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

[Marcus D. Leech]

On 04/06/2010 09:44 PM, John Gilmore wrote:
>> Which part of the Linux issue... sustained throughput or latency?  I 
>> wouldn't be surprised to find that latency hasn't
>> improved substantially because it's not a priority for server software.  
>> Even VoIP applications are not concerned
>> about a 1 msec improvement... whereas that makes or breaks a wireless MAC.
>>     
>
Simple test.  Core 2 Duo system, 2.33GHz, Fedora 11.

A 1500 byte ping test to localhost yields an average RTT of about
33usecs.  That tests most of
  the network stack except for hardware interfaces, and gives you some
notion of "best case"
  for latency/turn-around time.

If MACs have requirements that are more aggressive than 20-50usec
turnaround time, then relying
  purely on software in a running general-purpose operating system, even
on relatively-good hardware
  may be optimistic.


-- 
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org