[zeromq-dev] epgm protocol question

Emmanuel TAUREL taurel at esrf.fr
Tue Apr 13 13:59:54 CEST 2010

Hello all,

I am using zmq 2.0.6 on Ubuntu 9.04 boxes.
I am using PUB/SUB with the epgm protocol. I have one publisher on host 
A and 2 subscribers on host B.
The ZMQ_RATE is set to 20000 on both publishers and subscribers. I do 
not filter anything on the subscribers side. On the publisher side, I have
a ZMQ_HWM set to 100 and ZMQ_LWM set to 50.
I am sending 4 kbytes messages. The first byte within each message is a 
counter which allows me to check that I haven't lost any message.
My problem is that I am loosing messages!

I have wireshark on both sides (Host A and Host B). I have studied a 
little bit what happened during my transmission.
On Host B (the receiver), I notice a hole in the ODATA sequence number 
sent by Host A. Then, Host B send a NAK packet requesting the missing 
Host A reply to this NAK packet by a NCF packet which according to what 
I have read in RFC 3208 is correct. But I do not see any RDATA packet 
sent by the source (Host A) and therefore my subscribers loose the 
concerned messages!!

I agree that the wireshark on host A (the sender) tells me that the 
datagram missing on Host B (the receiver) have been sent but I guess 
these packets have been lost by the
switch between the 2 hosts. But as far as I have understood PGM, it is a 
reliable protocol and this case should be covered by some 
re-transmission which apparently in my case is only half-done.

Are you aware of some similar cases?

Thank's for your answers


Emmanuel Taurel

More information about the zeromq-dev mailing list