- Computers
store
binary numbers in
one of
2 possible order:
- Big endian ordering
- Little endian ordering
Graphically:
- Host byte ordering:
- Host byte ordering = the storage ordering of binary numbers used in a computer (= host)
- Fact:
- The function call:
sendto( s, data, len, flag, toAddr, toAddrLen )will transmit the len bytes (stored) in the variable data in the order stored in (host) memory
- The function call:
- Consider
the following
data transmission of
an integer binary number
from
little endian computer to
a big endian computer:
- A little endian computer
send the integer value 2 to
a big endian computer
- The big endian computer will
interpret the
integer binary number as
follows:
- A little endian computer
send the integer value 2 to
a big endian computer
- Example Program:
(Demo above code)
- Prog file:
- /home/cs455001/demo/netw-prog-ipv4/udp-send-int.c
- /home/cs455001/demo/netw-prog-ipv4/udp-recv-int.c
How to run the program:
- To compile:
- gcc -o udp-send-int udp-send-int.c on W301 (or a lab machine)
- gcc -o udp-recv-int udp-recv-int.c -lnsl -lsocket on compute
- To run:
- On compute: udp-recv-int 8000
- On W301: udp-send-int compute 8000
- Prog file:
- Technique to transmit
binary data:
- Sender:
- First,
convert the
binary data to
network byte ordering
- Then, send the converted data
Example:
int k = 1; // k is stored in host byte order printf("Sending: int value = %d\n", k); int x = htonl(k); // Convert to network byte ordering sendto(s, &x, sizeof(int), 0 /* flags */, (struct sockaddr *)&dest_addr, sizeof(dest_addr));
- First,
convert the
binary data to
network byte ordering
- Receiver:
- Receiver the
binary data
(we know it is in
network byte order
- Convert the
data to
host byte order using:
int ntohl( int ): convert 4 byte data from network byte ordering to host byte ordering short ntohs( short): convert 2 byte data from network byte ordering to host byte orderingExample:
int x; src_addr_len = sizeof(src_addr); len = recvfrom(s, &x, sizeof(int), 0 /* flags */, (struct sockaddr *) &src_addr, &src_addr_len); k = ntohl( x ); // Convert int from network byte ordering // to host byte ordering printf("k = %d", k);
- Receiver the
binary data
(we know it is in
network byte order
- Sender:
- Example Program:
(Demo above code)
- Prog file:
- Edit the
same demo programs:
- /home/cs455001/demo/netw-prog-ipv4/udp-send-int.c
- /home/cs455001/demo/netw-prog-ipv4/udp-recv-int.c
Uncomment the htonl( ) and ntohl( ) calls in the code
- Edit the
same demo programs:
How to run the program:
- To compile:
- gcc -o udp-send-int udp-send-int.c on W301 (or a lab machine)
- gcc -o udp-recv-int udp-recv-int.c -lnsl -lsocket on compute
- To run:
- On compute: udp-recv-int 8000
- On W301: udp-send-int compute 8000
- Prog file:
- Fact:
- Structured data can contain:
- String/text data (stored in the same order in both big endian computer and little endian computer)
- integer/float binary data (stored in different order in big endian computer and little endian computer)
- Structured data can contain:
-
How to
transmit
structured data:
-
Transmitting the
structured data:
- Use htonl( )
(or htons( )) to
convert
every
integer/float variable to
network byte order
- Send the converted struct using sendto( )
- Use htonl( )
(or htons( )) to
convert
every
integer/float variable to
network byte order
-
Transmitting the
structured data:
-
How to
receive
structured data:
-
Transmitting the
structured data:
- Use
recvfrom( )
to receive the
transmitted struct data
- Use ntohl( ) (or ntohs( )) to convert every integer/float variable to host byte order
- Use
recvfrom( )
to receive the
transmitted struct data
-
Transmitting the
structured data:
- Example Program:
(Demo above code)
- Prog file:
- /home/cs455001/demo/netw-prog-ipv4/udp-send-struct.c
- /home/cs455001/demo/netw-prog-ipv4/udp-recv-struct.c
How to run the program:
- To compile:
- gcc -o udp-send-struct udp-send-struct.c on W301 (or a lab machine)
- gcc -o udp-recv-struct udp-recv-struct.c -lnsl -lsocket on compute
- To run:
- On compute: udp-recv-struct 8000
- On W301: udp-send-struct compute 8000
- Prog file: