Re: [Discuss-gnuradio] packet interarrival time

[Veljko Pejovic]

Hi Eric,

2010/2/12 Eric Blossom <address@hidden>:
> 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?

I don't get any overruns/underruns reported, but, yes, there's some
packet loss. However, I'm only considering the interarrival time of
those packets with consecutive packet numbers.

> Is the USRP2 on a dedicated ethernet port?

yes, it is.

> Is there a switch between the host and the USRP2?

no

>
> Eric
>

cheers

Veljko