Lost packets

system · March 19, 2015, 10:46am

Hey,

I am using Arduino due as client with MVC as a server that runs on my local PC.
The arduino client is polling for actions from the server every 3 seconds.

The communication works fine most of the times, but once every 10-15 seconds the client can’t get a response from the server. I know that the server is getting all the requests from the arduino(writing a log in server), and also sends back a response (with using wireshark). When a message is not received in the arduino-client, it says on the wireshark:

_{62148 10:37:26.515258000 192.168.1.251 192.168.1.48 HTTP 254 [TCP Retransmission] HTTP/1.1 200 OK (text/html)}

and then:

_{62186 10:37:32.378177000 192.168.1.48 192.168.1.251 TCP 60 [TCP Dup ACK 62184#1] 49628→80 [ACK] Seq=253 Ack=1 Win=2048 Len=0}
_{62188 10:37:32.579896000 192.168.1.48 192.168.1.251 TCP 60 [TCP Spurious Retransmission] 49628→80 [FIN, ACK] Seq=252 Ack=1 Win=2048 Len=0}
_{62189 10:37:32.579919000 192.168.1.251 192.168.1.48 TCP 54 [TCP Dup ACK 62185#1] 80→49628 [ACK] Seq=692 Ack=253 Win=64050 Len=0}
_{62190 10:37:32.580089000 192.168.1.48 192.168.1.251 TCP 60 [TCP Dup ACK 62188#1] 49628→80 [ACK] Seq=253 Ack=1 Win=2048 Len=0}
_{62192 10:37:32.984329000 192.168.1.48 192.168.1.251 TCP 60 [TCP Spurious Retransmission] 49628→80 [FIN, ACK] Seq=252 Ack=1 Win=2048 Len=0}
_{62193 10:37:32.984365000 192.168.1.251 192.168.1.48 TCP 54 [TCP Dup ACK 62185#2] 80→49628 [ACK] Seq=692 Ack=253 Win=64050 Len=0}
_{62194 10:37:32.984545000 192.168.1.48 192.168.1.251 TCP 60 [TCP Dup ACK 62192#1] 49628→80 [ACK] Seq=253 Ack=1 Win=2048 Len=0}
_{62195 10:37:32.984570000 192.168.1.251 192.168.1.48 HTTP 744 [TCP Retransmission] HTTP/1.1 200 OK (text/html)HTTP/1.1 400 Bad Request (text/html)}

In my client i wait for chars like this:

_{//wait for chars to read (more than 0)}
_{while (!client.available())}
_{
_delay(1);
_sWait++;
_{if (sWait>250)}
_{
_{print.MyPrintln(“No chars to read from stream”, bDebugMode);}
_break;
_}
_}

and than reads all the chars in a different loop.

I don’t know if this packet loss a normal thing on arduino as a client.
What could it be?

SurferTim · March 19, 2015, 11:55am

You should post all your code. That snippet is not enough to determine what the problem is.

system · March 19, 2015, 12:18pm

I can’t post all of my code (it’s a very long one), but i’m posting some of it as an example:

a function that creates a JSON string and posts it to the server:

^{void AskWhatToDoFromServer()}
^{
^{String strRequest;}
^{byte * RequstResult;}
^{short RequestSize=0;}

^{if(client.connect(serverIP, 80))}
^{
^{print.MyPrintln(“connected”, bDebugMode);}
^{strRequest="{“actionNumber”:1,";}

^{SendDataToServer(m_bIsEncrypted, strRequest);}
^{ReadServerResponse();}
^}
^else
^{
^{print.MyPrintln(“Not Connected”, bDebugMode);}
^}
^}

SendDataToServer (in out case, the JSON string+other ID headers)

^{void SendDataToServer(bool bIsEncrypted, String strData)}
^{
^{byte * RequstResult=NULL;}
^{short RequestSize=0;}
^{client.print(“POST http://myServer/JSON”); //debug on my local pc}
^{client.print(" HTTP/1.1\r\n");}
^{client.println(“Host: myserver:80”);}
^{print.MyPrint("Content-Length: ", bDebugMode);}
^{print.MyPrintln(RequestSize*3 +24, bDebugMode);}
^{client.print("Content-Length: ");}
^{client.println(strData.length() +24);}
^{client.println(“Content-Type: json ; charset=UTF-8”);}
^{client.println(“Connection: keep-alive\r\n”);}

