Re: [Discuss-gnuradio] MAC layer development and USRP2

[Jeff Brower]

George-

>> Thanks for the reply George. I'm still looking for a little more
>> information on this topic.
>>
>> - What is PMT
>
> http://gnuradio.org/redmine/wiki/1/TypePMT
>
>> - Why was m-block removed
>
> http://osdir.com/ml/discuss-gnuradio-gnu/2010-01/msg00066.html
>
>> - Has anyone measured latency with the USRP2 and GigE
>
> I'm not sure.
>
>> - Is GigE alone not capable of handling MAC turnaround times or is
>> software to blame for this
>
> I think the latency is on hundreds of microseconds, which is greater than,
> say, an 802.11 ACK turnaround time (24us).

I would tend to blame Linux and buffering more than GbE itself (MAC + PHY).  
Here is an interesting doc where the
researchers were asking similar questions:

  http://www.hep.man.ac.uk/u/rich/atlas/docs/atlas_net_note_draft5.pdf

I'm not sure yet how much buffering is done in the USRP2 firmware but we hope 
to know shortly as a couple of our guys
are in the process of taking apart the logic, pulling out non-GbE related 
sections, and rebuilding.

-Jeff