[zeromq-dev] A PGM question

[Steven McCoy]

On 5 October 2011 07:11, Emmanuel TAUREL <taurel at esrf.fr> wrote:

> 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?
>
>
Often packet loss occurs in buffers not on the actual network, so the ODATA
packets may have been lost waiting delivery to user-space.

If you set the 0x100 log mask you will see all the causes behind drops and
NAKs in the receive window:

http://code.google.com/p/openpgm/wiki/OpenPgm5CReferenceErrorHandling

A worst case could be severe packet re-ordering and a long incoming buffer
causing PGM to send NAKs for ODATA packets still waiting to be read.

-- 
Steve-o
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