^{// add info to body: ardID + counter}
^{client.print("ARD: ");}
^{print.MyPrint(“ARD: “,bDebugMode);}
^{client.print(ArdID, HEX);}
^{print.MyPrint(ArdID, HEX, bDebugMode);}
^{client.print(” COMM COUNT: “);}
^{print.MyPrint(” COMM COUNT: “, bDebugMode);}
^{client.print(lMsgCounter, HEX);}
^{print.MyPrint(lMsgCounter, HEX, bDebugMode);}
^{print.MyPrint(” “, bDebugMode);}
^{if (strData.length()>1500)//splits long message if needed}
^{
^{print.MyPrintln(“more than 1500 bytes”, bDebugMode);}
^{int nLengthSent=0;}
^{while ( nLengthSent < strData.length() )}
^{
^{char buff[1500] ={0};}
^{int copySize = min(1500,strData.length());}
^{memcpy(&buff, &strData[nLengthSent], copySize-1);}
^{buff[1499]=NULL;}
^{client.print(buff);}
^{nLengthSent += copySize-1;}
^}
^{client.println();}
^}
^else
^{
^{client.print(strData);}
^}
^{print.MyPrint(strData, bDebugMode);}

^{client.println(); //important!}
^{print.MyPrintln(“request sent”, bDebugMode);}
^}
^{lMsgCounter++;}
^{strData=””;}
^}

ReadServerResponse (copied most of it from the forums, in order to ignore /n):

^{void ReadServerResponse()}
^{
^{//char responseFromServer=‘a’;}
^{boolean currentLineIsBlank = true;}
^{boolean bIsRead = false;}
^{short sWait=0;}
^{IncomingPostData="";}
^{print.MyPrintln("", bDebugMode);}
^{while(client.connected())}
^{
^{//wait for chars to read (more than 0)}
^{while (!client.available())}
^{
^delay(1);
^sWait++;
^{if (sWait>250)}
^{
^{print.MyPrintln(“No chars to read from stream”, bDebugMode);}
^break;
^}
^}

^{print.MyPrint("sWait is: ", bDebugMode);}
^{print.MyPrintln(sWait, bDebugMode);}
^{while (client.available())}
^{
^{char c = client.read();}
^{print.MyPrint(c, bDebugMode);}
^{if (m_bIsEncrypted)}
^{
^{if (c == ‘\n’ && currentLineIsBlank)}
^{
^{// Here is where the POST data is.}
^{while(client.available())}
^{
^{if (bIsRead ==true)}
^{
^{client.read();}
^}
^{//Serial.write(client.read());}
^{char read = (char)client.read();}
^{if (read>=‘0’ && read<=‘9’ || read>=‘A’ &&read<=‘F’ || read==’ ')}
^{
^{IncomingPostData += read;}
^}
^else
^{
^{bIsRead = true;}
^break;
^}

^}
^}
^{else if (c == ‘\n’)}
^{
^{// you’re starting a new line}
^{currentLineIsBlank = true;}
^}
^{else if (c != ‘\r’)}
^{
^{// you’ve gotten a character on the current line}
^{currentLineIsBlank = false;}
^}
^}
^{else //not encrypted}
^{
^{if (c == ‘\n’ && currentLineIsBlank)}
^{
^//body
^{while(client.available())}
^{
^{c=client.read();}
^{IncomingPostData += c;}
^}
^}
^{else if (c == ‘\n’)}
^{
^{// you’re starting a new line}
^{currentLineIsBlank = true;}
^}
^{else if (c != ‘\r’)}
^{
^{// you have a character on the current line}
^{currentLineIsBlank = false;}
^}

^}
^}
^{client.stop();}
^{print.MyPrint(“Body is: “, bDebugMode);}
^{print.MyPrintln(IncomingPostData, bDebugMode);}
^{print.MyPrintln(””, bDebugMode);}
^}
^}

Note: The print.MyPrint/ln() function is very similar to Serial.print only prints when in debug-Mode.

SurferTim · March 19, 2015, 12:40pm

How often do you send this request?

system · March 19, 2015, 12:45pm

most of the times in intervals of 3 sec, but it can go down to 100 milisec. I've seen it goes bad in both cases.

SurferTim · March 19, 2015, 1:21pm

Have you tried any other client code with your server? Here is mine.
http://playground.arduino.cc/Code/WebClient
Try this with a standard webpage on your server for a while and see if you get a fail with it.,

system · March 19, 2015, 2:54pm

I tried some other but it didn't quite fit out of technical reasons (parsing the responses from the server).
I think that i'm on something here, i disabled the polling mechanism:

while (!client.available())
{
delay(1);
sWait++;
if (sWait>250)
{
print.MyPrintln("No chars to read from stream", bDebugMode);
break;
}
}

And instead i put a constant "delay(250)" and after testing it for a couple of minutes i think that it really helps.
So what happened here? is the client.Available() function prevents the write to the buffer somehow?
The thing is that i want the program to respond as fast as possible after the response from the server arrives. This delay time might change if i upload my server or something like that. I will really appreciate if someone can point me to that direction.

SurferTim · March 19, 2015, 3:22pm

I use a 1ms delay between packets just for the timeout feature. Any more than that is not necessary.

system · March 19, 2015, 4:50pm

ok nevermind, it's not a solution for my problem. I'll try your client.
Thanks!

system · May 6, 2021, 10:53am