TCP/IP confusion

[dude_1967]

Hello,

I am using sockets with TCP/IP and the internet address family AF_INET to communicate with a digital oscilloscope. The communication protocol seems a bit confusing since this oscilloscope sends and receives messages using a protocol header. The header is 8 bytes long and the eighth byte is the number of meaningful data in the message.

Can anyone tell me if this is a standard known protocol header which needs to be handled with the proper settings of the socket, for example the third parameter to the call of socket(...)? Or do you think that this 8-byte header is a device-specific header?

The header consists of the following bytes:

81 01 01 00 00 00 00 NN

where NN is the number of meaningful data bytes in the command and response.

Thanks you.

Sincerely, Chris.

[nkhambal]

This is not a TCP header. This is the application level header beyond TCP/UDP layer. Application follows this format of Type/Length/Value. You can get this info like this

create a data structure

typedef struct data {
   unsigned long type;
   unsigned long length;
   unsigned char value[255];   /* Max size if data */
};

then recv() this data from the Oscilloscope.

data odata; 

int recv_bytes = recv(msocket, (data *)&odata, sizeof(odata),0);

/* take care if endianess below for type and length */

printf("%d ", odata.type); 
printf("%d ", odata.length);
for (int i = 0; i < odata.length, i++) {
    printf("0x%X ", odata.value[i]);
}

Thanks,

[dude_1967]

Thank you nkhambal. Chris.