiving application interpret a message as a function call

6. Client / Server Model Client Application Server Application - Always running - Listen for client requests - Respond to request - handles multiple clients -start anytime -connect to server -requests service -disconnect request response

7. TCP SOCKET CALL SEQUENCE Socket() Socket descriptor connect() OK send() recv() close() Socket() Socket descriptor bind() ok listen() ok Accept() New socket descriptor, Client ID recv() send() close() Dialog

8. Main socket functions Socket()- create a socket and return a socket handle bind()- bind socket to a local address listen()- set up client queue accept()- wait for connection requests connect()- attempt to establish connection send()- send data recv()- receive data close()- close the connections

9. Switch to a client socket on which to talk Accept() server listens on socket with server host Ip address and port# Client socket assigned by OS at runtime used to talk Clients must know server IP and port# Switch to a client socket on which to talk Multiple Connection Architecture Send() recv() Connect()

10. *Client must know Server host ID: - IP address - server name and translate to IP address using gethostbyname() *Client must know Server Port - well known ports - server advertisement - auxiliary communication *Both client and server must translate local data representations to network representations Helpful tips

11. Windows Sockets Byte-Order Conversion Functions(MFC) Function Purpose ntohsConvert a 16-bit quantity from network byte order to host byte order (Big-Endian to Little-Endian). NtohlConvert a 32-bit quantity from network byte order to host byte order (Big-Endian to Little-Endian). HtonsConvert a 16-bit quantity from host byte order to network byte order (Little-Endian to Big-Endian). HtonlConvert a 32-bit quantity from host byte order to network byte order (Little-Endian to Big-Endian).

12. Sample Programs Tcpserv.cFeit p777 tcpclient.cFeit p 782 wb_client.cppon filemaster wb_server.cppon filemaster

13. Compiling wb_client.cpp in VC++ 1)start VC++, and create a project File -> new -> Win32 Console Application -> enter your directory and project name “wb_client” 2) put the source file “wb_client.cpp” in the directory “wb_client” that was created by VC++ for your project. 3)Add the file to the project Project -> Add to Project ->file -> select “wb_client.cpp” 4)look at the file select FileV… tab, shows a tree of files, click on wb_client, 5)Compile :Build -> Build wb_client.exe, this should give no errors This creates an executable file debug/wb_client.exe 6)Run from VC++ Build -> Execute wb_client.exe

14. Setting Up Socket Communication With MFC Server Client // construct a socket CSocket sockSrvr; CSocket sockClient; // create the SOCKET sockSrvr.Create(nPort);1,2sockClient.Create( );2 // start listening sockSrvr.Listen( ); // construct a new, empty socket CSocket sockRecv; // accept connection// seek a connection sockSrvr.Accept( sockRecv ); sockClient.Connect(strAddr, nPort);

15. Important MFC Socket Member Functions AcceptAccepts a connection on the socket. AsyncSelectRequests event notification for the socket. BindAssociates a local address with the socket. CloseCloses the socket. ConnectEstablishes a connection to a peer socket. CreateCreates a socket IOCtlControls the mode of the socket. ListenEstablishes a socket to listen for incoming connection requests. ReceiveReceives data from the socket. ReceiveFromReceives a datagram and stores the source address. SendSends data to a connected socket. SendToSends data to a specific destination. ShutDownDisables Send and/or Receive calls on the socket.

16. Basic Tools Ping [localhost]test availability of network stack Ping [IP address]test availability of network Ping [remotehostname] test availability of DNS netstatget statistics on network activity Traceroute (Tracert)get topology of network ipconfig(NT, Unix)get the ethernet interface settings