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Networks - Project 0 1
Computer Networks
Project 0
Prof. Jerry Breecher
CSCI 280
Fall 2003
Networks - Project 0 2
What You Will Do In This Project.
The purpose of this project is to help you become familiar with
the UNIX/LINUX on the lab network. This means being able to do editing, compiling, etc. of simple programs. These programs will be written in C, so you may have some more learning/reviewing ahead of you.
You have one task before you:
1. Using your favorite editor, type in (or paste) the program
given later in this document. Compile it and run it and show that it produces communication between two instances of the program.
2. You will know you are done when you have demonstrated
to me that your program works.
Networks - Project 0 3
Where To Get Documentation
There are many sources of information to help you with this project. Here
are some of those sources:
Learning C:
Learning GDB โ how to debug:
Learning UNIX:
All of these skills can be acquired (I hope) from the documentation available
on my webpage โ see the bottom of the page at
babbage.clarku.edu/~jbreecher
If you donโt like these documents, there are plenty of other ones out on the
web. Go wild!
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Where To Get Documentation
For information in more detail than is available
off of my home page, see the following links:
GNU Debugger โ remote copy is at:
http://www.gnu.org/manual/gdb-4.17/html_mono/gdb.html
Local copy is at: http://babbage.clarku.edu/~jbreecher/docs/gdb.html
GCC โ Compiler: - remote copy is at:
http://gcc.gnu.org/onlinedocs/gcc-3.0.1/gcc.html
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Computer Chat
- How do we make computers talk?
- How are they interconnected?
Internet Protocol (IP)
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Internet Protocol (IP)
- Datagram (packet) protocol
- Best-effort service
- Loss
- Reordering
- Duplication
- Delay
- Host-to-host delivery
Networks - Project 0 9
IP Address
- 32-bit identifier
- Dotted-quad: 134.111.10.
- www.clarku.edu -> 140.232.1.
- Identifies a host interface (not a host)
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Transport Protocols
Best-effort not sufficient!
- Add services on top of IP
- User Datagram Protocol (UDP)
- Data checksum
- Best-effort
- Transmission Control Protocol (TCP)
- Data checksum
- Reliable byte-stream delivery
- Flow and congestion control
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Sockets
- Identified by protocol and local/remote address/port
- Applications may refer to many sockets
- Sockets accessed by many applications
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TCP/IP Sockets
UDP SOCK_DGRAM IPPROTO_UDP
SOCK_STREAM IPPROTO_TCP PF_INET
TCP
Family Type Protocol
- mySock = socket(family, type, protocol);
- TCP/IP-specific sockets
- Socket reference
- File (socket) descriptor in UNIX
- Socket handle in WinSock
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Specifying Addresses
unsigned short sa_family; /* Address family (e.g., AF_INET) */
char sa_data[14]; /* Protocol-specific address information */
unsigned short sin_family; /* Internet protocol (AF_INET) */
unsigned short sin_port; /* Port (16-bits) */
struct in_addr sin_addr; /* Internet address (32-bits) */
char sin_zero[8]; /* Not used */
struct in_addr
unsigned long s_addr; /* Internet address (32-bits) */
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Networks - Project 0 16
Overview of The
Connection Mechanism
socket()
TCP Client
connect()
write()
socket()
TCP Server
bind()
listen()
accept()
read()
write()
read()
close()
read()
write()
end-of-file notification
Connection establishment
Data (Request)
Data (Reply)
Networks - Project 0 19
proj0.c โ the code:
if ( argc < 2 ) { printf( "The program expects arguments\n" ); printf( "tcp <client|server>\n" ); exit(0); }
if ((fd = socket (family, type, 0)) < 0) SysError ("Error on socket");
sa.sin_family = family; sa.sin_port = htons(port); /* client & server see same port/ sa.sin_addr.s_addr = htonl(INADDR_ANY); / the kernel assigns the IP addr*/
strcpy( console_buffer, argv[1] );
Check that the argument
was input.
Open a socket. The
socket descriptor is
returned in fd.
Fill in the structure that
defines how we want to
connect to other programs.
Networks - Project 0 20
proj0.c โ the code:
if ( console_buffer[0] == 's' || console_buffer[0] == 'S' ) { if (bind (fd, (struct sockaddr *)&sa, sizeof(sa) ) == -1) SysError ("Error on bind");
if (listen (fd, SOMAXCONN) == -1) /* set up for listening */ SysError ("Error on listen");
fdListen = fd;
Check for an โSโ.
If found, it means we want a
server program here. Then
do the bind and listen.
Networks - Project 0 21
proj0.c โ the code:
while( TRUE ) { if ((fdConn = accept (fdListen, (struct sockaddr *)&sa, &lsa )) <0) SysError ("Error on accept");
bzero( ip_input_buffer, sizeof( ip_input_buffer ));
while ( recv( fdConn, ip_input_buffer, BUFFER_SIZE - 2, 0 ) > 0 ) { input_value = atoi( ip_input_buffer ); input_value = input_value + 1;
bzero( ip_output_buffer, sizeof( ip_output_buffer )); sprintf( ip_output_buffer, "%d", input_value );
if ( send( fdConn, ip_output_buffer, strlen(ip_output_buffer) +1, 0) <= 0 ) SysError( "Error on send" );
} /* End of while recv is successful / close (fdConn); } / End of while TRUE / } / End of server case */
Repeat forever
recv from client
Send back to the client
Calculate the new value
recv will keep on working until the client closes the connection. The recv will then
take an error in that case.
Networks - Project 0 22
proj0.c โ the code:
else { if (connect(fd, (struct sockaddr *)&sa, sizeof(sa) ) ) SysError ("Error on connect");
This is the else that says we did NOT ask for a server.
So the first thing a client
does is a connect to the
server.
