[Discuss-gnuradio] UDP Sink Size Limit - ERROR: send error:send_to: Message too long

[Andy Walls]

> From:         David Halls
>Subject:       [Discuss-gnuradio] UDP Sink Size Limit - ERROR: send
error:send_to: Message too long
>Date:  Fri, 25 Sep 2015 09:05:56 +0000

>Dear All,
>
>
>When I increase my packet length in a transmission flow graph to over
>16,000 bits, I get the following error
>
>
>"ERROR: send error:send_to: Message too long​"

This looks like the underlying sendto() system call is returning
EMSGSIZE.  From man sendto:

     EMSGSIZE
              The  socket  type  requires that message be sent atomically, and
              the size of the message to be sent made this impossible.




>this is from the UDP block which I am using in order to send the
>transmitted bits to the destination in order to perform BER. I am
>sending the packets in bursts, one packet every two seconds.


>I currently have the Payload size set to 147.2k and Send Null Pkt as
>EOF set to true.


>Is this some fundamental limit, or can I overcome the issue?

16,000 bits is 2000 bytes.  The default MTU is usually 1500 bytes (for
IP header, UDP header, and payload together).  Try modifying the MTU on
your machine's network interface to something larger, say 4000.

The MTU of the receiving machine or other network hardware might still
be only 1500, so the the UDP packet could get IP fragmented.  I'm not
sure how well UDP works when fragmented.

-Andy