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

[David Halls]

​Thanks for your reply Marcus, but does that mean there is no way around the problem?

Regards,

David

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From: address@hidden <address@hidden>
Sent: 25 September 2015 20:24
To: Andy Walls
Cc: David Halls; address@hidden; discuss-gnuradio-bounces+address@hidden
Subject: Re: [Discuss-gnuradio] UDP Sink Size Limit - ERROR: send error:send_to: Message too long

 

If the sending machine sets DF in the IP header, then any interstitial machine that must fragment will drop the packet as well.

Best to stick to MTU-sized payloads with UDP, since IP fragmentation is handled poorly in many cases--either due to policy, or bad implementations.

 

 

 

On 2015-09-25 15:17, Andy Walls wrote:

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


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