Re: [Discuss-gnuradio] packet interarrival time

[Eric Blossom]

On Fri, Feb 12, 2010 at 12:52:00PM -0800, Veljko Pejovic wrote:
> Hi,
> 
> I'm using two USRP2 with XCVR2450s, gnuradio 3.2.2 and Ubuntu 9.10.
> 
> I ran the benchmark_tx/rx example from gnuradio-examples/ofdm and
> measured packet inter-arrival times at the receiver. I also modified
> the sender to wait for some time (like 200ms) between individual
> packets. I also set the msg queue size to one. In python code I'm
> printing a bunch of time.time() values to keep the timeline of the
> events.
> 
> What I observe is the following:
> - inter-departure times are constant, the packet size and the bit rate
> would of course influence the time spent sending, but that would still
> be a relatively small value.
> - at the receiver, most packets are received with the inter-arrival
> time comparable to the inter-departure time at the sender, however,
> occasionally I would see a huge lag between two consecutive packets
> (almost a second).
> 
> I read the NSDI'09 paper
> (http://portal.acm.org/citation.cfm?id=1558984) that talks about USRP1
> performance, however, what I observe is way higher delay and it's
> USRP2. Thus, I'm sure that there's something I can do to fix this
> delay. Any hints?

Are packets getting dropped?
Is the USRP2 on a dedicated ethernet port?
Is there a switch between the host and the USRP2?

Eric