[zeromq-dev] ZMQ UDP Support

Martin Sustrik sustrik at 250bpm.com
Sat Apr 10 07:24:51 CEST 2010


Hi Bhavin,

> I notice no direct support for UDP. From snippets I read here and there 
> it seems that UDP usage is via PGM. Few quick questions –

There's a "epgm" (encapsulated PGM) transport. What it means is that 
standard PGM packets are wrapped in UDP packets. Thus it's still 
reliable multicast rather than unreliable unicast/multicast as you would 
expect with UDP.

Several people have hinted that they would like to write a real UDP 
transport for 0MQ but nobody have yet contributed anything.

> * Is there a difference in terms of performance or capability in this case?

EPGM should be more or less equal w.r.t. performance to PGM.

> * What if one wants to implement a unicast delivery over UDP? Can it be 
> done using PGM?

In theory, you can set PGM retransmit window so small that no repair 
happens.

That way you would actually mimic unreliable transport using a reliable 
one. The better idea (in terms of performance) would be to write real 
UDP transport for 0MQ. Not a big deal but someone has to do it :)

Martin



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