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CS4550 Computer Networks II

Socket Interface

Ref: Feit Chap 21Tanenbaum Chap 6

Socket interface

Application

TCP UDP

raw

IP

Data link

physical

Application

TCP UDP

raw

IP

Data link

physical

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

TCP/IP - Sidnei Feit Chapter 21

Unix Network - W. Richard Stevens Programming

Win 32 Network - Ralph DavisProgramming

References

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

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

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

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

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()

*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

Windows Sockets Byte-Order Conversion Functions(MFC)

Function Purpose

ntohs Convert a 16-bit quantity from network byte order to host byte order (Big-Endian to Little-Endian).

Ntohl Convert a 32-bit quantity from network byte order to host byte order (Big-Endian to Little-Endian).

Htons Convert a 16-bit quantity from host byte order to network byte order (Little-Endian to Big-Endian).

Htonl Convert a 32-bit quantity from host byte order to network byte order (Little-Endian to Big-Endian).

Sample Programs

Tcpserv.c Feit p777

tcpclient.c Feit p 782

wb_client.cpp on filemaster

wb_server.cpp on filemaster

Compiling wb_client.cpp in VC++1)start VC++ , and create a projectFile -> 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 projectProject -> 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.exe6)Run from VC++

Build -> Execute wb_client.exe

Setting Up Socket Communication With MFC

Server Client

// construct a socketCSocket sockSrvr; CSocket sockClient;

// create the SOCKETsockSrvr.Create(nPort);1,2 sockClient.Create( );2

// start listeningsockSrvr.Listen( );

// construct a new, empty socketCSocket sockRecv;// accept connection // seek a connectionsockSrvr.Accept( sockRecv ); sockClient.Connect(strAddr, nPort);

Important MFC Socket Member Functions

Accept Accepts a connection on the socket.AsyncSelect Requests event notification for the socket.Bind Associates a local address with the socket.Close Closes the socket.Connect Establishes a connection to a peer socket.Create Creates a socketIOCtl Controls the mode of the socket.Listen Establishes a socket to listen for incoming

connection requests.Receive Receives data from the socket.ReceiveFrom Receives a datagram and stores the source

address.Send Sends data to a connected socket.SendTo Sends data to a specific destination.ShutDown Disables Send and/or Receive calls on the

socket.

Basic ToolsPing [localhost] test availability of network stack

Ping [IP address] test availability of network

Ping [remotehostname] test availability of DNS

netstat get statistics on network activity

Traceroute (Tracert) get topology of network

ipconfig(NT, Unix) get the ethernet interface settings