[zeromq-dev] A PGM question

[Emmanuel TAUREL]

Hello all,

I would like to ask question to PGM gurus.
I have noticed in network packets exchanged between a publisher and 
subscribers using PGM transport some NAK and RDATA packets.
I understand NAK and RDATA packets when some ODATA packets are missing.
But what is  the reason for a receiver to send NAK requests for packets 
previously sent to the host in the ODATA transmission?
Is it linked to transmit / receive windows?

Thank's very much for your answers

Emmanuel Taurel