EE458 - Embedded Systems
Intro to Network Programming
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Outline
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TCP versus UDP
Introduction to Sockets
References
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Netburner Network Prog. Manual (Chs 11-12)
Netburner Runtime Library (Ch 21)
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Intro to Network Programming
TCP and UDP
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There are two TCP/IP transport protocols:
TCP (Transport Control Protocol) and UDP
(User Datagram Protocol).
UDP is a simple, unreliable, datagram
protocol. UDP is faster than TCP.
TCP is a sophisticated, reliable, byte-stream
(unlimited length) protocol.
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Intro to Network Programming
TCP and UDP
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There is no guarantee that a UDP datagram
will reach its destination. To ensure
delivery our application must handle timeouts, acknowledgments, retransmissions,
etc. UDP is a connectionless protocol.
TCP provides a connection between two
machines. When data is sent via TCP to
the other end, it is acknowledged. If it is
not then received the data will be resent.
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Intro to Network Programming
TCP and UDP
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TCP provides sequencing. When a lot of
data is sent via TCP, the data will be sent in
segments. If they arrive out of order, they
will automatically be reordered.
TCP provides flow control. A TCP peer
advertises how many bytes it can accept.
This prevents receive buffer overflow.
A TCP connection is full-duplex. Data can
be sent and received on the same socket.
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Intro to Network Programming
TCP and UDP Ports
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Multiple processes can use TCP or UDP
simultaneously. 16-bit integer port
numbers are used to distinguish processes.
Servers listen for connections on wellknown ports (ftp - port 21, ssh - port 22,
telnet - port 23, http - port 80).
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Intro to Network Programming
Client/Server Architecture
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Network applications are divided into client
and server parts. A particular client usually
communicates with a single server. While
a server communicates with several clients.
client
client
server
client
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Intro to Network Programming
BSD Sockets
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The Berkeley or BSD Sockets API is the
standard for network communication. It is
supported by all modern OSes (Windows,
Linux, BSD, and Mac OS). It is also
supported by the Netburner.
Most real-time OSes (RTEMS and uC/OS for
example) support the BSD sockets API as
the default networking API.
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Intro to Network Programming
BSD Sockets
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The client uses the connect() routine to
establish a connection. read() and
write() are used to send data across the
connection. Sockets are bidirectional.
The server uses the listen() routine to
prepare for an incoming connection. The
accept() routine is then used to wait for a
client connection. The server uses read()
and write() to transfer data.
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Intro to Network Programming
Client Routines
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A client uses the connect() routine to
establish a connection to a listening server.
int fd = connect(
IPADDR addr, WORD localport,
WORD remoteport, DWORD timeout);
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This routine returns a file descriptor that is
used with read() and write() routines to
transfer data.
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Intro to Network Programming
Client Routines
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addr is the binary IP address of the server,
localport is the port to be used on the
client (use 0 for automatic assignment).
remoteport is the server port to connect
to and timeout is the timeout in ticks to
wait for the connection (0 waits forever).
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Intro to Network Programming
Server Routines
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The server first calls listen() to set up a
queue for client connections:
listfd = listen(
IPADDR addr, WORD port,
BYTE maxpend);
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A file descriptor is returned. You must
accept() connections before you can
communicate with the client.
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Intro to Network Programming
Server Routines
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addr is the binary IP address from which to
accept connections. Use the macro
INADDR_ANY to accept connections from
any address. port is the port to listen on.
(This is the port the client connects to.)
maxpend is the number of pending
connections to store on this socket. A value
of 5 is typical. Client connections are held
in the queue until accepted by the server.
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Intro to Network Programming
Server Routines
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The server calls the accept() routine to
accept a client connection:
newfd = accept(
int listfd, IPADDR *addr,
WORD *port, WORD timeout);
accept() blocks until a connection is made.
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A new socket file descriptor is returned.
The server uses this file descriptor to
communicate with the client.
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Intro to Network Programming
Server Routines
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listfd is the file descriptor returned from
listen(). addr and port are return
arguments that contain the IP address and
port of the connecting client. These may be
NULL if that information is not needed.
timeout is the number of ticks to wait. A
value of 0 will wait forever.
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Intro to Network Programming
Utility Routines
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The Netburner API provides the ShowIP()
routine to display a binary IP address in
dotted-quad notation on the serial port:
ShowIP(ipaddr);
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The AsciiToIp() routine converts from
dotted-quad notation to a binary IP address:
IPADDR ipnb =
AsciiToIP(“192.168.0.2”);
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Intro to Network Programming
Network Byte Order
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Note that binary network addresses should
be in “network byte order” (big endian
order). Intel processors are little endian and
the following will NOT work when trying to
convert “10.5.50.100” to a network address
on an Intel processor:
unsigned int addr =
(10<<24) + (5<<16) + (50<<8) + 100;
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Intro to Network Programming
Network Byte Order
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The conversion on the previous slide will
work on the Netburner because the Coldfire
processor is big endian.
To convert 32-bit addresses between host
and network order use the HTONL() and
NTOHL() routines.
These routines do nothing on big endian
machines, but should be used for portability.
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Intro to Network Programming
Network Byte Order
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Port addresses are 16-bit integers (shorts).
Use the HTONS() and NTOHS() routines to
convert.
Pay careful attention to the documentation
to determine if a routine needs (or returns)
an address in network or host order.
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